Census of BPMG & other nearby associations with Gaia

For instance, using the model for Li depletion from Jeffries+ 2023MNRAS.523..802J, 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 30-50Myr 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/{chi}^1^ For (0.041_-0.007_^+0.009^, 34Myr), and declines again in the oldest two associations (40-50Myr). The origin of that peak and the nature of the M dwarf disks at >20Myr are unclear.