Precise High-Cadence Time Series of Five Variable Young Stars in Auriga with MOST

TL;DR

This study used the MOST satellite to obtain high-cadence, continuous optical photometry of five young stars, revealing complex variability patterns including both periodic and stochastic behaviors, with implications for understanding circumstellar disk influences.

Contribution

First high-cadence, long-duration optical monitoring of multiple young stars, demonstrating complex variability and highlighting the importance of multi-timescale analysis for star-disk interactions.

Findings

Stars show 1-10% brightness fluctuations on hours to weeks.

Identified significant periods for each star, but variability is dominated by stochastic behavior.

Variability patterns suggest influence from circumstellar disks.

Abstract

To explore young star variability on a large range of timescales, we have used the MOST satellite to obtain 24 days of continuous, sub-minute cadence, high-precision optical photometry on a field of classical and weak-lined T Tauri stars (TTS) in the Taurus-Auriga star formation complex. Observations of AB Aurigae, SU Aurigae, V396 Aurigae, V397 Aurigae, and HD 31305 reveal brightness fluctuations at the 1-10% level on timescales of hours to weeks. We have further assessed the variability properties with Fourier, wavelet, and autocorrelation techniques, identifying one significant period per star. We present spot models in an attempt to fit the periodicities, but find that we cannot fully account for the observed variability. Rather, all stars exhibit a mixture of periodic and aperiodic behavior, with the latter dominating stochastically on timescales less than several days. After removal of the main periodicity, periodograms for each light curve display power law trends consistent with those seen for other young accreting stars. Several of our targets exhibited unusual variability patterns not anticipated by prior studies, and we propose that this behavior originates with the circumstellar disks. The MOST observations underscore the need for investigation of TTS light variations on a wide range of timescales in order to elucidate the physical processes responsible; we provide guidelines for future time series observations.