2024AJ....168..159L

I have used the third data release of the Gaia mission to improve the reliability and completeness of membership samples in the β Pic moving group (BPMG) and other nearby associations with ages of 20-50 Myr (Sco Body, Carina, Columba, χ¹ For, Tuc-Hor, IC 2602, IC 2391, NGC 2547). I find that Carina, Columba, and χ¹ For are physically related and coeval, and that Carina is the closest fringe of a much larger association. Similarly, Tuc-Hor and IC 2602 form a coeval population that is spatially and kinematically continuous. Both results agree with hypotheses from Gagné et al. I have used the new catalogs to study the associations in terms of their initial mass functions, X-ray emission, ages, and circumstellar disks. For instance, using the model for Li depletion from Jeffries et al., I have derived an age of ${24.7}_{-0.6}^{+0.9}$ Myr for BPMG, which is similar to estimates from previous studies. In addition, I have used infrared photometry from the Wide-field Infrared Survey Explorer to check for excess emission from circumstellar disks among the members of the associations, which has resulted in a dramatic increase in the number of known disks around M stars at ages of 30-50 Myr and a significant improvement in measurements of excess fractions for those spectral types and ages. Most notably, I find that the W3 excess fraction for M0-M6 initially declines with age to a minimum in BPMG (<0.015), increases to a maximum in Carina/Columba/χ¹ For (${0.041}_{-0.007}^{+0.009}$, 34 Myr), and declines again in the oldest two associations (40-50 Myr). The origin of that peak and the nature of the M dwarf disks at >20 Myr are unclear.