Results of the ROTOR-program. II. The long-term photometric variability of weak-line T Tauri stars

TL;DR

This study analyzes 20-year photometric data of weak-line T Tauri stars, revealing stable long-term variability primarily caused by persistent cool spots, with some subtle secular changes in spot properties.

Contribution

It provides the longest homogeneous photometric dataset for WTTS, offering detailed analysis of their long-term variability and stable rotation periods over decades.

Findings

Most WTTS show very stable long-term variability.

Photometric periods remain stable over many years.

Spot properties change subtly, causing secular light curve variations.

Abstract

T Tauri stars exhibit variability on all timescales, whose origin is still debated. On WTTS the variability is fairly simple and attributed to long-lived, ubiquitous cool spots. We investigate the long term variability of WTTS, extending up to 20 years in some cases, characterize it statistically and discuss its implications for our understanding of these stars. We have obtained a unique, homogeneous database of photometric measurements for WTTS extending up to 20 years. It contains more than 9 000 UBV R observations of 48 WTTS. All the data were collected at Mount Maidanak Observatory (Uzbekistan) and they constitute the longest homogeneous record of accurate WTTS photometry ever assembled. Definitive rotation periods for 35 of the 48 stars are obtained. Phased light curves over 5 to 20 seasons are now available for analysis. Light curve shapes, amplitudes and colour variations are obtained for this sample and various behaviors exhibited, discussed and interpreted. Our main conclusion is that most WTTS have very stable long term variability with relatively small changes of amplitude or mean light level. The long term variability seen reflects modulation in the cold spot distributions. Photometric periods are stable over many years, and the phase of minimum light can be stable as well for several years. On the long term, spot properties do change in subtle ways, leading to secular variations in the shape and amplitudes of the light curves.