7547(  1) - 12/14/96 01:00  - [  0]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      7547
                                                       Version: 1
                                                       Check-in Date: 13-Dec-1996
                                                                      18:22:17

1.Proposal Title:
The Stellar Populations Inside Expanding HI Shells in the Spiral Galaxy M33
------------------------------------------------------------------------------------
2. Scientific Category   3. Proposal For  4. Cycle
INTERSTELLAR MATTER         AR               7
------------------------------------------------------------------------------------
5. Investigators
                                                                                     Contact?
    PI: Rene Walterbos                    New Mexico State University
   CoI: David Thilker                     New Mexico State University                   N
   CoI: Nichole King                      New Mexico State University                   N

------------------------------------------------------------------------------------
6. Abstract

Because of its vigorous star formation activity, favorable inclination, and relative
proximity, M33 is an ideal laboratory for the study of expanding HI shells in spiral
galaxies. Theoretical models show that the energy deposited into the ISM by high
mass stars in OB associations is capable of creating HI superbubbles. However,
sparse observational evidence exists to test these models in detail. One essential
ingredient of such a test is an improved census of stellar populations inside
expanding HI shells. Using multi-color archival HST images of M33, we will (1)
verify that association ages are consistent with dynamical ages of related shells
and with ages from model predictions for bubbles of matching size and kinematics;
(2) Constrain the IMF for each association by combining integrated ground-based
HAlpha fluxes with the population age, present day mass function, and luminosity
function derived from WFPC2 data; (3) Use this information to infer which fraction
of the integrated stellar mechanical luminosity is transferred to a shell over its
lifetime. Ground-based observations of associations inside expanding shells lack the
UV-sensitivity and spatial resolution to adequately address these issues. Our sample
of expanding neutral shells in M33 was selected using a new automated method for
analysis of HI datacubes. From this robust catalog we have identified more than 30
HI supershells in M33 already imaged with WFPC2 in suitable broadband filters
(F160BW, F170W, F336W, F439W, F555W, and F814W).
------------------------------------------------------------------------------------
  Data Distribution

  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:                                                              ,
------------------------------------------------------------------------------------

                                                7547(  1) - 12/14/96 01:00  - [  1]

            Summary Form for Proposal  7547

  Item                         Used in this proposal
------------------------------------------------------------------------------------------------------------------------------------
  Proposal Category            AR
------------------------------------------------------------------------------------------------------------------------------------
  Scientific Category          INTERSTELLAR MATTER
------------------------------------------------------------------------------------------------------------------------------------