PENELLOPE III. The peculiar accretion variability of XX Cha and its impact on the observed spread of accretion rates

TL;DR

This study reveals extreme accretion variability in the classical T Tauri star XX Cha over 11 years, highlighting the importance of accounting for variability in disk evolution models and population studies.

Contribution

It provides the first long-term comparison of accretion rates in XX Cha, demonstrating significant variability that challenges previous assumptions about stability at later star formation stages.

Findings

XX Cha shows nearly 2 dex variability in accretion rate over 11 years.

Accretion variability may be underestimated in spectral line studies.

Such variability could influence models of disk evolution and star formation.

Abstract

The processes regulating protoplanetary disk evolution are constrained by studying how mass accretion rates scale with stellar and disk properties. The spread in these relations can be used as a constraint to the models of disk evolution, but only if the impact of accretion variability is correctly accounted for. While the effect of variability might be substantial in the embedded phases of star formation, it is often considered limited at later stages. Here we report on the observed large variation in the accretion rate for one target, XX Cha, and we discuss the impact on population studies of classical T Tauri stars. The mass accretion rate determined by fitting the UV-to-near-infrared spectrum in recent X-Shooter observations is compared with the one measured with the same instrument 11 years before. XX Cha displays an accretion variability of almost 2 dex between 2010 and 2021. Although the timescales on which this variability happens are uncertain, XX Cha displays an extreme accretion variability for a classical T Tauri star. If such behavior is common among classical T Tauri stars, possibly on longer timescales than previously probed, it could be relevant for discussing the disk evolution models constrained by the observed spread in accretion rates. Finally, we remark that previous studies of accretion variability based on spectral lines may have underestimated the variability of some targets.