Absence of Significant Cool Disks in Young Stellar Objects Exhibiting Repetitive Optical Outbursts

TL;DR

This study uses high-resolution submillimeter observations to investigate the dust content of disks around young stellar objects with repetitive optical outbursts, finding generally low dust masses and suggesting limited reservoirs for outburst fueling.

Contribution

First high-resolution millimeter observations of EXor-type outbursting young stellar objects revealing low dust masses in their disks, indicating small-scale reservoirs for outbursts.

Findings

Most disks have low dust masses below detection limits.

NY Ori has a relatively massive disk among the sample.

VY Tau shows a surprisingly low upper limit on dust mass.

Abstract

We report Submillimeter Array (SMA) 1.3 mm high angular resolution observations towards the four EXor type outbursting young stellar objects (YSOs) VY Tau, V1118 Ori, V1143 Ori, and NY Ori. The data mostly show low dust masses $M_{dust}$ in the associated circumstellar disks. Among the sources, NY Ori possesses a relatively massive disk with $M_{dust} \sim 9 \times 10^{-4}$ $M_{\odot}$. V1118 Ori has a marginal detection equivalent to $M_{dust} \sim 6 \times 10^{-5}$ $M_{\odot}$. V1143 Ori has a non-detection also equivalent to $M_{dust} < 6 \times 10^{-5}$ $M_{\odot}$. For the nearest source VY Tau, we get a surprising non-detection which provides a stringent upper limit $M_{dust} < 6 \times 10^{-6}$ $M_{\odot}$. We interpret our findings as suggesting that the gas and dust reservoirs that feed the short duration, repetitive optical outbursts seen in some EXors may be limited to the small scale, innermost region of their circumstellar disks. This hot dust may have escaped our detection limits. Follow-up, more sensitive millimeter observations are needed to improve our understanding of the triggering mechanisms of EXor type outbursts.