Wednesday 10/30: Katja Poppenhaeger

Hot Jupiters and the Rotational History of their Host Stars

Dr. Katja Poppenhaeger (CfA)
CAS 500, 12:00 pm, October 30, 2013

Stellar rotation is the driver of magnetic dynamos. For cool stars, their thus generated magnetic fields lead to phenomena like flares, coronal mass ejections, and high-energy emission, generally summarized under the name “magnetic activity”. Magnetic activity shapes the environment of close-in exoplanets and can lead to the evaporation of exoplanetary atmospheres. To study this phenomenon, I have collected observations which yielded the first X-ray detection of an exoplanetary transit in front of its host star. These data show a surprisingly deep X-ray transit with three times the optical transit depth, which can be traced back to thin outer atmosphere layers of the planet that are transparent at optical wavelengths, but opaque to X-ray photons. With a larger sample of X-ray observations of such systems, there is now also accumulating evidence that Hot Jupiters may influence the rotation and activity of their host stars. Without external input of angular momentum, cool stars spin down over time due to magnetic breaking. However, if there is tidal interaction between a star and its Hot Jupiter, the spin-down of the host star does not necessarily follow the usual age/rotation/activity relations. I will present results from our ongoing observational campaign at X-ray wavelengths and in the optical, and present several outstanding systems which display significant age/activity discrepancies presumably caused by their Hot Jupiters.