6578( 11) - 05/05/97 11:43  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      6578
                                                       Version: 11
                                                       Check-in Date: 05-May-1997
                                                                      10:46:40

1.Proposal Title:
Optical Morphology of NGC 5128: X-ray Ridges and the Geometry of the Dust Lane
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2. Scientific Category   3. Proposal For  4. Cycle
GALAXIES & CLUSTERS         GO               6
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5. Investigators
                                                                                     Contact?
    PI: ETHAN SCHREIER                    SPACE TELESCOPE SCIENCE INSTITUTE
   CoI: Alessandro Capetti                Space Telescope Science Institute             N
   CoI: Duccio Macchetto                  Space Telescope Science Institute             N

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6. Abstract

We propose the first observations of NGC 5128 with WF/PC-2 to study the detailed
morphology of the dust lane. We will resolve the stellar associations and determine
the number, luminosities and spectral types of the sources seen along the edge of
the dust lane in earlier observations with WF/PC-I. We will quantitatively check the
interpretation that the X-ray ridges parallel to the dust lane are caused by massive
X-ray binaries associated with young stars. Simultaneously, we will study the disk
itself -- mapping the position of the stars and stellar associations along both
north and south edges of the disk, possibly observing a significant number within
the dust lane, and comparing the source distribution with the observed dust lane
morphology, we will determine if the clustering of the bright sources is a
projection of sources evenly distributed in or on a warped disk, or caused by
interaction between the disk and the galaxy. Simultaneously, the possible scattering
cloud near the nucleus will be studied using HST's highest available resolution in V
and I.
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                                                6578( 11) - 05/05/97 11:43  - [  2]

  Observations Description
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     For the primary observations, we will use WF/PC-2 with three different filters,
     F336W, F555W and F814W. First, we will center the PC on a region of the
     northern edge of the dust lane so as to include a significant number of the
     bright sources seen by WF/PC-I. We will be able simultaneously to observe
     several arcminutes of the southern edge of the dust lane along the two diagonal
     WF chips. A second observation will include the nucleus and a region of the
     southern edge of the dust lane in the aperture of the PC while simultaneously
     observing several arcminutes of the northern edge of the dust lane in the WF
     chips. Note that both the north and south ridges will be observed, since there
     is evidence from infrared, X-ray and optical observations (and the models) that
     they differ. The PC provides the highest (0.046") resolution for determining
     the number of individual stars and cluster shapes in the crowded regions, while
     the WF observations will provide the necessary larger field of view. By cross-
     comparing these observations, we will be able to extrapolate the high
     resolution results to the larger FOV. The selected filters will provide the
     widest reasonable color range for discriminating the young blue objects,
     hypothesized to explain the X-ray emission, from older populations of objects.
     A color-color reddening-free diagram will be obtained in order to obtain
     spectral information independent of the dust absorption, which appears to be
     significant in the regions of interest. The exposure time is calculated to
     allow the detection of isolated stars of spectral type B3 or earlier. Given the
     distance modulus of Cen A, 27.7 mag assuming a distance of 3.5 Mpc, the
     magnitudes of a B3 star are 25.3, 26.1 and 26.3 in the U, V and I standard
     filters respectively. To reach these brightness limits two orbits are required
     with F336W, while one orbit is needed for each of the F555W and F814W filters.
     Thus, four orbits are required for each of the two different primary pointings,
     a total of 8 orbits.

  Real Time Justification
  -----------------------

     None. None.

  Calibration Justification
  -------------------------


  Additional Comments
  -------------------

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  Data Distribution

  Media:           8MM
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:        UPS
  Email:
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                                                6578( 11) - 05/05/97 11:43  - [  3]

TARGET LIST    a) Fixed Targets
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Tar|   Target   |         Target        |            Target              |Coord   | Radial |             Flux data
No |    Name    |       Description     |           Position             |Eqnx    |  Vel.  |
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1   NGC5128-     GALAXY,Elliptical,Radio RA=13H 25M 30.3S +/- 0.1S, DEC=  2000     V = 550  V = 7.8+/-0.1
    RIDGEN       Galaxy                  -43D 00' 51" +/- 1"

11  NGC5128-     GALAXY,Elliptical,Radio RA=13H 25M 27.8S +/- 0.1S, DEC=  2000     V = 550  V = 7.8+/-0.1
    RIDGES       Galaxy                  -43D 01' 07" +/- 1"

                                                6578( 11) - 05/05/97 11:43  - [  4]

Visit: 01
     Visit Requirements:  ORIENT 115D TO 135D
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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11       NGC5128-RID WFPC2  IMAGE   PC1-FIX F336W            CR-SPLIT=0.75                     2   2420 S
         GES
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21       NGC5128-RID WFPC2  IMAGE   PC1-FIX F555W                                              1   300 S
         GES
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22       NGC5128-RID WFPC2  IMAGE   PC1-FIX F555W                                              1   2020 S
         GES
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31       NGC5128-RID WFPC2  IMAGE   PC1-FIX F814W                                              1   300 S
         GES
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32       NGC5128-RID WFPC2  IMAGE   PC1-FIX F814W                                              1   2020 S
         GES
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                                                6578( 11) - 05/05/97 11:43  - [  5]

Visit: 02
     Visit Requirements:  ORIENT 179D TO 181D FROM 1
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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11       NGC5128-RID WFPC2  IMAGE   PC1-FIX F336W            CR-SPLIT=0.75                     2   2600 S
         GEN
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21       NGC5128-RID WFPC2  IMAGE   PC1-FIX F555W                                              1   300 S
         GEN
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22       NGC5128-RID WFPC2  IMAGE   PC1-FIX F555W                                              1   2200 S
         GEN
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31       NGC5128-RID WFPC2  IMAGE   PC1-FIX F814W                                              1   300 S
         GEN
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32       NGC5128-RID WFPC2  IMAGE   PC1-FIX F814W                                              1   2200 S
         GEN
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                                                6578( 11) - 05/05/97 11:43  - [  6]

            Summary Form for Proposal  6578

  Item                         Used in this proposal
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  Configurations               WFPC2
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  Opmodes                      IMAGE
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  Optional Parameters          CR-SPLIT=0.75
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  Proposal Category            GO
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  Scientific Category          GALAXIES & CLUSTERS
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  Special Requirements         ORIENT 115D TO 135D ORIENT 179D TO 181D FROM 1
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  Spectral Elements            F336W F555W F814W
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  Target Names                 NGC5128-RIDGES NGC5128-RIDGEN
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