CoRoT 101186644: A transiting low-mass dense M-dwarf on an eccentric 20.7-day period orbit around a late F-star

TL;DR

This study reports the discovery of a dense, low-mass M-dwarf star in an eccentric 20.7-day orbit around a late F-star, with measurements challenging existing models of stellar radii.

Contribution

First detailed characterization of a very small, dense late M-dwarf in an eccentric orbit, providing data that may refine theoretical models.

Findings

The M-dwarf has a mass of 0.096 solar masses.

Its radius is approximately 0.104 solar radii, possibly the smallest and densest known.

The star's radius aligns with or is below theoretical predictions.

Abstract

We present the study of the CoRoT transiting planet candidate 101186644, also named LRc01_E1_4780. Analysis of the CoRoT lightcurve and the HARPS spectroscopic follow-up observations of this faint (m_V = 16) candidate revealed an eclipsing binary composed of a late F-type primary (T_eff = 6090 +/- 200 K) and a low-mass, dense late M-dwarf secondary on an eccentric (e = 0.4) orbit with a period of ~20.7 days. The M-dwarf has a mass of 0.096 +/- 0.011 M_Sun, and a radius of 0.104 +0.026/-0.006 R_Sun, which possibly makes it the smallest and densest late M-dwarf reported so far. Unlike the claim that theoretical models predict radii that are 5%-15% smaller than measured for low-mass stars, this one seems to have a radius that is consistent and might even be below the radius predicted by theoretical models.