Hubble Telescope Reexamines Some Kepler Candidates, Disputes Many Superearths in Habitable Zones

Revision of Earth-sized Kepler Planet Candidate Properties with High Resolution Imaging by Hubble Space Telescope

Authors:

Star et al

Abstract:

We present the results of our Hubble Space Telescope program and describe how our image analysis methods were used to re-evaluate the habitability of some of the most interesting Kepler planet candidates. Our program observed 22 KOI hosts, several of which were found to be multiple star systems unresolved by Kepler. We use our high-resolution imaging to provide a conversion to the Kepler photometric bandpass (Kp) from the F555W and F775W filters on WFC3/UVIS, and spatially resolve the stellar multiplicity of Kepler-296, KOI-2626, and KOI-3049. The binary system Kepler-296 has a projected separation of 0.217" (80 AU); KOI-2626 is a triple star system with a projected separation of 0.201" (70 AU) between the primary and secondary components and 0.161" (55 AU) between the primary and tertiary components; and the binary system KOI-3049 has a projected separation of 0.464" (225 AU). Using theoretical isochrones from the latest Victoria-Regina Stellar Models, we performed hierarchical fitting using our derived photometry and the synthetic photometry from the isochrones. We find that the individual components of the three systems range from mid-K dwarf to mid-M dwarf spectral types. We solved for the planetary properties in the three systems directly from the stellar and published transit parameters and from empirically derived relations. We find that the planets range in size from ~1.2Re to ~4Re, placing them in the Super Earth/mini-Neptune regime. As a result of the stellar multiplicity, we find that some planets previously in the Habitable Zone are, in fact, not, and that other planets may be in the HZ depending on their assumed stellar host.