A Bimodal Correlation between Host Star Chromospheric Emission and the Surface Gravity of Hot Jupiters
Abstract
The chromospheric activity index {log}{R}_{{HK}}^{\prime } of stars hosting transiting hot Jupiters appears to be correlated with the planets’ surface gravity. One of the possible explanations is based on the presence of condensations of planetary evaporated material located in a circumstellar cloud that absorbs the Ca ii H&K and Mg ii h&k resonance line emission flux, used to measure chromospheric activity. A larger column density in the condensations, or equivalently a stronger absorption in the chromospheric lines, is obtained when the evaporation rate of the planet is larger, which occurs for a lower gravity of the planet. We analyze here a sample of stars hosting transiting hot Jupiters tuned in order to minimize systematic effects (e.g., interstellar medium absorption). Using a mixture model, we find that the data are best fit by a twolinearregression model. We interpret this result in terms of the VaughanPreston gap. We use a Monte Carlo approach to best take into account the uncertainties, finding that the two intercepts fit the observed peaks of the distribution of {log}{R}_{{HK}}^{\prime } for mainsequence solarlike stars. We also find that the intercepts are correlated with the slopes, as predicted by the model based on the condensations of planetary evaporated material. Our findings bring further support to this model, although we cannot firmly exclude different explanations. A precise determination of the slopes of the two linear components would allow one to estimate the average effective stellar flux powering planetary evaporation, which can then be used for theoretical population and evolution studies of closein planets.
 Publication:

The Astrophysical Journal
 Pub Date:
 October 2015
 DOI:
 10.1088/20418205/812/2/L35
 arXiv:
 arXiv:1510.04691
 Bibcode:
 2015ApJ...812L..35F
 Keywords:

 planet–star interactions;
 stars: activity;
 stars: latetype;
 Astrophysics  Solar and Stellar Astrophysics;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 23 pages, 4 figures, 1 table, accepted for publication in ApJL