Analysis of Detached Eclipsing Binaries near the Turnoff of the Open Cluster NGC 7142

TL;DR

This study analyzes three eclipsing binary stars in NGC 7142 to determine stellar parameters, cluster age, and test models of stellar radius inflation, providing precise measurements and insights into stellar evolution.

Contribution

It presents detailed measurements of binary stars in NGC 7142, including a cluster member used to estimate age and distance, and tests the radius inflation hypothesis in short-period binaries.

Findings

The primary star's characteristics indicate an age of 3.6 Gyr for NGC 7142.

The secondary star shows radius inflation exceeding model predictions.

A precise distance modulus of (m-M)_V=12.86±0.07 was obtained.

Abstract

We analyze extensive BVRI photometry and radial velocity measurements for three double-lined deeply-eclipsing binary stars in the field of the old open cluster NGC 7142. The short period (P = 1.9096825 d) detached binary V375 Cep is a high probability cluster member, and has a total eclipse of the secondary star. The characteristics of the primary star (M=1.288+/-0.017 Sun) at the cluster turnoff indicate an age of 3.6 Gyr (with a random uncertainty of 0.25 Gyr), consistent with earlier analysis of the color-magnitude diagram. The secondary star (M = 0.871+/-0.008 Msun) is not expected to have evolved significantly, but its radius is more than 10% larger than predicted by models. Because this binary system has a known age, it is useful for testing the idea that radius inflation can occur in short period binaries for stars with significant convective envelopes due to the inhibition of energy transport by magnetic fields. The brighter star in the binary also produces a precision estimate of the distance modulus, independent of reddening estimates: (m-M)_V=12.86+/-0.07. The other two eclipsing binary systems are not cluster members, although one of the systems (V2) could only be conclusively ruled out as a present or former member once the stellar characteristics were determined. That binary is within 0.5 degrees of edge-on, is in a fairly long-period eccentric binary, and contains two almost indistiguishable stars. The other binary (V1) has a small but nonzero eccentricity (e=0.038) in spite of having an orbital period under 5 d.