Depletion of molecular gas by an accretion outburst in a protoplanetary disk

TL;DR

This study shows that a strong accretion outburst in the young star EX Lupi caused a significant depletion of molecular gas in its inner disk, with observable changes in spectral lines over six years.

Contribution

It provides direct observational evidence of rapid molecular gas depletion in a protoplanetary disk following an accretion outburst, supporting episodic accretion models.

Findings

Molecular gas mass decreased by an order of magnitude post-outburst

CO lines weakened but remained detectable in 2014

H2O and OH lines disappeared after the outburst

Abstract

We investigate new and archival 3-5 $\mu$m high resolution ($\sim3$ km s$^{-1}$) spectroscopy of molecular gas in the inner disk of the young solar-mass star EX Lupi, taken during and after the strong accretion outburst of 2008. The data were obtained using the CRIRES spectrometer at the ESO Very Large Telescope in 2008 and 2014. In 2008, emission lines from CO, H$_{2}$O, and OH were detected with broad profiles tracing gas near and within the corotation radius (0.02-0.3 AU). In 2014, the spectra display marked differences. The CO lines, while still detected, are much weaker, and the H$_{2}$O and OH lines have disappeared altogether. At 3 $\mu$m a veiled stellar photospheric spectrum is observed. Our analysis finds that the molecular gas mass in the inner disk has decreased by an order of magnitude since the outburst, matching a similar decrease in the accretion rate onto the star. We discuss these findings in the context of a rapid depletion of material accumulated beyond the disk corotation radius during quiescent periods, as proposed by models of episodic accretion in EXor type young stars.