Spectroscopic confirmation of M-dwarf candidate members of the Beta Pictoris and AB Doradus Moving Groups

Binks, A.S.; Jeffries, R.D.

Abstract

Optical spectroscopic observations are reported for 24 and 23, nearby, proper-motion-selected M-dwarf candidate members of the Beta Pictoris and AB Doradus moving groups (BPMG and ABDMG). Using kinematic criteria, the presence of both Halpha emission and high X-ray-to-bolometric luminosity, and position in absolute colour-magnitude diagrams, 10 and 6 of these candidates are confirmed as likely members of the BPMG and ABDMG respectively. Equivalent widths or upper limits for the Li I 6708A line are reported and the lithium depletion boundary (LDB) age of the BPMG is revisited. Whilst non-magnetic evolutionary models still yield an estimated age of 21 +/- 4 Myr, models that incorporate magnetic inhibition of convection imply an older age of 24 +/- 4 Myr. A similar systematic increase would be inferred if the stars were 25 per cent covered by dark magnetic starspots. Since young, convective M-dwarfs are magnetically active and do have starspots, we suggest that the original LDB age estimate is a lower limit. The LDB age of the ABDMG is still poorly constrained -- non-magnetic evolutionary models suggest an age in the range 35-150 Myr, which could be significantly tightened by new measurements for existing candidate members.

Citation

Binks, A., & Jeffries, R. (2016). Spectroscopic confirmation of M-dwarf candidate members of the Beta Pictoris and AB Doradus Moving Groups. Monthly Notices of the Royal Astronomical Society, 455(3), 3345-3358. https://doi.org/10.1093/mnras/stv2431

• Journal Article Type: Article
• Acceptance Date: Oct 28, 2015
• Online Publication Date: Nov 29, 2015
• Publication Date: Jan 21, 2016
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 455
• Issue: 3
• Pages: 3345-3358
• DOI: https://doi.org/10.1093/mnras/stv2431
• Keywords: stars, kinematics, pre-main-sequence, late-type
• Public URL: https://keele-repository.worktribe.com/output/405569
• Publisher URL: http://dx.doi.org/10.1093/mnras/stv2431