Optical Flares Detected on a Contact Binary: The First Photometric and Spectroscopic Analysis of a Long-period Low Mass Ratio Contact Binary HAT 307-0007476

TL;DR

This study presents the first combined photometric and spectroscopic analysis of a long-period, low-mass-ratio contact binary, HAT 307-0007476, revealing stellar activity, flare events, and orbital period changes.

Contribution

It provides the first detailed analysis of this specific contact binary, including flare detection, chromospheric activity, and orbital period variation insights.

Findings

Detected two superflares within four days.

Observed long-term orbital period increase.

Confirmed chromospheric activity via H-alpha emission.

Abstract

This paper presents the photometric and spectroscopic analysis of a long-period totally eclipsing contact binary (HAT 307-0007476) for the first time. This system is a low mass ratio ($q\sim0.114$) and medium contact binary ($f\sim37.1\%$). Two flare events were detected in multiple bands observations in December 2022. The interval between the two flare events is 4 days. The average duration of these two flares is about 2289s. Both the two flares achieve the energy levels of superflares. The excess emission of the H$_\alpha$ line in the LAMOST spectra of this object was analyzed, indicating its chromospheric activity. The $O-C$ diagram showed a long-term orbital period increase, which is due to the mass transfer between the two component stars. We conclude that HAT 307-0007476 is currently in a stable region based on both $J_{spin}/J_{orb}$ and the comparison between the instability parameters and its current values.