9944(  1) - 04/04/03 10:30  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9944
                                                       Version: 1
                                                       Check-in Date: 04-Apr-2003
                                                                      10:30:11

1.Proposal Title:
Analysis of Helix Nebula Observations During the Leonids Encounter of 2002
------------------------------------------------------------------------------------
2. Proposal For  3. Cycle
AR               11
------------------------------------------------------------------------------------
4. Investigators
                                                                                     Contact?
    PI: C. O'Dell                         Vanderbilt University
   CoI: Dr. Margaret Meixner              Space Telescope Science Institute             N
   CoI: Dr. Peter McCollough              Space Telescope Science Institute             N

------------------------------------------------------------------------------------
5. Abstract

We plan to perform a thorough analysis of the Helix Nebula (NGC 7293) images that
were obtained during the 2002 Leonids meteor stream encounter on program GO 9700.
This mosaic of nine ACS-WFC images in F502N ([OIII]) and F658N (Ha+[NII]) provides
the information necessary for understanding this closest bright planetary nebula.
The key to the analysis is a study of the knots which dot the nebula, which earlier
WFPC2 studies by the PI indicate as having as much total mass as the remainder of
the nebula. Since similar knots have now been found to exist in most nearby
planetary nebulae, the Helix represents our best opportunity for understanding an
important ingredient of what is being spewed into the ISM. In addition to studying
the knots, they can be used to determine the structure of the host nebula, since
each one casts an ionization shadow (the nature of which depends on the location of
the nebular material). As part of the study of the nebula, one can also determine
the 3-D distribution of the knots. These two portions of the study will give the
first direct determination of the mass distribution in a planetary nebula that is
free of assumptions of symmetry.
------------------------------------------------------------------------------------
                                                9944(  1) - 04/04/03 10:30  - [  2]

            Summary Form for Proposal  9944

  Item                         Used in this proposal
------------------------------------------------------------------------------------------------------------------------------------
  Proposal Category            AR
------------------------------------------------------------------------------------------------------------------------------------