Speaker
Description
Young stellar objects (YSOs) show variability on very different time scales and with different amplitudes due to several physical mechanisms including changes in the mass accretion rate. Eruptive YSOs show variability on longer time scales (from several months to a year or from decades to a century) and with amplitudes up to 6 magnitudes. Studying these examples of episodic accretion is important for understanding how Sun-like stars accumulated their mass.
Gaia24bux is a YSO candidate at a distance of $\sim$946 pc. It had a Gaia Alert in 2024 due to an approximately 2 year long brightening by about 3.4 magnitudes. The star had a previous, about 1.5 year long brightening event in 2015-2016, which had an amplitude of $\sim$2.8 magnitudes.
I used archival optical and infrared photometry, as well as near-infrared spectra obtained with the NASA Infrared Telescope Facility to understand the physical properties of Gaia24bux, as well as its recent brightening.
Based on its infrared photometry, I classified Gaia24bux as a Class II YSO. I used a grid of radiative transfer models to fit the quiescent spectral energy distribution of the star and found that it is most consistent with an effective temperature of 3672 K, a mass of 0.47 M$_\odot$ and a radius of 5.63 R$_\odot$.
The IRTF spectra of the star obtained at three epochs during the outburst show significant similarities to the spectra of FUor-type eruptive young stars, such as the absence of emission lines, weak hydrogen lines, a “triangular” H-band continuum, and strong CO absorption bands. However, there also are a few key differences between the spectra of Gaia24bux and FUors: it does not show molecular bands other than CO, and the equivalent widths of the CO lines versus the Na I (2.208 micron) and Ca I (2.256 micron) lines are more consistent with classical T Tauri stars rather than FUors. Also, Gaia24bux has faded back to its quiescent brightness after more than two years, which is inconsistent with FUors.
Based on our current results, Gaia24bux is most consistent with the Peculiar/V1647 Ori-like/MNor class of eruptive YSOs, which objects show intermediate properties of the two traditionally defined classes of eruptive YSOs.