6 papers
The Dearth of Massive, Helium-Rich White Dwarfs in Young Open Star Clusters
Jasonjot Singh Kalirai, Harvey B. Richer, Brad M. S. Hansen +2
Spectra have been obtained of 21 white dwarfs (WDs) in the direction of the young, rich open star cluster NGC 2099. This represents an appreciable fraction (>30%) of the cluster's…
HST Observations of the Main Sequence of M4
H. B. Richer, G. G. Fahlman, J. Brewer +8
This paper presents new results from a photometric study of the main-sequence stars in M4, the closest globular cluster to the sun. Multi-field, multi-epoch observations at approxi…
Stellar Collisions and Pulsar Planets
Brad M. S. Hansen
I describe models for the formation of planetary systems surrounding the remnants of stellar mergers and collisions. I focus primarily on models for the viscous evolution of disks…
Old White Dwarfs as a Microlensing Population
Brad M. S. Hansen
A popular interpretation of recent microlensing studies of the line of sight towards the Large Magellanic Cloud invokes a population of old white dwarf stars in the Galactic halo.…
Failed Oort Clouds and Planetary Migration
Brad M. S. Hansen
Planet formation is accompanied by the formation of comet clouds. In systems where planets migrate on rapid timescales, the diffusive evolution of comet orbits may stall, resulting…
The Observational Signature of Old White Dwarfs
Brad M. S. Hansen
The recent discovery of microlensing of stars in the Large Magellanic Cloud has excited much interest in the nature of the lensing population. Detailed analyses indicate that the m…