[Previous] | [Session 56] | [Next]
A. D. Forestell, S. R. Majewski, K. B. Westfall, R. J. Patterson (UVA), W. E. Kunkel (LCO)
We present results of a survey to determine the extended structural profile of the globular cluster NGC 288. Our mosaic of Swope 1-m telescope CCD fields covers approximately 1 square degree centered on the core of NGC288 and allows us to probe to twice the cluster's tidal radius. To map the cluster to very low densities, we search for stars that have a high likelihood of being (or having been) part of the cluster. First, we are aided by the very distinct, blue horizontal branch (BHB) population of the cluster, and look for all stars with such distinct colors. Second, we identify likely red giant (RGB) stars associated with the cluster. To do this, we image in the broadband Washington M and T2 filters as well as the stellar gravity sensitive DDO51 filter. Giant stars can be distinguished in the (M-T2, M-DDO51) diagram and we make a further winnowing to likely NGC 288 stars by limiting our search to only those giant stars candidates with color-magnitude combinations expected for the NGC 288 red giant and asymptotic branches.
A radial profile of the cluster derived from all of ``NGC 288-associated" stars (RGB, BHB, and AGB) shows the NGC 288 candidate stars to follow a King profile to the previously identified tidal radius. However, we do identify an extratidal population of stars at about 10-3 the central density of the cluster, and this results in a break from the King profile near the presumed tidal radius. Based on its structure and orbit, NGC 288 has previously been identified to be among those clusters with higher mass loss rates, and our identification of an ``extratidal tail" to the radial profile would seem to support a significant evaporation/tidal stripping rate. Clearly, at least some globular clusters are making a tangible contribution to the formation of the Milky Way halo. We will present Blanco 4-m + Hydra multifiber spectroscopy of a number of these extratidal RGB and BHB candidates, which will allow us to test the reliability of our extratidal density based on radial velocity membership.
This research was supported by the National Science Foundation, The Research Corporation and the David and Lucile Packard Foundation.
The author(s) of this abstract have provided an email address for comments about the abstract: amydove@astro.as.utexas.edu