A Bimodal Correlation between Host Star Chromospheric Emission and the Surface Gravity of Hot Jupiters
Journal
Date Issued
2015
Author(s)
Description
L.F. acknowledges financial support from the Alexander von Humboldt foundation. A.F.L. acknowledges support by INAF through the Progetti Premiali funding scheme of the Italian Ministry of Education, University, and Research. We thank the anonymous referee for the useful comments. This research has made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org .
Abstract
The chromospheric activity index log R'_HK 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 two-linear-regression model. We interpret this result in terms of the Vaughan-Preston 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 for main-sequence solar-like 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 close-in planets.
Volume
812
Issue
2
Start page
L35
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...812L..35F
Rights
open.access
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