A Sample of Thick-Disk Stars Hosting Hot Jupiters

Abstract: We present a homogeneous analysis of 268 confirmed and candidate transiting hot-Jupiter host stars with 4800K < Teff < 6200K. We combine high-resolution TRES spectra, Gaia, 2MASS and WISE photometry, and Gaia astrometry to determine these stars' Teff, log g, Rstar, [alpha/Fe] and [Fe/H]. Based on their [alpha/Fe] and [Fe/H], we classify the stars as members of the Milky Way's low-[alpha/Fe] thin disk, high-[alpha/Fe] thick disk or an ambiguous intermediate population. We identify two confirmed hot Jupiters (WASP-81 b and TOI-5322 b) and three candidate hot Jupiters (TOI-3118.01, TOI-2728.01, and TOI-5781.01) as orbiting previously-unrecognized members of the high-alpha thick disk. We compare the properties of the confirmed planets in the three populations and note two indications of a potential difference between the populations: both high-[alpha/Fe] confirmed planets and eight out of the eleven ambiguous-disk confirmed planets are less massive than the median low-[alpha/Fe] planet, and none of our high-[alpha/Fe] or ambiguous confirmed planets have orbital periods shorter than 2.7 d, when 22% of our low-[alpha/Fe] population do. These differences may reflect variations in giant-planet formation across galactic environments, evolutionary effects, or differing stellar properties between the high- and low-[alpha/Fe] populations. Our catalog is the largest sample of chemically-identified high-[alpha/Fe] thick-disk confirmed and candidate hot-Jupiter host stars. These ancient systems, with ages > 8 Gyr, may allow for a better understanding of how the formation of hot Jupiters depends on galactic environment, and how their orbits evolve over very long time scales.