Download Ground-based observations of Kepler asteroseismic targets

Ground-based observations
of Kepler asteroseismic targets
Joanna Molenda-Żakowicz
Instytut Astronomiczny Uniwersytetu Wrocławskiego
POLAND
Kepler asteroseismic targets

what are these objects?

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for what reason?

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pulsating, preferably solar-type stars that will be observed by
the Kepler space telescope
to study stellar interiors via asteroseismic methods
what this study will result in?

precise radius and mass of the stars can yield precise
parameters of their planetary systems providing that the
dedicated asteroseismic models of the stars are computed
Ground-based observations

of which objects?


for what reason?
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
stars that are candidates for Kepler asteroseismic targets
to determine their atmospheric parameters: Teff, logg, and
[Fe/H], and to measure their radial velocity, vr ,and projected
rotational velocity, v sin i
what this study will result in?

it will allow to compute dedicated asteroseismic and
evolutionary models of Kepler asteroseismic targets
Observing sites
Harvard-Smithsonian Center for Astrophysics, USA
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
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Oak Ridge Observatory,
Harvard Massachusetts: 1.5-m
Wyeth reflector
Fred Lawrence Whipple
Observatory, Mount Hopkins,
Arizona: 1.5-m Tillinghast
reflector
Multiple Mirror Telescope
(before it was converted to the
monolithic 6.5-m mirror)
Nordic Optical Telescope

Location: Canary
Islands, Spain
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Altitude: 2,382 m.a.s.l.
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Targets:


the faintest candidtes
for Kepler
asteroseismic targets

stars from open
clusters
Photo: Michael J.D. Linden-Vørnle
and Bob Tubbs
Nordic Optical Telescope

2.5-m telescope

FIES instrument


a cross-dispersed highresolution echelle spectrograph

maximum spectral resolution:
R = 65 000

the spectral range: 370-740 nm
Photo: Michael J.D. Linden-Vørnle and Bob Tubbs
Wrocław University Observatory


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Location: Astrophysical Observatory of
the University of Wrocław, Białków,
Poland
Targets: open clusters
In the figures: the dome and the 60 cm
Cassegrain telescope in Białków
Czech Academy of Sciences Observatory

Location: Ondrejov (Czech Republic)
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Altitude: 500 m.a.s.l.


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2-m telescope used for high-dispersion
coude spectroscopy
Targets: selected binaries from the list of
candidates for Kepler asteroseismic
targets
Photo: Josef Havelka and Aleš Kolář
Slovak Academy of Sciences Observatory


Location: Tatranska Lomnica (Slovak
Republic)
In the figures: the dome and the 60-cm
Cassegrain telescope in Tatranska Lomnica
Catania Astrophysical Observatory

Location: Fracastoro Mountain Station,
Mt. Etna. Italy

elevation 1,735 m a.s.l
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> 200 clear nights per year
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occasional breaks in observations due to
the activity of Etna
Catania Astrophysical Observatory
Instruments
Telescope
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Optical configuration: Cassegrain

Main mirror: 91-cm, paraboloid

Secondary mirror: 24-cm

Mount type: German (see the next
figure)
Photometer
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Single channel photometer
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Filters:



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Johnson system: U B V
Strömgren system: u b v y
Ha (narrow and wide)
Comet narrow band IHW
system
In the figure: the photometer
and additional equipment in the
Catania astrophysical
laboratory.
Spectrograph
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
Fiber-optics Reosc Echelle
Spectrograph of Catania Observatory,
FRESCO
Gratings
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echellette (cross-disperser),
reflection grating of 160x106 mm
with 300 l/mm

blazed at 4.3 deg

maximum efficiency 80% at the
blaze wavelength 5000 A
Spectrograph
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
Dispersion
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varies from 3.5 A/mm at Hg

to 6.8 A/mm at Ha (R=21,000)
The spectral range covered in one
exposure is about 2500 A in 19 orders
Spectrograph
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Performances
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radial velocity measurements
precision Dv < 0.3 km/s rms
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S/N at Ha 100 with Texp = 10 s for
V=6 mag star

limiting magnitude V=11 with S/N
=30 and Texp = 1 h
Calibration lamps

halogen flat field lamp at about
2,600oC

Thorium-Argon hollow cathode
lamp
Methodology of observations
Calibration images - Bias
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measured at the beginning
and the end of each night
(typically six
measurements in total)
the mean is subtracted
from flat fields, calibration
lamps and stellar spectra
Calibration images - Flat Field


measured at the beginning and
the end of each night (typically
six measurements in total)
needed for correction for the
shape of the blaze function
Calibration images - Flat Field


each spectrum
(calibration lamps and
stellar spectra) is
divided, order by order,
by the fit to the mean
flat field
in the figure - the
second order of the fit to
the mean flat field
Calibration images - Thorium-Argon Lamp
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
measured 2-3 times per night
needed to place the stellar
spectra on the Angstrom scale
Calibration images - Thorium-Argon Lamp


in the figure: emission
lines in the spectrum of
Thorium-Argon lamp
the emission lines have to
be identified in each order
Stars: b Oph (K2III)
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
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radial velocity standard
needed for measuring radial
velocity of program stars
observed each night
b Oph (K2III)
Targets of observations
Targets

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standard stars

radial velocity standards, e.g,. b Ophiuchi

stars with well-known spectral types needed for MK
classification
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fast rotating stars, e.g., Altair needed for the removal of
telluric lines
program stars

all the candidates for Kepler asteroseismic targets

at least two spectra per star
Primary asteroseismic targets
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15 stars which fall onto active pixels of Kepler CCDs

V = 9-11 mag
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have precise Hipparcos parallax so that their luminosity can
be computed from it
Secondary asteroseismic targets
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44 stars which fall onto active pixels of Kepler CCDs

V = 9-11 mag
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the Hipparcos parallax are not precise so that the star's luminosity
can not be computed from it
Brightest asteroseismic targets
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34 stars which fall onto active pixels of Kepler CCDs

V = 8-9 mag
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have precise Hipparcos parallax – star's distance and
luminosity can be computed
NGC 6811

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the candidates for Kepler
asteroseismic targets are
plotted with green
symbols
stars are labeled with
WEBDA numbers or with
running numbers
red rectangles show the
fields observed in
Tatranska Lomnica
NGC 6866
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
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the candidates for Kepler
asteroseismic targets are
plotted with green
symbols
stars are labeled with
WEBDA numbers or with
running numbers
red rectangles show the
fields observed in
Tatranska Lomnica
Results
Radial velocity measurements

The method: the cross-correlation; the template - b Oph

The tool: iraf software
HIP 94734 – SB1

discovered in the ground-based data to be a single-lined spectroscopic
binary (see Molenda-Żakowicz et al. 2007 AcA 57, 301)
SB2 stars
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show double peak in the cross-correlation function (here: an SB2
star HIP 94335)
SB2 stars – HIP 94335
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radial velocity of the primary (red) and secondary (blue) component of the
SB2 Algol-type system HIP 94335
Measurements of v sin i
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measured with the use of
a grid of Kurucz model
spectra
and with the Full Width
Half Maximum method
in the figure:
determination of of v sin i
of both components of
HIP 94335
Determination of atmospheric parameters

measured by comparison with the
grid of spectra of reference stars (see
Frasca et al. 2003 A&A 405, 149, Frasca et
al. 2006 A&A 454, 301)


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the method allows simultaneous and
fast determination of logTeff, log g
and [Fe/H] even for stars which
spectra have low signal-to-noise
ratio or limited resolution
requires a dense grid of template
spectra of stars with precisely
determined atmospheric parameters
in the figure: the reference stars in
the logTeff – log g – [Fe/H] space
How this method works



the spectrum of the program
star is compared with all
template spectra
the best-fitting five template
spectra are selected
adopted are weighted means
of Teff, log g and [Fe/H] of
the five templates that have
spectra most similar to the
spectrum of the program
star
log Teff – log g diagram
for Kepler primary asteroseismic targets
Evolutionary and asteroseismic models –
HIP 94734

model computed with the use of
Monte Carlo Markov Chains. On
the right: marginal distributions of
model parameters: age and mass.
(Bazot et al. in preparation)

mass = 1.114±0.023 M

age = 7.070 ±0.79 Gyr

large separation of solar-like
oscillations, Dn = 106.5 ± 3.8 Hz