7995(  1) - 04/16/98 14:11  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      7995
                                                       Version: 1
                                                       Check-in Date: 16-Apr-1998
                                                                      14:08:47

1.Proposal Title:
Global dynamics of the collapsed-core globular clusters M15 and NGC 6397
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2. Proposal For  3. Cycle
AR               7
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4. Investigators
                                                                                     Contact?
    PI: Haldan Cohn                       Indiana University
   CoI: Phyllis Lugger                    Indiana University                            N
   CoI: Jonathan Grindlay                 Harvard University                            N
   CoI: Charles Bailyn                    Yale University                               N
   CoI: Adrienne Cool                     San Francisco State University                N

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5. Abstract

We propose to use archival HST WFPC2 images to investigate the variation of the
stellar luminosity function (LF) in the outer regions of the collapsed-core globular
star clusters NGC 6397 and M15 (NGC 7078). Deep F606W (wide V-band) and F814W (I-
band) imaging has been carried out at radial offsets of about 4arcm6 and 8arcm1 from
the centers of both clusters. We will perform careful photometry of these images in
order to derive luminosity and mass functions (MF) in the halos of these clusters.
We will tie these data together with HST determinations of the LF and MF in the
inner regions, using global Fokker-Planck models that include two-body relaxation,
binary heating, a stellar mass spectrum, velocity-space anisotropy, and tidal
effects. The approach will allow us to investigate the degree to which the outer
regions of both clusters have been modified by interaction with the galactic tidal
field. In particular, we will further investigate: (1) the suggestion by Piotto et
al.\ (1997) that NGC 6397 has suffered significantly more tidal mass loss than has
either M15, M30, or M92, and (2) the indication, from our WIYN-Hydra study of the
velocity field of M15 (Drukier et al.\ 1998), that tidal heating becomes important
at just 7'\ from the cluster center, well inside the nominal tidal radius of about
23'.
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  Data Distribution

  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:
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                                                7995(  1) - 04/16/98 14:11  - [  2]

            Summary Form for Proposal  7995

  Item                         Used in this proposal
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  Proposal Category            AR
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