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

Mátéfy, Ádám and Nagy, Zsófia and Kóspál, Ágnes and Ábrahám, Péter and Cruz-Sáenz de Miera, Fernando and Szilágyi, Máté and Siwak, Michal and Fiorellino, Elenonora and Giannini, Teresa and Kun, Mária and Szabados, László and Marton, Gábor and Németh, Patrik and Nisini, Brunella and Szabó, Zsófia Marianna (2026) Gaia21bja: pre-main sequence star with quasi-periodic bursts. ASTROPHYSICAL JOURNAL. ISSN 1538-4357 (In Press)

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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 ∼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 ± 77 days. We derived the stellar parameters as R⋆ = 0.78 ± 0.04 R⊙, L⋆ = (4.5 ± 0.3) × 10−2 L⊙, and M⋆ = 0.16 ± 0.03 M⊙. 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.

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