Variability of the Great Disk Shadow in Serpens

TL;DR

This study uses multi-epoch Hubble imaging to observe the highly variable Great Disk Shadow in Serpens, revealing rapid inner disk dynamics and potential non-axisymmetric structures on scales of about 1 au.

Contribution

It provides the first detailed temporal analysis of the disk shadow variability, suggesting non-axisymmetric inner disk changes and proposing models involving disk warps or binary companions.

Findings

Inner disk position angle varies on monthly timescales.

Shadow changes are non-axisymmetric, indicating complex disk dynamics.

Observations suggest possible presence of disk warps or binary influences.

Abstract

We present multi-epoch Hubble Space Telescope imaging of the Great Disk Shadow in the Serpens star-forming region. The near-infrared images show strong variability of the disk shadow, revealing dynamics of the inner disk on time scales of months. The Great Shadow is projected onto the Serpens reflection nebula by an unresolved protoplanetary disk surrounding the young intermediate-mass star SVS2/CK3/EC82. Since the shadow extends out to a distance of at least 17,000 au, corresponding to a light travel time of 0.24 years, the images may reveal detailed changes in the disk scale height and position angle on time scales as short as a day, corresponding to the angular resolution of the images, and up to the 1.11 year span between two observing epochs. We present a basic retrieval of temporal changes in the disk density structure, based on the images. We find that the inner disk changes position angle on time scales of months, and that the change is not axisymmetric, suggesting the presence of a non-axisymmetric dynamical forcing on $\sim$1\,au size scales. We consider two different scenarios, one in which a quadrupolar disk warp orbits the central star, and one in which an unequal-mass binary orbiting out of the disk plane displaces the photo-center relative to the shadowing disk. Continued space-based monitoring of the Serpens Disk Shadow is required to distinguish between these scenarios, and could provide unique, and detailed, insight into the dynamics of inner protoplanetary disks not available through other means.