A Stellar Census of the 32 Ori Moving Group

The 32 Ori moving group was discovered almost a decade ago and despite the fact that it represents the first northern, young (~20 Myr) stellar aggregate within 100 pc of the Sun, a comprehensive characterisation of the stellar content of the group has yet to be performed. We hereby present the first large-scale spectroscopic survey for new (predominantly low-mass K- and M-type) members of the 32 Ori moving group after combining kinematic and photometric data to select candidate members with Galactic space motion and positions in colour-magnitude space consistent with group membership. Final memberships are assigned on the basis of a combination of radial velocity, Hα emission and Li absorption diagnostics. We identify ~25 new members, thereby increasing the number of known 32 Ori moving group members by a factor of ~3. Finally, we demonstrate consistent ages for the group based on isochronal fitting in the colour-magnitude diagram and the location of the Li depletion boundary. This consistency suggests that the group is essentially coeval with the Beta Pictoris moving group with an age in the range 20-25 Myr. In the era of SPHERE, GPI, ALMA, etc. this group therefore represents a benchmark region for direct-imaging studies of circumstellar disc evolution (especially during the epoch of terrestrial planet formation) and, of course, extrasolar planets.

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CC BY 4.0