V899 Mon: a peculiar eruptive young star close to the end of its outburst

TL;DR

V899 Mon, a young eruptive star exhibiting both FUor and EXor traits, has been gradually fading after its second outburst, with spectroscopic evidence indicating decreasing accretion and mass loss rates, and it is likely concluding its outburst phase.

Contribution

This study provides detailed multi-wavelength monitoring and spectroscopic analysis of V899 Mon, revealing its physical evolution and constraining its stellar mass during the outburst decline.

Findings

Accretion rate has significantly decreased since the outburst

Mass loss rate is weakening over time

Disk and jet emission are consistent with a Keplerian disk model

Abstract

V899 Mon is an eruptive young star showing characteristics of both FUors and EXors. It reached a peak brightness in 2010, then briefly faded in 2011, followed by a second outburst. We conducted multi-filter optical photometric monitoring, as well as optical and near-infrared spectroscopic observations of V899 Mon. The light curves and color-magnitude diagrams show that V899 Mon has been gradually fading after its second outburst peak in 2018, but smaller accretion bursts are still happening. Our spectroscopic observations taken with Gemini/IGRINS and VLT/MUSE show a number of emission lines, unlike during the outbursting stage. We used the emission line fluxes to estimate the accretion rate and found that it has significantly decreased compared to the outbursting stage. The mass loss rate is also weakening. Our 2D spectro-astrometric analysis of emission lines recovered jet and disk emission of V899 Mon. We found the emission from permitted metallic lines and the CO bandheads can be modeled well with a disk in Keplerian rotation, which also gives a tight constraint for the dynamical stellar mass of 2 ${M_{\odot}}$. After a discussion of the physical changes that led to the changes in the observed properties of V899 Mon, we suggest this object is finishing its second outburst.