! Proposal 6611, submission 1
! PI: Kenneth M. Lanzetta
! Received Tue Feb 13 13:47:40 EST 1996
! From: lanzetta@sbast3.ess.sunysb.edu
Proposal_Information
              Title:  A Group or Cluster of Ly-alpha-Absorbing
                      Galaxies at z ~ 0.26
  Proposal_Category:  GO
Scientific_Category:  QSO Absorption Lines
             Cycle:    6

Investigators
     PI_name:         Kenneth M. Lanzetta
     PI_Institution:  State University of New York at Stony Brook

          CoI_Name:   John K. Webb
   CoI_Institution:   University of New South Wales
           Contact:   N

          CoI_Name:   Xavier Barcons
   CoI_Institution:   Instituto de Fi sica de Cantabria
           Contact:   N


Abstract:

    We have recently identified seven galaxies of a group or
    cluster that appears to be associated with a pair of Ly-alpha\
    absorption features at z ~ 0.26 toward the QSO 3CR 323.1.
    Here we propose to measure the covering factor of the
    absorbing material by obtaining a high-resolution spectrum of
    the Ly-alpha\ absorption lines using the GHRS.  The outcome of
    the proposed observation will have important implications for
    establishing the nature and origin of gas around galaxies:
    Either galaxies in groups or clusters can possess extended
    gaseous disks or halos, or galaxy clusters can contain cool,
    smoothly distributed gas.  We note that 3CR 323.1 is a
    particularly bright QSO and that the Ly-alpha\ absorption
    profile occurs at the peak of Ly-alpha\ emission, where the
    observed flux is f_Lambda = 4 * 10^-14 erg s^-1 cm^-2 AA^-1.
    This makes the acquisition of a GHRS spectrum extremely
    practical, hence 3CR 323.1 provides a unique opportunity to
    study the relationship between a Ly-alpha\ absorption line and
    a group or cluster of galaxies.

Questions

Observing_Description:

    We will use the GHRS with G160M and LSA to obtain a spectrum
    of spectral resolution   FWHM ~ 14 kms\ and signal-to-noise
    ratio   S/N ~ 12 per diode with a total exposure time of
    10,800 s. To estimate the required exposure time, we
    determined the actual ultraviolet flux from the HST spectrum
    and used the sensitivity and dark count values quoted in the
    Hubble Space Telescope Goddard High Resolution Spectrograph
    (GHRS) Instrument Handbook, Version 6.0.  At the wavelength
    Lambda = 1537 Angstrom\ of interest, the observed flux is
    f_Lambda = 4 * 10^14 erg s^-1 cm^-2 AA^-1.  Interpolating
    from Table 8--2 yields a count rate of 0.0189 count s^-1.
    ing for a dark rate of 0.008 count s^-1, the Case 2
    equation on page 34 yields a signal-to-noise ratio of 12 per
    diode in an exposure time of 10,800 s.  Our simulations have
    shown that this is sufficient to meet our scientific goals.
    Allowing for acquisition and overhead, we require five orbits
    to reach the required exposure time.

Real_Time_Justification:

Calibration_Justification:

Additional_Comments:


Fixed_Targets

  Target_Number: 1
    Target_Name: 3CR323.1
    Description: GALAXY,QSO
       Position: RA = 15H 47M 43.53S +/- 0.07S,
                 DEC = +20D 52' 17.5" +/- 0.1",
                 PLATE-ID=0280
        Equinox: 2000
        RV_or_Z: Z = 0.264
           Flux: V =  16.69 +/- 0.3,
                 B-V = 0.11 +/- 0.1,
                 U-B = -0.85 +/- 0.1
       Comments:

Visits

      Visit_Number: 1
Visit_Requirements:

     Exposure_Number: 1
         Target_Name: 3CR323.1
              Config: FOS/BL
              Opmode: ACQ/BINARY
            Aperture: 4.3
          Sp_Element: MIRROR
Number_of_Iterations: 1
   Time_Per_Exposure: 20.0S
Special_Requirements: ONBOARD ACQ FOR 2

     Exposure_Number: 2
         Target_Name: 3CR323.1
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G160M
          Wavelength: 1537.0
 Optional_Parameters: STEP-PATT=DEF, FP-SPLIT=NO, COMB=FOUR
Number_of_Iterations: 14
   Time_Per_Exposure: 299.2S
Special_Requirements: 

     Exposure_Number: 3
         Target_Name: 3CR323.1
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G160M
          Wavelength: 1537.0
 Optional_Parameters: STEP-PATT=DEF, FP-SPLIT=NO, COMB=FOUR
Number_of_Iterations: 14
   Time_Per_Exposure: 299.2S
Special_Requirements: 

     Exposure_Number: 4
         Target_Name: 3CR323.1
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G160M
          Wavelength: 1537.0
 Optional_Parameters: STEP-PATT=DEF, FP-SPLIT=NO, COMB=FOUR
Number_of_Iterations: 14
   Time_Per_Exposure: 299.2S
Special_Requirements: 

Data_Distribution

         Medium: 8MM
Blocking_Factor: 10
        Ship_To: Department of Earth and Space Sciences
                 State University of New York at Stony Brook
                 Stony Brook, NY 11794-2100
       Ship_Via: UPS

Recipient_Email: lanzetta@sbastc.ess.sunysb.edu