The FUV Spectrum of FU Ori South

TL;DR

This study presents the UV spectrum of FU Ori South, revealing active accretion and providing new extinction estimates, which are crucial for understanding the outburst mechanisms of FU Ori stars.

Contribution

First UV spectral analysis of FU Ori South resolving its components, offering new insights into its accretion activity and extinction properties.

Findings

Detection of NUV continuum emission and bright emission lines.

Presence of C II] 2325 multiplet and H₂ lines indicating active accretion.

UV spectrum suggests lower extinction ($A_V < 4$) than previous NIR estimates.

Abstract

The eruptive YSO FU Ori is the eponym of its variable class. FU Ori stars are known to undergo outbursts with amplitudes of $>4$ magnitudes in the $V$ band and durations of several decades. Interaction with a binary companion is one proposed outburst trigger, so understanding both components of the FU Ori system is crucial. A recent HST/STIS observation of the FU Ori system clearly resolves its North and South components. We report here on the spectrum of FU Ori South. We detect NUV continuum emission but no FUV continuum, although several bright emission lines consistent with those seen in T Tauri stars are present. The presence of the C II] 2325 multiplet and many H$_2$ lines indicate active accretion. We estimate the extinction to the source and find that the UV spectrum favors $A_V < 4$, contrary to past estimates based on the NIR spectrum.