10939(  1) - 04/03/06 11:00  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10939

Version: 1    Check-in Time: 03-Apr-2006 15:00:40

Title
Binary Burning in Globular Clusters
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Prof. Joel N. Bregman             University of Michigan
   CoI: Dr. Mario L. Mateo                University of Michigan                        N
   CoI: Dr. Patrick O. Seitzer            University of Michigan                        N

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Abstract

In globular cluster evolution, binary stars are destroyed (?burned?) through close
stellar encounters over several dynamical relaxation times, a process that delays
the onset of core collapse. Dynamical interactions plus mass segregation causes the
binary fraction to rise in the core but fall at larger radii. These changes in the
binary fraction properties with time can be tested because some clusters have
undergone only a few relaxation times while others are core collapse systems. The
presence of binaries thickens the Main Sequence in a color-magnitude diagram, a
technique used to measure the binary fraction in 4 globular clusters, with
surprising results. For example, one core collapse system has a large binary
fraction (25%) while the other has only a upper limit (< 5%). We propose to use the
archival data of about two dozen clusters to determine their binary properties and
test whether they evolve as models predict.
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