A new low-mass eclipsing binary: NSVS 02502726

TL;DR

This study precisely measures the masses and radii of the low-mass eclipsing binary NSVS 02502726, revealing larger-than-expected stellar radii and signs of stellar activity, and estimates its age as about 126 million years.

Contribution

First detailed empirical determination of masses and radii for both stars in NSVS 02502726, highlighting discrepancies with models and evidence of stellar activity.

Findings

Both stars are in a circular orbit with a 0.56-day period.

Secondary star's radius exceeds model predictions for its mass.

Stars are approximately 126 million years old, near the zero-age main sequence.

Abstract

We present optical spectroscopy and extensive $RI$ differential photometry of the double-lined eclipsing binary NSVS 02502726 (2MASS J08441103+5423473). Simultaneous solution of two-band light curves and radial velocities permits determination of precise emprical masses and radii for both components of the system. The analysis indicates that the primary and secondary components of NSVS 02502726 are in a circular orbit with 0.56-day orbital period and have stellar masses of M$_1$=0.714$\pm$0.019 \Msun, and M$_2$=0.347$\pm$0.012 \Msun. Both of the components have large radii, being R$_1$=0.67$\pm$0.01 \Rsun, and R$_2$=0.76$\pm$0.01 \Rsun. The principal parameters of the mass and radius of the component stars are found with an accuracy of 3% and 1%, respectively. The secondary component's radius is significantly larger than model predictions for its mass, similar to what is seen in almost all of the other well-studied low-mass stars which belong to double-lined eclipsing binaries. Strong H$_{\alpha}$ emission cores and considerable distortion at out-of-eclipse light curve in both $R$ and $I$ bandpasses, presumably due to dark spots on both stars, have been taken as an evidence of strong stellar activity. The distance to system was calculated as 173$\pm$8 pc from the $BVRIJHK$ magnitudes. The absolute parameters of the components indicate that both components are close to the zero-age main-sequence. Comparison with current stellar evolution models gives an age of 126 $\pm$30 Myr, indicating the stars are in the final stages of pre-main-sequence contraction.