A New Lower Main Sequence Eclipsing Binary with Detached Components

TL;DR

This paper reports the discovery and detailed analysis of a new detached eclipsing binary system of late K dwarfs, providing precise measurements of stellar parameters and insights into magnetic activity effects on stellar radii.

Contribution

It presents the first detailed characterization of NGC2204-S892, including accurate masses, radii, and activity indicators, highlighting the impact of magnetic activity on stellar structure.

Findings

Both stars are oversized compared to models.

High magnetic activity correlates with radius inflation.

System's parameters align with empirical mass-radius relations.

Abstract

We present an analysis of NGC2204-S892 -- a new detached eclipsing binary composed of two late K dwarfs. Based on three photometric campaigns launched in 2008 we obtained 5 light curves (3 in V, 1 in B and 1 in I), and derived an orbital period of 0.451780+-0.000001 d. We also obtained 20 VLT/UVES spectra, enabling accurate radial velocity measurements. The derived masses and radii of the components (m1 = 0.733 +-0.005 Msun and R1 = 0.72 +-0.01 Rsun; m2 = 0.662 +-0.005 Msun and R2 = 0.68 \+-0.02 Rsun) are consistent with the empirical mass-radius relationship established recently for lower main sequence stars in binary systems; in particular we find that both stars are oversized compared to theoretical models. NGC2204-S892 is very active: both components show variable emission in Halpha and Hbeta and are heavily spotted, causing the light curve to show appreciable changes on a timescale of weeks. Our results add to the increasing evidence that the observed inflation of the radii of K and M stars is related to high levels of magnetic activity.