A portrait of the rotation of Ultra-Cool Dwarfs revealed by TESS

Abstract

This study presents the results of a search for rotation signature in 250 Gaia DR3 Ultra-Cool Dwarfs (UCDs) with TESS light curves. We identified 71 targets with unambiguous periodicities, of which 61 present rotation signatures and a single source behavior, with periods between 0.133 and 5.81 days. Five UCDs show double-dip features, namely variations with two periods, one approximately double or half the other. The remaining ten UCDs with unambiguous variability present a likely non-single behavior. We also found 20 UCDs showing complex behavior in their light curves, with noticeable fluctuations and irregular structure, with a few exhibiting apparent changes in their temporal structure. The remaining 159 targets show noisy light curves corresponding to low-amplitude signals, whose temporal variation cannot be easily identified. The distribution of the UCDs with rotation signature in the CMD diagram points to a lack of rotating objects within about $11.5<M_{G}<12.5$ and $G-G_{RP}<1.5$ separating them into two regimes, one mainly composed of less massive late-M stars with $P_{rot} \geq 1.0$ d, and another mainly composed of more massive early-M stars with $P_{rot}<1.0$ d. It is important to emphasize that by separating stars into age intervals, one observes that UCDs with $P_{rot} \geq 1.0$ d tend to be located in regions of younger objects, and, in contrast, those with $P_{rot}<1.0$ d are mainly concentrated in regions of older objects. Whether these trends of stars contrasting the sample separation is physical or produced by observational biases is a question to be verified in future studies.