Improved period variations of 32 contact binaries with rapidly decreasing periods in the Galactic Bulge

TL;DR

This study analyzes period variations in 32 contact binary systems in the Galactic bulge, revealing significant period decreases and potential third-body effects, contributing to understanding binary mergers and luminous red nova progenitors.

Contribution

It provides updated eclipse timing analyses of 32 contact binaries, identifying period decreases and third-body influences, which is novel for this specific stellar population.

Findings

32 contact binaries with periods 0.370-1.238 days

Period decreasing rates from -3.0 to -13.1×10^{-6} day yr^{-1}

24 systems show third-body effects with orbital periods 9.1-26.5 years

Abstract

We present detailed analyses of updated eclipse timing diagrams for 32 contact binary merger candidates in the Galactic bulge. The photometric data was obtained from 2016 to 2021 using the Korea Microlensing Telescope Network (KMTNet) with the 1.6 m telescopes located at three southern sites (CTIO, SAAO, and SSO). The times of minimum lights were determined by applying the binary star model to full light curves created at half-year intervals from the observations. The orbital period variations of the binary systems were analyzed using the $O-C$ diagrams from our new timings with the others published in the literature (Hong et al.), which are based on the OGLE observations from 2001 to 2015. As results, the orbital periods and period decreasing rates of 32 binary systems were located to be in the ranges of 0.370$-$1.238 days and from $-3.0$ to $-13.1\times10^{-6}$ day yr$^{-1}$, respectively. Out of these stars, 24 systems show a combination effect of a parabola and a light travel time caused by a third body and their outer orbital periods are in the range of 9.1$-$26.5 yr, respectively. We propose that all of our merger candidates need additional monitoring observations to study a luminous red nova (LRN) progenitor.