A stable quasi-periodic 4.18 d oscillation and mysterious occultations in the 2011 MOST light curve of TWHya

TL;DR

This study analyzes 2011 MOST satellite data of TW Hya, revealing a stable 4.18-day oscillation likely caused by stellar rotation and hot spots, along with mysterious brightness dips possibly due to occultations by accretion-related clumps.

Contribution

It identifies a stable quasi-periodic oscillation and introduces the discovery of semi-periodic brightness dips, suggesting a new interpretation involving occultations by accretion-related clumps.

Findings

Detection of a 4.18-day stable oscillation linked to stellar rotation.

Observation of 19 brightness dips over 43 days, similar to previous data.

Proposed explanation of dips as occultations by accretion clumps.

Abstract

We present an analysis of the 2011 photometric observations of TW Hya by the MOST satellite; this is the fourth continuous series of this type. The large-scale light variations are dominated by a strong, quasi-periodic 4.18 d oscillation with superimposed, apparently chaotic flaring activity; the former is most likely produced by stellar rotation with one large hot spot created by a stable accretion funnel in the stable regime of accretion while the latter may be produced by small hot spots, created at moderate latitudes by unstable accretion tongues. A new, previously unnoticed feature is a series of semi-periodic, well defined brightness dips of unknown nature of which 19 were observed during 43 days of our nearly-continuous observations. Re-analysis of the 2009 MOST light curve revealed the presence of 3 similar dips. On the basis of recent theoretical results, we tentatively conclude that the dips may represent occultations of the small hot spots created by unstable accretion tongues by hypothetical optically thick clumps.