Andrew W. Mann, Eric Gaidos, Sébastien Lépine, Eric Hilton
We estimate the stellar parameters of late K and early M-type Kepler target
stars. We obtained medium resolution visible spectra of 388 stars with Kp-J>2
(~K5 and later spectral type). We determine luminosity class by comparing the
strength of gravity-sensitive indices (CaH, K I, Ca II, and Na I) to their
strength in a sample of stars of known luminosity class. We find that giants
constitute 95\pm1% of the bright (Kp < 14) red Kepler target stars, and 7\pm2%
of dim (Kp < 14) stars, significantly higher than fractions based on the
stellar parameters quoted in the Kepler Input Catalog. The KIC effective
temperatures are systematically (135 K) higher than temperatures determined
from fitting our spectra to PHOENIX stellar models. Through Monte Carlo
simulations of the Kepler exoplanet candidate population, we find that there
are 0.38\pm0.08 planets per star when giant stars are properly removed,
somewhat higher than when a KIC log(g)>4 criteria is used (0.27\pm0.05).
Lastly, we show that there is no significant difference in g-r color (a probe
of metallicity) between late-type Kepler stars with transiting Earth-to-Neptune
sized exoplanet candidates and dwarf stars with no detected transits, in line
with what is seen for solar-type stars. We show that a previous claimed offset
between these two populations is most likely an artifact of including a large
number of misidentified giants.
View original:
http://arxiv.org/abs/1202.5394
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