Rosette Nebula Outburst Gaia 24djk from the Young Stellar Object V557 Mon

TL;DR

This paper reports on a young stellar object, V557 Mon, undergoing a significant outburst detected by Gaia, with spectral features indicating rapid accretion and potential evolution into an FU Ori-type event.

Contribution

It presents the first detailed spectral analysis of V557 Mon's outburst, suggesting it may develop into a classic FU Ori event, expanding understanding of YSO outburst phenomena.

Findings

Rapid brightening observed in V557 Mon in late 2024

Spectrum dominated by emission lines and continuum excess

Potential transition from emission to absorption spectrum indicating FU Ori outburst

Abstract

A previously faint young stellar object (YSO), V557 Mon, rapidly brightened in late 2024 and is currently at least $\Delta G=3.3$ magnitudes brighter than its typical pre-outburst brightness. The ongoing outburst is identified in the Gaia Alerts system as Gaia24djk. We obtained a 1-2.5 $\mu$m spectrum of the object and find the spectrum is dominated by line emission and continuum excess consistent with rapid YSO accretion, similar to the star EX Lup during its outburst state. We speculate that the burst, which has not yet reached its peak brightness, may become an FU Ori outburst, which would be evidenced by the emission spectrum turning into an absorption spectrum.