The Interstellar Medium in the Kepler Search Volume

Abstract

The properties of the interstellar medium (ISM) surrounding a planetary system can impact planetary climate through a number of mechanisms, including changing the size of the astrosphere (one of the major shields for cosmic rays) as well as direct deposition of material into planetary atmospheres. In order to constrain the ambient ISM conditions for exoplanetary systems, we present observations of interstellar Na I and K I absorption towards seventeen early-type stars in the Kepler prime mission field of view. We identify 39 Na I and 8 K I velocity components, and attribute these to eleven ISM clouds. Six of these are detected towards more than one star, and for these clouds we put limits on the cloud properties, including distance and hydrogen number density. We identify one cloud with significant (>1.5 cm${}^{-3}$) hydrogen number density located within the nominal ~100 pc boundary of the Local Bubble. We identify systems with confirmed planets within the Kepler field of view that could lie within these ISM clouds, and estimate upper limits on the astrosphere sizes of these systems under the assumption that they do lie within these clouds. Under this condition, the Kepler-20, 42, and 445 multiplanet systems could have compressed astrospheres much smaller than the present-day heliosphere. Among the known habitable zone planet hosts, Kepler-186 could have an astrosphere somewhat smaller than the heliosphere, while Kepler-437 and KOI-4427 could have astrospheres much larger than the heliosphere. The thick disk star Kepler-444 may have an astrosphere just a few AU in radius.

Accepted for publication in ApJ. 19 pages, 9 figures

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