Photometric Properties of the Near-contact Binary GW Geminorum

TL;DR

This study presents the first multiband CCD photometry and analysis of GW Gem, revealing its semi-detached near-contact configuration, ongoing mass transfer, and period increase, with detailed light curve modeling and spot analysis.

Contribution

First multiband CCD photometry and eclipse timing analysis of GW Gem, providing new insights into its structure, period change, and spot activity.

Findings

GW Gem is a semi-detached near-contact binary.

The orbital period is increasing at a rate of about 1.2×10^{-10}.

Light curve modeling suggests a cool spot on the secondary star.

Abstract

New multiband CCD photometry is presented for the eclipsing binary GW Gem; the $RI$ light curves are the first ever compiled. Four new minimum timings have been determined. Our analysis of eclipse timings observed during the past 79 years indicates a continuous period increase at a fractional rate of +(1.2$\pm$0.1)$\times10^{-10}$, in excellent agreement with the value $+1.1\times10^{-10}$ calculated from the Wilson-Devinney binary code. The new light curves display an inverse O'Connell effect increasing toward longer wavelengths. Hot and cool spot models are developed to describe these variations but we prefer a cool spot on the secondary star. Our light-curve synthesis reveals that GW Gem is in a semi-detached, but near-contact, configuration. It appears to consist of a near-main-sequence primary star with a spectral type of about A7 and an evolved early K-type secondary star that completely fills its inner Roche lobe. Mass transfer from the secondary to the primary component is responsible for the observed secular period change.