Hunting for exoplanets around K giants Achim Weiss Michaela P. Döllinger Luca Pasquini Leo Girardi Johny Setiawan Licio da Silva Thüringer Landes- sternwarte Tauten- burg Artie P. Hatzes Jose Renan de Medeiros ESO Garching, 08/06/2009 Fellows Symposium 2009

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

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

RV variability amplitudes multi- periodic time scales dwarfs giants short-period long-term 10-300 m/s 2-10 days 1-600 days 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

Long-term, low-amplitude RV variations planetary companions (long-lived and coherent RV variations) rotational modulation caused by the passage of large surface inhomogeneities (cool starspot crosses the observers line-of- sight as the star rotates - distorations in the spectral line profiles – detected as RV variations with the rotation period of the star) ESO Garching, 08/06/2009 Fellows Symposium 2009

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

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

Star sample 62 stars Northern hemisphere Instrument: Starlist: 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 Starlist: new Observatories: ThüringerLandessternwarte Tautenburg (TLS) Observations: since February 2004 Telescope: 2m Alfred-Jensch ESO Garching, 08/06/2009 Fellows Symposium 2009

Tautenburg Alfred-Jensch 2m telescope ESO Garching, 08/06/2009 Fellows Symposium 2009

Star sample 300 stars Southern hemisphere Instruments: Starlist: high resolution spectro- graphs FEROS (R=48,000) and HARPS (R=100,000) with simultaneous Th-Ar calibration 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 Fellows Symposium 2009

La Silla HARPS FEROS 1.5m ESO telescope 2.2m MPG/ESO telescope ESO Garching, 08/06/2009 Fellows Symposium 2009

Data reduction using IRAF routines spectra ESO Garching, 08/06/2009 Fellows Symposium 2009

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

RV statistics: FEROS, TLS and HARPS analysed stars: 77 62 300 constant stars: 6 (8 %) 2 (3 %) ? binary/multiple systems: 15 (16 %) 13 (21 %) ? planetary companions: 7 (9 %) 9 (15%) 45 (15 %) stellar oscillations: 7 (9 %) 17 (27 %) ? ESO Garching, 08/06/2009 Fellows Symposium 2009

Results and future work RV statistics 9 (15 %) planets [Fe/H] stellar parameters Teff, logg, microturbulence evolutionary tracks (Girardi 2000) Joergenson & Lindegren’s method (2005) pollution metal-poor MS stars radius, mass, age refine planet formation as a function of stellar mass Chara Array stellar oscillations other elements ESO Garching, 08/06/2009 Fellows Symposium 2009