The High-Energy Environment of Extrasolar Planets

1. The High-Energy Environment of Extrasolar Planets J. Schmitt Hamburger Sternwarte Email: jschmitt@hs.uni-hamburg.de Internet: http://www.hs.uni-hamburg.de X-ray Universe 2011

2. Outline: Motivation: The Sun as an X-ray jjjjsource X-ray properties of planet-bearing kkstars Star-planet interactions (SPI) Conclusions

3. Subject of X-ray emission and extrasolar planets is further persued by: Session A.1 Monday 15:20 Scott Walk: X-ray Observations of Hot Jupiters Poster A13: K. Poppenhaeger: Star-Planet Interactions in X-rays - mimicked by selection effects ?

4. What would the Sun/solar system look like to an extrasolar astronomer (equipped with our instrumentation) ?

5. The SOHO Sun

6. Robrade et al. (2009)

7. k RV-signal dominated by Jupiter !

9. (Hypothetical) Extraterrestrial astronomers know that Sun is a (weak) X-ray source Sun shows cyclic activity with a period of 11 years Sun possesses a cold Jupiter with a period of about 11/12 years

10. „Types“ of extrasolar planets: Radial velocity detections (blue, nearby)) Transit detections (green, further away) Microlensing detections (brown, very distant)

11. Spectral type distribution of extrasolar planet host stars Poppenhaeger et al. (2010)

12. Volume-limited sample of F,G,K,M dwarfs: FX vs. MV Mean X-ray surface flux F GK M Log FX Solar coronal hole MV Schmitt & Liefke (2004)

13. Saturation limit Solar level Hot stars Pizzolato et al. (2003) Rossby number

14. Oxygen VII + VIII XMM-Newton RGS: α Centauri A+B (inactive star) (Liefke & Schmitt 2006)

15. Chandra LETGS:

16. Accretion/Jet sources Courtesy: J. Robrade

17. An analogy from close binaries ?

18. What are we talking about ? Courtesy K. Poppenhaeger

19. Why do we care about X-rays ? Star-Planet interaction: Star influences planet (trivial at first sight) Planet influences star

20. Planet might affect star through tidal interaction (Earth-Moon system !) magnetic interaction (joint magnetospheres) Jupiter-Io-like interaction Half period full period full period

21. Clarke et al. (2002) X-ray Universe 2011

22. Key elements of Jupiter-Io interaction: Strong magnetic field of Jupiter Evaporation due to volcanism and formation of plasma torus (high density environment) Corotation of Jupiter‘s magnetosphere beyond Io Magnetospheric rotation is super-Keplerian at Io‘s distance All required ingredients present in late-type stars albeit not necessarily in any given star ! X-ray Universe 2011

23. Application to Planet X around a young star: Dipole field Corotating plasma Kepler‘s 3 law X-ray Universe 2011

24. Claims for SPI at X-ray wavelengths (1): Kashyap et al., 2008, ApJ, 687, 1339 „We carry out detailed statistical analysis on a volume-limited sample of main-sequence star systems with detected planets, comparing subsamples of stars that have close-in planets with stars that have more distant planets. This analysis reveals strong evidence that stars with close-in giant planets are on average more X-ray active by a factor of 4 than those with planets that are more distant.“ close-in planets distant planets

25. Claims for SPI at X-ray wavelengths (2): Scharf, C., 2010, ApJ, 722, 1547 „We examine the X-ray emission of stars hosting planets and find a positive correlation between X-ray luminosity and the projected mass of the most closely orbiting exoplanets …. Luminosities and upper limits are consistent with the interpretation that there is a lower floor to stellar X-ray emission dependent on close-in planetary mass. Under the hypothesis that this is a consequence of planet-star magnetic field interaction, and energy dissipation, we estimate a possible field strength increase of a factor of ~8 between planets of 1 and 10 MJ . … The high-energy photon emission of planet-star systems may therefore provide unique access to the detailed magnetic, and hence geodynamic, properties of exoplanets.“

26. Scharf (2010)

27. X-ray census of planet bearing host stars Poppenhaeger et al. (2010): Known host stars within a volume of 30 pc: 72 20 pc XMM-Newton 31 detections/4 upper limits (20d/1 ul) ROSAT 23 detections/11 upper limits (20d/3 ul) Total 54 detections/15 upper limits (40d/4 ul) (Uncensored) LX-distribution of nearby host stars is known Spectral information avaialble for stronger sources

28. No correlation ! Poppenhaeger et al. (2010)

29. Poppenhaeger & Schmitt (2011)

30. Two case studies:

31. Then not known as planet host Courtesy K. Poppenhaeger

32. Poppenhäger et al. (2009) source+background source OVII background

33. Alonso et al. (2008): CoRoT-2a + b Spots transits

34. Host star LX ~ 2 1029 erg/s Companion LX < 1027 erg/s Schröter et al. (2011)

35. Stellar radiation responsible for: planetary heating (optical and UV) ionosphere generation (XUV and X-ray) (all planets with atmospheres in the solar system have ionospheres !)

36. A little comparison …… Mass loss of (extrasolar ) planets: 1. „Jeans“ escape: atmosphere becomes collisionless 2. Hydrodynamic blowoff: Parker wind

37. collisionless collisional Planetary „surface“ escape velocity:

38. Jean‘s flux: rms speed: escape temperature:

39. Escape temperatures of extrasolar planets: Exospheric temperatures of extrasolar planets: ??????????? Scaling relation from solar system gas giants: Obtain ridiculous values for CoRoT 2b Exospheric temperatures ought to exceed escape temperature !

40. X-ray Universe 2011

41. How large is the mass loss ? Energy limited flux: Energy limited mass loss: BUT is the outflow really energy limited ? there is radiative cooling conduction expansion ….

42. eclipse Chandra CoRoT 2 Schröter et al. (2011)

43. Conclusions: (Almost) all extrasolar host stars are X-ray kksources Planet-star interactions are elusive Expect ionospheres and hydrodynamic kkblowoff for the close extrasolar planets „X-ray radii“ of extrasolar planets should kkbe much larger than their „visual radii“