Kinks and Dents in Protoplanetary Disks: Rapid Infrared Variability as Evidence for Large Structural Perturbations

TL;DR

This study observes rapid infrared variability in young stellar objects, revealing large structural perturbations in protoplanetary disks likely caused by stellar hot spots, indicating dynamic inner disk environments.

Contribution

It provides the first detailed synoptic infrared variability analysis linking rapid fluctuations to large-scale structural changes in protoplanetary disks.

Findings

High variability fraction in young stars correlates with age and environment.

Infrared fluctuations are consistent with dynamic inner disk structures.

Variability correlates with X-ray luminosity, suggesting stellar activity influences disk changes.

Abstract

We report on synoptic observations at 3.6 and 4.5micron of young stellar objects in IC 348 with 38 epochs covering 40 days. We find that among the detected cluster members, 338 at [3.6] and 269 at both [3.6] and [4.5], many are variable on daily to weekly timescales with typical fluctuations of ~0.1 mag. The fraction of variables ranges from 20% for the diskless pre-main sequence stars to 60% for the stars still surrounded by infalling envelopes. We also find that stars in the exposed cluster core are less variable than the stars in the dense, slightly younger, south-western ridge. This trend persists even after accounting for the underlying correlation with infrared SED type, suggesting that the change in variable fraction is not simply a reflection of the change in relative fraction of class I vs. class II sources across the cloud, but instead reflects a change in variability with age. We also see a strong correlation between infrared variability and X-ray luminosity among the class II sources. The observed variability most likely reflects large changes in the structure of the inner wall located at the dust sublimation radius. We explore the possibility that these structural perturbations could be caused by a hot spot on the star heating dust above the sublimation temperature, causing it to evaporate rapidly, and increasing the inner radius for a portion of the disk. Under a number of simplifying assumptions we show that this model can reproduce the size and timescale of the 3.6 and 4.5micron fluctuations. Regardless of its source, the infrared variability indicates that the inner disk is not a slowly evolving entity, but instead is a bubbling, warped, dented mass of gas and dust whose global size and shape fluctuate in a matter of days.