The 2008 extreme outburst of the young eruptive variable star Ex Lupi

TL;DR

The 2008 outburst of EX Lupi was a rare, intense event characterized by significant optical brightening, spectral changes, and evidence of an inner disk gap, providing insights into eruptive young star phenomena.

Contribution

This study presents detailed spectroscopic observations and modeling of EX Lupi's 2008 outburst, revealing disk structure and accretion rates during a rare extreme event.

Findings

Significant spectral line changes between observations.

Evidence of an inner gas disk gap from CO emission modeling.

Estimated accretion rate during outburst was ~2x10^-7 Msun/yr.

Abstract

In early 2008, the young low-mass star EX Lupi, the prototype of the EXor class of eruptive variables, optically brightened by over five magnitudes for a period of 7 months. The previous time a change of such amplitude had been observed in EX Lup was over 50 years ago. In this Letter we present new optical and near-IR high resolution spectroscopy of EX~Lup during the 2008 outburst. We investigate the physical characteristics of the outburst both soon after it began and some four months later, and consider the energetics and kinematics observed. Emission line strengths, widths, and profiles changed significantly between the two observations. Also, modeling of the 2.2935 um CO overtone bandhead emission suggests that an inner gap in the circumstellar gas disk around the star may be present and it is from the inner edge of the gas disk that the CO overtone emission probably arises. We derive a mass accretion luminosity and rate during the extreme outburst of ~2+-0.5~Lsun and ~2+-0.5x10^-7 Msun yr^-1, respectively, which suggests that this outburst was indeed one of the strongest witnessed in EX Lup, yet not as strong as those observed in FU Orionis stars.