Rotation of Low-Mass Stars in Upper Centaurus Lupus and Lower Centaurus Crux with TESS

TL;DR

This study measures rotation periods of young stars in UCL and LCC using TESS data, revealing patterns related to stellar age, mass, and disk presence, and providing insights into early stellar rotational evolution.

Contribution

First TESS-based analysis of rotation rates in UCL and LCC, highlighting disk influence and rotation evolution in young low-mass stars.

Findings

90% of stars show spot-modulated periods

Distribution of rotation periods aligns with age and mass expectations

Disked M stars tend to have P~2 days, indicating disk influence

Abstract

We present stellar rotation rates derived from Transiting Exoplanet Survey Satellite (TESS) light curves for stars in Upper Centaurus-Lupus (UCL; ~136 pc, ~16 Myr) and Lower Centaurus-Crux (LCC; ~115 pc, ~17 Myr). We find spot-modulated periods (P) for ~90% of members. The range of light curve and periodogram shapes echoes that found for other clusters with K2, but fewer multi-period stars may be an indication of different noise characteristics of TESS, or a result of the source selection methods here. The distribution of P as a function of color as a proxy for mass fits nicely in between that for both older and younger clusters observed by K2, with fast rotators found among both the highest and lowest masses probed here, and a well-organized distribution of M star rotation rates. About 13% of the stars have an infrared (IR) excess, suggesting a circumstellar disk; this is well-matched to expectations, given the age of the stars. There is an obvious pile-up of disked M stars at P~2 days, and the pile-up may move to shorter P as the mass decreases. There is also a strong concentration of disk-free M stars at P~2 days, hinting that perhaps these stars have recently freed themselves from their disks. Exploring the rotation rates of stars in UCL/LCC has the potential to help us understand the beginning of the end of the influence of disks on rotation, and the timescale on which the star responds to unlocking.