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

TL;DR

This paper reports a significant spin-orbit misalignment in the hot-Jupiter HATS-14b, challenging existing theories that predict aligned orbits for such planets around stars with convective envelopes.

Contribution

It presents the first measurement of a high obliquity for HATS-14b using a novel velocity extraction technique from low S/N spectra.

Findings

HATS-14b has a projected obliquity of 76 degrees.

The velocity measurement technique achieved 4 m/s precision.

HATS-14b's misalignment challenges tidal realignment theories.

Abstract

We report a spin-orbit misalignment for the hot-Jupiter HATS-14b, measuring a projected orbital obliquity of |lambda|= 76 -5/+4 deg. 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, optimised for low signal-to-noise spectra, achieving a high precision of 4 m/s 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 vsini prior that is imposed in our modelling. 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.