A Kine-Chemical Investigation of the AB Dor Moving Group "Stream"

TL;DR

This study combines chemical and kinematic analyses to assess whether the AB Dor stream members form a true physical group, finding only some members are chemically homogeneous and likely share a common origin, with an age over 110 million years.

Contribution

It provides the first combined chemical and kinematic assessment of AB Dor stream members, challenging their status as a single stellar group and estimating the group's age.

Findings

Only half of the stream members are chemically homogeneous.

Some members were far from the nucleus 100 million years ago.

The AB Dor group is older than 110 million years.

Abstract

The AB Dor Moving Group consists of a "nucleus" of ~10 stars at d ~ 20 pc, along with dozens of purported "stream" members distributed across the sky. We perform a chemical and kinematic analysis of a subsample of AB Dor stream stars to test whether they constitute a physical stellar group. We use the NEMO Galactic kinematic code to investigate the orbits of the stream members, and perform a chemical abundance analysis using high resolution spectra taken with the Magellan Clay 6.5-m telescope. Using a chi^2 test with the measured abundances for 10 different elements, we find that only half of the purported AB Dor stream members could possibly constitute a statistically chemically homogeneous sample. Some stream members with 3D velocities were hundreds of parsecs from the AB Dor nucleus ~10^8 yr ago, and hence were unlikely to share a common origin. We conclude that the published lists of AB Dor moving group stream members are unlikely to represent the dispersed remnant of a single star formation episode. A subsample of the stream stars appears to be both statistically chemically homogeneous and in the vicinity of the AB Dor nucleus at birth. Their mean metallicity is [Fe/H] = 0.02 +/- 0.02 dex, which we consider representative for the AB Dor group. Finally, we report a strong lower limit on the age of the AB Dor nucleus of >110 Myr based on the pre-MS contraction times for K-type members which have reached the main sequence.