! Proposal 5946, submission 2
! PI: Chris Impey
! Received Fri Oct 27 17:00:28 EDT 1995
! From: pi16@stsci.edu
! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template
! $Id: 5946,v 7.1 1996/04/24 10:36:30 pepsa Exp $
!
!   Refer to the HST Phase II Proposal Instructions to fill this out
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!             Phone: 410 338-4506    , E-mail: wallace@stsci.edu
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! This partially completed template was generated from a Phase I proposal.
! Date generated: Sat Dec 17 11:08:26 EST 1994
!

Proposal_Information                           
              Title:  The Stellar Populations of Low Surface
                      Brightness Galaxies
  Proposal_Category:  GO
Scientific_Category:  Stellar Populations
             Cycle:    5

Investigators
     PI_name:         Chris Impey
     PI_Institution:  Steward Observatory

          CoI_Name:   Greg Bothun
   CoI_Institution:   University of Oregon
           Contact:   

          CoI_Name:   James Schombert
   CoI_Institution:   Infrared Processing and Analysis Center
           Contact:  

          CoI_Name:   Stacey McGaugh
   CoI_Institution:   University of Cambridge
           Contact: 


Abstract:  
    We propose to take WFPC2 images of 10 extremely low surface
    brightness (LSB) galaxies.  Images in the U(F300W), V(F555W),
    and I(F814W) bands with the WFC will dramatically improve on
    the existing ground based constraints on the stellar
    populations and ages of these enigmatic galaxies, as well as
    their possible link to galaxies at higher redshift. These
    galaxies offer a profound challenge to our understanding of
    galaxy evolution in that: (a) the most extreme LSB galaxies
    are 100 times more luminous than normal galaxies at a given
    metal-abundance, (b) some are so so blue that either the
    implied mean age is 1-2 Gyr, or there is a huge population of
    blue horizontal branch stars, (c) their stellar volume mass
    densities are at an unprecedentedly low level for normal star
    formation to have occurred. These incongruent properties
    coupled with the unexpectedly large co-moving space density of
    faint blue galaxies suggest an evolutionary link only under
    the extreme hypothesis that the galaxies remain blue while
    fading. Such a hypothesis is possible in the context of non-
    standard stellar populations. The spatial resolution of WFPC2
    can be used to study stellar populations in LSB galaxies using
    the technique of luminosity fluctuations. The fluctuations
    signals are expected to be 20-40%, and they can be studied
    with a sensitivity that cannot be achieved from the ground.

Questions 

     Observing_Description:
         We propose to use the Wide Field Camera at f/12.9 to image 10
         extremely low surface brightness galaxies. All the galaxies
         will be observed in the I(F814W) bands, and all but one 
         will be observed in the U(F330W) band. The typical
         integration times per galaxy are 20 minutes (F330W), 10 minutes
         (F555W), and 10 minutes (F814W). The galaxies are selected to be
         the bluest among 60 extreme LSB dwarfs with surface
         photometry in the Virgo and Fornax clusters. The galaxies are
         representative in surface brightness of over 500 dwarfs in
         these two clusters in the range 23-26 V mag/square arcsec.
         Analysis of ten objects is required to draw firm
         conclusions about this ultra-faint galaxy population. The
         targets are at known distances (i.e. cluster membership at
         velocities less than 1500 km/s, so distances are well known
         in the context of a model for large scale structure in the
         local universe). The WFC filters are chosen for high
         throughput, broad combined wavelength coverage, and
         photometric characteristics that allow easy comparison with
         ground-based data. A V(F555W) frame of a single target will
	 provide a reference
         with existing surface photometry. Most of the galaxies are in
         the fields of the Virgo and Fornax clusters, and have
         diameters at the 27 V mag/square arcsec isophote of 1-2
         arcminutes. Therefore, we will take full advantage of the 2.5
         arcmin field-of-view of the camera. The exposure times are
         chosen to match the instrument sensitivity and sky background
         with the colors of LSB galaxies, and give an equivalent blue
         surface brightness limit of 28.5 mag/square arcsec. This assumes
         flat fielding to 1%. With this setup, sky noise will dominate
	 the errors in both bands, and the full
         advantage of the space environment will be realized. For the
         Wide Field Camera, total counts are calculated for a central
         surface brightness of 25 V mag/square arcsec, or 30 V mag per
         WFC pixel. The galaxies are chosen to have flat central
         regions, so this surface brightness applies over a region of
         5-20 arcseconds across. Using the sensitivities and filter
         transmissions in the WFPC2 Instrument Handbook (Version 2.0,
         May 1994), and assuming colors for the LSB galaxies of U-V =
         0.5, and V-I = 1.0, the following number of electrons per
         pixel will be collected for the surface brightness and
         average integration times quoted:  F330W -  5e (galaxy),
         48e (sky); F555W - 4.4e (galaxy), 63e (sky); F814W - 14e
         (galaxy), 135e (sky). A few of the LSB galaxies are at least
         a factor of 2-3 brighter, so these are conservative
         estimates. In each filter the observations are background
         limited, so the signal to noise per pixel will be: F330W -
         SNR = 0.59; F555W - SNR = 0.55; F814 - SNR = 1.20. This
         gives us roughly equal sensitivity to fluctuations in each 
         filter. Sky surface brightness of 29.8 mag/pixel
         (F330W), 27.3 mag/pixel (F555W), and 26.7 mag/pixel
         (F814W) have been assumed. We note that the HST sky
         brightness is 3 mag fainter in the U band and 2 mag fainter
         in the I band than can be achieved from the ground. Assuming
         flat-fielding to 1%, we can see that the flat field limit corresponds
         to the following percentage of the expected galaxy signal per
         pixel: F330W - 12%; F555W - 14%; F814W - 10%.  Therefore 
	 by averaging over as few as 4
         pixels, we can detect a fluctuation signal of 10%, and the
	 sensitivity level over the large flat 5-20 arcsecond regions of the
         galaxies is even greater. Basically, there will be many
         independent samples with which to look for a small difference
         between the variance of the sky signal and the variance of
         the galaxy signal. The fluctuation signal in the U band may
         well be dominated by a single star. The project was awarded
         10 orbits. Integrations of more than 10 minutes will be split
         to avoid excessive cosmic ray problems. In the viewing time
         available in one orbit, there is time for a guide star
         acquisition, three 10 minute exposures, and 2 associated
         readouts (U and I band exposures). 

   Real_Time_Justification:
         None.

         We have an approved UIT Astro-2 program to measure fluxes at
         2000 Angstroms for a large sample of these LSB objects.
         Pushing the observation of luminosity fluctuations with WFPC2
         as far into the blue as possible will be an important tie-in
         to the UIT data and will help isolate the stellar types which
         dominate the UV light.


Calibration_Justification:             
	 None.

      Additional_Comments:


Fixed_Targets

  Target_Number:  01
    Target_Name:  V1L4
    Description:  Galaxy, LSB
       Position:  RA = 12H 32M 11.3S +/- .7S,
		  DEC = +14D 29' 56" +/- 5"
        Equinox:  1950
        RV_or_Z:
           Flux:  V = 16.1 +/- 0.5,
		  B-V = 0.37 +/- 0.2
       Comments:

  Target_Number:  02
    Target_Name:  V2L8
    Description:  Galaxy, LSB
       Position:  RA = 12H 28M 44.7S +/- .7S,
		  DEC = +14D 54' 59" +/- 5"
        Equinox:  1950
        RV_or_Z:
           Flux:  V = 18.4 +/- 0.5,
 		  B-V = 0.30 +/- 0.2
       Comments:

  Target_Number:  03
    Target_Name:  V7L3
    Description:  Galaxy, LSB
       Position:  RA = 12H 26M 24.3S +/- .7S,
		  DEC = +13D 11' 15" +/- 5"
        Equinox:  1950
        RV_or_Z:
           Flux:  V = 17.2 +/- 0.5,
		  B-V = 0.52 +/- 0.2
       Comments:


  Target_Number:  04
    Target_Name:  UGC12695
    Description:  Galaxy, LSB
       Position:  RA = 23H 36M 2.2S +/- 1S,
		  DEC = +12D 52' 32.6" +/- 1"
        Equinox:  2000
        RV_or_Z:
           Flux:  V = 15.2 +/- 0.5,
		  B-V = 0.37 +/- 0.2
       Comments:

  Target_Number:  05
    Target_Name:  MALIN1
    Description:  Galaxy, LSB
       Position:  RA = 12H 34M 28.1S +/- .7S,
		  DEC = +14D 36' 19" +/- 5"
        Equinox:  1950
        RV_or_Z:
           Flux:  V = 14.2 +/- 0.5,
		  B-V = 0.50 +/- 0.2
       Comments:


Visits              

      Visit_Number:  1
Visit_Requirements: 
    Visit_Comments:

     Exposure_Number:  1
         Target_Name:  V1L4
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F300W
          Wavelength:  2911 
 Optional_Parameters:  SUM=2x2
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  U Filter

     Exposure_Number:  2
         Target_Name:  V1L4
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F814W
          Wavelength:  7940
 Optional_Parameters: 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  I Filter


      Visit_Number:  2
Visit_Requirements: 
    Visit_Comments:

     Exposure_Number:  1
         Target_Name:  V2L8
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F300W
          Wavelength:  2911 
 Optional_Parameters:  SUM=2x2 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  U Filter

     Exposure_Number:  2
         Target_Name:  V2L8
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F814W
          Wavelength:  7940 
 Optional_Parameters: 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  I Filter


      Visit_Number:  3
Visit_Requirements: 
    Visit_Comments:

     Exposure_Number:  1
         Target_Name:  V7L3
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F300W
          Wavelength:  2911 
 Optional_Parameters:  SUM=2x2 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  U Filter

     Exposure_Number:  2
         Target_Name:  V7L3
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F814W
          Wavelength:  7940 
 Optional_Parameters: 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  I Filter

      Visit_Number:  4
Visit_Requirements: 
    Visit_Comments:

     Exposure_Number:  1
         Target_Name:  UGC12695
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F300W
          Wavelength:  2911 
 Optional_Parameters:  SUM=2x2 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  U Filter

     Exposure_Number:  2
         Target_Name:  UGC12695
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F814W
          Wavelength:  7940 
 Optional_Parameters: 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  I Filter


      Visit_Number:  5
Visit_Requirements: 
    Visit_Comments:

     Exposure_Number:  1
         Target_Name:  MALIN1
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F300W
          Wavelength:  2911 
 Optional_Parameters:  SUM=2x2 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  U Filter

     Exposure_Number:  2
         Target_Name:  MALIN1
              Config:  WFPC2
              Opmode:  IMAGE
            Aperture:  WFALL
          Sp_Element:  F814W
          Wavelength:  7940 
 Optional_Parameters: 
Number_of_Iterations:  4
   Time_Per_Exposure:  500S
Special_Requirements:  EXPAND
            Comments:  I Filter

Data_Distribution                       ! Defaults indicated; change if desired

         Medium:        8MM             ! 8MM or 6250BPI or 1600BPI
Blocking_Factor:        10              ! 10 or 1
                                        ! Only astronomers with very old 9-
                                        ! track tape drives should consider
                                        ! a blocking factor of 1

        Ship_To:        PI_Address      ! STSCI or PI_Address or <free-text>
                                        ! PI Address from Phase I is:
                                        !
                                                 !  University of Arizona,
                                                 !  Tucson AZ 85721
                                        !
                                        !
       Ship_Via:        UPS             ! UPS (2-day) or OVERNIGHT
                                        ! Overnight shipping done at PI expense

Recipient_Email:                        ! Needed if Ship_To: is not PI_Address
                                        ! <free-text>

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