# A stellar census of the nearby, young 32 Orionis group

## TL;DR

This paper presents the first large-scale spectroscopic survey of the 32 Orionis group, identifying new members, determining its age as approximately 24 million years, and estimating its debris disc fraction, thereby enhancing understanding of this nearby young stellar group.

## Contribution

It provides the first comprehensive membership catalog, age estimation, and debris disc fraction for the 32 Orionis group, using combined kinematic, photometric, and spectroscopic data.

## Key findings

- Identified 30 new group members, tripling the known population.
- Estimated the group's age as 24±4 million years.
- Determined a debris disc fraction of approximately 32%.

## Abstract

The 32 Orionis group was discovered almost a decade ago and despite the fact that it represents the first northern, young (age ~ 25 Myr) stellar aggregate within 100 pc of the Sun ($d \simeq 93$ pc), a comprehensive survey for members and detailed characterisation of the group has yet to be performed. We present the first large-scale spectroscopic survey for new (predominantly M-type) members of the group after combining kinematic and photometric data to select candidates with Galactic space motion and positions in colour-magnitude space consistent with membership. We identify 30 new members, increasing the number of known 32 Ori group members by a factor of three and bringing the total number of identified members to 46, spanning spectral types B5 to L1. We also identify the lithium depletion boundary (LDB) of the group, i.e. the luminosity at which lithium remains unburnt in a coeval population. We estimate the age of the 32 Ori group independently using both isochronal fitting and LDB analyses and find it is essentially coeval with the {\beta} Pictoris moving group, with an age of $24\pm4$ Myr. Finally, we have also searched for circumstellar disc hosts utilising the AllWISE catalogue. Although we find no evidence for warm, dusty discs, we identify several stars with excess emission in the WISE W4-band at 22 {\mu}m. Based on the limited number of W4 detections we estimate a debris disc fraction of $32^{+12}_{-8}$ per cent for the 32 Ori group.