MG1-688432: A Peculiar Variable System

TL;DR

This paper presents a detailed study of the peculiar variable star MG1-688432, revealing its binary nature, unusual outbursts, and potential mechanisms involving planetary debris or a white dwarf companion, based on 20 years of observations.

Contribution

It provides the first comprehensive analysis of MG1-688432, combining photometry, spectroscopy, and Gaia data to propose new hypotheses about its nature and variability mechanisms.

Findings

Displays high-energy optical outbursts up to 10^31 joules.

Identified as a binary system with a K3 subgiant primary and an unseen companion.

Suggests possible causes include planetary debris impacts or a white dwarf companion.

Abstract

The short period variable star MG1-688432 has been discovered to exhibit occasional extremely high energy optical outbursts as high as 10^31 joules. Outbursts are typically of several hours duration. These events are often highly structured, resembling sequential associated releases of energy. Twenty years of time sequence photometry is presented, indicating a basic sinusoidal light curve of mean period 6.65d, with some phase shifting and long-term temporal trends in amplitude and mean brightness. Spectroscopy reveals a peculiar star, best resembling a K3 subgiant that has evolved off the main sequence moderately red-ward of the giant branch. Spectroscopic and radial velocity analyses indicate a binary system orbiting its barycenter with an unseen companion to the K3IV primary. This is not an eclipsing system with the inclination of the orbit precluding eclipse by the secondary. The system is at a distance of 1.5kpc and analysis of GAIA observations leads to the conclusion that the HR diagram position of MG1-688432 is established by an intrinsic feature of the system, most likely either the stellar evolutionary state of the observed star or the presence of small (non-gray) dust within the system. Two mechanisms that might give rise to the system are 1) impacts with tidally disrupted planetary debris, and 2) magnetically induced chromospheric activity. An intriguing idea that requires further investigation suggests that the unseen companion is perhaps a white dwarf star which has encountered a planet and tidally shredded it to produce a debris and dust veil that modulates the brightness of the primary.