2020AJ....160..164H

We report photometry and spectroscopy of the outburst of the young stellar object Gaia19bey. We have established the outburst light curve with archival Gaia "G," ATLAS "Orange," Zwicky Transient Facility r-band, and Pan-STARRS "rizy"-filter photometry, showing an outburst of ∼4 yr duration, longer than typical EX Lupi objects but shorter than FU Orionis objects. Its pre-outburst spectral energy distribution shows a flat far-infrared spectrum, confirming the early evolutionary state of Gaia19bey and its similarity to other deeply embedded young stars experiencing outbursts. A lower limit to the peak outburst luminosity is ∼182 L_☉ at an assumed distance of 1.4 kpc, the minimum plausible distance. Infrared and optical spectroscopy near maximum light show an emission line spectrum, including H I lines, strong red Ca II emission, other metal emission lines, infrared CO bandhead emission, and a strong infrared continuum. Toward the end of the outburst, the emission lines have all but disappeared and the spectrum has changed into an almost pure continuum spectrum. This indicates a cessation of magnetospheric accretion activity. The near-infrared colors have become redder as Gaia19bey has faded, indicating a cooling of the continuum component. Near the end of the outburst, the only remaining strong emission lines are forbidden shock-excited emission lines. Adaptive optics integral-field spectroscopy shows the H₂ 1-0 S(1) emission with the morphology of an outflow cavity and the extended emission in the [Fe II] line at 1644 nm with the morphology of an edge-on disk. However, we do not detect any large-scale jet from Gaia19bey.