Exoplanet Host Stars

1. Exoplanet Host Stars

2. The Hertzsprung-Russel (HR)Diagram

3. The Hertzsprung-Russel (HR)Diagram Standard Doppler Surveys

4. The Hertzsprung-Russel (HR)Diagram Direct Imaging detections Standard Doppler Surveys

5. The Dependence of Planet Formation on Stellar Mass • Don’t forget observational selection effects! • Are trends real?

6. Exoplanets around massive stars Difficult with the Doppler method because more massive stars have higher effective temperatures and thus fewer spectral lines. They also rotate faster. Result: Only a few planets around early-type, more massive main sequence stars, and these are mostly around F-type stars (~ 1.4 solar masses) A way around this is to look for planets around evolved (subgiant and giant) stars.

7. One way to detect planets around more massive stars with the RV method: A 1.9 Mסּ main sequence star A 1.9 Mסּ K giant star

8. The Hertzsprung-Russel (HR)Diagram Direct Imaging detections Standard Doppler Surveys

9. The Hertzsprung-Russel (HR)Diagram Sub-/Giants feasible with Doppler Direct Imaging detections Standard Doppler Surveys

10. Early Evidence for Planets around Giant stars (Hatzes & Cochran 1993) Careful! Rotation periods of giants ~ hundreds of days…

11. P = 1.5 yrs M = 9 MJ Frink et al. 2002 Planet around the giant star Iota Dra (M ~ 2.2 MSun)

12. Johnson et al. (2010): Planets around „retired“ A stars Johnson et al. also estimate that ~25% of stars with mass > 1.5 Msun have giant planets

13. Planet Mass Distribution for Solar-type main sequence stars with P> 100 d Planet Mass Distribution for Giant and Main Sequence stars with M > 1.1 Mסּ N More massive stars tend to have more massive planets and at a higher frequency M sin i (Mjupiter)

14. The Hertzsprung-Russel (HR)Diagram Sub-/Giants feasible with Doppler Direct Imaging detections Standard Doppler Surveys Doppler 8-10m Microlensing

15. M Dwarfs in a Nutshell: • complex spectra (high opacity due to TiO, VO and other molecules) • Mass = 0.6 – 0.1 MSun • MV = 7.5 – 20 (absolute magnitude, at 10pc) • L ~ 0.2 – 5 x 10-4 LSun (Luminosity) • Teff ~ 3800 – 2100 K • Radii = 0.5 – 0.1 RSun • slow rotators, still exhibit activity related phenomena (flares, spots, etc) • most numerous stars

16. Exoplanets around low mass stars Microlensing statistics point toward lower frequency of giant planets around M dwarfs (Gaudi et al. 2002) • Doppler programs (past & on-going): • ESO UVES program (Kürster, Endl et al.): 40 stars • HET Program (Endl, Cochran et al.) : 100 stars • Keck Program (Marcy, Butler et al.): 200 stars • HARPS Program (Mayor et al.):~200 stars • Results from Doppler method of nearby M dwarfs: • Giant planets within 1-2 AU are rarer around M dwarfs than around F,G,K stars (Endl et al. 2006). Confirmed by Keck & HARPS results • BUT: Hot neptunes & Superearths more frequent (HARPS).

17. Proxima Cen [M5Ve] 0.12 MSun Endl et al. (2007):

18. Mstar ~ 1.4 Msun Mstar ~ 1 Msun Mstar ~ 0.4 Msun Exoplanets around main sequence stars of different masses Don’t forget obs. selection effects!

19. Preliminary conclusions: more massive stars have more massive planets with higher frequency. Less massive stars have less massive planets → planet formation is a sensitive function of the stellar mass.

20. Astronomer‘s Metals More Metals ! Even more Metals !! Planets and the Properties of the Host Stars: The Star-Metallicity Connection

21. The „Bracket“ [Fe/H] Take the abundance of heavy elements (Fe for instance) Ratio it to the solar value Take the logarithm e.g. [Fe/H] = –1 → 1/10 the iron abundance of the sun

22. The Planet-Metallicity Connection: These are stars with metallicity of 0.3 to 3.16 x solar Valenti & Fischer There is believed to be a connection between metallicity and planet formation. Stars with higher metalicity tend to have a higher frequency of planets. This is often used as evidence in favor of the core accretion theory of giant planet formation

23. Cochran, Endl et al. 2007: HD 155358 two giant planets and.. …[Fe/H] = –0.68. This certainly muddles the metallicity-planet connection

24. Summary: • Giant planet frequency is a strong function of stellar mass • Giant planets are more frequent around metal-rich stars