Sub-Millimeter Variability in the Envelope & Warped Protostellar Disk of the Class 0 Protostar HOPS 358

TL;DR

This study investigates sub-millimeter and infrared variability in the Class 0 protostar HOPS 358, revealing correlated brightness changes, a warped disk structure, and exploring potential links between disk warping and observed luminosity fluctuations.

Contribution

First detailed ALMA observations of HOPS 358's disk variability and warp, linking small-scale disk features with large-scale brightness changes in a Class 0 protostar.

Findings

HOPS 358 exhibits brightness variability consistent across multiple wavelengths.

The protostellar disk is warped by approximately 16 degrees at 35 au.

At least one of the protostar or its companion shows variability over years.

Abstract

The JCMT Transient Survey recently discovered that the Class 0 protostar HOPS 358 decreased in 350 GHz continuum brightness by $\sim25$% over the course of four years before brightening again for the next four. The JCMT lightcurve can be fit by a long timescale dip lasting roughly eight years. A shorter timescale periodicity is also apparent with a period of 1.75 years and a small 3% amplitude. NEOWise monitoring reveals that the mid-IR wavelength brightness of HOPS 358 follows a similar long-term pattern in time. Here, we present a study of nine epochs of ALMA observations of HOPS 358 taken over the course of the decline and subsequent rise in brightness seen with the JCMT to test whether the variation seen on $\sim15"$ scales, covering both disk and envelope, is also observed on smaller, $<1"$ scales that primarily probe HOPS 358's protostellar disk. We detect both HOPS 358 and its southern companion, HOPS 358B, in our ALMA observations, and find that at least one of the two is varying. Assuming that HOPS 358 is the variable, the light curve has the same shape as that found by the JCMT. Additionally, our high resolution ALMA imaging of HOPS 358 reveals that the disk is warped, with a $16^{\circ}$ warp at a disk radius of 35 au, about halfway through the extent of the disk. The physical origin of the warp along with how it relates to the variability seen towards HOPS 358, however, remain unclear.