Download RADIAL VELOCITY VARIATIONS and

Hunting for exoplanets around K giants
Achim Weiss
Michaela P. Döllinger
Luca Pasquini
Leo Girardi
Johny Setiawan
Licio da Silva
Jose Renan de Medeiros
ESO Garching, 08/06/2009
Thüringer Landessternwarte Tautenburg
Artie P. Hatzes
Fellows Symposium 2009
1
Definitions
What are exoplanets?
Exoplanets are planets around other stars.
What are G-K giants?
G-K giants are cool, evolved stars in the intermediate
mass range.
How exoplanets are indicated?
Exoplanets are indicated by long-term, low-amplitude
radial velocity (RV) variations.
ESO Garching, 08/06/2009
Fellows Symposium 2009
2
Astronomers are persons with big wishes …
cool, evolved stars, which have
moved off the main sequence
(MS) and span the entire red
giant branch (RGB)
plenthora of spectral lines
slowly rotating
amenable for RV method
occupy intermediate mass
range
different mass range in
comparison to MS stars
investigation of planet
formation as a function of
the stellar mass
ESO Garching, 08/06/2009
Fellows Symposium 2009
3
RV variability
multiperiodic
time scales
amplitudes
short-period long-term
2-10 days
1-600 days
dwarfs
10-300 m/s
giants
10-500 m/s
(lower gravity and
extended atmospheres)
low
high
exoplanets binaries
Caused by at least three mechanisms (exoplanets, rotational
modulation (surface features) or/and pulsations (radial and
nonradial p-mode oscillations))
ESO Garching, 08/06/2009
Fellows Symposium 2009
4
Long-term, low-amplitude RV variations
planetary
companions
(long-lived and
coherent RV
variations)
ESO Garching, 08/06/2009
rotational modulation
caused by the
passage of large
surface
inhomogeneities
(cool starspot crosses
the observers line-ofsight as the star rotates distorations in the spectral
line profiles – detected as
RV variations with the
rotation period of the star)
Fellows Symposium 2009
5
Discrimination between the mechanisms
planetary companions
rotational modulation
produce RV variations
without altering the line
shapes (investigated by
crosschecking the asymmetry
in the spectral line profiles
(bisector velocity span) ) and
without inducing variations
in stellar activity indicators
(Ca II H & K lines)
orbital period differs
substantially from the
rotational period
variations of chromospheric
activity indicators with the
RV period indicate surface
features
ESO Garching, 08/06/2009
Fellows Symposium 2009
6
RV method
planetary companion orbiting a star
produces a measurement (“wobble”)
of the star around the center of mass
in a planetary system due to the
gravitational interactions between
star and planetary companion
resulting Doppler shift of the
spectral lines can be detected in the
spectra of the star taken over a long
time span
consequence of the motion of the
star, the light can be Doppler shifted
to bluer (shorter) or redder (longer)
wavelengths caused by approaching
or recending the Earth
ESO Garching, 08/06/2009
Fellows Symposium 2009
7
Star sample
62 stars
Northern hemisphere
Starlist:
new
Observatories:
ThüringerLandessternwarte
Tautenburg (TLS)
Observations:
since February 2004
Telescope:
2m Alfred-Jensch
ESO Garching, 08/06/2009
Instrument:
high resolution coude
echelle spectrometer
(R=67,000) plus iodine cell
resulting iodine absorption
spectrum is superposed on
top of the stellar spectrum
providing a stable
wavelength reference
against which the stellar RV
is measured
Fellows Symposium 2009
8
Tautenburg
Alfred-Jensch 2m telescope
ESO Garching, 08/06/2009
Fellows Symposium 2009
9
Star sample
300 stars
Southern hemisphere
Starlist:
3 years spectroscopic
survey with FEROS (Setiawan
et al. 2003) is integrated
Observatory:
ESO, La Silla
Telescopes:
1.52m ESO and presently the
2.2m MPG/ESO,
3.6m ESO
ESO Garching, 08/06/2009
Instruments:
high resolution spectrographs
FEROS (R=48,000) and
HARPS (R=100,000)
with
simultaneous Th-Ar
calibration
Fellows Symposium 2009
10
La Silla
1.5m ESO
telescope
2.2m MPG/ESO
telescope
3.6 m ESO
telescope
ESO Garching, 08/06/2009
HARPS
FEROS
Fellows Symposium 2009
11
Data reduction using IRAF routines
extracted
and
rebined
biassubtracted
spectra
flatfielded
ESO Garching, 08/06/2009
Fellows Symposium 2009
12
Method: RV measurements
• RVs are calculated by modeling the observed spectra
with a high signal-to-noise ratio S/N template of the star
(without iodine) and a scan of our iodine cell taken at
very high resolution with the Fourier Transform
spectrometer of the McMath-Pierce telescope at Kitt
Peak
• compute the relative velocity shift between stellar and
iodine absorption lines as well as to model the temporal
and spatial variations of the instrumental profile
• spectrum is divided in 125 segments (“chunks”), where
the values are determined for each chunk
• RV accuracy is 3-5 m/s
ESO Garching, 08/06/2009
Fellows Symposium 2009
13
RV statistics: FEROS, TLS and HARPS
analysed stars:
77
62
constant stars:
6 (8 %)
2 (3 %)
binary/multiple systems:
planetary companions:
stellar oscillations:
ESO Garching, 08/06/2009
300
?
15 (16 %) 13 (21 %) ?
7 (9 %)
9 (15%) 45 (15 %)
7 (9 %)
Fellows Symposium 2009
17 (27 %) ?
14
Results and future work
RV statistics
9 (15 %) planets
pollution
[Fe/H]
stellar parameters
Teff, logg, microturbulence
evolutionary
tracks (Girardi
2000)
metal-poor
Joergenson &
Lindegren’s
method (2005)
MS stars
refine
planet formation
as a function of
stellar mass
Chara
Array
other elements
ESO Garching, 08/06/2009
radius, mass, age
Fellows Symposium 2009
stellar
oscillations
15