Constraining the Chemical Signatures and the Outburst Mechanism of the Class 0 Protostar HOPS 383

TL;DR

This study investigates the chemical signatures, disk structure, and potential outburst mechanisms of the first known outbursting Class 0 protostar HOPS 383 in Orion, using multi-wavelength observations and modeling.

Contribution

It provides detailed chemical, structural, and dynamical analysis of HOPS 383, highlighting the role of gravitational instability in early protostellar outbursts.

Findings

HOPS 383 shows chemical signatures consistent with CO evaporation affecting N2H+ and HCO+.

A resolved disk of ~62 AU radius is observed, with potential for higher mass estimates at longer wavelengths.

The disk's Toomre Q parameter suggests gravitational instability could trigger outbursts.

Abstract

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.