10853(  2) - 05/11/06 11:35  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10853

Version: 2    Check-in Time: 11-May-2006 15:34:51       STScI Edit Number: <none>

Title
M82 as a Fossil Starburst: Probing the Super Star Cluster Content of Region B
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Type             Cycle     Parallel Pointing Tolerance
GO               15        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Linda J. Smith                University College London
   CoI: Dr. Nate Bastian                  University College London                     N
   CoI: Prof. John S. Gallagher III       University of Wisconsin - Madison             N
   CoI: Mr. Mark Gieles                   Universiteit Utrecht, Sterrekundig            N
                                          Instituut
   CoI: Dr. Richard de Grijs              University of Sheffield                       N
   CoI: Mr. Iraklis Konstantopoulos       University College London                     N
   CoI: Dr. Soeren S. Larsen              European Southern Observatory - Germany       N
   CoI: Prof. Robert W. O'Connell         The University of Virginia                    N
   CoI: Mr. Mark Westmoquette             University College London                     N

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Abstract

The importance of M82 as a benchmark for starburst studies has been recognised by
the STScI-sponsored ACS/WFC mosaic of M82 in the B, V, I and H alpha filters. This
proposal supplements this unique legacy dataset by obtaining U-band observations
(F330W filter) of the fossil starburst region B in M82. This region is rich in
compact intermediate age (~ 1 Gyr) star clusters. The combination of U-band
photometry with the ACS/WFC STScI BVI survey and archival NICMOS JH data will allow
us to derive accurate ages, luminosities and masses for this rare population of
intermediate age massive star clusters. The U-band is essential for determining ages
of clusters < 2 Gyr old because it measures the depth of the Balmer jump. We will
use these data to determine the true shape of the cluster luminosity function (CLF)
for the M82-B fossil starburst region and thus address the question of whether young
massive clusters will eventually become globular clusters.
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  Observations Description
  ------------------------

     We have chosen the ACS/HRC camera in preference to WFPC2 because the proposed
     dataset will complement the few U-band observations of M82 (A, C, F) that exist
     which have all been obtained with ACS/HRC. The HRC also has the advantage that
     the light profiles of the clusters in M82 will be much better defined than the
     PC because of the smaller pixel size. At the distance of M82, 1 HRC pixel
     approximately equals 0.5 pc compared to a typical cluster diameter of 6 pc. To
     calculate exposure times, we are guided by the study of M82-B by de Grijs et
     al. (2001, AJ, 121, 768) which reached a 50% completeness limit at V of 22.5
     mag. This translates to a mass of 50, 000 solar masses for a 1 Gyr old cluster
     which is a factor of two deeper than the mass corresponding to the peak of the
     globular cluster mass function at 10^5 solar masses. In fact, we expect to go
     deeper than this because the STScI BVI mosaic of M82 will reach fainter V
     magnitudes than those of de Grijs et al. (2001). The extinction in region B is
     variable; from previous studies, we adopt an upper limit of E(B-V)=1.0. This
     will ensure that we go deep enough at U to match the new, deeper ACS BVI data.
     With the F330W filter and an A7V spectral type (appropriate for a cluster with
     an age of ~ 1 Gyr), a S/N of 10 is reached in 130 min for V=22.5. To cover
     region B with HRC, we will use two separate pointings; M82-B1 and M82-B2. We
     therefore require a total exposure time of 260 min. The exposures will be
     broken down into sub-exposures and will be acquired using the ACS dither-line
     pattern to remove hot pixels.

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

     None

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

     None

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

     None
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                                                10853(  2) - 05/11/06 11:35  - [  3]

TARGET LIST    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   MESSIER-082- GALAXY, STARBURST       RA=09H56M1.6033S +/- 0.1",       J2000             V = 19.0
    B-1                                  DEC=+69D41'9.92" +/- 0.1"
    Reference Frame: Other: HST Image

2   MESSIER-082- GALAXY, STARBURST       RA=09H55M56.3123S +/- 0.1",      J2000             V = 19.0
    B-2                                  DEC=+69D41'2.06" +/- 0.1"
    Reference Frame: Other: HST Image

                                                10853(  2) - 05/11/06 11:35  - [  4]

Patterns
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Pattern_Number: 1

                    Primary_Pattern                   Secondary_Pattern
Pattern_Type        ACS-HRC-DITHER-LINE
Pattern_Purpose     DITHER
Number_Of_Points    3
Point_Spacing       0.198
Line_Spacing        <none>
Coordinate_Frame    POS-TARG
Pattern_Orient      44.28
Angle_Between_Sides <none>
Center_Pattern      NO

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                                                10853(  2) - 05/11/06 11:35  - [  5]

Visit: 01
     Visit Priority:      <none>
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: None


Exposures
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Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |       Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
------------------------------------------------------------------------------------------------------------------------------------
1    MESSIER-082 ACS/HRC  ACCUM   HRC       F330W            CR-SPLIT=NO,GAIN=2             1   2777 S     PATTERN 1 1
     -B-2
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Sub Exposures
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Target             | Exp |Instr   | Oper. |  Aper  |Spectral|Cent.|Primary     |Secondary   |Iteration |CR-SPLIT  |Orbit  |Duration
Name               | Num |Config  | Mode  | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num       |Num       |Number |
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MESSIER-082-B-2     1     ACS/HRC  ACCUM   HRC      F330W          1            none         none       none       1       N/A
MESSIER-082-B-2     1     ACS/HRC  ACCUM   HRC      F330W          2            none         none       none       2       N/A
MESSIER-082-B-2     1     ACS/HRC  ACCUM   HRC      F330W          3            none         none       none       3       N/A
                                                10853(  2) - 05/11/06 11:35  - [  6]

Visit: 02
     Visit Priority:      <none>
     Visit Requirements:  SAME ORIENT AS 01
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |       Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
------------------------------------------------------------------------------------------------------------------------------------
1    MESSIER-082 ACS/HRC  ACCUM   HRC       F330W            CR-SPLIT=NO,GAIN=2             1   2777 S     PATTERN 1 1
     -B-1
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Sub Exposures
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Target             | Exp |Instr   | Oper. |  Aper  |Spectral|Cent.|Primary     |Secondary   |Iteration |CR-SPLIT  |Orbit  |Duration
Name               | Num |Config  | Mode  | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num       |Num       |Number |
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MESSIER-082-B-1     1     ACS/HRC  ACCUM   HRC      F330W          1            none         none       none       1       N/A
MESSIER-082-B-1     1     ACS/HRC  ACCUM   HRC      F330W          2            none         none       none       2       N/A
MESSIER-082-B-1     1     ACS/HRC  ACCUM   HRC      F330W          3            none         none       none       3       N/A
                                                10853(  2) - 05/11/06 11:35  - [  7]

            Summary Form for Proposal  10853

  Item                         Used in this proposal
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  Apertures                    HRC
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  Configurations               ACS/HRC
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  Opmodes                      ACCUM
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  Optional Parameters          CR-SPLIT=NO GAIN=2
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  Special Requirements         PATTERN 1 1; SAME ORIENT AS 01;
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  Spectral Elements            F330W
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  Target Names                 MESSIER-082-B-2 MESSIER-082-B-1
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