Stable and Unstable Regimes of Mass Accretion onto RW Aur A

TL;DR

This study monitors RW Aur A over several years, revealing that its mass accretion rate fluctuates between stable and unstable regimes, evidenced by spectral line variations and brightness changes, with implications for understanding young stellar object accretion processes.

Contribution

It provides the first detailed spectroscopic analysis correlating optical variability with accretion stability states in RW Aur A over multiple years.

Findings

Unstable accretion correlates with bright phases and spectral line variability.

Stable accretion occurs during faint phases with minimal spectral line variation.

Spectroscopic evidence suggests complex interplay of circumstellar material and accretion activity.

Abstract

We present monitoring observations of the active T Tauri star RW Aur, from 2010 October to 2015 January, using optical high-resolution (R>10000) spectroscopy with CFHT-ESPaDOnS. Optical photometry in the literature shows bright, stable fluxes over most of this period, with lower fluxes (by 2-3 mag.) in 2010 and 2014. In the bright period our spectra show clear photospheric absorption, complicated variation in the Ca II 8542 A emission}profile shapes, and a large variation in redshifted absorption in the O I 7772 and 8446 A and He I 5876 A lines, suggesting unstable mass accretion during this period. In contrast, these line profiles are relatively uniform during the faint periods, suggesting stable mass accretion. During the faint periods the photospheric absorption lines are absent or marginal, and the averaged Li I profile shows redshifted absorption due to an inflow. We discuss (1) occultation by circumstellar material or a companion and (2) changes in the activity of mass accretion to explain the above results, together with near-infrared and X-ray observations from 2011-2015. Neither scenario can simply explain all the observed trends, and more theoretical work is needed to further investigate their feasibilities.