Constraining the Chemical Signatures and the Outburst Mechanism of the
  Class 0 Protostar HOPS 383
  We present observations toward HOPS 383, the first known outbursting Class 0
protostar located within the Orion molecular cloud using ALMA, VLA, and SMA.
The SMA observations reveal envelope scale continuum and molecular line
emission surrounding HOPS 383 at 0.85 mm, 1.1 mm, and 1.3 mm. The images show
that HCO$^+$ and H$^{13}$CO$^+$ peaks on or near the continuum, while
N$_2$H$^+$ is reduced at the same position. This reflects the underlying
chemistry where CO evaporating close to the protostar destroys N$_2$H$^+$ while
forming HCO$^+$. We also observe the molecular outflow traced by $^{12}$CO ($J
= 2 \rightarrow 1$) and ($J = 3 \rightarrow 2$). A disk is resolved in the ALMA
0.87 mm dust continuum, orthogonal to the outflow direction, with an apparent
radius of $\sim$62 AU. Radiative transfer modeling of the continuum gives disk
masses of 0.02 M$_{\odot}$ when fit to the ALMA visibilities. The models
including VLA 8 mm data indicate that the disk mass could be up to a factor of
10 larger due to lower dust opacity at longer wavelengths. The disk temperature
and surface density profiles from the modeling, and an assumed protostar mass
of 0.5 M$_{\odot}$ suggest that the Toomre $Q$ parameter $< 1$ before the
outburst, making gravitational instability a viable mechanism to explain
outbursts at an early age if the disk is sufficiently massive.
