Submillimeter Variability in the Envelope and Warped Protostellar Disk of the Class 0 Protostar HOPS 358

Abstract The James Clerk Maxwell Telescope (JCMT) Transient Survey recently discovered that the Class 0 protostar HOPS 358 decreased in 350 GHz continuum brightness by ∼25% over the course of 4 yr before brightening again for the next 4. The JCMT light curve can be fit by a long-timescale dip lasting roughly 8 yr. A shorter-timescale periodicity is also apparent with a period of 1.75 yr and a small 3% amplitude. NEOWISE monitoring reveals that the mid-infrared wavelength brightness of HOPS 358 follows a similar long-term pattern in time. Here, we present a study of nine epochs of Atacama Large Millimeter/submillimeter Array (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 ∼15″ 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° warp at a disk radius of 35 au, about halfway through the extent of the disk. The physical origin of the warp and how it relates to the variability seen toward HOPS 358, however, remain unclear.