10585(  3) - 06/11/05 10:13  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10585

Version: 3    Check-in Time: 11-Jun-2005 14:12:00

Title
NGC 4449: a Testbed for Starbursts in the Low- and High-Redshift Universe
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Type             Cycle     Parallel Pointing Tolerance
GO               14        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Alessandra Aloisi             Space Telescope Science Institute - ESA
   CoI: Dr. Francesca Annibali            Scuola Internazionale Superiore di Studi      N
                                          Avanzati
   CoI: Dr. Claus Leitherer               Space Telescope Science Institute             N
   CoI: Dr. Marco Sirianni                Space Telescope Science Institute - ESA       N
   CoI: Dr. Monica Tosi                   Osservatorio Astronomico di Bologna           N
   CoI: Dr. Roeland P. van der Marel      Space Telescope Science Institute             N

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Abstract

We will obtain deep ACS/WFC broad-band imaging in F435W, F555W, and F814W of the
Magellanic irregular galaxy NGC 4449 in order to infer the properties of the
resolved (young and old) stellar population, compare the current strong star-
formation activity to that at earlier epochs, trace the major episodes of star
formation over cosmic time, and relate them to the past history of
interaction/merging of this galaxy. NGC 4449 is one of the closest (< 5 Mpc) global
starbursts with a widespread star-formation activity that could have been triggered
by interaction or accretion. It is, therefore, the perfect laboratory where to
address issues related to star formation in extreme environments and investigate
processes connected to the formation and evolution of galaxies in the early
universe. At a distance of 4.2 Mpc, the stellar content in NGC 4449 can easily be
resolved with HST. Yet, up to date no comprehensive dataset has been collected that
is suited to infer a global star-formation history of the galaxy and to better
understand its evolution. ACS/WFC provides the angular resolution and sensitivity to
easily reach magnitude limits necessary for the detection of individual stars at the
tip of the red giant branch (i.e., with ages from 1 Gyr up to 12 Gyr) with the
required accuracy. A mosaic of 2 pointings along the major axis will give a good
coverage of the galaxy and will allow us to infer a star-formation history unbiased
by local properties of peculiar regions. Narrow-band imaging in F658N (Halpha) will
provide a map of the ionized gas. Finally, WFPC2 parallel observations in F555W and
F814W will allow to search deep in the HI halo of NGC 4449 for evidence of stars
belonging to tidal streams. Our investigation of NGC 4449 will benefit from the
wealth of observations already available over almost the whole electromagnetic
spectrum and will be crucial in better understanding how starbursts can be
influenced by merging phenonema in both the low- and high-redshift universe.
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                                                10585(  3) - 06/11/05 10:13  - [  2]

  Observations Description
  ------------------------

     We will use ACS/WFC to study the resolved stellar population of NGC 4449. We
     will perform a mosaic with 2 different pointings in a rectangle shape along the
     major axis of the galaxy. Our expertise suggests that the V and I filters are
     best suited for this type of investigation. We will thus observe in the two
     broad-band filters F555W and F814W. F555W is preferred to F606W because it is a
     more standard filter for HST stellar population studies and it is much less
     contaminated by nebular emission (F606W includes Halpha). We will infer the
     ancient star formation history of NGC 4449 from simulations tailored to
     reproduce the observed I vs. V-I CMD. We also require broad-band imaging in
     F435W in order to better characterize the hot young stars and correct each
     single star for intrinsic differential reddening along the line of sight with
     multi-band photometry. And finally, we will also do narrow-band imaging in
     F658N to map the distribution of the ionized gas through Halpha emission. At
     each of the two major axis pointings we will observe for 4 orbits in one visit.
     The exposure times for the different filters were chosen to reach at least one
     magnitude fainter than the TRGB (I = 24.1) with a photometric error below 0.1
     mag (S/N > 10) in the broad-band filters. The exposures in each filter will be
     executed with a standard primary+secondary dithering pattern suitable to get
     rid of cosmic rays, remove hot/bad pixels, fill the gap between the two CCDs of
     the ACS/WFC, and improve the PSF sampling. Finally, parallel WFPC2 observations
     for each ACS pointing will be taken in F606W and F814W. It will be possible to
     allocate about 2 orbits per WFPC2 filter, per pointing. The goal to properly
     mosaic the galaxy along its major axis restricts the ORIENT of the
     observations. We want the CCD edges perpendicular to the major axis, which
     limits the ORIENT to 50 degrees, modulo 90. In addition, we want the most
     important parts of the galaxy to fall on WFC2, which has the smallest PSF
     variations over the field. We also want the chip gap to be away from the most
     interesting parts of the galaxy. And finally, the observations must of course
     be schedulable. These considerations leave ORIENT=320 degrees as the only
     available option. To provide sufficient flexibility for scheduling in two-gyro
     mode, we allow a +/- 10 degree range around this value. We also increase SCHED
     to 60% from its default value of 30%. This provides increased opportunities for
     scheduling, but with a slightly reduced visibility time (2.5 minutes) per
     orbit. The visit planner shows that the observations can schedule for a full 6
     weeks in Oct-Dec 2005. This should provide sufficient flexibility for
     scheduling. The single orbit in visit 3 allows for additional deeper imaging in
     Halpha and F814W at a slightly different pointing.

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


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


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

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                                                10585(  3) - 06/11/05 10:13  - [  3]


                                                10585(  3) - 06/11/05 10:13  - [  4]

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   NGC4449-POSA GALAXY, AMORPHOUS       RA=12H28M15.7467S +/- 1",        J2000             V = 9.7+/-0.6
                 IRREGULAR               DEC=+44D06'53.28" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

2   NGC4449-POSB GALAXY, AMORPHOUS       RA=12H28M3.0627S +/- 1",         J2000             V = 9.7+/-0.6
                 IRREGULAR               DEC=+44D05'7.37" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

3   NGC4449-POSC GALAXY, INTERACTING     RA=12H28M12.1516S +/- 0.1",      J2000    V =      V = 9.99
                 GALAXY, STARBURST,      DEC=+44D05'45.40" +/- 0.1",               207.0
                 MAGELLANIC IRREGULAR    PLATE-ID=00XX
    Coordinate Source: GSC_SURVEY_PLATE
    Comments: Position adjusted to fit low-surface brightness
              narrow-line emitting regions surrounding the main
              visible body of the galaxy in the FOV.

                                                10585(  3) - 06/11/05 10:13  - [  5]

Patterns
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Pattern_Number: 1

                    Primary_Pattern                   Secondary_Pattern
Pattern_Type        ACS-WFC-DITHER-LINE               ACS-WFC-DITHER-LINE
Pattern_Purpose     DITHER                            DITHER
Number_Of_Points    2                                 2
Point_Spacing       2.994                             0.149
Line_Spacing        <none>                            <none>
Coordinate_Frame    POS-TARG                          POS-TARG
Pattern_Orient      85.27                             34.25
Angle_Between_Sides <none>                            <none>
Center_Pattern      NO                                NO

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Pattern_Number: 2

                    Primary_Pattern                   Secondary_Pattern
Pattern_Type        ACS-WFC-DITHER-LINE
Pattern_Purpose     DITHER
Number_Of_Points    3
Point_Spacing       3.011
Line_Spacing        <none>
Coordinate_Frame    POS-TARG
Pattern_Orient      85.28
Angle_Between_Sides <none>
Center_Pattern      NO

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                                                10585(  3) - 06/11/05 10:13  - [  6]

Visit: 01
     Visit Priority:      <none>
     Visit Requirements:  PCS MODE FINE; SCHED 60%; ORIENT 310.0D TO 330.0 D
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
------------------------------------------------------------------------------------------------------------------------------------
Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |       Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
------------------------------------------------------------------------------------------------------------------------------------
1    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F658N            CR-SPLIT=NO                    1   75 S       PATTERN 1 1-6; PAR 5-6
     A                                                                                          see below  WITH 1-4
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2    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F555W            CR-SPLIT=NO                    1   600 S
     A                                                                                          see below
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3    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F814W            CR-SPLIT=NO                    1   500 S
     A                                                                                          see below
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4    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F435W            CR-SPLIT=NO                    1   900 S
     A                                                                                          see below
------------------------------------------------------------------------------------------------------------------------------------
5    ANY         WFPC2    IMAGE   WFALL     F606W            CR-SPLIT=NO                    1   800 S
                                                                                                see below
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6    ANY         WFPC2    IMAGE   WFALL     F814W            CR-SPLIT=NO                    1   1400 S
                                                                                                see below
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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 |
------------------------------------------------------------------------------------------------------------------------------------
NGC4449-POSA        1     ACS/WFC  ACCUM   WFCENTER F658N          1            1            none       none       1       83.0 S
NGC4449-POSA        1     ACS/WFC  ACCUM   WFCENTER F658N          1            2            none       none       2       90.0 S
NGC4449-POSA        1     ACS/WFC  ACCUM   WFCENTER F658N          2            1            none       none       3       91.0 S
NGC4449-POSA        1     ACS/WFC  ACCUM   WFCENTER F658N          2            2            none       none       4       96.0 S
NGC4449-POSA        2     ACS/WFC  ACCUM   WFCENTER F555W          1            1            none       none       1       608.0 S
NGC4449-POSA        2     ACS/WFC  ACCUM   WFCENTER F555W          1            2            none       none       2       615.0 S
NGC4449-POSA        2     ACS/WFC  ACCUM   WFCENTER F555W          2            1            none       none       3       616.0 S
NGC4449-POSA        2     ACS/WFC  ACCUM   WFCENTER F555W          2            2            none       none       4       621.0 S
NGC4449-POSA        3     ACS/WFC  ACCUM   WFCENTER F814W          1            1            none       none       1       508.0 S
NGC4449-POSA        3     ACS/WFC  ACCUM   WFCENTER F814W          1            2            none       none       2       515.0 S
NGC4449-POSA        3     ACS/WFC  ACCUM   WFCENTER F814W          2            1            none       none       3       516.0 S
NGC4449-POSA        3     ACS/WFC  ACCUM   WFCENTER F814W          2            2            none       none       4       521.0 S
NGC4449-POSA        4     ACS/WFC  ACCUM   WFCENTER F435W          1            1            none       none       1       908.0 S
NGC4449-POSA        4     ACS/WFC  ACCUM   WFCENTER F435W          1            2            none       none       2       915.0 S
NGC4449-POSA        4     ACS/WFC  ACCUM   WFCENTER F435W          2            1            none       none       3       916.0 S
NGC4449-POSA        4     ACS/WFC  ACCUM   WFCENTER F435W          2            2            none       none       4       921.0 S
ANY                 5     WFPC2    IMAGE   WFALL    F606W          1            1            none       none       1       900.0 S
                                                10585(  3) - 06/11/05 10:13  - [  7]
Sub Exposures
------------------------------------------------------------------------------------------------------------------------------------
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 |
------------------------------------------------------------------------------------------------------------------------------------
ANY                 5     WFPC2    IMAGE   WFALL    F606W          1            2            none       none       2       900.0 S
ANY                 5     WFPC2    IMAGE   WFALL    F606W          2            1            none       none       3       900.0 S
ANY                 5     WFPC2    IMAGE   WFALL    F606W          2            2            none       none       4       900.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          1            1            none       none       1       1500.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          1            2            none       none       2       1500.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          2            1            none       none       3       1500.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          2            2            none       none       4       1500.0 S
                                                10585(  3) - 06/11/05 10:13  - [  8]

Visit: 02
     Visit Priority:      <none>
     Visit Requirements:  PCS MODE FINE; SCHED 60%; SAME ORIENT AS 01; AFTER 01
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
------------------------------------------------------------------------------------------------------------------------------------
Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |       Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
------------------------------------------------------------------------------------------------------------------------------------
1    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F658N            CR-SPLIT=NO                    1   75 S       PATTERN 1 1-6; PAR 5-6
     B                                                                                          see below  WITH 1-4
------------------------------------------------------------------------------------------------------------------------------------
2    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F555W            CR-SPLIT=NO                    1   600 S
     B                                                                                          see below
------------------------------------------------------------------------------------------------------------------------------------
3    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F814W            CR-SPLIT=NO                    1   500 S
     B                                                                                          see below
------------------------------------------------------------------------------------------------------------------------------------
4    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F435W            CR-SPLIT=NO                    1   900 S
     B                                                                                          see below
------------------------------------------------------------------------------------------------------------------------------------
5    ANY         WFPC2    IMAGE   WFALL     F606W            CR-SPLIT=NO                    1   800 S
                                                                                                see below
------------------------------------------------------------------------------------------------------------------------------------
6    ANY         WFPC2    IMAGE   WFALL     F814W            CR-SPLIT=NO                    1   1400 S
                                                                                                see below
------------------------------------------------------------------------------------------------------------------------------------

Sub Exposures
------------------------------------------------------------------------------------------------------------------------------------
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 |
------------------------------------------------------------------------------------------------------------------------------------
NGC4449-POSB        1     ACS/WFC  ACCUM   WFCENTER F658N          1            1            none       none       1       83.0 S
NGC4449-POSB        1     ACS/WFC  ACCUM   WFCENTER F658N          1            2            none       none       2       90.0 S
NGC4449-POSB        1     ACS/WFC  ACCUM   WFCENTER F658N          2            1            none       none       3       91.0 S
NGC4449-POSB        1     ACS/WFC  ACCUM   WFCENTER F658N          2            2            none       none       4       96.0 S
NGC4449-POSB        2     ACS/WFC  ACCUM   WFCENTER F555W          1            1            none       none       1       608.0 S
NGC4449-POSB        2     ACS/WFC  ACCUM   WFCENTER F555W          1            2            none       none       2       615.0 S
NGC4449-POSB        2     ACS/WFC  ACCUM   WFCENTER F555W          2            1            none       none       3       616.0 S
NGC4449-POSB        2     ACS/WFC  ACCUM   WFCENTER F555W          2            2            none       none       4       621.0 S
NGC4449-POSB        3     ACS/WFC  ACCUM   WFCENTER F814W          1            1            none       none       1       508.0 S
NGC4449-POSB        3     ACS/WFC  ACCUM   WFCENTER F814W          1            2            none       none       2       515.0 S
NGC4449-POSB        3     ACS/WFC  ACCUM   WFCENTER F814W          2            1            none       none       3       516.0 S
NGC4449-POSB        3     ACS/WFC  ACCUM   WFCENTER F814W          2            2            none       none       4       521.0 S
NGC4449-POSB        4     ACS/WFC  ACCUM   WFCENTER F435W          1            1            none       none       1       908.0 S
NGC4449-POSB        4     ACS/WFC  ACCUM   WFCENTER F435W          1            2            none       none       2       915.0 S
NGC4449-POSB        4     ACS/WFC  ACCUM   WFCENTER F435W          2            1            none       none       3       916.0 S
NGC4449-POSB        4     ACS/WFC  ACCUM   WFCENTER F435W          2            2            none       none       4       921.0 S
ANY                 5     WFPC2    IMAGE   WFALL    F606W          1            1            none       none       1       900.0 S
                                                10585(  3) - 06/11/05 10:13  - [  9]
Sub Exposures
------------------------------------------------------------------------------------------------------------------------------------
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 |
------------------------------------------------------------------------------------------------------------------------------------
ANY                 5     WFPC2    IMAGE   WFALL    F606W          1            2            none       none       2       900.0 S
ANY                 5     WFPC2    IMAGE   WFALL    F606W          2            1            none       none       3       900.0 S
ANY                 5     WFPC2    IMAGE   WFALL    F606W          2            2            none       none       4       900.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          1            1            none       none       1       1500.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          1            2            none       none       2       1500.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          2            1            none       none       3       1500.0 S
ANY                 6     WFPC2    IMAGE   WFALL    F814W          2            2            none       none       4       1500.0 S
                                                10585(  3) - 06/11/05 10:13  - [ 10]

Visit: 03
     Visit Priority:      <none>
     Visit Requirements:  ORIENT 310.0D TO 325.0 D; AFTER 02
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
------------------------------------------------------------------------------------------------------------------------------------
Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |       Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
------------------------------------------------------------------------------------------------------------------------------------
1    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F814W            CR-SPLIT=NO                    1   200 S
     C
------------------------------------------------------------------------------------------------------------------------------------
2    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F814W            CR-SPLIT=NO                    1   340 S      POS TARG -0.25, 3
     C
------------------------------------------------------------------------------------------------------------------------------------
3    NGC4449-POS ACS/WFC  ACCUM   WFCENTER  F658N            CR-SPLIT=NO                    1   513 S      POS TARG -0.24,-3;
     C                                                                                                     PATTERN 2 3
------------------------------------------------------------------------------------------------------------------------------------

Sub Exposures
------------------------------------------------------------------------------------------------------------------------------------
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 |
------------------------------------------------------------------------------------------------------------------------------------
NGC4449-POSC        1     ACS/WFC  ACCUM   WFCENTER F814W          none         none         none       none       1       N/A
NGC4449-POSC        2     ACS/WFC  ACCUM   WFCENTER F814W          none         none         none       none       1       N/A
NGC4449-POSC        3     ACS/WFC  ACCUM   WFCENTER F658N          1            none         none       none       1       N/A
NGC4449-POSC        3     ACS/WFC  ACCUM   WFCENTER F658N          2            none         none       none       1       N/A
NGC4449-POSC        3     ACS/WFC  ACCUM   WFCENTER F658N          3            none         none       none       1       N/A
                                                10585(  3) - 06/11/05 10:13  - [ 11]

            Summary Form for Proposal  10585

  Item                         Used in this proposal
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  Apertures                    WFCENTER WFALL
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  Configurations               ACS/WFC WFPC2
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  Opmodes                      ACCUM IMAGE
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  Optional Parameters          CR-SPLIT=NO
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  Proposal Category            GO
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  Special Requirements         PCS MODE FINE; SCHED 60%; ORIENT 310.0D TO 330.0 D PATTERN 1 1-6; PAR 5-6 WITH 1-4 PCS MODE FINE;
                               SCHED 60%; SAME ORIENT AS 01; AFTER 01 ORIENT 310.0D TO 325.0 D; AFTER 02 POS TARG -0.25, 3 POS
                               TARG -0.24,-3; PATTERN 2 3
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  Spectral Elements            F658N F555W F814W F435W F606W
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  Target Names                 NGC4449-POSA ANY NGC4449-POSB NGC4449-POSC
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