Download Conference Abstract Booklet here.

wide-field variability surveys:
a 21st-century perspective
22nd Los Alamos Stellar Pulsation Conference Series meeting
San Pedro de Atacama, Chile, Nov. 28 – Dec. 2, 2016
ABSTRACT BOOKLET
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Abstracts of talks are listed in the same order as they appear in the program.
Posters are listed in alphabetical order, according to the presenting author’s family
name.
In both cases, the presenting author’s name is shown in boldface type.
TALKS
(Abstracts of talks are listed in the same order as they appear in the
program. The presenting author’s name is shown in boldface type.)
T1
The Impact of Large-Scale, Long-Term Optical
Surveys on Pulsating Star Research
Igor Soszyński
The era of large-scale photometric variability surveys began a quarter of a century ago,
when three microlensing projects - EROS, MACHO, and OGLE - started their operation.
These surveys initiated a revolution in the field of variable stars and in the next years
they inspired many new observational projects. Large-scale optical surveys multiplied the
number of variable stars known in the Universe. The huge, homogeneous and complete
catalogs of pulsating stars, such as Cepheids, RR Lyrae stars, or long-period variables,
offer an unprecedented opportunity to calibrate and test the accuracy of various distance
indicators, to trace the 3D structure of the Milky Way and other galaxies, to discover
exotic types of intrinsically variable stars, or to study previously unknown features and
behaviors of pulsators. I will present recent findings on various types of pulsating stars
obtained from the optical large-scale surveys, with particular emphasis on the OGLE
project which currently offers the largest photometric database among surveys for stellar
variability.
T2
Synergies between Transient Surveys and
Variable Star Research
A. J. Drake
The age of very widefield synoptic surveys is upon us. For the past decade optical
surveys such as CRTS, PanSTARRS, and PTF have regularly covered tens of thousands of
degrees of visible sky. These surveys have uncovered an ever growing zoo of transient
astrophysical phenomena. The archival data legacy of these surveys is now being
harvested to reveal the myriad of variable stars. In the next decade this field will
continue grow as even larger surveys move to deeper exploration of the time domain.
I will present results from our initial steps along this road.
T3
OGLE Cepheids in the Milky Way
Andrzej Udalski
OGLE Galaxy Variability Survey is a long-term sky survey covering over 2000 square
degrees along the Galactic plane, conducted as a part of the OGLE-IV program. Results of
the search for Galactic Cepheids in the data collected in the years 20132016 will be
presented.
T4
Pulsating Star Products from the Palomar
Transient Factory: Ultra-Long Period
Cepheids in M31 and RR Lyrae in Kepler Field
Chow-Choong Ngeow
The Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF), are
wide-field synoptic sky surveys aimed to detect transients. PTF/iPTF uses a robotic 48inch Schmidt telescope, also known as the P48 Telescope, located at the Palomar
Observatory to carry out the surveys. The P48 Telescope is equipped with a wide-Field
mosaic camera that consists of eleven 2K x 4K CCDs with a field-of-view of 7.3 degreesquared. Nominal observations of PTF/iPTF was carried out in either g or R filters. With an
exposure time of 60-second, the PTF/iPTF data can reach to a depth of ~20.5 mag.
Even though the main science goal for PTF/iPTF is to detect various type of transients,
the synoptic nature of the surveys can also be used for the study of variable stars. In this
Presentation, I will first give a brief introduction to PTF/iPTF, followed by the two
pulsating stars studies using the PTF/iPTF data: the Ultra-Long Period Cepheids (ULPC) in
M31 and the RR Lyrae in Kepler Field. For the formal study, we searched the M31's ULPC
using PTF imaging data, and follow-up the candidates with other telescopes. Our finding
revealed that there are only two ULPC in M31. I will give a brief implication of our finding
in distance scale studies. For the later study, I will present our on-going work to calibrate
the metallicity-light curve relation in native PTF/iPTF R-band using the RRab stars in the
Kepler Field.
T5
Outward Bound: RR Lyr in the Outer Part of the
Milky Way Halo
Judith Cohen
Branimir Sesar
Anushka Asnodar
the PTF and iPTF team
We have isolated a large sample of RR Lyrae variables at distances beyond 50 kpc in the
Milky Way halo from the Palomar Transient Facility database. We are using these to
probe the density distribution in the outer halo out to about 100 kpc as well as the total
mass of the Milky Way galaxy, which is still controversial and is important for near field
cosmology. A spectroscopic program to obtain radial velocities for the most distant of
these variables at the Keck Observatory now has vr for 112 outer halo RR Lyr, more than
a third of which are beyond 80 kpc. We believe we have found one new outer halo
structure. We discuss the potential and the issues of using RR Lyr for this purpose.
T6
Blazhko Modulation in First-Overtone RR Lyrae
Stars from the OGLE Collection
Henryka Netzel
Radoslaw Smolec
and OGLE team
Blazhko effect is a long-term quasi-periodic amplitude and/or phase modulation of
pulsations of RR Lyrae stars. After its discovery in 1907 by Sergey Blazhko, its origin
remains a mystery. This phenomenon has not been extensively studied in firstovertone
(RRc) RR Lyrae stars yet. The Optical Gravitational Lensing Experiment (OGLE) is a
source of excellent quality photometry for more than 10 000 RRc stars in the Galactic
bulge. These stars were monitored regularly from 2010 in the fourth phase of the OGLE.
Additionally, for some stars data from earlier phases of the OGLE project are available.
Therefore the OGLE Collection of Variable stars is an excellent database to study longterm behaviour of period changes and Blazhko effect in a large sample of RRc stars.
In this talk we present results of the first comprehensive study of Blazhko effect in RRc
stars. Input sample for our analysis consists of almost 11 000 stars, for which we used
six seasons of the OGLE observations spanning from 2010 to 2015. Incidence rate based
on this study is around five per cent. High fraction of RRc stars show period changes,
which are often irregular and can be confused with Blazhko effect. For these stars we
used, if possible, observations from previous phases of the OGLE project to study longterm behaviour of pulsations. In Blazhko stars we detected both dublet and triplet
structures in power spectra. Shortest modulation period is 5 days for a star with
detectable triplet and below 5 days for a star with doublet only. We also detected
quintuplets in some stars. Particularly interesting stars are these with multiple
modulation periods. We also found modulated stars which show additional variability due
to non-radial modes. All these findings in RRc stars, based on statistically significant
sample, might shed new light on mysterious Blazhko phenomenon.
T7
Synergies between Exoplanet Surveys and
Variable Star Research
Géza Kovács
With the discovery of the first transiting extrasolar planetary system back to 1999, a
great number of projects started to hunt for other similar systems. Because of the
incidence rate of such systems was unknown and the length of the shallow transit events
is only a few percent of the orbital period, the goal was to monitor continuously as many
stars as possible for at least a period of a few months. Small aperture, large field of view
automated telescope systems have been installed with a parallel development of new
data reduction and analysis methods, leading to better than 1% per data point precision
for thousands of stars. With the successful launch of the photometric satellites CoRot and
Kepler, the photometric precision increased further by one-two orders of magnitude.
Millions of stars have been analyzed and searched for transits. In the history of variable
star astronomy this is the biggest undertaking so far, resulting in photometric time series
inventories immensely valuable for the whole field. In this review we briefly discuss the
methods of data analysis that were inspired by the main science driver of these surveys
and highlight some of the most interesting variable star results that start to impact the
field.
T8
Pulsating Stars in SuperWASP
Daniel Holdsworth
SuperWASP is one of the largest ground-based surveys for transiting exoplanets. To date,
it has observed over 31 million stars. Such a extensive database of time resolved
photometry holds the potential for extensive searches of stellar variability, and provide
solid candidates for the upcoming TESS mission. Previous work by e.g. Smalley et al
(2011), Holdsworth et al (2014), Paunzen et al (2015) have shown that the WASP
archive provides a wealth of pulsationally variable stars. In this talk I will provide an
overview of the SuperWASP project, present some of the published results from the
survey, and some of the on-going work to identify key targets for the TESS mission.
T9
Pulsating White Dwarfs in Large Surveys
Kepler Oliveira (S. O. Kepler)
The Sloan Digital Sky Survey has allowed us to increase the number of known white
dwarfs by a factor of five and consequently the number of known pulsating white dwarfs
also by a factor of five. It has also allowed us to discover new types of variable white
dwarfs, as the variable hot DQs, and to study the new class of Extremely Low Mass white
dwarfs. With the Kepler Mission, it has been possible to discover new phenomena, the
outbursts present in a few pulsating white dwarfs.
T10
A Survey of Pulsating DA and DB White Dwarfs
with the Whole Earth Telescope
Judith Provencal
Mike Montgomery
Harry Shipman
WET Collaboration
White dwarfs represent the end point of stellar evolution for the majority of stars. As
such, they are excellent astrophysical laboratories. They are structurally simple, with
electron degenerate cores surrounded by thin surface layers of helium and/or hydrogen.
The g-mode pulsations provide a window into their internal structure. The Whole Earth
Telescope has been conducting a long-term survey of pulsating white dwarfs with the
goal of providing an empirical map of convection parameters across the DA and DB
instability strips. We discuss our current results, and present interesting things we've
noticed in the course of our investigation.
T11
Time-Series Surveys and Pulsating Stars:
The Near-Infrared Perspective
Noriyuki Matsunaga
I'm going to review current and future near-infrared time-series surveys. The potentials
and limitations of infrared surveys will be discussed with a particular emphasis on
importance of characterizing interstellar extinction.
T12
Pulsating Stars and the VVV Survey
Dante Minniti
The VVV Survey is mapping the innermost regions of the Milky Way in the near-IR
passbands ZYJHKs, using the VISTA telescope at ESO Paranal Observatory. In this talk I
will concentrate on the latest results regarding pulsating variable stars. In particular, we
discovered a dozen RR Lyrae in the Galactic center, which has implications for the
formation of the nuclear star cluster. Also, I will present a new globular cluster
discovered in the inner Milky Way disk using RR Lyrae stars. Finally, I will conclude with
the future perspectives offered by the VVVX, which is the extension of the VVV survey to
a larger area and time baseline.
T13
Multiwavelength Theoretical and Observed Light
Curve Parameters of Cepheid and RR Lyrae
Variables
Anupam Bhardwaj
Shashi Kanbur
Marcella Marconi
Lucas Macri
Marina Rejkuba
We analyse the multiwavelength theoretical (UBVRIJKL) and observed (VIJHK3.6/4.5)
light curves of Cepheid variables using the Fourier decomposition and principal
component analysis methods. The theoretical Cepheid light curves are obtained using the
full amplitude, nonlinear, convective hydrodynamical models for chemical compositions
relative to Cepheids in the Galaxy (Y=0.28, Z=0.02), Large Magellanic Cloud (Y=0.25,
Z=0.008) and Small Magellanic Cloud (Y=0.25, Z=0.004). We studied the variation of
light curve parameters with period, wavelength and metallicity. We observed a decrease
in Fourier amplitude parameters and an increase in Fourier phase parameters with
increasing wavelength at a given period for both theoretical and observed light curves.
However, the amplitudes for the theoretical light curves are systematically higher than
the observed amplitudes over entire period range. We found that for periods longer than
about 20 days, the values of the Fourier amplitude parameters increase sharply for
shorter wavelengths as compared to wavelengths longer than the J-band. The central
period of the Hertzsprung progression was found to increase with wavelength in the case
of the Fourier amplitude parameters and decrease with increasing wavelength in the case
of phase parameters. We also observed a small variation of the central period of the
progression between the Galaxy and LMC, presumably related to metallicity effects. We
find two distinct populations in the first principal component for optical and near-infrared
wavelengths. The VI-band principal components for Magellanic Cloud Cepheid models are
consistent with observations. We also studied the theoretical light curves adopted from
pulsation models of RR Lyraes for a wide range of the metal abundances (Z=0.0001 to
solar abundant 0.02) in the optical (UBVRI) and near-infrared(JKL) bands and compared
their light curve parameters with observed light curves from OGLE and VVV surveys.
T14
Spitzer Observations of Large Amplitude Variables
in IC1613
Patricia Whitelock
I will discuss the large amplitude variables in the Local Group dwarf irregular galaxy,
IC 1613, based on multi-epoch data from the Spitzer spacecraft. This uses observations
obtained as parting of the SPIRITS (PI Mansi Kasliwal) and DUSTiNGS (PI Martha Boyer)
collaborations. Although we detected Cepheid and supergiant variables, the majority of
large amplitude sources are AGB stars. They have a range of initial masses and include
hot bottom burning stars. These extensive datasets provide new insight on the infrared
amplitudes period-luminosity relations. As such they are an important step on the road to
understanding comparable data that JWST will obtain for more distant galaxies.
T15
Pulsations and Declines in R Coronae Borealis
Stars
Geoffrey Clayton
RCB stars form a class of cool, carbon-rich supergiants that have almost no hydrogen.
They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the
formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin
of an RCB star: the merger of a CO/He WD binary and a final helium-shell flash. RCB
stars show periodic or semi-periodic light and radial velocity fluctuations due to both
radial and non-radial pulsations. A number of RCB stars are now being studied with K2.
A correlation between pulsation phase and the timing of dust formation has been found in
several RCB stars. This relationship shows that the dust forms near the surface of the
RCB star due to density and temperature perturbations caused by the stellar pulsations.
The distribution on the sky and radial velocities of the RCB stars tend toward those of the
bulge population but a much larger sample of stars is needed to determine the true
population. In order discover more RCB stars, we have used a series of WISE IR colorcolor cuts, to produce a sample of several thousand candidates that may yield over 200
new RCB star identifications. Solving the mystery of how the RCB stars evolve will lead to
a better understanding of other important types of stellar merger events such as Type Ia
SNe.
T16
Look Behind You! The Past Can Contribute
Uniquely to the Future
Elizabeth Griffin
The surveys which are the chief foci of this meeting are almost exclusively concerned
with recent and upcoming electronic surveys. But the practice of surveying the night sky
is not new; one of the first coordinated observatory activities involved surveys, of various
hues and sizes. For many decades the IAU itself paid tribute to that activity by supporting
a special Commission for it. The wealth of past surveys will be described briefly. Though
now regarded as limited in quality, early surveys carry date-stamps which enable their
contents to add usefully, sometimes critically, to modern science.
T17
LSST and Its Potential for Variable Star Research
Melissa Graham
Ž. Ivezić
The Large Synoptic Survey Telescope (LSST) will be a large (6.7m effective aperture),
wide-field (9.6 sq.deg. field-of-view) ground-based system designed to obtain deep
photometric data in six broad bands (ugrizy, 320-1050 nm). Each sky position will be
observed multiple times, with several hundred observations per band collected over the
main survey area (20,000 sq.deg. with equatorial declination<+34.5 deg) during the
anticipated 10 years of operations. The current observing strategy calls for about 10,000
sq.deg. of sky to be covered using pairs of 15-second exposures in two photometric
bands spaced by about an hour within a night, and every three nights on average, with
5-sigma depth for point sources of r~24.5. The measured properties of newly discovered
and known astrometric and photometric transients will be publicly reported within 60 sec
after closing the shutter. I will briefly review the status of LSST construction project and
will discuss opportunities for variable star research to be enabled by LSST.
T18
Pulsating Star Research and the Gaia Revolution
Laurent Eyer
Gaia is currently observing variability behaviours in unprecedented ways. All instruments
of Gaia will contribute to the description of variability phenomena. The astrometry, will
provide absolute magnitudes, the BP and RP spectrophotometry will be able to derive
colours. Astrometry combined with spectrophotometry is allowing to place the stars in the
HR diagram. The RVS instrument will also be able to measure radial velocities. The time
series of these different quantities will be able to determine how the magnitude, the
colour, change during a pulsation cycle. The release scenario will be explained. The
current strategy is to release the variability gradually during the mission, with more and
more stars, with longer time series and more data types at each release.
T19
The Hubble Catalog of Variables
Kirill Sokolovsky
Alceste Bonanos
Panagiotis Gavras
Maria Ida Moretti
Ming Yang
We aim to construct an exceptionally deep catalog of variable objects in selected Galactic
and extragalactic fields visited multiple times by the Hubble Space Telescope with the
same instrument/filter combination. While some of these fields were searched for specific
types of variables before (most notably, the extragalactic Cepheids), we attempt a
systematic study of the population of variable objects of all types at the magnitude range
not easily accessible with ground-based telescopes. The variability timescales that can be
probed range from hours to years depending on how often a particular field has been
visited. For source extraction and cross-matching of sources between visits we rely on
the Hubble Source Catalog (HSC) which includes 107 objects detected with WFPC2, ACS,
and WFC3 instruments in at least one visit. The lightcurves extracted from the HSC are
corrected for systematic effects by applying local zero-point corrections and are screened
for bad measurements. For each lightcurve we compute variability indexes sensitive to a
broad range of variability types. The indexes characterize the overall lightcurve scatter
and degree of correlation between consecutive brightness measurements. Candidate
variables in each field are selected as having variability index values significantly higher
than expected for objects of similar brightness in the given set of observations. The
candidates are inspected to distinguish true variables from objects with measurements
corrupted by blending or imaging artifacts. The completeness of the variable object
selection is evaluated through simulations. Our variability detection technique is
applicable to other time-domain surveys. This work is supported by the European Space
Agency (ESA) under contract No. 4000112940.
T20
Cepheids with the Eyes of Photometric Space
Telescopes
László Molnár
Aliz Derekas
Emese Plachy
Róbert Szabó
László Szabados
Space photometric missions have been steadily accumulating observations of Cepheids in
recent years, leading to a flow of new discoveries. The four-year data of lone Kepler
Cepheid, V1154 Cyg, revealed period jitter, modulation, granulation noise and the lack of
solar-like oscillations. MOST discovered period doubling in the modulated Cepheid V473
Lyr, suggesting that modulation may have similar origins in RR Lyrae and Cepheid stars.
And since the start of the K2 mission, Kepler already observed dozens of Cepheid stars in
the regular campaigns, and covered the nearby galaxy IC1613 and the galactic bulge
where hundreds of such variables reside, including many type II Cepheids, a class that
was scarcely observed from space before.
T21
Gaia’s Cepheids and RR Lyrae stars and the PL
Relations Based on Tycho-Gaia astrometric
Solution Parallaxes
Gisella Clementini
We have used parallaxes of Galactic Cepheids (Classical and Population II) and RR Lyrae
stars published in Gaia Data Release 1 as part of the Tycho-Gaia Astrometric Solution
(TGAS), along with literature (V, I, J, K) photometry and spectroscopy, to build:
i) period-luminosity (PL) and period-Wesenheit (PW) relations for both classical and type
II Cepheids; and ii) near-infrared PL, PL-metallicity (PLZ) and optical luminositymetallicity (Mv-[Fe/H])relations for the RR Lyrae stars, with zero points based on TGAS
parallaxes.
The classical Cepheids were selected as to remove known and suspected binary systems
and further reduced by retaining only sources with sigma_Pi/Pi < 0.5. Similar cuts were
also applied to both Type II Cepheids and a RR Lyrae stars. We present results from
application of these TGAS-based relations to estimate the distance to the Large
Magellanic Cloud. We also discuss the comparison of the TGAS parallaxes with Hipparcos
and HST parallaxes as well as with parallaxes inferred from the Baade-Wesselink method
and the theoretical model fitting of multi-band light curves.
T22
Asteroseismology and Galactic Archaeology in the
Era of Large Surveys
Víctor Silva Aguirre
Large spectroscopic and photometric surveys are strongly complimentary to the wealth of
asteroseismic data delivered by the Kepler and K2 missions. Combined they can provide
accurate properties of stars across the Galaxy and unveil the history of formation and
evolution of the Milky Way. In this talk I present the first results in this field from the
APOGEE and SAGA surveys, where we have measured for the first time the vertical age
gradient in the galactic disk, constructed the age metallicity relation for the population,
and determined the age difference between the thick and the think components of the
disk. I discuss the tests currently underway to ensure the robustness of stellar properties
from asteroseismology (ages in particular) and the future prospects for the field with the
advent of the TESS and PLATO missions.
T23
The K2 RR Lyrae Survey
Róbert Szabó
We have initiated a large survey with K2, to observe thousands of RR Lyrae stars along
the ecliptic. The high photometric precision and the 80-90-day continuous coverage will
allow us to investigate the light variation of these galactic structure tracer variable stars
with an unprecedented detail. The survey will help us to conduct a thorough statistical
study of RR Lyrae pulsation dynamics including old and recently discovered dynamical
phenomena, like resonances, non-radial modes, period-doubling and the Blazhko-effect.
In this talk I describe the survey, present the first results and discuss the prospects in
the light of what the combination of the survey and LSST (and also Gaia) will have to
offer in the context of galactic structure studies.
T24
RR Lyrae Star Distance Scale and Kinematics from
Inner Bulge to 50 kpc
Andrey Dambis
Leonid Berdnikov
Eva Grebel
Alexey Kniazev
Ivan Katkov
We compile the currently most complete sample of almost 5000 Galactic RR Lyrae
variables with available radial-velocity and spectroscopic [Fe/H] measurements adopted
from dedicated studies (about 440 stars), large-scale spectroscopic surveys (SDSS,
RAVE, LAMOST, a total of over 4200 stars), and based on the results of our program
aimed at acquiring spectra of relatively bright RR Lyrae variables carried out at South
African Large Telescope yielded radial velocities and metallicities (~200 hitherto
spectroscopically unexplored RR Lyraes). We complement the radial-velocity data for
these stars with accurate proper motions from the upcoming Tycho-Gaia catalog and
compute proper motions for fainter stars based on the UCAC4, URAT1, 2MASS, and
WISE, and DSS Schmidt plate positions reduced to the frame defined by UCAC4 catalog.
We further determine the mutually consistent preliminary distances to our RR Lyraes
based on our recent calibrations (Dambis et al. 2013, 2014) applied to WISE infrared
data, published photoelectric and CCD V-band data, reduced Catalina Sky Survey data,
and our own photoelectric (more than 1200 multicolor measurements) and CCD (more
than 40000 frames) photometry. We use the 3D velocity data obtained to perform a
statistical-parallax analysis for a subsample of ~1000 RR Lyraes brighter than V=16m to
refine the parameters of optical and IR period-metallicity-luminosity relations and adjust
our preliminary distances. We use the kinematic data for the entire sample to explore the
dependence of the halo and thick-disk RR Lyrae velocity ellipsoids on Galactocentric
distance from the inner bulge out to R~50 kpc, probe the mass distribution in the
Galactic halo, and estimate the distance to the Galactic center..
T25
Faint Variable Stars in the Milky Way dSph
Satellites
Kathy Vivas
Mario Mateo
Javier Alonso-García
Alistair Walker
David Nidever
Pulsating variable stars below the horizontal branch provide an interesting tool to study
the stellar population present in dSph galaxies. The region of the CMD may include not
only main sequence stars of a young and/or intermediate age population but also blue
stragglers from an old population. dSph galaxies contain stars that inhabit a different
age/metallicity range than found anywhere else in the Galaxy and so offer the chance to
study these faint variables from unique and otherwise hard to study populations. The
combination of a large FOV camera such as DECam in a 4meter class telescope presents
a unique opportunity to search for these variables in some of the satellites of the Milky
Way. We discuss results obtained in Sextans and Sagittarius galaxies.
T26
Pulsating Stars and the Virtual Observatory
Juan Carlos Suárez
Virtual Observatory is one of the most used internet-based protocols in astronomy.
It has become somewhat “natural” to find, manage, compare, visualize and download
observations from very different archives of astronomical observations with no effort. The
VO technology beyond that is now being a reality for asteroseismology, not only for
observations but also for theoretical models. This talk will give a brief description of the
most important VO tools related with asteroseismology, as well as a rough outline of the
current development in this field.
T27
Stellar Astrophysics from the Evryscope: The First
Simultaneous All-Sky High-Cadence Survey
Octavi Fors
Nicholas M. Law
Jeffrey Ratzloff
Daniel del Ser
Henry T. Corbett
The Evryscope is an array of 24 telescopes which covers a gigapixel-scale, instantaneous
8000-square-degree field-of-view at two-minute cadence. This telescope opens a new
parameter space in time-domain astronomy, trading instantaneous depth (g~16mag) and sky
sampling (~13”) for continuous coverage (97% survey time efficiency) of the largest sky area
of any active survey. The system provides percent-level photometry at two minute cadences
on bright (g<12) stars, with a per-exposure limiting magnitude of g~16 in a 100-degree
declination range. The photometric performance improves to 5-7 mmags when a ~30minute
binning is applied. The Evryscope team is using a list of 4500+ white dwarfs (WDs) candidates
down to g=17 and Dec<+10deg to conduct a large-scale survey (>1000+ targets per night)
for habitable planets transiting WDs. This exploration comprises the brightest, most nearby
WDs, and with higher precision than past ground-based surveys and faster cadence than
Kepler’s standard mode. With Evryscope simultaneously observing hundreds of WDs with
better than 10% photometric precision in each two-minute exposure, its data set allows us to
directly measure the population of small transiting objects around WDs. In addition, it enables
the possibility of obtaining long-term measurements of WDs pulsations, eclipsing WD binaries
and periodically variable WDs, and other objects which can constrain WDs fundamental
physics. As the Evryscope is also building 1%-precision, many-year-length, high-cadence light
curves for every accessible object brighter than g~16mag, its data set enables the discovery
and characterization of a wide range of stellar variability, including measuring the mass-radius
relation using by producing a complete inventory of eclipsing binary systems with orbital
periods < 60 days, detecting young stars by their flare behavior, and detecting stellar merger
events, accreting compact objects, and exotic pulsators.
The examples of the first pulsations and variability detections from both specific WDs and
synoptic stellar astrophysics surveys will be presented and discussed. The Evryscope was
deployed at CTIO in May 2015. The telescope is fully operational, streaming raw imaging data
per night at 109MB/sec, meaning 59TB of raw data have collected so far, totaling ~700,000
images. All data is stored and analyzed on-site by a high-speed server. Two more Evryscopes
are planned to be deployed in near future: at Mount Laguna Observatory (collaboration with
SDSU) and in the High Arctic (collaboration with NARIT and University of Toronto).
T28
Challenges in the Automated Classification of
Variable stars in Large Databases
Matthew J. Graham
With ever-increasing numbers of astrophysical transient surveys, new facilities and
archives of astronomical time series, time domain astronomy is emerging as a
mainstream discipline. However, the sheer volume of data alone - hundreds of
observations for hundreds of millions of sources - necessitates advanced statistical and
machine learning methodologies for scientific discovery: characterization, categorization,
and classification. Whilst these techniques are slowly entering the astronomer’s toolkit,
their application to astronomical problems is not without its issues. In this talk, we will
review some of the challenges posed by trying to identify variable stars in large data
collections, including appropriate feature representations, dealing with uncertainties,
establishing ground truths, and simple discrete classes.
T29
Compilation and Classification of Light-Curves
Catalogues for HiTS
Jorge Martínez Palomera
Francisco Förster
Pavlos Protopapas
The High Cadence Transient Survey is an effort to characterize fast transient objects
using high cadence, wide and deep observations, the data were taken using DECam at
Blanco/CTIO. My work consist in generate catalogues of detected sources and build light
curves of point-like, non-moving sources. The main goal is classify all variable objects
using time series analysis, starting from feature extraction, build the training set using
Transfer and Active Learning, to final classification with Machine Learning. We have about
2 millions light curves with data mainly in g and r band with a cadence of ~1.6 hours.
I will present results about catalogues (photometry calibration, efficiency, limiting and
completeness magnitude), light curves (main statistics), feature extraction and
preliminary results of classification of variable sources. This is my PhD thesis research.
T30
Studying Stellar Variability with a Decade of
HATNet Observations
John Hoffman
Joel Hartman
Gáspár Bakos
The Hungarian-made Automated Telescope Network (HATNet) has been carrying out
wideangle high-cadence photometric monitoring of the sky since 2004. Light curves have
been generated for over 5 million stars with 9 < r < 14.5. The typical star has 10,000
observations, and the precision reaches 4 mmag per three minute cadence at the bright
end. We report on our ongoing efforts to carry out a comprehensive study of stellar
variability with these data using machine-learning techniques.
T31
Finding Binaries from Phase Modulation of
Pulsating Stars with Kepler
Hiromoto Shibahashi
Simon Murphy
Tim Bedding
We explore the detection limits of the phase modulation (PM) method of finding binary
systems among multi-periodic pulsating stars. The method is an attractive way of finding
non-transiting planets in the habitable zones of intermediate mass stars, whose rapid
rotation inhibits detections via the radial velocity (RV) method. While oscillation
amplitudes of a few mmag are required to find planets, many  Scuti stars have these
amplitudes. In sub-optimal cases where the signal-to-noise of the oscillations is lower,
low-mass brown dwarfs (~13 MJup) are detectable at orbital periods longer than about
1 yr, and the lowest mass main-sequence stars (0.1-0.2 M) are detectable at all orbital
periods where the PM method can be applied. We use purpose-written Markov chain
Monte Carlo (MCMC) software for the calculation of the PM orbits, which offers robust
uncertainties for comparison with RV solutions. Using Kepler data and ground-based
RVs, we verify that these two methods are in agreement, even at short orbital periods
where the PM method undersamples the orbit. We develop new theory to account for the
undersampling of the time delays, which is also necessary for the inclusion of RVs as
observational data in the MCMC software. We show that combining RVs with time delays
substantially refines the orbits because of the complementarity of working in both the
spatial (PM) and velocity (RV) domains simultaneously. Software outputs were tested
through an extensive hare and hounds exercise, covering a wide range of orbital
configurations including binaries containing two pulsators.
T32
Survey-Invariant Variable Star Classification
using Bayesian Domain Adaptation
Pavlos Protopapas
Supervised data mining and machine learning rely on the availability of labeled data.
When sufficient training data is available, supervised models achieve high performance in
many domains. However, labeled data is often much scarcer than unlabeled data and
much more expensive and difficult to obtain. Moreover, when models that perform well in
one setting are applied to data from a different but related domain –e.g. from a different
population, a different geographical location, or a different instrument or sensor –
performance often drops significantly. Additionally, the enormous rate at which unlabeled
data is being generated greatly surpasses the rate at which labeled data becomes
available. Domain adaptation aims to learn from a domain where labeled data is
available, the 'domain', and through some adaptation perform well on a different domain,
the 'target domain'. In this talk, I present a new probabilistic model that represents the
source and target distributions as two Gaussian mixtures and finds a transformation
between the feature spaces of the domains to transfer labeled data between them. Our
approach allows working with data available in one domain as if it belonged to the other,
enabling the training of models in the target domain from training sets adapted from the
source domain. We evaluate our proposal in simulated data and the problem of variable
star classification. In the latter, we use data from two different astronomical surveys with
different characteristics in terms of sensor sensitivity, geographical location and
atmospheric conditions, and data sampling frequency, among others.
T33
The Impact of Gaia Parallaxes on Asteroseismic
Inferences from Kepler
Travis Metcalfe
Orlagh Creevey
et al.
The Kepler space telescope yielded unprecedented data for the study of solar-like
oscillations in other stars. The large samples of multi-year observations posed an
enormous data analysis challenge that has only recently been surmounted. Asteroseismic
modeling has also become more sophisticated over time, with better methods gradually
developing alongside the improved observations. We have applied the latest version of
the Asteroseismic Modeling Portal (AMP) science code to the full-length Kepler data sets
for 57 stars, deriving reliable estimates of the stellar properties including a theoretical
parallax for each target. We compare our predictions to the measured parallaxes from
the first data release of Gaia, and we quantify the level of improvement in asteroseismic
inferences when Gaia data are used to constrain the modeling.
T34
The VVV Galactic Cepheid Program: A Journey to
the Far Side of the Milky Way
István Dékány
Dante Minniti
Gergely Hajdu
Wolfgang Gieren
Márcio Catelan
Half of our Milky Way galaxy is located in a narrow stripe of the sky along the Galactic
equator, disguised by extreme extinction and foreground stellar populations. Mapping
these vast, distant Galactic regions using stellar tracers was impossible before the
existence of deep infrared time-domain observations. Unique data from the VVV Survey
now enables us to probe these regions using distant Galactic Cepheids, accurate standard
candles and well-understood population tracers. Unlike velocity-distance techniques,
these stellar beacons require no putative assumptions of the Galaxy’s kinematics, and
they are also useful along the Galactic center sight-line. In the framework of the VVV
Galactic Cepheid Program, we are conducting a deep census of both classical and type II
Cepheids along the Galactic plane and toward the bulge. We employ these valuable
beacons to probe the the far side of the disk, properties of the flared outer disk and the
inner disk region in the bulge volume; and search for hitherto unknown satellites of the
Milky Way beyond the far edge of its disk. By complementing photometry with
kinematical and elemental abundance measurements of the Cepheids, we are aiming to
probe the chemo-dynamical properties of the obscured inner bulge and the far side of the
Galactic disk, and infer global properties of the Galaxy such as general symmetry, spiral
arm configuration, abundance gradients, and bulk kinematics.
T35
Pulsating Variable Stars and Large Spectroscopic
Surveys
Peter De Cat
In the past decade, the research of pulsating variable stars has taken a giant leap
forward thanks to measurements provided by space missions like MOST, CoRoT and
Kepler. These missions have provided quasi uninterrupted photometric time-series with
an ultra-high quality and a total length that is unachievable with Earth-based
observations. However, many of the success stories could not have been achieved
without ground-based spectroscopic follow-up observations. Indeed, spectroscopy has
some important assets as it can provide (more) accurate information about:
(1) stellar parameters like the effective temperature, surface gravity, metallicity, and
abundances (that are mandatory important parameters for an in-depth asteroseismic
study),
(2) the radial velocity (that is important for the detection of binaries and for the
confirmation of cluster membership, if applicable), and
(3) the projected rotational velocity (that allows the study of the effects of rotation on
pulsations). Fortunately, several large spectroscopic surveys are (becoming) available
that can be been used for these purposes (like SEGUE, RAVE, APOGEE, and LAMOST). In
some cases, (sub)projects have been initiated with the specific goal to complement the
space-based photometry. In this review, several spectroscopic surveys are introduced
and compared with each other. Their impact on pulsating variable star research is
illustrated with some well-chosen examples. It highlights their potential both for in-depth
studies of individual stars and as ground-based support for (future) space missions.
T36
APOGEE and Pulsating Stars
Steve Majewski
The APOGEE survey, now in Phase 2 (APOGEE-2 in SDSS-IV) and soon to begin
operations in Chile, is continuing to deliver high resolution, near-infrared H-band spectra
of hundred of thousands of targets around the whole sky. Among the numerous primary
goals of the main APOGEE-2 survey is both a large survey of RR Lyrae stars in the
Galactic bulge as well as a continued focus on targets with asteroseismic data (described
more fully in a separate talk by M. Pinsonneault) from the CoRoT, Kepler and K2
missions. However, by both chance and design, the APOGEE project has sampled a few
other categories of pulsational variables, from hot blue varieties to Cepheids. The
APOGEE instruments play a major role in plans for “After Sloan IV”, opening a variety of
opportunities for further contributions to pulsational variable science, including all-sky
and time-series spectroscopic surveys.
T37
The LAMOST Spectroscopic Survey of Stars in the
Kepler Field of View: Activity Indicators and
Stellar Parameters
Joanna Molenda-Zakowicz
Antonio Frasca
Peter De Cat
Giovanni Catanzaro
For 51,385 stars of spectral types ranging from B to M located in the Kepler field of view,
we derived the atmospheric parameters (Teff, log g and [Fe/H]) and the radial velocities
(RV). Our results have been based on the low-resolution spectroscopic observations
obtained with the LAMOST facility in the framework of the LAMOST-Kepler project. The
accuracy of the parameters derived from the LAMOST data are typically 10–15 km/s in
RV, about 3.5 % in Teff, 0.3 dex in log g, and 0.2 dex in [Fe/H]. We notice a systematic
difference of about 0.2 dex between spectroscopic and photometric metallicities which is
consistent with earlier findings based on smaller data samples. The analysis of H alpha
and Ca II-IRT fluxes which allowed us to detect 442 chromospherically active stars, one
of which is a likely accreting object. Then, we made use of the precise rotation periods
from the Kepler photometry and we studied the dependency of the chromospheric fluxes
on the rotation rate for a quite large sample of field stars. Finally, we report on detection
of stars variable in RV, stars with very high projected rotational velocity (v sin i > 150
km/s), and emission-line objects.
T38
APOKASC 2.0: Asteroseismology and
Spectroscopy of Red Giants
Marc Pinsonneault
The APOGEE survey has obtained and analyzed high resolution H band spectra of more
than 10000 cool dwarfs and giants in the original Kepler fields, with up to 16,000 Kepler
stars anticipated in the 4th Sloan Digital Sky Survey. Spectra for an additional 13,000
giants with K2 data will also be obtained. The APOKASC effort combines this data with
asteroseismology, resulting in more than 7,000 stellar mass estimates for dwarfs and
giants with high quality abundances, temperatures, and surface gravities, with many
more anticipated. We highlight the main results from this effort so far, which include a
tight correlation between surface abundances in giants and stellar mass, precise absolute
surface gravity calibrations, and the discovery of unexpected stellar populations, such as
young alpha-enhanced stars. We discuss grid modeling estimates for stellar masses and
compare the absolute asteroseismic mass scale to calibrators in star clusters and the
halo. Directions for future efforts are discussed.
T39
Asteroseismology: The Kepler Revolution
Tim Bedding
Asteroseismology has entered a new golden age, thanks to wonderfully precise
measurements being returned by NASA's Kepler mission. Kepler is a 0.9-metre space
telescope that has been monitoring the brightness of more than 100,000 stars with
extraordinary accuracy for more than four years. Its main goal is to discover extra-solar
planets by detecting the small dips in light as they transit their parent stars. The mission
has been spectacularly successful, with thousands of candidates reported. Meanwhile,
Kepler's observations of oscillations in thousands of stars have led to a revolution in
asteroseismology. Key results include detecting gravity modes in red giant stars and
characterizing stars found to host exoplanets. Upcoming results from ESA's Gaia mission
will add to the excitement, as will the launch next year of TESS, which is an all-sky
follow-up mission to Kepler.
T40
TESS and the Future of Asteroseismology from
Space
Hans Kjeldsen
The Transiting Exoplanet Survey Satellite (TESS) is a NASA Explorer mission that will
observe several hundred thousand stars at a cadence of 2 minutes, as well as generating
Full Frame Images (FFI’s) at cadence of 30 minutes. TESS aims to do wide-field surveys
with the fine photometric precision and long intervals of uninterrupted observation, as
can only be done in a space mission. Compared to Kepler, TESS will examine stars that
are generally brighter by 4-5 magnitudes over a FOV at each pointing that is larger by a
factor of 25. TESS will observe at each pointing for 27 d, and the overlap between fields
means that a given target will be observed continuously for between 27d and 355 d,
depending on the ecliptic latitude. The TESS photometric data represent a unique
resource for asteroseismic investigations of the global properties and internal structure of
a large number of stars having a broad range of different types. Through investigation of
a broad range of stars the asteroseismic investigation will substantially improve our
understanding of general stellar evolution, and hence strengthen the use of such
modelling to further constrain the properties and evolution of the stars and systems
investigated in the TESS extrasolar planet program. In this talk I will discuss the
asteroseismic part of the TESS projects which is organized under the TESS Asteroseismic
Science Consortium (TASC). The goal of the TASC science program is to do asteroseismic
characterization of planet-hosting stars, including mass, age and particularly radius as
well as understanding general stellar properties, including stellar structure modelling and
contributing to stellar characterization. I will also discuss the future of asteroseismology
in relation to future spaces missions in particular the ESA PLATO mission.
T41
Asterosesimology of Main-Sequence Solar-Like
Stars with K2
Mikkel Lund
After the failure of a second of Kepler’s four reaction wheels, the mission was expertly
re-purposed into the ecliptic plane K2 mission. Compared to the nominal Kepler mission,
K2 will observe many nearby bright stars, providing the opportunity to apply asteroseismology to study the local solar neighbourhood. The bright targets provide powerful
tests of stellar structure and evolution, because follow-up and complementary
observations may be more readily obtained and combined with asteroseismology.
Importantly, K2 allows us to study many interesting stellar clusters, which were only
sparsely represented in the nominal Kepler mission, especially young clusters, such as
the Hyades, the Pleiades, Praesepe/M44, and M67, in addition to the old globular cluster
M4. I will in this talk present recent results obtained on solar-like oscillators observed
during K2 Campaigns 1-5.
T42
Asteroseismology of Red Giants in the Open
Cluster M67 – Finally!
Dennis Stello
M67 is arguably one of the most studied open clusters in history. This continuing interest
has been sparked by its near solar age and metallicity making it resemble the birth space
of the Sun. With the prospects of applying seismic techniques, as successfully done for
the Sun, recent decades also saw studies aimed at detecting solar-like oscillations in the
cluster stars, but with limited success due to the extremely low amplitude oscillations.
However, recent space missions have revolutionised our ability to perform asteroseismic
inferences on cool stars. From the the unfortunate end to NASA's Kepler mission arose
its successful ecliptic mission K2. Unlike previous missions, K2 can observe several
interesting stellar clusters; and M67 is one of them. In this talk I will show hot of the
press results on the asteroseismology of red giants in M67 observed by K2, from which
I will demonstrate the potential of this beautiful data set, which is already showing
interesting results among the red giants.
T43
Understanding Mixing Processes in A and F Stars
through Asteroseismology
Victoria Antoci
The A and F type stars occupy a region in the HRD where several physical processes
occur: it is in the classical instability strip where the transition between deep and efficient
to shallow convective envelopes takes place. This has an impact not only on pulsational
stability but also on stellar evolution, activity and transport of angular momentum. In this
talk I will highlight what we have learned about delta Scuti and gamma Doradus stars
from Kepler and K2 observations and show how ensemble studies of these stars can
contribute to our understanding of mixing processes such as atomic diffusion and
rotation.
I will further show that unlike what is generally accepted, the kappa mechanism is not
the sole mechanism to excite oscillations in delta Scuti stars. Models using timedependent non-local convection treatment predict the turbulent convection in the
hydrogen ionisation zone to coherently excite pulsations. Our results are consistent with
observations and can also explain the large fraction of pulsating chemically peculiar Am
stars. These stars are expected to be constant as due to the settling of He, this element
is not sufficiently abundant in the He II zone for the kappa mechanism to drive
pulsations.
T44
The  Dor Stars as Revealed by Kepler: A Key to
Reveal Deep-Layer Rotation in A and F Stars
Sébastien Salmon
Rhita Ouazzani
V. Antochi
T. Bedding
S. Murphy
I. Roxburgh
The  Dor pulsating stars present high-order gravity modes, which make them important
targets in the low-mass main-sequence region of the Hertzsprung-Russell diagram.
Whilst we have only access to rotation in the envelope of the Sun, the g modes of  Dor
stars can in principle deliver us constraints on the deep layers close to their convective
core. Yet, their pulsations remain hard to detect from the ground for their periods are
close to one day. While CoRoT space mission first revealed very puzzling frequency
spectra, the long and almost uninterrupted 4-year photometry from Kepler eventually
shed a new light on them. It revealed regularities in the spectra, expected to bear
signature of phycical processes in the shear layers close to the convective core. We
present here our effort to derive exploitable seismic diagnosis for mid- to fast rotators
among  Dor stars. These latter are based on the spacing in period between modes of
consecutive order. We systematicly explore a grid of  Dor models presenting a broad
range of stellar parameters and various physical prescriptions. With help of appropriate
pulsation codes, we determine the possible degeneracy induced by various set of stellar
parameters and explore how to derive the internal profile of rotation unequivocally. We
then deliver a first theoretical interpretation of some Kepler  Dor pulsation spectra.
T45
Pulsating Star Research from Antarctica
Merieme Chadid
In this invited talk, we implement a new way to study the stellar oscillations, pulsations
and their evolutionary properties with long uninterrupted and continuous precision
observations over 150 days from the ground, and without the regular interruptions
imposed by the earth rotation. PAIX–First Robotic Antarctica Polar Mission– gives a new
insight to cope with unresolved stellar enigma and stellar oscillation challenges. The
project is made of low cost commercial components, and achieves astrophysical
measurement time-series of stellar physics fields, challenging photometry from space
that shows large gaps in terms of flexibility during the observing runs, the choice of
targets, the repair of failures and the inexorable high costs. PAIX has yet more
advantages than space missions in observing in U BV RI bands and then collecting
unprecedented simultaneous multicolor light curves of several targets.
We describe the first polar robotized mission PAIX and the outcome of stellar physics
from the heart of Antarctica during several polar nights. We briefly discuss our first
results and perspectives on the pulsating stars and its evolution from Antarctica,
Finally, we highlight the impact of PAIX on the stellar physics study and the remaining
challenges to successfully accomplish the Universe explorations under extreme
conditions.
T46
Exposing White Dwarf Core Structures: Towards
Observational Constraints on Nuclear Burning and
Chemical Mixing of He-Core-Burning Phases
Noemi Giammichele
Stéphane Charpinet
Gilles Fontaine
Pierre Brassard
We present our latest results obtained from asteroseismic analyses of four pulsating
white dwarfs from the Kepler and Kepler 2 fields. Our seismic procedure using the
forward method based on physically sound, static models, includes a new core
parameterization leading us to reproduce the periods of these stars at the precision of the
observations. These new fits outperform current state-of-the art standards by order of
magnitudes. We precisely establish the internal structures of these stars and unravel the
inner C/O stratification of their core. By studying their internal chemical compositions,
and more precisely the C/O profiles, we can give better observational constraints on key
processes such as nuclear burning, convection, and mixing, that shape this stratification
over time.
T47
Core Overshoot and Convection in delta Scuti and
gamma Doradus Stars
Catherine Lovekin
Joyce Guzik
The effects of rotation on pulsation in delta Scuti and gamma Doradus stars are poorly
understood. Stars in this mass range span the transition from convective envelopes to
convective cores, and realistic models of convection are thus a key part of understanding
these stars. In this work, we use 2D asteroseismic modelling of 6 stars observed with the
Kepler satellite to provide constraints on the age, mass, rotation rate, and convective
core overshoot. We use Period04 to calculate the frequencies based on short cadence
Kepler observations of six gamma Doradus and delta Scuti stars observed with Kepler.
We then produce 2D rotating models of stars in the mass range 1.5 - 1.8 solar masses
and use a 2D pulsation code to calculate the adiabatic pulsation frequencies. Comparison
of these models with the pulsation frequencies of three stars observed with Kepler
allowed us to place constraints on the age, mass, and rotation rate of these stars. All
frequencies not identified as possible combinations were compared to theoretical
frequencies calculated using 2D models including the effects of rotation and overshoot.
The best fitting models for all six stars are slowly rotating at the best fitting age and have
moderate convective core overshoot. In this work, we will discuss the results of the
frequency extraction and fitting process.
T48
Inferences for Stellar Opacities from Seismic
Studies of the Hybrid  Cep/SPB Pulsators
Przemysław Walczak
Jadwiga Daszyńska-Daszkiewicz
Alexey Pamyatnykh
The hybrid pulsators, that exhibit oscillations both in low order p/g modes and high order
g modes, pose a challenge for pulsation theory and input physics because the range of
their observed frequencies cannot be explained by any standard model. To overcome this
shortcoming an increase of stellar opacities at certain depths has been invoked. It goes in
line with the recent experimental results which give the higher opacities for iron and
nickel. Although some achievements in seismic modelling with the modified opacities
have been made, still too few hybrid pulsators have been studied in that way to draw
some general conclusions and indicate a more clear direction. In order to explore
comprehensively the problem of mode excitation, we investigate the four  Cep/SPB
stars:  Eridani, 12 Lacertae,  Pegasi and Lupi. By changing the mean opacity profile as
a function of the depth, (log T), we try to account for both the observed frequency
range and the values of the frequencies. In order to decrease the number of possible
solutions, we make use of the non-adiabatic parameter f, whose value is very sensitive to
the structure of the subphotospheric layers where pulsations are driven. Our preliminary
results of this complex seismic modelling show the need for a significant modification of
the opacity profile to meet all the required conditions.
T49
Recent Progress in the Theoretical Modelling of
Cepheids and RR Lyrae Stars
Marcella Marconi
Cepheids and RR Lyrae are among the most important primary distance indicators to
calibrate the extragalactic distance ladder and excellent stellar population tracers, for Pop
I and Pop II, respectively. In this presentation I first mention some recent theoretical
studies of Cepheids and RR Lyrae obtained with different theoretical tools. Then I focus
the attention on new results based on nonlinear convective pulsation models in the
context of some international projects, including VMC@VISTA and the Gaia collaboration.
The open problems for both Cepheids and RR Lyrae are briefly discussed together with
some challenging future application.
T50
On the Effect of Rotation on the Evolution and
Pulsation Properties of Classical Cepheids
Richard I. Anderson
Hideyuki Saio
Sylvia Ekström
Georges Meynet
Here we present the important effects of rotation on the pulsational and evolutionary
properties of classical Cepheid variable stars. Rotation affects the luminosity, lifetime,
structure, and chemical composition of massive and intermediate-mass stars. Classical
Cepheids are intermediate-mass stars observed during an evolutionary phase that is
particularly sensitive to such effects, thus providing stringent tests for stellar models.
Moreover, Cepheids find versatile applications throughout astrophysics thanks to being
standard candles as well as tools for dating stellar populations. We have carried out the
first investigations into the effect of rotation on Cepheid properties based on Geneva
stellar evolution models covering a wide range of masses, metallicities, and initial
rotation rates. In this talk, we specifically present 1) mass-luminosity relations and how
rotation explains the Cepheid mass discrepancy; 2) observables affected by rotational
mixing; 3) results of a linear pulsation analysis; 4) period-age relations that depend on
the rotational history of Cepheid progenitors. Time permitting, we shall also show that
Cepheids obey a tight flux-weighted gravity-luminosity relation, which enables a distance
estimate complementary to the famous Leavitt law.
T51
Petersen Diagram Revolution
Radoslaw Smolec
Wojciech Dziembowski
Paweł Moskalik
et al.
Over the recent years, the Petersen diagram for classical pulsators, Cepheids and RR Lyr
stars, populated with a few hundreds of new multiperiodic variables. We will review our
analyses of the OGLE data, which resulted in the significant extension of the known, and
in the discovery of a few new and distinct forms of multiperiodic pulsation. The showcase
includes not only radial mode pulsators, but also radial-non-radial pulsators and stars
with significant modulation observed on top of the beat pulsation. First theoretical models
explaining the new forms of stellar variability will be briefly discussed. These include e.g.
excitation of strongly trapped non-radial modes of moderate degrees, both in Cepheids
and in RR Lyr stars, or resonant excitation of beat pulsation accompanied with
modulation. Some of the discovered variability types, e.g. with radial first overtone as the
dominant pulsation mode, and with additional variability, which is too slow to be
reconciled with the radial fundamental mode, still represent a challenge for stellar
pulsation theory.
T52
Pulsating Stars and the Extragalactic Distance
Scale: The State of the Art
Lucas Macri
I will present recent results from the SH0ES project, which obtained homogeneous
Cepheid photometry for ~3500 objects in V&I and ~2300 variables in H across 19
supernova hosts and 4 calibrators to determine the value of H0 with a total uncertainty of
2.4%. I will discuss the current 3.4 sigma "tension" between this local measurement and
predictions of H0 based on CMB observations and an assumed cosmological model.
I will review ongoing work by members of the SH0ES team on the absolute calibration of
the Milky Way Period-Luminosity relations using a novel astrometric technique with the
Hubble Space Telescope.
Lastly, I will highlight recent results from another collaboration on the development of
new statistical techniques to detect, classify and phase extragalactic Miras using noisy
and sparsely-sampled observations. I will present preliminary Mira P-L relations at
various wavelengths based on the application of these techniques to a survey of M33.
T53
Araucaria Project: Pulsating Stars in Eclipsing
Binary Systems
Bogumił Pilecki
Wolfgang Gieren
Dariusz Graczyk
Grzegorz Pietrzyński
The use of Cepheids as distance indicators has a long history and has proven to be very
useful. Our knowledge on these objects, however, was quite limited. The breakthrough
came with the discovery of a classical Cepheid in an eclipsing binary system, which let us
determine accurate physical parameters of the pulsating star, including its mass and
radius. Since than several other pulsating stars in eclipsing binary systems were
confirmed and analyzed by the Araucaria Project, including Type II Cepheids and an
object of a new class - Binary Evolution Pulsator. These discoveries has also made
possible the study of the projection factor determined directly from the modeling of light
and radial velocity curves. I will give a short summary on the published results and
present the current work and new challenges.
T54
Towards a Renewed Galactic Cepheid Distance
Scale from Gaia and Optical Interferometry
Pierre Kervella
Antoine Mérand
Alexandre Gallenne
Nicolas Nardetto
We are assembling a comprehensive understanding of the pulsation and close
environment of Cepheids. We developed a dedicated data analysis tool (SPIPS) that
combines all available observables (angular diameters from interferometry, radial
velocimetry, spectroscopic Teff, photometry) to derive the physical parameters of the
star (effective temperature, presence of infrared excess, reddening,...) and the ratio
distance/p-factor. Only a handful of trigonometric parallaxes of nearby Cepheids is
currently available, mainly from HST's Fine Guidance Sensor. The first Tycho-Gaia data
release in September 2016 will soon provide a sample of homogeneous distances to
nearby Cepheids, but with a limited accuracy. Within a few years, the full Gaia data
releases will solve the d/p degeneracy for a large number of stars and therefore allow us
to address the major systematics of the SPIPS technique. The outcome will be a robust
and accurate calibration of the Cepheid distance scale based on well-known Galactic
Cepheids. Binary systems including Cepheids are important for two reasons: (1) they can
provide us with highly precise independent distances and dynamical masses, (2) we can
directly measure the photometric bias imposed on the Cepheid’s apparent flux by the
companion. We are engaged in long term observing programs with the CHARA and VLTI
interferometers to secure an extensive set of interferometric measurements of Cepheids,
including angular diameters and binary orbits. I will present the first results and
prospects of our observing program.
T55
VEGA/CHARA and HARPS-N Observations of the
Prototype Classical Cepheid Delta Cep
N. Nardetto
A. Merand
E. Poretti
D. Mourard
M. Rainer
J. Storm
W. Gieren
The B-W method is used to determine the distance of Cepheids and consists in combining
the angular size variations of the star, as derived from infrared surface-brightness
relations or interferometry, with its linear size variation, as deduced from visible
spectroscopy using the projection factor. Observations of Delta Cep were secured with
the VEGA/CHARA interferometer over the full pulsation cycle of the star. These visible
interferometric data are consistent in first approximation with a quasi-hydrostatic model
of pulsation surrounded by a static circumstellar environment (CSE) with a size of CSE =
8.9+/-3.0 mas and a relative flux contribution of fcse = 0.07 +/- 0.01. A model of visible
nebula (a background source filling the field of view of the interferometer) with the same
relative flux contribution is also consistent with our data at small spatial frequencies. In a
second study, we analyze new HARPS-N spectra of Del Cep to measure its cycleaveraged atmospheric velocity gradient in order to better constrain the projection factor.
We found that these new HARPS-N observations of Delta Cep are consistent with our
decomposition of the projection factor.
T56
Properties of Anomalous and Type II Cepheids in
the SMC and LMC
Monika I. Jurkovic
Martin A. T. Groenewegen
The Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC) give us the
possibility to study individual variable star types in a new way. Literature data provide us
with photometric information about objects from the ultraviolet to the infra-red. Here we
would like to show the results of our study of 247 anomalous and Type II Cepheids in the
SMC and LMC detected by OGLE. Using the code: More of DUSTY (MoD), a modified
version of the DUSTY radiative transfer code, and the assumption that our objects are at
a known distance, luminosity and effective temperature were deteremined. From these
data the HRD of these objects was compared with the theoretical models. The radius and
masses of the examined stars was estimated, too. In the end, we have given the periodluminosity relations for the anomalous and Type II Cepheids.
T57
Pulsating Stars in  Centauri: Near-IR Properties
and Period-Luminosity Relations
Camila Navarrete
Márcio Catelan
Rodrigo Contreras Ramos
Javier Alonso-García
 Centauri (NGC 5139) contains many variable stars of different types including Type II
Cepheids, RR Lyrae and SX Phoenicis. We carried out on a deep, wide-field, near-infrared
variability survey of  Cen, using the VISTA telescope. We assembled an unprecedented
homogeneous and complete NIR catalog of RR Lyrae and SX Phoenicis stars in the field of
 Cen. In this contribution, in addition to describing our catalog and presenting the
derived light curves, we discuss the main characteristics of these variable stars, including
mean magnitudes, amplitudes, and transformation relations between those parameters in
the optical and JKs bands. Near-IR period-luminosity relations are also derived and used
to determine an updated (pulsational) distance modulus for  Cen, and compare with the
distance modulus that we obtained using the Type II Cepheid populations in the cluster.
For SX Phoenicis, we were able to derive, for the first time, empirical Period-Luminosity
relations in both the J and Ks bands.
T58
RR Lyrae Observations with Spitzer: Towards
A High Precision Population II Cosmological
Distance Scale
Massimo Marengo
Jillian Neeley
Giuseppe Bono
Vittorio Braga
Massimo Dall'Ora
The cosmological distance ladder, currently relying on Population I standard candles such
as Local Group Cepheids, is at odds with findings from Cosmic Microwave Background
Radiation experiments. Results from the Planck Collaboration reveal a ~3.0 sigma
“tension” in the measured value of H0 that could be a strong indication of new physics in
the current Lambda CDM models. To resolve this fundamental issue we are developing an
independent route to the cosmological distance scale, based on infrared observations of
Population II stellar indicators: RR Lyrae variables. We present here the first results from
our Spitzer Space Telescope survey of RR Lyre in the field and Galactic globular clusters.
We demonstrate that period-luminosity-metallicity relations for these stars at near(Braga et al. 2015) and mid-infrared (Neeley et al. 2015) wavelengths allow measuring
distances with better than 2% accuracy. We show how our results, combined with
upcoming instrumentation (e.g. JWST and WFIRST) capable to extract RR Lyre light
curves within the entire Local Group of galaxies, will enable the calibration of an
independent distance ladder anchored on these Population II pulsators, and the globular
clusters where they are commonly found.
POSTERS
(Posters are listed in alphabetical order, according to the presenting author’s
family name. The latter is shown in boldface type.)
P1
Variable stars in the VVV globular clusters
Javier Alonso-García
Márcio Catelan
Rodrigo Contreras Ramos
István Dékány
Dante Minniti
The VVV survey has been observing the inner regions of the Milky Way during the last 6
years. There are 36 known Galactic globular clusters in the surveyed area. Most of them
are poorly known, due to the elevated presence of gas and dust in their lines of sight.
The VVV survey allows us not only to observe these globular clusters from their very
centers out to their tidal radii and beyond at near-infrared wavelengths were the effect of
extinction are highly diminished, but also to search for their variable stars thanks to its
multi-epoch observations. In our contribution, we will show the first results of the
analysis of the color magnitude diagrams of these clusters and the light-curves of their
variable stars. We will explore what these analyses tell us about the physical parameters
of these globular clusters and the extinction towards these objects. We will also discuss
their Oosterhoff properties, and how they fit in the Oosterhoff dichotomy paradigma that
seems to be present in our Galaxy.
P2
Physical and pulsation characteristics of the
CoRoT-observed Be star HD 171219
Learte Andrade
Eduardo Janot-Pacheco
Marcelo Emilio
Yves Fremat
We analyzed the Be Star HD 171219, observed with the CoRoT satellite during a 77.56
day run, in order to determine its physical and pulsation characteristics. High resolution
ground-based spectroscopic observations with HARPS and SOPHI were also obtained
during the month preceding the CoRoT observations. Tens of frequencies have been
detected in the object compatible with non-radial g-modes, including a quintuplet
centered around 1.113 c/d (12.88 µHz) identified as a pulsation of degree l~2. The star
underwent at least 6 small outbursts during the CoRoT observations. The relative
intensity of the main frequencies varied after each outburst suggesting that the stability
of the star and the feeding of the envelope are linked to the pulsation regime.
P3
Intermittent Mass Blowout of the Red Supergiant
S Persei
Yoshiharu Asaki
Hiroshi Imai
S-.H. Cho
and ESTEMA team
Red supergiants (RSGs) are in the near-final stage evolved from OB stars whose mass is
higher than ten times of Sun’s. Although severe mass loss is often observed for RSGs, it
is still unclear what can trigger the event and how the mass loss is connected to the RSG
physical structures because it is said that RSGs have lower pulsation amplitudes. Here we
report high spatial resolution images of single epoch three SiO maser transitions and one
H2O maser transitions. Simultaneous observation of the masers claim that the SiO
masers are spatially distributed in the central 100 AU region surrounded by the 400 AU
H2O maser distribution. From the long period visual lightcurve, S Persei has repeated
active and quenched pulsation phases by turn for several decades. It is considered that
S Persei has had intermittent mass blowout repeatedly when the pulsation is active for
several years.
P4
Pulsational instabilities in blue and extreme prehorizontal branch stars
Tiara Battich
Marcelo M. Miller Bertolami
Alejandro H. Córsico
Leandro G. Althaus
The -mechanism is a self-excitation mechanism of pulsations which acts on the regions
inside the star where nuclear burning takes place. Due to the strong dependence of
nuclear burning rates on temperature, the temperature perturbations induced by
pulsations lead to an increase in the oscillation energy at the expense of the thermal
energy of the star. Although the mechanism works wherever nuclear reactions are active,
the pulsation amplitudes tend to be small in the high temperature layers where nuclear
energy is generated so that the -mechanism is usually very weak. To the date there is
not confirmation of -mechanism as the responsible of the excitation of pulsations of any
star. However, it has been shown that -mechanism can excite pulsations in stellar
models that undergo a hot helium-core flash, and the subsequent subflashes, before the
star model settles into the stable helium core-burning phase. Moreover, it has been
shown that the pulsations of LS IV-14o116, the only He-sdBV detected to the date, could
be explained that way. In the present work we aim to extend the study of the mechanism effects on stellar models appropriate for stars on the blue and extreme prehorizontal branch, that undergo the helium sub-flashes that take place before the heliumcore burning phase. With this aim we perform detailed computations of non-adiabatic
nonradial pulsations on such stellar models, adopting different values of metallicity, initial
helium abundances and mass of the hydrogen envelope at the time of the main helium
P5
Variable stars around selected open clusters in
the VVV area
Jura Borissova
Nicolas Medina
Radostin Kurtev
Márcio Catelan
We will present some resent results of variable stars investigation in the close vicinity of
selected galactic open clusters projected in the VVV area.
P6
A Review of Spectroscopic Frequencies and Modes
in  Doradus Stars
Emily Brunsden
K. R. Pollard
P. L. Cottrell
D. J. Wright
This work presents the spectroscopic frequency analysis and mode identification of the
class prototype,  Doradus. In addition the results of 22 further stars studied using
ground-based observations in both photometry and spectroscopy are reviewed. Of these
stars two are binary stars and one is a hybrid  Scuti -  Doradus Star. Despite the small
numbers of classifications, there are enough to identify some class features and compare
these to pure frequency identifications such as those from Kepler.
P7
Asteroseismology of the GW Virginis stars
SDSS J0349 - 0059 and VV 47
Leila Magdalena Calcaferro
Alejandro Hugo Córsico
Leandro Gabriel Althaus
GW Virginis stars are a well-studied class of nonradial g-mode pulsators. SDSS J03490059 and VV 47 are two PG 1159 star members of this class of variable stars. SDSS
J0349-0059 is an interesting GW Vir star that shows a complete pulsation spectrum that
includes rotational splitting of some of its frequencies. VV 47 is a pulsating PG 1159 star
surrounded by a planetary nebula. This star is particularly interesting because it exhibits
a rich and complex pulsation spectrum. We present an asteroseismological study of SDSS
J0349-0059 and VV 47 aimed mainly at deriving their total mass on the basis of state-ofthe-art PG 1159 evolutionary models. We computed adiabatic nonradial g-mode pulsation
periods for PG 1159 evolutionary models with stellar masses ranging from 0.515 to 0.741
Msun, that take into account the complete evolution of the progenitor stars. We first
estimated a mean period spacing for both SDSS J0349-0059 and VV 47 and then
constrained the stellar mass of these stars by comparing the observed period spacing
with the asymptotic period spacing and with the average of the computed period
spacings. We also employed the individual observed periods to search for a
representative seismological model for each star. Finally, we estimated the rotation
period of SDSS J0349-0059.
P8
Pulsational stability of very hot, high-luminosity
pre-white-dwarf stars evolved from
low-metallicity progenitors
María E. Camisassa
Leila M. Calcaferro
Alejandro H. Córsico
Leandro G. Althaus
Hiromoto Shibahashi
White dwarf models evolved from low-metallicity progenitors have a thick hydrogen
envelope, which makes hydrogen shell burning be the most important energy source. We
investigate the pulsational stability of pre-white-dwarf models to see whether nonradial
g-mode pulsations are triggered by hydrogen burning, with the aim of placing constraints
on hydrogen shell burning in hot, high-luminosity white dwarfs. We extend the study by
Maeda & Shibahashi (2014) who predicted that some low-order g modes are excited by
the  mechanism due to vigorous hydrogen shell burning in very hot and luminous prewhite dwarfs with hydrogen-rich envelopes derived from solar metallicity progenitors.
P9
Whiting1: confirmation of its accretion by the
Milky Way
Julio A. Carballo-Bello
Globular clusters have played an important role in the study of the processes that led to
the formation of our Galaxy. Moreover, the dual Galactic globular cluster system is
considered a manifestation of its hierarchical formation in the context of the LambdaCDM scenario. Wide-field imaging and spectroscopy, as the ones obtained for our project,
are crucial tools to unveil the remnants of their progenitor dwarf galaxies, already
assimilated by the Milky Way. In this poster, we present our results for Whiting1, where
VLT/VIMOS MOS spectroscopy reveals the presence of a component of the Sagittarius
tidal stream with a radial velocity – and distance – compatible with that of the globular
cluster. Therefore, we conclude that Whiting1 was formed in the interior of the
Sagittarius dSph and later accreted by the Milky Way.
P10
A machine learned classifier for RR Lyrae in the
VVV survey
Felipe Elorrieta
Susana Eyheramendy
Andrés Jordán
István Dékány
Márcio Catelan
Rodolfo Angeloni
et al.
Variable stars of RR Lyrae type are a prime tool with which to obtain distances to old
stellar populations in the Milky Way. One of the main aims of the Vista Variables in the
Via Lactea (VVV) near-infrared survey is to use them to map the structure of the Galactic
Bulge. Owing to the large number of expected sources, this requires an automated
mechanism for selecting RR Lyrae, and particularly those of the more easily recognized
type ab (i.e., fundamental-mode pulsators), from the 106−107 variables expected in the
VVV survey area. In this work we describe a supervised machine-learned classifier
constructed for assigning a score to a Ks-band VVV light curve that indicates its likelihood
of being ab-type RR Lyrae. We describe the key steps in the construction of the classifier,
which were the choice of features, training set, selection of aperture, and family of
classifiers. We find that the AdaBoost family of classifiers give consistently the best
performance for our problem, and obtain a classifier based on the AdaBoost algorithm
that achieves a harmonic mean between false positives and false negatives of ≈7% for
typical VVV light-curve sets. This performance is estimated using cross-validation and
through the comparison to two independent datasets that were classified by human
experts.
P11
Determining the core stratification in white
dwarfs with asteroseismology
Stephane Charpinet
Noemi Giammichele
Pierre Brassard
Gilles Fontaine
We present a novel approach to determine the C/O stratification in the core of pulsating
white dwarfs using asteroseismology. This stratification, inherited from previous
evolutionary phases, is one of the most uncertain aspect of white dwarf internal structure
and more generally traces back to major shortcomings in our understanding of the
helium core burning phases and beyond. In this contribution, we discuss the method and
tests demonstrating the feasibility of this approach.
P12
Catalogue of Variable Stars in Milky Way Globular
Clusters
Christine Clement
I continue to work on updating the catalogue of variable stars in Galactic globular clusters
(Clement et al. 2001, AJ, 122, 2587). It is posted on my website:
www.astro.utoronto.ca/~cclement/read.html. The catalogue is arranged as a set of 149
files, one for each cluster. In my presentation, I will report on the current census of
variable stars in Galactic globular clusters and show how it has changed over the years.
P13
Large Binocular Telescope (LBT) view of
Andromeda's dwarf spheroidal satellites
F. Cusano
A. Garofalo
G. Clementini
et al.
Results are presented from deep time series observations of four dwarf spheroidal
galaxies (dSphs) in the Andromeda (M31) complex, namely, And XIX, And XXI, And XXV
and And XXVII, that we have resolved in stars using the Large Binocular Cameras of the
Large Binocular Telescope (LBT). Thanks to the LBT observations we discovered a total of
over 200 RR Lyrae stars and 20 Anomalous Cepheids in these M31 satellite galaxies. We
have characterized the stellar populations and the spatial distributions of their resolved
stars and found evidence for different stellar generations and processes of merging and
disruption occurring in these M31 dSphs. We have also identified a candidate globular
cluster in the center of And XXV, thus further increasing the observational evidence that
globular clusters sitting in the core of dwarf galaxies are not an unusual feature both
among the Milky Way and Andromeda's satellites.
P14
Looking for the nature of Stellar Rotation in solartype stars
Cristián Cortés
Márcio Catelan
José Renan De Medeiros
Alejandra Recio-Blanco
Rotation is one of the most important observable for our understanding of the evolution
of stars. The CoRoT and Kepler space missions represent unique possibilities for the
measurements of rotation period for statistically robust sample of stars, offering the
necessary tools for the study of rotation and its role on stellar evolution. In this context,
an essential step is the physical characterization of stars, in particular because the
computation of reliable photometric period of from CoRoT and Kepler observations, would
became a hard work without the help of the stellar parameters. This project is carrying
out a complete analysis of the stellar rotation and momentum on a sample of solar-type
stars (understood as main-sequence stars of spectral types FGK, and their more evolved
counterparts) with different masses along the HR diagram. These stars were observed by
the CoRoT satellite and also, will be observed by the Kepler satellite in the Kepler 2 (K2)
mission. This analysis takes into account the combination of spectroscopic (groundbased) data and photometric observations from CoRoT and Kepler in order to pin down
the stellar rotation.
P15
Effective temperatures of Cepheids and the
distance scale problem
Alexey Rastorguev
Andrey Dambis
Marina Zabolotskikh
Maria Ostashova
Multi-phase measurements of the effective temperatures of 33 Milky Way Cepheids
derived by Luck, Andrievsky, Kovtyukh et al. (2005-2008) from high-resolution spectra,
are used to estimate directly their luminosities and distances. Cepheid's radii variations
are calculated by the generalized L. Balona technique on the base of BV photometry and
precise radial velocity measurements obtained with CORAVEL-type spectrometer during
last 25 years. Cepheid PL relation is derived.
P16
The evolved slowly pulsating B star 18 Peg: A
testbed for upper main sequence stellar evolution
Andreas Irrgang
Peter De Cat
Andrew Tkachenko
Conny Aerts
The predicted width of the upper main sequence in stellar evolution models depends on the
empirical calibration of the convective overshooting parameter. Despite decades of
discussions, its precise value is still unknown and further observational constraints are
required to gauge it. Based on a photometric and preliminary asteroseismic analysis, Irrgang
et al. (2016, A&A 591, L6) showed that the mid B-type giant 18 Peg is one of the most
evolved members of the class of slowly pulsating B stars and, thus, bears tremendous
potential to derive a tight lower limit for the width of the upper main sequence. In addition,
18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric,
more than 6-year orbit. However, to exploit the full potential of this star as benchmark object
for stellar evolution theory, additional observations are required. In 2016, 18 Peg is
approaching periastron and is hence in the orbital phase were the orbital velocity is changing
fast. We therefore organised a follow-up campaign with the HERMES spectrograph attached to
the 1.2-m Mercator telescope (Roque de Los Muchachos Observatory, La Palma, Canary
Islands) to gather high-quality, high-resolution spectra appropriate for the fine-tuning of the
orbit and for a detailed study of the main pulsation mode. In this poster, we will present
updated results based on the new spectroscopic data. To complete the asteroseismic study,
18 Peg has been proposed as a target for the BRITE-constellation and will (probably) be
observed for 27 days with the future space-mission TESS (to be launched in December 2017)
to gather a complementary time-series of accurate photometry with a sufficiently long timebase to be able to study the expected low amplitude modes that have remained unobserved
so far.
P17
Between Cepheids and the Cosmos
Nancy R. Evans
Scott Engle
Ed Guinan
Hilding Neilson
Massimo Marengo
Lynn Matthews
Moritz Guenther
We have a number of tantalizing clues about material above the photosphere in classical
Cepheids: Spitzer fluxes including an apparent resolved bow shock in Delta Cephei itself,
H I 21 cm observations, and circumstellar shells from interferometric observations. The
understanding of how these are related is patchy. There are a number of photospheric/
chromospheric diagnostics from HST UV spectra, confirming pulsation related activity
immediately following minimum radius. The recent addition to these diagnostics is a brief
X-ray increase at the surprising phase of maximum radius (when the photospheric UV
lines are quiescent). The fast increase and subsequent fast decline suggest a shock
phenomenon. The simplest characterization is a shock at about 2 stellar radii. The phase
dependence ties this activity to pulsation. We will discuss the observational evidence and
also plans for theoretical studies. This new clue is related to the questions of pulsation
driven mass loss, and also the use of the IR in the Leavitt relation.
P18
RR Lyrae stars as tracers of halo substructures
Sonia Duffau
Kathy Vivas
Julio Carballo-Bello
Camila Navarrete
Márcio Catelan
The study of the substructures present in the Galactic halo provides vital information
about its origin and history, as well as constraints on the models of hierarchical galaxy
formation and evolution. RR Lyrae stars have proven to be excellent tracers of halo
substructures, due to the quality of the distances that can be derived from them, and the
relatively straightforward methods that lead to their clean identification. In this poster I
will present the techniques we have used and developed to unveil halo substructures
using RR Lyrae stars. I will present a spectroscopic survey we are conducting using
Catalina Real-time Transient Survey RR Lyrae targets in the southern sky, and show how
our preliminary results connect (if they do) with structures discovered studying the
Northern sky.
P19
4-Years Interferometric Observations of Galactic
Binary Cepheids: Update and Status
Alexandre Gallenne
Cepheid stars are powerful astrophysical laboratories providing fundamental clues for
studying the pulsation and evolution of intermediate-mass stars. However, one of the
most fundamental parameters, the mass, is a long-standing problem since decades
because of the 10-20% difference between masses predicted from stellar evolution and
pulsation models. Cepheids in binary system are the only tool to constrain models and
progress on this mass discrepancy. Unfortunately, most of the companions are too close
to the Cepheid (< 40 mas) to be observed with 8-meter class telescopes, and the highcontrast between the companions and the Cepheids makes the detection even more
difficult. A technique able to reach high spatial resolution and high dynamic range is longbaseline interferometry (LBI). This talk aims at giving an update on our long-term
interferometric program starting in 2012, which aims at detecting and measuring the
astrometric positions of the companions. Using the VLTI/PIONIER and CHARA/MIRC
instruments, we have now detected several components, and we start having a good
orbital coverage for some of them. By combining interferometry and radial velocities, we
can now derive all the orbital elements of the systems, and we will be soon able to
measure the Cepheid masses.
P20
A search for low-metallicity pulsating B stars
Chris Engelbrecht
We report on our latest results from a long-term UBVI survey of various fields in the LMC,
with the aim of identifying and classifying pulsating B stars (i.e. Beta Cephei, SPB and
hybrid pulsators) in the selected fields.
P21
Machine Learning Techniques to Select Variable
Stars
José Alejandro García-Varela
M. F. Pérez-Ortiz
B. E. Sabogal
A. J. Quiroz
Long time variability surveys are producing a very large number of high quality light
curves. Machine learning techniques and, particularly, statistical pattern recognition
methods have proved to be quite useful in classification of variable stars. In the existing
literature, quantities related to the magnitude density of the light curves and their Fourier
coefficients are chosen as features. However, the calculation of Fourier coefficients is
computationally expensive for large data sets. In order to perform a supervised
classification, we propose and evaluate a set of six features, extracted from the
magnitude density of the light curves, and used to train the automatic classification
system. These features are based on robust descriptive statistics that can be calculated
efficiently and do not need to be checked externally. We calculate the set of features on
six types of OGLE-III variable stars and also on a set of Be Star Candidates reported in
the literature. We evaluate its performance over the following state-of-the-art classifiers:
K-nearest neighbors, classification trees, random forests, support vector machines, and
gradient boosted trees. We use 10-fold cross-validation to estimate the recall and
precision of these classifiers. We implement the classifiers in the R statistical computing
environment, and validate them on a set of OGLE-IV light curves.
P22
Infrared surface-brightness Bade-Wesselink
analysis for selected Cepheids in the SMC
Marek Gorski
Wolfgang Gieren
Bartlomiej Zgirski
Piotr Konorski
The basis of the Bade-Wesselink (BW) distnce measurement method is very well
established, since it is a conceptually simple semi-geometrical method. Unfortunately, up
to this day only one precise zeropoint calibration exist.
We present the preliminary results of Infrared surface-brightness Bade-Wesselink
analysis for 20 Cepheids in the Small Magellanic Cloud. Results are based on a precise
radial velocity measurements and photometry in the infrared K and optical V bands.
Presented measurements will allow to calibrate the zero point of this method and
calculate the p-factor value, which will substantial improve the Bade-Wesselink distance
estimation method.
P23
The comparison of eclipsing binary and BaadeWesselink distances to OGLE-LMC-CEP-0227
Dariusz Graczyk
The eclipsing binary cepheid CEP-0227 in the LMC is one of the prime targets of our
program to understand fully systematics connected with Baade-Wesselink method of
distance determination. Because of favorable geometrical configuration of this binary
system we can determine very precisely physical parameters of both components: a
short period fundamental Cepheid and a nonvariable ordinary red giant star. We
measured distance to the system by two mostly independent ways: eclipsing binary
method and Baade-Wesselink method applied to the pulsating components. By
comparison of resulting distances we derive directly p-factor for this cepheid and we
discuss this result in a wider context of p-factor “controversy”.
P24
Infrared excess in Semi-Regular variables in the
Magellanic Clouds
Martin Groenewegen
By systematically exploring the ViZier database we constructed the spectral energy
distribution of about 100 LPVs that have I, (V-I) colours similar to Type-II Cepheids. We
are interested in objects that have lightcurves similar to RV Tau objects but with periods
longer than the formal limit used by the OGLE team in their selection of Type-II
Cepheids. By fitting stellar photosphere models we determine luminosity and effective
temperature, but of interest here are stars that might show an infrared excess. First
results will be presented.
P25
Stellar Observations Network Group (SONG)
Frank Grundahl
Victoria Antoci
Mads F. Andersen
Jørgen Christensen-Dalsgaard
Hans Kjeldsen
SONG is a Danish-led collaborative project set to design and build a global network of
small telescopes that should specifically target the study of stars and planetary systems
around stars. The objective was to develop a prototype of a new modern robotic
telescope that would be inexpensive and efficient to run. The Hertzsprung SONG
Telescope, i.e. the prototype of the SONG network, is located at the Observatorio del
Teide (OT) of the Instituto de Astrofisica de Canarias (IAC) in Tenerife. The telescope is
equipped with a high-resolution spectrograph aiming at precise radial velocity
measurements and will have the capability of performing photometry using the Lucky
Imaging technique.
P26
RR Lyrae binary systems in the Galactic bulge
Gergely Hajdu
Márcio Catelan
RR Lyrae stars are fundamental stellar probes of astrophysics: their easily identifiable,
characteristic light curves, together with their well-known magnitudes, makes them
excellent distance indicators. Furthermore, the properties of their pulsation (period, lightcurve amplitude and shape) are strongly dependent on the stellar interior, thus providing
important constraints on the theory of the structure and evolution of old, low-mass stars.
However, the theories of stellar pulsation and evolution both lack a crucial constraint: no
direct mass measurements for any RR Lyrae star has ever been reported, which can be
mainly attributed to the lack of reported RR Lyrae stars in binary systems. Lately, there
has been a renewed interest in finding RR Lyrae binary systems by multiple independent
groups. Among these, our search utilizing the decade-long photometry of the OGLE
project towards the Galactic bulge has proven the most successful so far, with ~20
strong candidates found among the analysed ~2000 highest-quality light curves. In this
poster, we describe our continued search and preliminary results for RR Lyrae binaries,
utilizing the treasure trove of OGLE photometry.
P27
Using APASS and 2GSS for Studying Variable
Stars
Arne A. Henden
Stephen Levine
Doug Welch
Dirk Terrell
The AAVSO Photometric All-Sky Survey (APASS) provides calibrated magnitudes in the
range 7 < V < 17 for the entire sky, in BVugriZ_sY bandpasses. It has had 10 data
releases, and is available at VizieR or from the AAVSO web site. While primarily designed
for 0.02mag calibration, it provides photometry over a many-year baseline, and also has
near daily cadence in the standard field regions on the equator. Likewise, the 2nd
Generation Synoptic Survey (2GSS) is designed to be a follow-on to APASS, and will
provide daily cadence in two passbands for the entire sky. While APASS has low cadence,
it has wide spectral coverage, essential for disentangling many variable-star types. While
2GSS has daily cadence, it still pales in comparison with other transient surveys.
However, it provides simultaneous 2-color photometry with finer resolution than even
APASS. Combined, these two surveys enable variable-star studies in a different regime
than any other existing survey. This paper will describe some methods of utilizing APASS
and 2GSS, present some caveats, and suggest future directions for optimal all-sky
surveys.
P28
Fast template periodogram: application to
targeted searches of periodic variable stars
John Hoffmann
Not yet available.
P29
Newly identified young “dipper” stars in Upper
Scorpius and Rho Ophiuchus star-forming regions
Valentin D. Ivanov
Young stars are typically irregular variables, and they change their brightness on
different time scales, due to a number of mechanisms. The starts with disks tend to be
more variable than the rest, and some of them show relatively short (usually up to 1-3
days) and sharp flux drops on the top of smooth light curves. We applied a combination
of automated search and visual inspection of the K2 mission Campaign 2 data to identify
24 “dippers” in the Upper Scorpius and the Rho Ophiuchus star-forming regions, nearly
doubling the existing sample. This behaviour is more common than previously tough, and
extends down to the brown dwarf mass regimen.
P30
The status and preliminary results of KMTNet
Young-Beom Jeon
The KMTNet (Korea Microlensing Telescope Network) was completed on October 2nd in
2015. There are three 1.6 m telescopes in Chile (CTIO), Australia (SSO) and South Africa
(SAAO), respectively. The field of view of the CCD camera is 2 arc degree x 2 arc degree.
We are monitoring and observing the bulge region for 24-hour continuous observation
using the KMTNet telescopes. I will present the characteristics of CCD camera and
telescope, and the status of observation programs. We are still developing CCD cameras
and telescopes to accurate photometry. I will show also preliminary results for exoplanet
search program, super nova search program, minor planet search program and extra
galaxy observation program, etc., respectively. And we can obtain 24-hour huge
continuous time-series data for many variable stars.
P31
Precise distances to Local Group galaxies from
infrared photometry of RR Lyrae stars
Paulina Karczmarek
In course of the Araucaria Project we determined true distance moduli from near-infrared
photometry of RR Lyrae stars to five Local Group galaxies: LMC, SMC, Sculptor dSph,
Carina dSph, and Fornax dSph. We applied period-luminosity-metallicity calibrations
available in the literature to high-quality data obtained with SOFI/NTT and HAWKI/VLT
instruments, located on La Silla and Paranal, Chile. Our data were collected, reduced and
analyzed in consistent and homogeneous way, and yielded results with precision of 5% or
better. This method is particularly suitable for galaxies and globular clusters that lack
young standard candles, like Cepheids.
P32
The connection between period spectra and
constraints in white dwarf asteroseismology
Agnes Kim
White dwarfs are the end product of evolution for around 98% of the stars in our Galaxy.
Buried in their interiors are the records of physical processes that take place during
earlier stages in the life of the star. Not long after the discovery of the first pulsating
white dwarf, the promise of asteroseismology to unveil the interior structure of white
dwarfs and therefore help us constrain their prior evolution became apparent. In recent
years, a well-established theory of non-radial oscillations, improved white dwarf models,
year of expertise built up in the field of white dwarf asteroseismic fitting, and computing
power have culminated in the asteroseismology finally delivering what it promised: a
detailed map of the interior structure of white dwarfs. As always in science, new results
raise new questions. We perform a number of numerical experiments to better
understand the connection between a given set of periods varying in the number of
periods and in the set of radial overtones and the quality of the constraints on interior
structure one obtains from fitting these periods.
P33
Little Bear's Pulsating Stars: Variable Star Census
of dSph UMi Galaxy
Karen Kinemuchi
Katie Grabowski
Charles Kuehn
James Nemec
Recent observations and a photometric search for variable stars in the Ursa Minor dwarf
spheroidal galaxy (UMi dSph) are presented. Our observations were taken at Apache
Point Observatory in 2014 and 2016 using the 0.5m ARCSAT telescope and the 3.5m
telescope with the SPICam and ARCTIC instruments. Previously known RR Lyrae stars in
our field of view of the UMi dSph are identified, and we also catalog new variable star
candidates. Tentative classifications are given for some of the new variable stars. We
have conducted period searches with the data collected with the ARCSAT telescope. With
the 3.5m telescope, higher resolution time-series photometry was performed on two
irregular variable stars, V80 and v3977, to clearly classify their variability. With our
sample of RR Lyrae stars, we investigate any period and amplitude modulation from our
datasets. Our ultimate goal is to create an updated catalog of variable stars in the UMi
dSph and to compare the RR Lyrae stellar characteristics to other RR Lyrae stars found in
the Local Group dSph galaxies. The comparisons can give us insights to the near-field
cosmology of the Local Group.
P34
Preliminary spectroscopic indication for Classical
Cepheids in non-eclipsing binary
Piotr Konorski
Wolfgang Gieren
Grzegorz Pietrzynski
Bogumil Pilecki
The Araucaria Project spectroscopic campaign on Classical Cepheids in Small Magellanic
Cloud reveals a small number of objects with indication of additional variability
superimposed on pulsation radial velocity curves. We present initial attempt to constrain
orbital motion of presumably non-eclipsing binary systems, which - once confirmed would mark the first spectroscopic discovery of such systems in Magellanic Clouds.
P35
Photometric Variability of L dwarfs
Radostin Kurtev
L brown dwarfs present tiny photometric variability on time-scales of hours. This
rotationally modulated variability is due to magnetic phenomena and/or inhomogeneous
cloud cover. However, inhomogeneous cloud cover alone can explain the observations.
Here we present light curves, periods and amplitudes for two of our targets based on a
very precise Js-band SOFI/NTT NIR photometry. Combining Js-band amplitudes with
quasi-simultaneous SPITZER MIR amplitudes suggests that the regions with the thickest
clouds also have the lowest effective temperature.
P36
Faint Variable Stars observed with Kepler
Catherine Lovekin
Jasmin Tompkins
We present preliminary analysis of approximately 10 variable stars observed with Kepler.
The sample stars are faint (14th and 15th magnitude), and have temperatures greater
than 8000 K. The stars were observed for up to three quarters (Q14-Q16) in long
cadence mode. Frequencies were extracted with Period04, and 1-21 frequencies were
detected in each quarter, with an average of 8 frequencies per quarter. Some variability
is detected from quarter to quarter, while the dominant frequencies remain unchanged.
We fit the frequencies using MESA models between 1.5 and 3 solar masses, and varied
the core overshoot. Best fitting properties of each of these stars will be discussed.
These stars have not previously been classified, and we will present our categorization of
them here.
P37
Rotation and magnetic activity of oscillating solarlike stars with the Kepler mission
Savita Mathur
For the last few decades the investigation of stellar magnetic activity has been conducted
through spectroscopic and spectropolarimetric surveys. This led not only to the detection
of magnetic cycles in other stars but also to variable and magnetic activity. For the Sun,
the magnetic activity is described as the interaction between convection, rotation, and
magnetic field. To study magnetic activity of solar-like stars we need to have the
knowledge of the surface rotation period, the properties of magnetic activity, and the
structure of the stars. This information can feed into dynamo models that are currently
used to better understand the solar magnetic activity. The Kepler mission has been
providing high-precision photometric data almost continuously for four years for around
200,000 stars. For a subset of solar-like stars, asteroseismic analyses have provided
precise properties of the stars and their internal structure. Moreover with the photometric
data we can measure surface rotation periods based on the presence of spots passing on
the visible disk. This latter measurement can be done when a star is active meaning that
we can also study changes in the magnetic activity of these stars by doing a timefrequency analysis. In this talk I will present the results obtained from the stellar
dynamics studies of Kepler solar-like targets in terms of rotation periods, magnetic
activity proxies and magnetic activity cycles detected. We can then combine this
information with asteroseismic studies to have a broader picture of stellar magnetic
activity. This work provided a large number of well-characterized solar-like stars that will
put constraints on dynamo models to better understand the magnetic activity of our own
Sun.
P38
Variable stars in the northern Galactic plane from
KISOGP
Noriyuki Matsunaga
KISOGP Team
We have been conducting a large-scale survey of the northern plane using Kiso WideField Camera attached to Schmidt telescope at Kiso observatory. The KISOGP (KWFC
Intensive Survey of the Galactic Plane) project have made 40-70 epoch observations in Iband of about 320 sq. degrees for over 3 years starting in 2012. The limiting magnitude
is around 16.5 mag in I. In the data analysis so far, we detected a couple of thousands of
variable stars including approximately 100 Cepheids and more than 700 Miras. Roughly
90% of them were not previously reported as variable stars, indicating that there are still
many relatively bright variables to be found in the galactic plane. We'll present a
preliminary map of the Cepheids and Miras together with results of spectroscopic followup observations for these objects.
P39
Searching for distant RR Lyrae stars using the
High cadence Transient Survey
Gustavo Medina Toledo
We present the results from an RR Lyrae search using data from the High cadence
Transient Survey (HiTS). HiTS is a deep optical campaign carried out with the Dark
Energy Camera (DECam) imager at the Blanco (4m) telescope on Cerro Tololo, Chile,
aimed at detecting early supernovae explosions. However, the cadence of the survey and
the strategy followed are well matched for RR Lyrae detection as well. Using data from
2014 we were able to detect new RR Lyrae stars out to at least 100 kpc from the Sun. In
this poster we show the preliminary results of the search for RR Lyrae stars using HiTS'
data from 2015, and discuss possible implications of these findings.
P40
Spectro-Photo-Interferometry of Stellar Pulsation
(SPIPS)
Antoine Mérand
We present our implementation of the parallax-of-pulsation which integrates all
observables and physical modelling of the photosphere to get the best statistical precision
and controlled biased. This method has been validated on well known stars (delta Cep
and eta Aql), and used to estimate observationally the projection factor of the HST-FGS
sample. Our future developments include application to the GAIA Cepheids and modelling
of the spectrum.
P41
VVV Maps of the Inner Milky Way
Dante Minniti
The VVV survey has been mapping the MW bulge and inner southern disk in the near
infrared, covering ~540 sqdeg in the ZYJHKs filters. We present the current maps of the
Milky Way bulge and disk obtained from VVV Survey observations. They include a color
view, photometric completeness and photometric depth in all pass-bands, source density
map, reddening maps, and photometric metallicity map. These maps can be used to
obtain a global view of the bulge and study its constituent stellar populations. We also
show our unique VVV collaboration model.
P42
The additional-mode garden of RRab stars
László Molnár
Emese Plachy
Péter Klagyivik
Áron Juhász
Róbert Szabó
Space-based photometric missions revealed a surprising abundance of millimagnitudelevel additional modes in RR Lyrae stars. We now know that the majority of the
fundamental- mode stars that experience Blazhko modulation also show one or more
such modes, that can be ordered into four major categories. The most common features
are period doubling, caused by the resonant ninth overtone, and the mode at ~0.6 P0
that may potentially correspond to the second overtone. In more rare cases (including
the star RR Lyr itself), the additional modes can be identified with the first overtone, and
finally some fall outside the above mentioned categories, so they are likely non-radial
modes. Here we present a census of the additional modes from several hundred stars
observed during the early K2 campaigns.
P43
Insights on Milky Way and M31 halo formation
mechanisms from RR Lyrae variables
Matteo Monelli
Giuliana Fiorentino
Clara Martínez-Vázquez
et al.
Insights on Milky Way and M31 halo formation mechanisms from RR Lyrae variables.
Short Summary: We will present a study the early formation history of the stellar halos
of spiral galaxies, and the nature of their possible building blocks, based on the
pulsational properties of the RR Lyrae (RRL) variable stars. In particular, we will show
that the period and amplitude distributions of RRL stars show distinctive features in
different stellar systems. This occurrence can be related to the parent stellar populations
properties, such as the maximum metallicity attained by the RRL progenitors. In
particular, High Amplitude Short Period (HASP) variables are common in the Milky Way
(MW) and M31 halos, in globular clusters with [Fe/H] > -1.5 and in massive dwarfs, but
not found in low metallicity globular clusters and faint dwarf galaxies. The comparison of
the period distribution of RRL in the M31 and MW inner halos shows that the properties of
RRL are similar in both, suggesting similar early formation histories. The HASP tail
present in both indicates an important contribution to their formation from bright
satellites. Additionally, MW halo RRL present a significant change in their period
distribution when moving from the inner (R < 14 Kpc) to the outer (R > 14 Kpc) halo,
suggesting formation from dissimilar progenitors or events.
P44
Non-radial modes in AGB stars
Josefina Montalban
S. Bressan
R. Suflaire
P. Marigo
The success of asteroseismology in characterising G-K giants has motivated the
extension of the same techniques for stars after the central He burning and M-giants. The
latter have been usually studied only as radial pulsators. The high density contrast
between the central region and the envelope gives rise to serious numerical problems in
the computation of non-radial modes of oscillations. In this poster we will present the
theoretical results of this preliminary effort to compute and interpret the non-radial
spectrum of stars from the Early AGB to the TP-AGB phases.
P45
Multiperiodic RR Lyrae stars in the field of
NGC6362
P. Moskalik
R. Smolec,
J. Kałużny,
W. Pych,
M. Różyczka,
I. B. Thompson
Population of known RR Lyrae-type stars in the globular cluster NGC6362 consists of 16
RRc and 18 RRab variables. We have analyzed 11 years of ground-based photometry of
these objects, collected between 1999 and 2009. In 10 RRc stars (63% of the sample)
nonradial modes with period ratio in the range of 0.608-0.631 to the dominant radial
mode have been detected. This finding is yet another confirmation that excitation of such
modes is very common in the RRc pulsators. Blazhko effect (long term amplitude and
phase modulation) has been found in 3 RRc star (19% of the sample), in 1 of them the
modulation is double-periodic. In case of RRab stars, no secondary modes have been
detected. However, the Blazhko modulation is very common and affects ~70% of these
variables. In two stars previously classified as RRab pulsators, V3 and V34, a week first
radial overtone has been found. In both variables the resulting period ratio is non-typical,
being close to 0.73, and the radial modes show long-term Blazhko-type modulation.
Thus, V3 and V34 have to be re-classified as members of a newly defined group of
anomalous RRd stars (Soszyński et al. 2016, submitted).
P46
Variable Stars in massive star clusters in our
Galaxy, as revealed by VVV
Claudio Navarro Molina
Jura Borissova
Márcio Catelan
et al.
In this poster we will report some new results of search and analysis of the variable stars
around two young and massive clusters in our Galaxy, namely Arches and Quintuplet.
P47
Applying Survival Analysis on Cepheid PeriodLuminosity Relation at 70-Micron
Chow-Choong Ngeow
In this Poster, I apply the survival analysis to re-derive the Cepheid period-luminosity
relation at 70-micron, at which about 2/3 of the currently available data only contains
upper limits in flux. The survival analysis is a type of statistical technique to deal with
data that has upper or lower limits – which is commonly seen in astronomy. I will also
discuss preliminary results in the Poster.
P48
New R Coronae Borealis and DY Persei Candidates
in the SMC
Fatemeh Nikzat
Márcio Catelan
R Coronae Borealis (RCB) stars are C-rich, H-deficient red supergiants that undergo
dramatic dimming episodes at irregular intervals. The dimming episodes are believed to
be caused by self-obscuration by dust, occurring as a consequence of mass loss events.
The purpose of this contribution is to report on a new search for RCB stars in the Small
Magellanic Cloud (SMC), carried out using V I light curves from the OGLE project. To
detect candidates, the V I light curves of all SMC red variable stars were visually
inspected, and compared against templates from the literature. New RCB candidates
were detected in the process, which had previously been classified as semi-regular or
Mira variables. Additionally, DY Persei candidates were also identified. Compared to their
RCB counterparts, the DY Per stars tend to be cooler, have slower decline rates, and
more symmetrical declines. If confirmed, these detections would lead to a significant
increase in the number of known RCB + DY Per stars in the SMC.
P49
Constraints on rotation of B-type pulsators from
the nitrogen abundance
Jakub Ostrowski
Jadwiga Daszyńska-Daszkiewicz
Rotation is one of the most important parameters that determine the evolution and the
ultimate fate of a star. The effects of rotationally induced mixing modify the internal
structure and, consequently, change conditions for excitation of stellar pulsations and the
values of eigenfreqeuncies. Besides the difficulty in modeling the effects of rotation, there
is also the problem in determining the rotation velocity from observations and usually
only its projected value is known. In the presence of moderate-to-fast rotation, the
abundance of surface nitrogen should increase during the course of evolution as an effect
of rotational mixing processes. Here, we make an attempt to estimate the values of the
rotational velocity and inclination angle for selected massive pulsators by comparing the
measured nitrogen overabundances with the values predicted by evolutionary models
computed with MESA code.
P50
Eclipsing Binary Stars in the Era of Massive
Surveys: First results and future prospects
A. Papageorgiou
M. Catelan
Our thinking about eclipsing binary stars has undergone a tremendous change in the last
decade. Eclipsing binary stars are one of nature’s best laboratories for determining the
fundamental physical properties of stars and thus for testing the predictions of theoretical
models. The largest such variable star surveys are the photometric multi-epoch Catalina
Real-time Transient Survey (CRTS) and the VISTA Variables in the Via Lactea survey
(VVV). These enormous surveys contain a large amount of photometric data and plenty
of information about eclipsing binaries that wait to be extracted and exploited. We
present a fully detailed eclipsing binary star catalog from CRTS with a) revised period
determination using various techniques and b) phenomenological and physical
parameters of selected eclipsing binary stars. Finally, we also present the progress of the
analysis of VVV, including stellar variability investigation, future prospects in fundamental
parameter determination, interesting examples from both surveys, as well as our first
results so far.
P51
Multi-site, multi-colour and space photometry of a
Southern Delta Scuti star, 38 Eri
Margit Paparo
We present the preliminary results obtained on our large amount of data. We compare
the ground-based data to the space data obtained by MOST The multi-site campaign and
the MOST runs are divided by years, which gives possibility for checking the stability of
the pulsation. Both Stromgren and Johnson photometry are available from the groundbased multi-site campaign.
P52
Ultra-precise analysis of the light curves of CoRoT
and Kepler delta Scuti stars
Javier Pascual-Granado
Rafael Garrido Haba
Juan Carlos Suárez Yanes
Jose Ramón Rodón Ortiz
It is well known that the residuals of the multifrequency analysis of delta Scuti stars are
correlated giving rise to challenging features such as a plateau (HD 50844, HD 50870,
HD 49434, …) of non-resolved frequencies with amplitude higher than the expected noise
level. Several hypotheses have been advanced to explain these features: effective
convection, rotation, non-linear interactions, etc. We have recently demonstrated that in
some cases the underlying function describing the light variations of delta Scuti stars has
not the property of being analytic. The strong consequence of this result is that the
Fourier expansion in which the harmonic analysis is based on, could be no justified. In
order to know the extension of this phenomenon among delta Scuti stars, we have used
photometric data from CoRoT seismofield and a large set of Kepler stars (short cadence).
A discussion of the different hypotheses that could be on the origin of the non-analyticity
follows the results. Work is in progress to overcome this inconsistency in the application
of harmonic analysis.
P53
Obtaining Accurate Radial Velocities for Cepheid
Companions Using the STIS Echelles
Charles Proffitt
We use recent STIS echelle observations of hot companions of Cepheids to study the
precision and repeatability of radial velocity measurements made using this instrument's
E140H grating. The stability of the STIS optical bench, the optimal use of its calibration
lamps, and the impact of aperture centering accuracy are discussed. We identify a
number of ISM lines in the spectra of our targets that we use to quantify the repeatability
of the absolute wavelength scale over time scales from minutes to years, and also
discuss how the signal-to-noise and line widths of the stellar spectrum affect the
precision that can be obtained in practice. The ultimate goal for this project is to
determine the masses of the Cepheids. Any improvements in the accuracy of these
companion velocities will translate directly into improved accuracy for these mass
determinations.
P54
Searching for Be Star Candidates within Large
Databases
Beatriz Eugenia Sabogal Martinez
A. García-Varela
Be stars are non-supergiant B stars that show or have shown Hydrogen emission lines in
their spectra. These stars are also non-radial pulsators whose light curves show
stochastic or quasi-periodic variations in different time scales. Long time surveys yield
many high quality light curves among their subproducts, useful to identify candidate to
Be stars that can also be confirmed by spectroscopic follow ups. We present in this work
different techniques we have used to select new Be star candidates in the Milky Way and
the Magellanic Clouds, from OGLE-II and ASAS databases. We also present the result of a
new search for Be star candidates in the OGLE-IV Gaia South Ecliptic Pole Field.
P55
Comparing the asteroseismic properties of
pulsating extremly low mass pre-white dwarf
stars and Delta Scuti stars
Julieta Paz Sanchez Arias
Pulsating Extremely Low Mass pre-white dwarfs, with masses between ~0.15Mo and
~0.30Mo, constitute a class of pulsating white dwarfs called pre-ELMV stars which exhibit
radial-, p- and possibly g-mode pulsations with periods between 380 and 3500 sec,
driven by the kappa mechanism operating in the zone of the second ionization of He. On
the other hand, main sequence Delta Scuti stars, with masses between 1.22.5Mo, pulsate
in low-order g and p modes in the range of [700:36300] sec, driven by the kappa
mechanism operating in the HeII ionization zone. Interestingly enough, the pre-ELMV
white dwarf and the Delta Scuti instability domains nearly overlap in the log Teff vs. log g
diagram, leading to a degeneracy in the classification of the stars. In principle,
asteroseismology can be employed to distinguish these very different kinds of stars.
Motivated by this fact, we addressed an adiabatic asteroseismic comparison between
these two families of pulsating stars, with the aim of providing tools for their correct
classification.
P56
Variability survey of young star forming region
Saurabh Saurabh
It is now well established that circumstellar discs are an integral part of star formation
and are potential sites for planet formation Young star forming regions have significant
number of pre-main-sequence (PMS) stars with circumstellar disc and are unique
laboratories to study the evolution of discs of PMS stars. These stars are contracting
towards MS or just reached the MS. Both WTTSs and CTTSs show variation in their
brightness. These variations are found to occur at all wavelengths, from X-ray to
infrared. Variability time- scale of TTSs ranges from a few minutes to years. The
photometric variations are believed to originate from several mechanisms like rotation of
a star with an asymmetrical distribution of cool spots, variable hot spots or obscuration
by circumstellar dust The Herbig Ae/Be stars also show variability as they move across
the instability region in the Hertzsprung–Russell diagram on their way to the MS. Several
systematic studies of TTSs have been carried out which revealed different type of
variabilities. It is now well known that some of them show periodic variability. In this
poster, I will be presenting the results of our analyses related to the multi-epoch V-band
photometry of various star forming regions taken with different telescopes to identify
photometric variable stars in the region. This will help us to find any relation in the
periods and amplitudes of the variable in optical wavelength with their evolution stage
and mass.
P57
The Blazhko RR Lyrae variables and phase
modulation in binary systems
Hiromoto Shibahashi
The Blazhko phenomenon is the quasi-periodic amplitude and phase modulation seen in a
fairly large fraction of RR Lyrae variables. The uninterrupted photometry with high
precision from space missions revolutionised observations of these stars and revealed
(i) a two-cycle amplitude modulation of the light curve, – the period doubling, (ii) a 2:9
resonance between a low-order mode and a high-order mode, and (iii) a presence of
high-order multiplets. Nevertheless the Blazhko phenomenon still remains as a long-lived
enigma to be explained. Frequency fine structures can also be seen in pulsating stars in
binary systems. By carefully investigating the multiplets seen in RR Lyrae stars, I
demonstrate that some of stars classified as Blazhko variables can be explained as binary
systems and also show that some stars classified as binary systems are actually not
binaries.
P58
Finding Beat Cepheids in M33 and Their Use in
Measuring the Metallicity Gradient
Lawrence Short
David Bersier
The period ratio between the two different pulsation modes of beat Cepheids is directly
affected by the metallicity of the star. This is backed up by observations of the Milky
Way, LMC and SMC thus is used as an important constraint for stellar models. The aim of
this project is to find all of the beat Cepheids in M33 and determine their metallicities by
comparing them to Cepheids with known metallicity (Petersen diagram). This will allow us
to accurately derive the metallicity gradient across M33. To achieve this we have images
of M33 taken using the INT covering 13 nights over 19 months in addition to the CFHT
variability survey conducted by Hartman et al (2006) covering 27 nights over 17 months
giving a total of ~90 epochs. The two data sets need to be cross-calibrated then a period
search will be applied in order to find all Cepheids in M33. I will present work on the
calibration along with preliminary light curves of found Cepheids.
P59
A 2-year orbital-period RR Lyrae Binary candidate
Ádám Sódor
Marek Skarka
Jiri Liska
Zsófia Bognár
We discovered a new Kepler first-overtone RR Lyrae pulsator. The pulsation shows large,
0.1 d amplitude, systematic phase variations that can be interpreted as light travel-time
effect caused by orbital motion in a binary system, superimposed on a linear pulsationperiod decrease. The assumed eccentric (e=0.47) orbit with the period of about 2 yr is
the shortest among the non-eclipsing RR Lyrae binary candidates. The binary model gives
a lowest estimate for the mass of the companion of 8.4 M_Sun, that places it among
black hole candidates. Beside the first-overtone pulsation, numerous additional non-radial
pulsation frequencies were also identified. We detected an ~47-d Blazhko-like irregular
light-curve modulation.
P60
TOUCAN. The VO gateway to stellar models
Juan Carlos Suárez
Carlos Rodrigo
Enrique Solano
José R. Rodón
Virtual Observatory has gone beyond the realm of observations to connect scientists also
with models. TOUCAN represents a step forward the on-line management and
interoperability between stellar models collections. Currently devoted to asteroseismic
models, this VO tool developed by the Spanish Virtual Observatory team, makes the life
of scientists and work teams easier.
P61
Distance scale calibration based on early-type
binaries
Mónica Taormina
Grzegorz Pietrzyński
Bogumil Pilecki
Dariusz Graczyk
Ian Thompson
Wolfgang Gieren
Our main goal is to establish a firm empirical calibration of the surface brightness vs.
(V - K) color relation for early type stars based on high quality spectroscopic and infrared
observations of early-type detached eclipsing systems in the LMC. Our calibration of this
relation will allow distance determinations accurate to about 2.5 % to a single object
located well beyond the Magellanic Clouds. This will let us calibrate other distance
indicators, including the P-L relations for Cepheids. The first step of the project is to
determine precise parameters for a sample of B-type systems in the LMC. Here I present
the preliminary results from the analysis of light and radial velocity curves for selected
objects, including measurement of the masses and radii.
P62
Asteroseismic inferences from red giants in
binaries and clusters
Nathalie Themessl
Oscillating red giants in eclipsing binaries and in open clusters provide tight constraints
for testing theories of stellar structure and evolution. Thanks to the high-precision and
long-term photometry obtained by the Kepler space mission, we are able to carry out
comprehensive studies of red giants in a number of binary systems and open clusters.
Through the oscillation spectra we deduce their stellar properties and evolutionary stages
(asteroseismology), while at the same time the stellar properties can also be determined
independently through the orbital analysis (binaries) or isochrones (clusters). In our
study, we compare the derived stellar parameters from asteroseismology against
independently determined stellar parameters to validate the asteroseismic methods. We
also extract individual frequencies of oscillation modes that provide essential constraints
for detailed stellar models and stellar ages.
P63
Pulsation Models of O-rich and C-rich Long Period
Variables
Michele Trabucchi
Paola Marigo
Josefina Montalban
Peter Wood
Leo Girardi
Low to intermediate mass stars experience the Asymptotic Giant Branch (AGB) during
their late evolution, undergoing a number of complex and strongly interacting
phenomena such as stellar oscillations, mass loss, dust formation, thermal pulses and
dredge-up events. Their observed variability is currently attributed to radial pulsation in
modes of low-radial orders. The study of stellar pulsation provides a way to probe the
internal structure of such objects, and therefore to refine our understanding of late stellar
evolution. However, updated theoretical pulsation models of such stars, especially of Cstars, have been missing from scientific literature for a few decades. We produced a new
set of such models, intended to provide a broad coverage of the parameters space in
terms of mass, luminosity, temperature and composition. Since the surface carbo-tooxygen ratio can be significantly altered by dredge-up events, we are especially
interested in the effects of chemical composition, studied with up-to-date data for the
metal mixture and detailed opacities for the outermost layers of such cool stars. We
analyze how periods and growth rates depend upon global stellar parameters, and we
compare our results with the OGLE-III observations of LPVs in the Magellanic Clouds. We
aim to realize a large set of pulsation models to be made public in preparation for future
observational surveys such as LSST.
P64
Asteroseismology of the Kepler target
KIC 9204718
Ceren Ulusoy
Ivanka Stateva
Iliani Iliev
Burak Ulas
We present the first preliminary results of a new investigation aimed to identify pulsation
modes of KIC 9204718. The star is listed to be a binary system with a delta Scuti type
pulsating component by Uytterhoeven et al. (2011). In order to determine the frequency
content Kepler photometry is used. Spectroscopic and Photometric Observations are
carried out with the 2 m RCC and 0.60 m Cassegrain Telescopes of the Bulgarian National
Astronomical Observatory, Rozhen Bulgaria. The Ground-based multi-colour photometry
is obtained to investigate modal behaviour of the star. High dispersion spectroscopic data
is also used to derive the projected rotational velocity and atmospheric parameters.
Tentative identifications of pulsation modes show that the component star shows Hybrid
type pulsational characteristics.
P65
Asteroseismology of the ZZ Ceti and DAZ white
dwarf GD 133
J.N. Fu
G. Vauclair
J. Su
et al.
GD 133 is a DAZ white dwarf with an atmosphere polluted by heavy elements accreted
from a debris disk formed by the disruption of rocky planetesimals whose orbits bring
them at the white dwarf tidal radius. To reach such orbits implies the potential presence
of a perturbing planet. GD 133 is a ZZ Ceti pulsator close to the blue edge of the
instability strip. The presence of a planet could be revealed by the periodical modulation
of the observed pulsation periods induced by the orbital motion of the white dwarf around
the barycenter of the system. We started a multi-site photometric follow-up aimed at
detecting the signature of this potential planet. As a preliminary result of this work in
progress, we analyzed the data obtained during the 2011 campaign from which we derive
the parameters of GD 133 from asteroseismology.
P66
Important consequences of atomic diffusion
inside main-sequence stars: opacities,
extra-mixing, oscillations
Morgan Deal
Sylvie Vauclair
Olivier Richard
Atomic diffusion, including the effect of radiative accelerations on individual elements,
leads to important variations of the chemical composition inside the stars. The
accumulation of some important elements in specific layers leads to a local increase of
the average opacity and to hydrodynamic instabilities that modify the internal stellar
structure. We studied these effects in A-type stars using the Toulouse-Geneva Evolution
Code (TGEC), where radiative accelerations are computed with the Single Valued
Parameter (SVP) method. We took into account the induced double-diffusive convection
with mixing coefficients deduced from three-dimensional (3D) simulations. We compared
the resulting surface abundances with the observations. We discuss the consequences of
these important physical processes for various stellar types.
P67
The EREBOS project: Determining the influence of
substellar objects on stellar evolution
Maja Vuckovic
Planets and brown dwarfs in close orbits around main sequence stars will inevitably
interact with their stellar hosts once they ascend the red giant branch. The details and
outcomes of these interactions are currently unclear. Recent discoveries of brown dwarfs
and planets orbiting post-red giant branch hot subdwarf stars implies that the substellar
objects are not only sufficient for ejecting the outer layers of a red giant’s atmosphere,
but that they can also survive the engulfment phase. Thirty-six new eclipsing hot
subdwarf binaries with cool, low-mass companions were discovered from light curves
obtained by the OGLE project, tripling the number of known systems. Here we present
the Eclipsing Reflection Effect Binaries from the OGLE Survey (EREBOS) project to
determine the orbital velocities and atmospheric parameters of the sdB primaries and,
ultimately, the companion masses. The final aim of this large project is to use this
homogeneously-selected sample to derive the mass distribution of the companions and
determine the minimum mass needed to strip off the red-giant envelope and survive the
common envelope phase.
P68
Stellar variability from Dome A, Antarctica
Lingzhi Wang
The Antarctic plateau is one of the best observing sites on the surface of the Earth thanks
to its extremely cold, dry, stable and transparent atmosphere conditions. So far images
have been collected from a 10-cm quad-telescope called the Chinese Small Telescope
ARray (CSTAR) and the first of a trio of 50-cm Antarctic Survey Telescope (AST3-1). I will
present the results of stellar variability from CSTAR and AST3-1, and the two targets'
follow-up observations from Chile.
P69
Distance to Small Magellanic Cloud from
multiband P-L relations of classical Cepheids
Piotr Wielgórski
Grzegorz Pietrzyński
Using OGLE optical and IRSF infrared photometry of Magellanic Clouds we derived
extinction free P-L relations for classical cepheids in Large Magellanic Cloud and
measured distance modulus of Small Magellanic Cloud in each band not corrected for
extinction. From reddening law we also calculated extinction and E(B-V) ratio in each
band. Relation between this ratio and distance modulus is linear and fitting straight line
gives us distance modulus of SMC corrected for extinction and mean E(B-V) towards
SMC. Because it is possible, that P-L relation changes its slope around 10 days we applied
this method in two cases: for whole sample of cepheids in LMC and with periods of
pulsation longer than 2.5 days in SMC, and for cepheids with periods longer than 10 days
both in LMC and SMC. Our results are as follows: in first case 0.482+-0.005(stat) and
0.094+-0.004(stat) and in second case 0.471+-0.008(stat) and 0.103+-0.007(stat) for
distance modulus and mean E(B-V) respectively.
P70
The Araucaria Project. The Distance to the
Sculptor Group Galaxy NGC 7793 from
Near-Infrared Photometry of Cepheid Variables
Bartlomiej Zgirski
Paulina Karczmarek
Marek Górski
Grzegorz Pietrzyński
We performed deep near-infrared J and K photometry of a field in the Sculptor Group
spiral galaxy NGC 7793 using ESO VLT and HAWK-I instrument. We produced a sample of
14 Cepheids which locations and periods of pulsations were known from our previous
paper on distance determination to this galaxy based on V and I bands. We determined
mean J and K magnitudes based on measurements from two nights and produced periodluminosity relations for both filters. Using those near-infrared dependencies together with
relations for bands V and I obtained before, we were able to obtain true distance modulus
for the NGC 7793. We also calculated the mean reddening affecting our Cepheids.