A high obliquity orbit for the hot-Jupiter HATS-14b transiting a 5400K star

Abstract

We report a spin–orbit misalignment for the hot-Jupiter HATS-14b, measuring a projected orbital obliquity of |λ| = 76_(-5)^(+4)^○. HATS-14b orbits a high metallicity, 5400 K G dwarf in a relatively short period orbit of 2.8 days. This obliquity was measured via the Rossiter–McLaughlin effect, obtained with observations from Keck-HIRES. The velocities were extracted using a novel technique, optimized for low signal-to-noise spectra, achieving a high precision of 4 m s^-1 point-to-point scatter. However, we caution that our uncertainties may be underestimated. Due to the low rotational velocity of the star, the detection significance is dependent on the v sin i prior that is imposed in our modeling. Based on trends observed in the sample of hot Jupiters with obliquity measurements, it has been suggested that these planets modify the spin axes of their host stars, with an efficiency that depends on the stellar type and orbital period of the system. In this framework, short-period planets around stars with surface convective envelopes, like HATS-14b, are expected to have orbits that are aligned with the spin axes of their host stars. HATS-14b, however, is a significant outlier from this trend, challenging the effectiveness of the tidal realignment mechanism.

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