Gaia21bja: pre-main sequence star with quasi-periodic bursts

TL;DR

Gaia21bja is a young stellar object exhibiting quasi-periodic bursts with a 916-day cycle, characterized by increased accretion activity and eruptive behavior similar to EX Lupi-type stars.

Contribution

This study provides detailed photometric and spectroscopic analysis of Gaia21bja, identifying its periodicity, physical properties, and eruptive nature, expanding understanding of young stellar object variability.

Findings

Quasi-periodic bursts with a 916-day cycle observed.

Accretion rate increases by a factor of 5.5-6 during bursts.

Spectra resemble EX Lupi-type eruptive stars.

Abstract

Gaia21bja is a Gaia alerted young stellar object (YSO) that exhibits at least seven quasi-peridoic brightenings over a 20 year-long light curve with durations of 1.5-2 years and amplitudes up to $\sim$1.7 mag in the Gaia $G$-band. We analyze its optical and near-infrared photometry and spectra taken using the IRTF and VLT in its faint and bright states in order to characterize its physical properties. A Lomb-Scargle periodogram analysis results in a most significant period of $916\pm77$ days. We derived the stellar parameters as $R_\star= 0.78 \pm 0.04~R_\odot$, $L_\star=(4.5\pm0.3) \times 10^{-2}~L_\odot$, and $M_\star= 0.16 \pm 0.03~M_\odot$. The spectra taken during the burst are dominated by emission lines and are similar to those of EX Lupi-type eruptive young stars (EXors). We found that the accretion luminosity and mass accretion rate increased by a factor of $5.5-6$ during the burst. Based on this, and the quasi-periodic bursts, we suggest that Gaia21bja is an eruptive YSO, and is most consistent with the `Periodic' category of the Outbursting YSOs Catalogue.