Discovery and characterisation of detached M-dwarf eclipsing binaries in the WFCAM Transit Survey

TL;DR

This paper reports the discovery and detailed characterization of 16 detached M-dwarf eclipsing binaries from the WFCAM Transit Survey, providing precise measurements of their fundamental parameters and investigating radius inflation.

Contribution

It presents the first detailed measurements of M-dwarf binary parameters using infrared light curves and examines the ongoing radius inflation problem across different activity levels.

Findings

Measured masses and radii of three M-dwarf binaries with ~3.5-6.4% mass uncertainties.

Found radius inflation of 3-12% above models, consistent with magnetic activity effects.

No significant correlation between orbital period and radius inflation was observed.

Abstract

We report the discovery of 16 detached M-dwarf eclipsing binaries with J<16 mag and provide a detailed characterisation of three of them, using high-precision infrared light curves from the WFCAM Transit Survey (WTS). Such systems provide the most accurate and model-independent method for measuring the fundamental parameters of these poorly understood yet numerous stars, which currently lack sufficient observations to precisely calibrate stellar evolution models. We fully solve for the masses and radii of three of the systems, finding orbital periods in the range 1.5<P<4.9 days, with masses spanning 0.35-0.50 Msun and radii between 0.38-0.50 Rsun, with uncertainties of ~3.5-6.4% in mass and ~2.7-5.5% in radius. Close-companions in short-period binaries are expected to be tidally-locked into fast rotational velocities, resulting in high levels of magnetic activity. This is predicted to inflate their radii by inhibiting convective flow and increasing star spot coverage. The radii of the WTS systems are inflated above model predictions by ~3-12%, in agreement with the observed trend, despite an expected lower systematic contribution from star spots signals at infrared wavelengths. We searched for correlation between the orbital period and radius inflation by combining our results with all existing M-dwarf radius measurements of comparable precision, but we found no statistically significant evidence for a decrease in radius inflation for longer period, less active systems. Radius inflation continues to exists in non-synchronised systems indicating that the problem remains even for very low activity M-dwarfs. Resolving this issue is vital not only for understanding the most populous stars in the Universe, but also for characterising their planetary companions, which hold the best prospects for finding Earth-like planets in the traditional habitable zone.