The Gaia alerted fading of the FUor-type star Gaia21elv

TL;DR

This study documents the fading of Gaia21elv, a FUor-type young star, through multi-epoch spectroscopy and photometry, revealing typical FUor features and a likely increase in circumstellar extinction during its decline.

Contribution

It provides detailed spectroscopic and photometric analysis of Gaia21elv's fading, confirming it as a classical FUor and identifying signs of jet activity and changing accretion rates.

Findings

Gaia21elv shows typical FUor spectral signatures.

Fading is likely due to increased circumstellar extinction.

Spectral analysis indicates a decrease in accretion rate.

Abstract

FU Orionis objects (FUors) are eruptive young stars, which exhibit outbursts that last from decades to a century. Due to the duration of their outbursts, and to the fact that only about two dozens of such sources are known, information on the end of their outbursts is limited. Here we analyse follow-up photometry and spectroscopy of Gaia21elv, a young stellar object, which had a several decades long outburst. It was reported as a Gaia science alert due to its recent fading by more than a magnitude. To study the fading of the source and look for signatures characteristic of FUors, we have obtained follow-up near infrared (NIR) spectra using Gemini South/IGRINS, and both optical and NIR spectra using VLT/X-SHOOTER. The spectra at both epochs show typical FUor signatures, such as a triangular shaped $H$-band continuum, absorption-line dominated spectrum, and P Cygni profiles. In addition to the typical FUor signatures, [OI], [FeII], and [SII] were detected, suggesting the presence of a jet or disk wind. Fitting the spectral energy distributions with an accretion disc model suggests a decrease of the accretion rate between the brightest and faintest states. The rapid fading of the source in 2021 was most likely dominated by an increase of circumstellar extinction. The spectroscopy presented here confirms that Gaia21elv is a classical FUor, the third such object discovered among the Gaia science alerts.