Long-Term Light Curve of Highly-Variable Protostellar Star GM Cep

TL;DR

This study compiles and analyzes over a century of archival and observational data to characterize the long-term light variability of the protostellar star GM Cep, revealing dips likely caused by extinction rather than accretion-driven outbursts.

Contribution

It provides the first extensive long-term light curve analysis of GM Cep, ruling out several types of variable stars and accretion mechanisms based on historical data.

Findings

Light curves show dips likely due to extinction, not outbursts.

GM Cep is not a FUor, EXor, or McNeil's Nebula type star.

No periodicity detected, excluding KH 15D classification.

Abstract

We present data from the archival plates at Harvard College Observatory and Sonneberg Observatory showing the field of the solar type pre-main sequence star GM Cep. A total of 186 magnitudes of GM Cep have been measured on these archival plates, with 176 in blue sensitivity, 6 in visible, and 4 in red. We combine our data with data from the literature and from the American Association of Variable Star Observers to depict the long-term light curves of GM Cep in both B and V wavelengths. The light curves span from 1895 until now, with two densely sampled regions (1935 to 1945 in B band, and 2006 until now in V band). The long-term light curves do not show any fast rise behavior as predicted by an accretion mechanism. Both the light curves and the magnitude histograms confirm the conclusion that the light curves are dominated by dips (possibly from extinction) superposed on some quiescence state, instead of outbursts caused by accretion flares.Our result excludes the possibility of GM Cep being a FUor, EXor, or McNeil's Nebula type star. Several special cases of T Tauri stars were checked, but none of these light curves are compatible with that of GM Cep. The lack of periodicity in the light curve excludes the possibility of GM Cep being a KH 15D system.