HAT-P-31b,c: A Transiting, Eccentric, Hot Jupiter and a Long-Period, Massive Third-Body

TL;DR

This paper reports the discovery of a transiting hot Jupiter with high eccentricity and evidence for a long-period massive third body, highlighting a new observational approach and potential dynamical interactions.

Contribution

It demonstrates the feasibility of discovering transiting exoplanets without follow-up photometry and identifies a possible long-period companion affecting the system's dynamics.

Findings

HAT-P-31b is a 2.17 Mj, 1.1 Rj planet with a 5-day period and high eccentricity.

Detected a quadratic radial velocity trend indicating a third body, HAT-P-31c.

Dynamical simulations suggest orbital stability and potential eccentricity driving by the third body.

Abstract

We report the discovery of HAT-P-31b, a transiting exoplanet orbiting the V=11.660 dwarf star GSC 2099-00908. HAT-P-31b is the first HAT planet discovered without any follow-up photometry, demonstrating the feasibility of a new mode of operation for the HATNet project. The 2.17 Mj, 1.1Rj planet has a period P = 5.0054 days and maintains an unusually high eccentricity of e = 0.2450+/-0.0045, determined through Keck, FIES and Subaru high precision radial velocities. Detailed modeling of the radial velocities indicates an additional quadratic residual trend in the data detected to very high confidence. We interpret this trend as a long-period outer companion, HAT-P-31c, of minimum mass 3.4Mj and period >2.8 years. Since current RVs span less than half an orbital period, we are unable to determine the properties of HAT-P-31c to high confidence. However, dynamical simulations of two possible configurations show that orbital stability is to be expected. Further, if HAT-P-31c has non-zero eccentricity, our simulations show that the eccentricity of HAT-P-31b is actively driven by the presence of c, making HAT-P-31 a potentially intriguing dynamical laboratory.