ABSENCE OF SIGNIFICANT COOL DISKS IN YOUNG STELLAR OBJECTS EXHIBITING REPETITIVE OPTICAL OUTBURSTS

Abstract

ABSTRACT We report Submillimeter Array 1.3 mm high angular resolution observations toward the four EXor-type outbursting young stellar objects 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 ∼ 9 × 10−4 M ⊙. V1118 Ori has a marginal detection equivalent to M dust ∼ 6 × 10−5 M ⊙. V1143 Ori has a non-detection also equivalent to M dust < 6 × 10−5 M ⊙. For the nearest source, VY Tau, we get a surprising non-detection that provides a stringent upper limit M dust < 6 × 10−6 M ⊙. 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.