The EBLM Project I-Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the Brown Dwarf limit

TL;DR

This study examines the physical and orbital characteristics, including spin-orbit angles, of two low-mass eclipsing binaries near the brown dwarf limit, providing insights into their alignment and orbital dynamics.

Contribution

It reports detailed measurements of spin-orbit angles and orbital parameters for two low-mass eclipsing binaries, including a brown dwarf, enhancing understanding of their formation and evolution.

Findings

Both objects have aligned orbital planes with their primaries' equators.

Neither primary star is synchronized with the orbit.

J1219-39b's properties agree with the mass-radius relationship.

Abstract

This paper introduces a series of papers aiming to study the dozens of low mass eclipsing binaries (EBLM), with F, G, K primaries, that have been discovered in the course of the WASP survey. Our objects are mostly single-line binaries whose eclipses have been detected by WASP and were initially followed up as potential planetary transit candidates. These have bright primaries, which facilitates spectroscopic observations during transit and allows the study of the spin-orbit distribution of F, G, K+M eclipsing binaries through the Rossiter-McLaughlin effect. Here we report on the spin-orbit angle of WASP-30b, a transiting brown dwarf, and improve its orbital parameters. We also present the mass, radius, spin-orbit angle and orbital parameters of a new eclipsing binary, J1219-39b (1SWAPJ121921.03-395125.6, TYC 7760-484-1), which, with a mass of 95 +/- 2 Mjup, is close to the limit between brown dwarfs and stars. We find that both objects orbit in planes that appear aligned with their primaries' equatorial planes. Neither primaries are synchronous. J1219-39b has a modestly eccentric orbit and is in agreement with the theoretical mass--radius relationship, whereas WASP-30b lies above it.