Low mass stars and the structure of the Pleiades cluster
This thesis presents a large scale search for new low mass members of the Pleiades cluster using near-infrared photometry from the Two Micron All Sky Survey and proper motions derived from digitized Palomar Observatory Sky Survey photographic plates. The search extends to a 10° radius around the cluster, well beyond the presumed tidal radius, and to a limiting magnitude of R ∼ 20, corresponding to a lower mass limit of ∼0.07 [special characters omitted] at the distance and age of the Pleiades. Photometric and proper motion selection has identified roughly 1200 probable cluster members, including several hundred new candidates, from nearly 106 stars in the field. Multi-object spectroscopy for 528 candidates verifies that the search was extremely effective at detecting cluster stars in the 1–0.1 [special characters omitted] mass range using the distribution of Hα emission strengths as an estimate of sample contamination by field stars.
When combined with previously identified, higher mass stars, this search provides a sensitive measurement of the stellar mass function and dynamical structure of the Pleiades. The cluster halo is substantially more elongated than expected from standard N body simulation results, although the elongation does lie nearly parallel to the Galactic plane as a static tidal model predicts. While the high mass stars are clearly centrally concentrated with respect to low mass stars, stars with mass less than ∼1 [special characters omitted] share a similar radial distribution, indicating that they share a similar velocity dispersion. The mass function becomes flat near 0.1 [special characters omitted] which implies that objects more massive than those near the hydrogen burning mass limit dominate the total mass. The total stellar mass contains ∼790 [special characters omitted]. These results are discussed in the context of past studies of low mass objects in the Pleiades.