KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion

KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion 

Authors:

Siverd et al

Abstract:

We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V∼9.9) A8V star TYC 764-1494-1. We confirm the planetary nature of the companion via a combination of low-precision radial velocities, which limit the mass to MP less than 4.1MJ (3σ), and a clear Doppler tomography signal, which indicates a retrograde projected spin-orbit misalignment of λ=−179.7+3.7−3.8 degrees. Global modeling indicates that the Teff=7500±110K host star has M∗=1.62+0.25−0.20M⊙ and R∗=1.83±0.10R⊙. The planet has a radius of RP=1.91±0.11RJ and receives a stellar insolation flux of ∼3.2×109ergs−1cm−2, leading to an inferred equilibrium temperature of Teq∼1935K assuming zero albedo and complete heat redistribution. With a vsinI∗=84.8±2.0kms−1, the host star is rapidly-rotating. Interestingly, its vsinI∗ is relatively low compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic species such as strontium but deficient in others such as calcium, suggesting that it is likely an Am star. KELT-19A would be the first definitive detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late G9V/early K1V spectral type at a projected separation of ≈160AU. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary.