The Rapid Outbursting Star GM Cep: An EX-or in Tr 37?

TL;DR

GM Cep is a young, solar-type star exhibiting rapid brightness variations likely caused by episodic accretion events similar to EX-or phenomena, supported by multi-wavelength observations indicating a massive, possibly unstable disk and potential binary interactions.

Contribution

This study provides detailed multi-wavelength observations of GM Cep, highlighting its episodic accretion behavior and disk properties, and explores the potential role of a binary companion in triggering outbursts.

Findings

GM Cep shows high, variable accretion rates up to ~10^{-6} Msun/yr.

The star has a massive, flared disk with signs of grain growth.

Possible binary companion could be responsible for disk instabilities.

Abstract

We present optical, IR and millimeter observations of the solar-type star 13-277, also known as GM Cep, in the 4 Myr-old cluster Tr 37. GM Cep experiences rapid magnitude variations of more than 2 mag at optical wavelengths. We explore the causes of the variability, which seem to be dominated by strong increases in the accretion, being similar to EX-or episodes. The star shows high, variable accretion rates (up to ~10$^{-6}$ Msun/yr), signs of powerful winds, and it is a very fast rotator (Vsini~43 km/s). Its strong mid-IR excesses reveal a very flared disk and/or a remnant envelope, most likely out of hydrostatic equilibrium. The 1.3 millimeter fluxes suggest a relatively massive disk (Mdisk~0.1 Msun). Nevertheless, the millimeter mass is not enough to sustain increased accretion episodes over large timescales, unless the mass is underestimated due to significant grain growth. We finally explore the possibility of GM Cep having a binary companion, which could trigger disk instabilities producing the enhanced accretion episodes.