X-ray Universe 2011 The High-Energy Environment of Extrasolar Planets J. Schmitt Hamburger Sternwarte Internet:

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

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 ?

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

The SOHO Sun

Robrade et al. (2009)

k RV-signal dominated by Jupiter !

(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

„Types“ of extrasolar planets: 1.Radial velocity detections (blue, nearby)) 2.Transit detections (green, further away) 3.Microlensing detections (brown, very distant)

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

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

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

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

Chandra LETGS:

Courtesy: J. Robrade Accretion/Jet sources

An analogy from close binaries ?

Courtesy K. Poppenhaeger What are we talking about ?

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

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

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

X-ray Universe 2011 Key elements of Jupiter-Io interaction: 1.Strong magnetic field of Jupiter 2.Evaporation due to volcanism and formation of plasma torus (high density environment) 3.Corotation of Jupiter‘s magnetosphere beyond Io 4.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 Application to Planet X around a young star: Dipole fieldCorotating plasma Kepler‘s 3 law

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

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 M J. … The high-energy photon emission of planet-star systems may therefore provide unique access to the detailed magnetic, and hence geodynamic, properties of exoplanets.“

Scharf (2010)

X-ray census of planet bearing host stars Poppenhaeger et al. (2010): Known host stars within a volume of 30 pc: 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) L X -distribution of nearby host stars is known Spectral information avaialble for stronger sources

Poppenhaeger et al. (2010) No correlation !

Poppenhaeger & Schmitt (2011)

Two case studies:

Then not known as planet host Courtesy K. Poppenhaeger

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

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

Schröter et al. (2011) Host star L X ~ erg/s Companion L X < erg/s

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 !)

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

Planetary „surface“ collisional collisionless escape velocity:

Jean‘s flux: rms speed: escape temperature:

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

X-ray Universe 2011

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

Schröter et al. (2011)Chandra CoRoT 2 eclipse

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“