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An Understanding of the Shoulder of Giants: Jovian Planets around Late K Dwarf Stars and the Trend with Stellar Mass
Analyses of exoplanet statistics suggest a trend of giant planet occurrence
with host star mass, a clue to how planets like Jupiter form. One missing piece
of the puzzle is the occurrence around late K dwarf stars (masses of
0.5-0.75Msun and effective temperatures of 3900-4800K). We analyzed four years
of Doppler radial velocities data of 110 late K dwarfs, one of which hosts two
previously reported giant planets. We estimate that 4.0+/-2.3% of these stars
have Saturn-mass or larger planets with orbital periods <245d, depending on the
planet mass distribution and RV variability of stars without giant planets. We
also estimate that 0.7+/-0.5% of similar stars observed by Kepler have giant
planets. This Kepler rate is significantly (99% confidence) lower than that
derived from our Doppler survey, but the difference vanishes if only the single
Doppler system (HIP 57274) with completely resolved orbits is considered. The
difference could also be explained by the exclusion of close binaries (without
giant planets) from the Doppler but not Kepler surveys, the effect of
long-period companions and stellar noise on the Doppler data, or an intrinsic
difference between the two populations. Our estimates for late K dwarfs bridge
those for solar-type stars and M dwarfs and support a positive trend with
stellar mass. Small sample size precludes statements about finer structure,
e.g. a "shoulder" in the distribution of giant planets with stellar mass.
Future surveys such as the Next Generation Transit Survey and the Transiting
Exoplanet Satellite Survey will ameliorate this deficiency.Comment: Accepted to The Astrophysical Journa
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