Spitzer Observations of Long Term Infrared Variability Among Young Stellar Objects in Chamaeleon I

TL;DR

This study uses Spitzer space telescope data to analyze infrared variability in young stellar objects over 200 days, revealing that such variability is common and likely driven by dynamic dust structures in the inner disk regions.

Contribution

It provides the first long-term, high-cadence infrared variability analysis of young stellar objects, highlighting the dynamic nature of their inner disks.

Findings

80% of cluster members show variability

Color changes suggest fluctuations in disk emission or extinction

Power spectral density indicates significant low-frequency variability

Abstract

Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about a month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster whose low declination makes it observable by the Spitzer space telescope over a 200 day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find such variability is common, occurring in ~80% of the detected cluster members. The change in [3.6]-[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200 day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ~0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic.