6618( 11) - 08/19/97 16:11  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      6618
                                                       Version: 11
                                                       Check-in Date: 19-Aug-1997
                                                                      14:00:18

1.Proposal Title:
A Hidden Power Source in the QSO PG 1630+377
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2. Scientific Category   3. Proposal For  4. Cycle
AGN                         GO               6
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5. Investigators
                                                                                     Contact?
    PI: ROBERT GOODRICH                   THE W.M. KECK OBSERVATORY
   CoI: Anuradha Koratkar                 Space Telescope Science Institute             N
   CoI: Robert Antonucci                  University of California, Santa Barbara       N

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6. Abstract

Previous (Cycle 3) FOS polarimetry of the QSO PG 1630+377 has shown a steep rise in
polarization well shortward of the redshifted Lyman edge (912 Angstrom). The high
polarizations seen at the shortest wavelengths, P ~ 20\%, (.) probably indicate that
we are seeing scattering of some hidden source. Any direct light from the source
would dilute the polarization from the scattering region to much lower levels. For
this hidden source to be so bright as seen only through scattering indicates that it
may be intrinsically the most significant power source shortward of the Lyman edge.
In order to confirm and follow-up the FOS observations we will use the FOC to study
three wavelength regions in PG 1630+377, including the important region below the
short wavelength limit of the FOS data. The FOC is the only instrument capable of
performing these measurements, since the G130H grating in the FOS will not be
calibrated for polarimetry observations.
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                                                6618( 11) - 08/19/97 16:11  - [  2]

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

     The UV polarimetry necessary to confirm and extend our earlier FOS observations
     of PG 1630+377 is available only with HST, and only with the FOC. We will use
     three passbands, F140W, F170M, and F231M+F130LP. The F140W band will probe the
     UV at wavelengths shorter than the existing FOS observations. Note that the
     post-COSTAR FOS will not be calibrated for polarimetry with the G130H grating,
     so we cannot use the FOS to probe these wavelengths without a prohibitive
     calibration overhead. This wavelength region is critical for testing the
     theories proposed for the high polarization in PG 1630+377. The F170M filter
     will probe the wavelengths which were observed to have high polarization with
     the FOS. This is important to confirm the FOS polarimetry. Several QSOs have
     shown a rise in P at short wavelengths with the FOS (Impey et al. 1995;
     Koratkar et al. 1995), so this confirmation will help to interpret those data
     as well. The F231M filter will probe wavelengths longer than the rise in P seen
     in the FOS. The calculated count rate from the F231M filter is 1.2 count pixel^
     -1 s^-1, above the 1 count pixel^-1 s^-1 limit to the linear regime of the FOC,
     so we will use the F130LP as a weak ND filter to keep the count rate within the
     linear range (0.8 count pixel^-1 s^-1 with the F130LP filter). Important
     caveat. One of the three polarizers in the FOC, POL60, does not transmit
     shortward of 2000 Angstrom. Hence we will require a slightly different
     technique to measure the polarization using only two of the polarizers. Ideally
     we would roll the telescope -30degrees from the nominal roll angle, and take a
     set of POL0 and POL120 exposures. Then we would roll the telescope +30degrees
     and use the POL0 polarizer to reproduce the POL60 position angle.
     Unfortunately, RPS2 testing using a mockup of a proposal file shows that we
     cannot reach +/- 30degrees roll angles from nominal for PG1630+377. The maximum
     we can get is +/- 26degrees. This will make the data reduction slightly
     different than the usual reduction using polarizers at angles of 0degrees,
     60degrees, and 120degrees, but since we will know the actual roll angles
     accurately it will not compromise our results. One of us (RWG) already has
     experience in reducing polarimetry using non-optimal polarizer angles using
     WFPC2. The exposure times and signal-to-noise ratios (S/N) were calculated with
     FOCSIM, using the observed total flux spectrum of PG 1630+377, based on FOS,
     IUE, and ground-based spectra, as the input spectrum. The ground-based spectra
     are important for quantifying the red leaks of the filters, the fraction of
     recorded photons which are actually leaking through from wavelength longward of
     the nominal passband. The red leaks are small (6\\\\\\\\% for F140M, 2\\\\\\\\%
     for F170M, and 0.7\\\\\\\\% for F231M and for photons with wavelengths above
     3000 Angstrom). The FOCSIM results will allow us to correct for the red leaks
     if necessary. Single-orbit exposures per polarizer are adequate for
     polarization uncertainties of <= 3\\\\\\\\% in the shorter passbands. Half-
     orbit exposures suffice for the F231M+F130LP combination. With three filter
     combinations and three polarizer angles each, we require 8 orbits total.

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

     We will require specific spacecraft rolls, as described in the Description of
     the Observations. We have used RPS2 and a mockup of a Cycle 5 proposal to see
     what roll angles are available, and have found that we can get -26degrees and
     +26degrees from the nominal roll angle during a short interval in July. Of
     course, the time period of optimum schedulability will change somewhat with
     Cycle 6, but our mockup shows that these roll angles are feasible. None.

  Calibration Justification
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  Additional Comments
  -------------------

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                                                6618( 11) - 08/19/97 16:11  - [  3]

  Data Distribution

  Media:           8MM
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:
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                                                6618( 11) - 08/19/97 16:11  - [  4]

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   PG1630+377   GALAXY, QSO             RA=16H 32M 1.16S +/- 1",DEC=37D  J2000    Z=1.466  V = 16.1+/-0.2
                                         37' 49.7" +/- 1"                                   F-CONT(1700)=1.3+/-0.13e-15
                                                                                            F-CONT(1900)=1.5+/-0.15e-15
                                                                                            F-CONT(2000)=1.9+/-0.2e-15
                                                                                            F-CONT(2200)=2.5+/-0.3e-15
                                                                                            F-CONT(2500)=3.1+/-0.3e-15
                                                                                            F-CONT(3000)=2.7+/-0.3e-15

                                                6618( 11) - 08/19/97 16:11  - [  5]

Visit: 51
     Visit Requirements:  <none>
     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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1        PG1630+377  FOC/96 IMAGE   512X512 POL0,            PIXEL=25X25                       1   1110 S
                                            F170M
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2        PG1630+377  FOC/96 IMAGE   512X512 POL120,          PIXEL=25X25                       1   1110 S
                                            F170M
   Comments:  POL0 and POL120 in exposures 1 and 2 displace
              the image nearly the same amount, so we won't
              use a POS TARG to make sure the images are in
              the same spot.
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3        INTFLAT     FOC/96 RESEAU  512X512 CLEAR            PIXEL=25X25,LED=BLUE,LED-STEP=3   1   600 S
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4        INTFLAT     FOC/96 RESEAU  512X512 CLEAR            PIXEL=25X25,LED=BLUE,LED-STEP=4   1   600 S
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5        PG1630+377  FOC/96 IMAGE   512X512 POL0,            PIXEL=25X25                       1   1256 S  POS TARG 0.2,0.2
                                            F170M
   Comments:  We use a POS TARG here to sample a different
              region of the FOC detector, to get an idea of
              flat field uncertainties.
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6        PG1630+377  FOC/96 IMAGE   512X512 POL120,          PIXEL=25X25                       1   1256 S  POS TARG 0.2,0.2
                                            F170M
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7        INTFLAT     FOC/96 RESEAU  512X512 CLEAR            PIXEL=25X25,LED=BLUE,LED-STEP=5   1   600 S
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8        INTFLAT     FOC/96 RESEAU  512X512 CLEAR            PIXEL=25X25,LED=BLUE,LED-STEP=6   1   600 S
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9        PG1630+377  FOC/96 IMAGE   512X512 POL0,            PIXEL=25X25                       1   1256 S
                                            F231M,
                                            F130LP
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10       PG1630+377  FOC/96 IMAGE   512X512 POL120,          PIXEL=25X25                       1   1256 S
                                            F231M,
                                            F130LP
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                                                6618( 11) - 08/19/97 16:11  - [  6]

Visit: 52
     Visit Requirements:  ORIENT 54D TO 60D FROM 51 AFTER 51 BY 0 D TO 5 D
     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
------------------------------------------------------------------------------------------------------------------------------------
1        PG1630+377  FOC/96 IMAGE   512X512 POL0,            PIXEL=25X25                       1   1110 S
                                            F170M
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2        PG1630+377  FOC/96 IMAGE   512X512 POL120,          PIXEL=25X25                       1   1110 S
                                            F170M
   Comments:  POL0 and POL120 displace the image nearly the
              same amount, so we won't use a POS TARG to
              make sure the images are in the same spot.
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3        INTFLAT     FOC/96 RESEAU  512X512 CLEAR            PIXEL=25X25,LED=BLUE,LED-STEP=7   1   600 S
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4        INTFLAT     FOC/96 RESEAU  512X512 CLEAR            PIXEL=25X25,LED=BLUE,LED-STEP=8   1   600 S
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5        PG1630+377  FOC/96 IMAGE   512X512 POL0,            PIXEL=25X25                       1   1256 S
                                            F231M,
                                            F130LP
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6        PG1630+377  FOC/96 IMAGE   512X512 POL120,          PIXEL=25X25                       1   1256 S
                                            F231M,
                                            F130LP
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                                                6618( 11) - 08/19/97 16:11  - [  7]

            Summary Form for Proposal  6618

  Item                         Used in this proposal
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  Configurations               FOC/96
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  Opmodes                      IMAGE RESEAU
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  Optional Parameters          PIXEL=25X25 LED-STEP=3 LED-STEP=4 LED-STEP=5 LED-STEP=6 LED-STEP=7 LED-STEP=8
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  Proposal Category            GO
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  Scientific Category          AGN
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  Special Requirements         POS TARG 0.2,0.2 ORIENT 54D TO 60D FROM 51 AFTER 51 BY 0 D TO 5 D
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  Spectral Elements            POL0,F170M POL120,F170M CLEAR POL0,F231M,F130LP POL120,F231M,F130LP
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  Target Names                 PG1630+377 INTFLAT
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