A Census of the beta Pic Moving Group and Other Nearby Associations with Gaia

TL;DR

This study uses Gaia DR3 data to refine membership and properties of young stellar associations like beta Pic, revealing new insights into their structure, ages, and circumstellar disks, especially around M stars, with implications for star formation and disk evolution.

Contribution

It provides improved membership catalogs, confirms the physical association of certain groups, and reports new findings on ages, initial mass functions, and disk fractions, especially around M stars.

Findings

Carina, Columba, and chi1 For are physically related and coeval.

Derived age of beta Pic MG as approximately 25 Myr.

Detected a peak in circumstellar disk fraction around M stars at ~34 Myr.

Abstract

I have used the third data release of the Gaia mission to improve the reliability and completeness of membership samples in the beta Pic moving group (BPMG) and other nearby associations with ages of 20-50 Myr (Sco Body, Carina, Columba, chi1 For, Tuc-Hor, IC 2602, IC 2391, NGC 2547). I find that Carina, Columba, and chi1 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 Gagne et al. (2021). 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. (2023), I have derived an age of 24.7+0.9/-0.6 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 chi1 For (0.041+0.009/-0.007, 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.