KELT-6b: Another Hot Saturn

KELT-6b: A P ~ 7.9 DAY HOT SATURN TRANSITING A METAL-POOR STAR WITH A LONG-PERIOD COMPANION*

Authors:

Collins et al

Abstract:

We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T eff = 6102 ± 43 K, $\log g_\star =4.07_{-0.07}^{+0.04}$, and [Fe/H] = –0.28 ± 0.04, with an inferred mass M sstarf = 1.09 ± 0.04 M ☉ and radius $R_\star =1.58_{-0.09}^{+0.16} \,R_\odot$. The planetary companion has mass MP = 0.43 ± 0.05 M Jup, radius $R_{P}=1.19_{-0.08}^{+0.13} \,R_{\rm Jup}$, surface gravity $\log g_{P}=2.86_{-0.08}^{+0.06}$, and density $\rho _{P}=0.31_{-0.08}^{+0.07}\,{\rm g\,cm^{-3}}$. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity $e=0.22_{-0.10}^{+0.12}$, which is roughly consistent with circular, and has ephemeris of T c(BJDTDB) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ~4}-7}. KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ~0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images.