Ryan Goldsbury

The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters

We present new measurements of the centers for 65 Milky Way globular clusters. Centers were determined by fitting ellipses to the density distribution within the inner

THE SPECTRAL ENERGY DISTRIBUTIONS OF WHITE DWARFS IN 47 Tucanae: THE DISTANCE TO THE CLUSTER*

2\arcmin

Quantifying Mass Segregation and New Core Radii for 54 Milky Way Globular Clusters

of the cluster center, and averaging the centers of these ellipses. The symmetry of clusters was also analyzed by comparing cumulative radial distributions on opposite sides of the cluster across a grid of trial centers. All of the determinations were done with stellar positions derived from a combination of two single-orbit ACS images of the core of the cluster in

A MEASUREMENT OF DIFFUSION IN 47 TUCANAE

F606W

Comparing the white dwarf cooling sequences in 47 tuc and NGC 6397

and

WHEN DO STARS IN 47 TUCANAE LOSE THEIR MASS

F814W

Constraining Neutrino Cooling using the Hot White Dwarf Luminosity Function in the Globular Cluster 47 Tucanae

. We find that the ellipse-fitting method provides remarkable accuracy over a wide range of core sizes and density distributions, while the symmetry method is difficult to use on clusters with very large cores, or low density. The symmetry method requires a larger field, or a very sharply peaked density distribution.

Dynamical estimate of post main sequence stellar masses in 47 Tucanae

We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs (WDs) to pure hydrogen atmosphere WD models. Our photometric data set is obtained from a 121-orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 arcmin{sup 2} and extend over a radial range of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Using a likelihood analysis, we obtain a best-fitting unreddened distance modulus of (m - M){sub o} = 13.36 {+-} 0.02 {+-} 0.06 corresponding to a distance of 4.69 {+-} 0.04 {+-} 0.13 kpc, where the first error is random and the second is systematic. We also search the WD photometry for infrared excess in the F160W filter, indicative of low-mass companions, and find no convincing cases within our sample.

FORMATION AND EVOLUTION OF BLUE STRAGGLERS IN 47 TUCANAE

We present core radii for 54 Milky Way globular clusters determined by fitting King-Michie models to cumulative projected star count distributions. We find that fitting star counts rather than surface brightness profiles produces results that differ significantly due to the presence of mass segregation. The sample in each cluster is further broken down into various mass groups, each of which is fit independently, allowing us to determine how the concentration of each cluster varies with mass. The majority of the clusters in our sample show general agreement with the standard picture that more massive stars will be more centrally concentrated. We find that core radius versus stellar mass can be fit with a two-parameter power law. The slope of this power law is a value that describes the amount of mass segregation present in the cluster, and is measured independently of our distance from the cluster. This value correlates strongly with the core relaxation time and physical size of each cluster. Supplementary figures are also included showing the best fits and likelihood contours of fit parameters for all 54 clusters.

Proper Motions and Internal Dynamics in the Core of the Globular Cluster M71

Using images from the Hubble Space Telescope Wide-Field Camera 3, we measure the rate of diffusion of stars through the core of the globular cluster 47 Tucanae using a sample of young white dwarfs identified in these observations. This is the first direct measurement of diffusion due to gravitational relaxation. We find that the diffusion rate