# Long-term Photometric Behavior of the Eclipsing Binary GW Cephei

## TL;DR

This study presents a 4-year photometric analysis of GW Cep, revealing light and period variations caused by magnetic activity, spots, and a potential third star, with implications for understanding binary star dynamics.

## Contribution

It provides new long-term photometric data and models the light and period variations, suggesting the presence of a third companion and magnetic activity effects.

## Key findings

- Light curves show significant long-term changes.
- Period variation suggests a third body or magnetic cycle.
- Hot and cool spots are linked to magnetic activity and mass transfer.

## Abstract

New CCD photometry during 4 successive years from 2005 is presented for the eclipsing binary GW Cep, together with reasonable explanations for the light and period variations. All historical light curves, obtained over a 30-year interval, display striking light changes, and are best modeled by the simultaneous existence of a cool spot and a hot spot on the more massive cool component star. The facts that the system is magnetically active and that the hot spot has consistently existed on the inner hemisphere of the star indicate that the two spots are formed by (1) magnetic dynamo-related activity on the cool star and (2) mass transfer from the primary to the secondary component. Based on 38 light-curve timings from the Wilson-Devinney code and all other minimum epochs, a period study of GW Cep reveals that the orbital period has experienced a sinusoidal variation with a period and semi-amplitude of 32.6 yrs and 0.009 d, respectively. In principle, these may be produced either by a light-travel-time effect due to a third body or by an active magnetic cycle of at least one component star. Because we failed to find any connection between luminosity variability and the period change, that change most likely arises from the existence of an unseen third companion star with a minimum mass of 0.22 $M_\odot$ gravitationally bound to the eclipsing pair.