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

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 1 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 that 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.

Observational signatures of outbursting protostars - I: From hydrodynamic simulations to observations

“…This is similar to what is inferred from observations (e.g. Scholz et al 2013;Hillenbrand & Findeisen 2015;Fischer et al 2019) (see also Peña et al 2019, for longer outburst timescale estimates for older, Class I/II, YSOs). It is assumed that in the quiescent phase gas accretes onto the protostar at a rate oḟ M = 10 −6 M yr −1 (this is a free parameter in our calculation) and the protostellar luminosity is then on the order of ∼ 1 L .…”

“…These flux increases happen on a timescale of decades to centuries. The authors note that although the continuum flux increases are smaller than observed in classical FUOrs, the variability found in their models is larger than currently observed for non-eruptive young protostars (Rebull et al 2015;Flaherty et al 2016;Rigon et al 2017). The variability of their models is also larger than that found by the TRANSIENT Survey (Mairs et al 2017;Johnstone et al 2018;Mairs et al 2018), which reports secular changes of order 5-10% per year from about 10% of the protostars bright enough to get good measurements.…”

Investigation of a Vorticity-preserving Scheme for the Euler Equations

“…Abramowicz et al (1992) suggested that vortices in hot accretion disks may explain the variability in their X-ray temporal power spectra. Similar temporal variability is observed in young stellar objects (Flaherty et al 2016), which may also be caused by vortices.…”

The Inner Disk and Accretion Flow of the Close Binary DQ Tau

“…Jensen et al (2007) found a periodicity in the optical light curve of UZ Tau E which matched the orbital period, however the flux variations were much slower with low amplitude, and direct accretion probes such as Hα showed inconclusive correlations. Three protostellar objects have also been found to exhibit periodic infrared brightenings that look very much like pulsed accretion (Muzerolle et al 2013;Hodapp & Chini 2015;Flaherty et al 2016), although no evidence of binarity has yet been published.…”