Infrared Variability of Evolved Protoplanetary Disks: Evidence for Scale Height Variations in the Inner Disk

TL;DR

This study investigates infrared variability in evolved protoplanetary disks, revealing significant scale height fluctuations in the inner disk that are likely driven by dynamical processes rather than stellar activity or accretion rate changes.

Contribution

It provides multi-wavelength, multi-epoch observational evidence for scale height variations in the inner disks of evolved protoplanetary systems, highlighting dynamical causes over stellar or accretion variability.

Findings

Infrared flux varies by 10-60% over weeks to months.

Stellar flux remains relatively constant, indicating disk-related variability.

Accretion rates are variable but unlikely to cause observed IR changes.

Abstract

We present the results of a multi-wavelength multi-epoch survey of five evolved protoplanetary disks in the IC 348 cluster that show significant infrared variability. Using 3-8micron and 24micron photometry along with 5-40micron spectroscopy from the Spitzer Space Telescope, as well as ground-based 0.8-5micron spectroscopy, optical spectroscopy and near-infrared photometry, covering timescales of days to years, we examine the variability in the disk, stellar and accretion flux. We find substantial variations (10-60%) at all infrared wavelengths on timescales of weeks to months for all of these young stellar objects. This behavior is not unique when compared to other cluster members and is consistent with changes in the structure of the inner disk, most likely scale height fluctuations on a dynamical timescale. Previous observations, along with our near-infrared photometry, indicate that the stellar fluxes are relatively constant; stellar variability does not appear to drive the large changes in the infrared fluxes. Based on our near-infrared spectroscopy of the Pa-beta and Br-gamma lines we find that the accretion rates are variable in most of the evolved disks but the overall rates are probably too small to cause the infrared variability. We discuss other possible physical causes for the variability, including the influence of a companion, magnetic fields threading the disk, and X-ray flares.