Occultation of the T Tauri Star RW Aurigae A by its Tidally Disrupted Disk

TL;DR

This study reports a deep, long-lasting dimming event of RW Aur A, attributed to a fragment of its tidally disrupted disk occulting the star, providing insights into the star's circumstellar environment post-interaction.

Contribution

The paper presents observational evidence linking a dimming event to a tidally disrupted disk fragment, offering new understanding of circumstellar disk dynamics after stellar fly-bys.

Findings

The dimming lasted approximately 180 days with a depth of ~2 magnitudes.

The occulter's velocity matches the relative velocity of the tidally disrupted arm.

The occulting feature is not part of the star's circumstellar disk.

Abstract

RW Aur A is a classical T Tauri star, believed to have undergone a reconfiguration of its circumstellar environment as a consequence of a recent fly-by of its stellar companion, RW Aur B. This interaction stripped away part of the circumstellar disk of RW Aur A, leaving a tidally disrupted arm and a short truncated circumstellar disk. We present photometric observations of the RW Aur system from the Kilodegree Extremely Little Telescope (KELT) survey showing a long and deep dimming that occurred from September 2010 until March 2011. The dimming has a depth of ~2 magnitudes, a duration of ~180 days and was confirmed by archival observations from American Association of Variable Star Observers (AAVSO). We suggest that this event is the result of a portion of the tidally disrupted disk occulting RW Aur A, specifically a fragment of the tidally disrupted arm. The calculated transverse linear velocity of the occulter is in excellent agreement with the measured relative radial velocity of the tidally disrupted arm. Using simple kinematic and geometric arguments, we show that the occulter cannot be a feature of the RW Aur A circumstellar disk, and we consider and discount other hypotheses. We also place constraints on the thickness and semi-major axis of the portion of the arm that occulted the star.