6100(  7) - 04/09/96 10:55  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      6100
                                                       Version: 7
                                                       Check-in Date: 09-Apr-1996
                                                                      10:50:05

1.Proposal Title:
Measuring the Characteristic Size of Lyman-Alpha Forest Clouds
------------------------------------------------------------------------------------
2. Scientific Category   3. Proposal For  4. Cycle
Quasars                     GO               5
------------------------------------------------------------------------------------
5. Investigators
                                                                                     Contact?
    PI: Craig Foltz                       Multiple Mirror Telescope Observatory
   CoI: Chris Impey                       Steward Observatory                           N
   CoI: Nadine Dinshaw                    Steward Observatory                           Y
   CoI: Ray Weymann                       Observatories of the Carnegie Institution     N
                                          of Washington
   CoI: Simon Morris                      Dominion Astrophysical Observatory            N

------------------------------------------------------------------------------------
6. Abstract

We are obtaining FOS UV spectra (GO Program 5320) of three pairs of quasars with
projected separations less than two arcminutes in order to constrain the sizes of
Lyman-Alpha forest clouds. We anticipated that these observations would yield
improved upper limits of ~ 100 kpc and so were surprised when the spectra of the
first pair, Q0107-025 A,B (z = 0.956, 0.952, separation 1.44 arcmin), showed a large
number of absorption lines common to both spectra. Assuming that these are Lyman-
Alpha forest lines, the directly-measured lower limit on the sizes of the clouds at
0.32 <= z <= 0.90 is between 300 and 450 kpc (H_0=80, q_0=0.5). This is an order of
magnitude larger than the best published lower limit. Furthermore, the rms velocity
difference between the absorption lines along the two lines of sight is only about
100 km/sec. These results challenge all current theoretical models for the
absorbers. Perhaps even more exciting is the fact the there is a third bright
quasar, LBQS 0107-0232 (z=0.728, B_J=18.4), lying a few arcminutes away from the
pair (separations 2.00 and 2.93 arcmin from Q0107-025 A,B), which will allow us to
sample scales from 300 kpc to nearly 1 Mpc. We are requesting time to make FOS
observations of these three quasars in order to: (1) extend the wavelength coverage
of the observations of Q0107-025A,B to contain the Lyman alpha emission line and (2)
obtain spectra of the Lyman-Alpha forest in LBQS 0107-0232.
------------------------------------------------------------------------------------
                                                6100(  7) - 04/09/96 10:55  - [  2]

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

     Spectroscopic observations of the three quasars fall into two categories:
     First, FOS/RD observations of LBQS 0107-0232 with G190H. The difference in B_J
     magnitude between Q0107-0232 and Q0107-025A is well-known from the LBQS plates
     to be 0.3 +/- 0.1 mag (barring variability). The exposure time was then
     calculated from the S/N realized in the GO 5320 observations of Q0107-025A,
     using this magnitude difference and assuming that both quasars have the same
     spectral slope. The latter assumption is more-or-less consistent with the
     optical data; if anything, Q0107-0232 is somewhat bluer than Q0107-025A. Our
     calculations indicate that 420 minutes of integration (11 orbits) will give S/N
     approximately equal to that of the Q0107-025A,B spectra obtained in GO 5320.
     The predicted count rates are a factor of 15 above the dark rate, which we have
     therefore assumed to be negligible in estimating the exposure time. Second,
     FOS/RD observations of all Q0107-025 A,B will be taken with G270H to extend the
     wavelength coverage to contain the Lyman alpha emission lines in each quasar.
     This will also complete our spectral coverage on these two objects from 1200 to
     5500 Angstrom. Count rates for these observations were estimated from Figure
     1.2.3 in the FOS Manual by extrapolating the GO program 5320 fluxes to longer
     wavelength (the spectra are essentially flat in F_Lambda). In one orbit we
     would expect to achieve a S/N of about 16 (per diode) at the short wavelength
     end of the spectrum of Q0107-025A (the fainter of the pair), inadequate for our
     purposes. In two orbits we will realize a S/N greater than 25 (per diode) at
     all wavelengths in the range 2200 - 3100 Angstrom. Therefore, we will use two
     orbits on each of the two quasars Q0107-025A,B for these data. We are very
     concerned about the accuracy of the wavelength calibration since it limits the
     accuracy of measurements of velocity differences between the three lines of
     sight. We therefore specify that a wavelength calibration exposure be taken
     upon each visit to a target and after a grating change. Furthermore, we request
     that the same guide star be used for both of the G270H observations.
     Spectroscopic observations covering the range from 3150 to 5500 Angstrom at a
     resolution of 1 Angstrom have been collected at the Multiple Mirror Telescope.
     These will overlap the G270H spectra of Q0107-025 A&B at their blue ends and
     extend to longward of the Mg II Lambda2798 emission line, thereby completing
     the coverage from shortward of Lyman Alpha emission to longward of Mg II.
     Coupled with the G270H spectra, these should allow us to identify any metal-
     line absorption systems which could have members which are mis-identified as
     Lyman Alpha forest lines. More importantly, the G270H data will allow us to
     identify absorption lines in the Lyman alpha emission line, which could be
     effected by the ionizing flux from the quasars (the proximity effect).

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


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

     The success of this proposal relies on whether the absorption features in one
     quasar can be unambiguously identified as common (or not) to those in the other
     quasar in the pair. This demands accurate zero-point calibration of the
     wavelength scale. According to Papers I and II of the HST Quasar Absorption
     Line Key Project, the rms scatter in the zero point is about 0.5 Angstrom (60-
     80 km/sec) in the G190H and G270H gratings. The offsets can be determined from
     the Galactic absorption lines, however in calibrating the G190H spectra only
     the AlII 1670 line is suitable and is not always well detected. Therefore, one
     wavelength calibration frame following an exposure of LBQS 0107-0232 with the
     G190H is requested. We will not need a calibration frame for every exposure
     because the relative zero-point shifts between exposures of a given quasar can
     be calculated by cross-correlating the individual exposures of the same quasar.
     Note that the GO 5320 observations achieved an uncertainty in the difference in
     wavelengths between the members of a common pair of about 40 km/sec because the
     observations of the two quasars used the same guide star, thereby minimizing
     the uncertainty in the relative positioning of the two quasars in the
     spectrograph aperture. We request that the same procedure be used for the G270H
     observations of Q0107-025 A,B, i.e. the same guide stars should be used for
     both observations.

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

------------------------------------------------------------------------------------

                                                6100(  7) - 04/09/96 10:55  - [  3]

  Data Distribution

  Media:           8MM
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:        UPS
  Email:                                                              ,
------------------------------------------------------------------------------------

                                                6100(  7) - 04/09/96 10:55  - [  4]

TARGET LIST    a) Fixed Targets
------------------------------------------------------------------------------------------------------------------------------------
Tar|   Target   |         Target        |            Target              |Coord   | Radial |             Flux data
No |    Name    |       Description     |           Position             |Eqnx    |  Vel.  |
------------------------------------------------------------------------------------------------------------------------------------
1   Q0107-025A   Galaxy, Lyman Alpha     RA = 01H 10M 13.16S +/- 1S, DEC  J2000    Z=0.956  V = 18.2
                 Cloud                   = -02D 19' 54.2" +/- 1", PLATE-
                                         ID = 00WM
    Comments: COMPONENT A OF QUASAR PAIR Q0107-025A,B

   Epoch of Position    RA proper motion (seconds of time/yr)    DEC Proper Motion (arcsec/yr)    Annual Parallax (arcsec)
   1982.886             0.0                                      0.0                              0.0

2   Q0107-025B   Galaxy, Lyman Alpha     RA = 01H 10M 16.28S +/- 1S, DEC  J2000    Z=0.952  V = 17.4
                 Cloud                   = -02D 18' 52.4" +/- 1", PLATE-
                                         ID = 00WM
    Comments: COMPONENT B OF QUASAR PAIR Q0107-025A,B

   Epoch of Position    RA proper motion (seconds of time/yr)    DEC Proper Motion (arcsec/yr)    Annual Parallax (arcsec)
   1982.886             0.0                                      0.0                              0.0

3   Q0107-0232   Galaxy, Lyman Alpha     RA = 01H 10M 14.47S +/- 1S, DEC  J2000    Z=0.728  V = 18.5
                 Cloud                   = -02D 16' 58.9" +/- 1"

   Epoch of Position    RA proper motion (seconds of time/yr)    DEC Proper Motion (arcsec/yr)    Annual Parallax (arcsec)
   1982.886             0.0                                      0.0                              0.0

                                                6100(  7) - 04/09/96 10:55  - [  5]

Visit: 01
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: USE SAME GUIDE STARS FOR TARGETS 1 AND 2 AND FOR ALL EXPOSURES IN THIS
                          VISIT


Exposures
------------------------------------------------------------------------------------------------------------------------------------
Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|   Optional    |Num|  Time |               Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|  Parameters   |Exp|       |             Requirements
------------------------------------------------------------------------------------------------------------------------------------
1        Q0107-025A  FOS/RD ACQ/BIN 4.3     MIRROR                           1   62.6S   ONBOARD ACQ FOR 2-5
                            ARY
------------------------------------------------------------------------------------------------------------------------------------
2        Q0107-025A  FOS/RD ACCUM   1.0     G270H    2223-                   1   26M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
3        Q0107-025A  FOS/RD ACCUM   1.0     G270H    2223-                   1   40M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
4        Q0107-025A  FOS/RD ACCUM   1.0     G270H    2223-                   1   40M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
5        Q0107-025A  FOS/RD ACCUM   1.0     G270H    2223-                   1   40M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
6        Q0107-025B  FOS/RD ACQ/BIN 4.3     MIRROR                           1   32.7S   ONBOARD ACQ FOR 7-9
                            ARY
   Comments:  USE SAME GUIDE STARS AS FOR TARGET 1
------------------------------------------------------------------------------------------------------------------------------------
7        Q0107-025B  FOS/RD ACCUM   1.0     G270H    2223-                   1   28M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
8        Q0107-025B  FOS/RD ACCUM   1.0     G270H    2223-                   1   40M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
9        Q0107-025B  FOS/RD ACCUM   1.0     G270H    2223-                   1   40M
                                                     3278
------------------------------------------------------------------------------------------------------------------------------------
                                                6100(  7) - 04/09/96 10:55  - [  6]

Visit: 02
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: USE SAME GUIDE STARS FOR ALL EXPOSURES IN THIS VISIT; KEEP TELESCOPE
                          POSITION AND ORIENTATION THE SAME FOR ALL EXPOSURES IN THIS VISIT


Exposures
------------------------------------------------------------------------------------------------------------------------------------
Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|   Optional    |Num|  Time |               Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|  Parameters   |Exp|       |             Requirements
------------------------------------------------------------------------------------------------------------------------------------
10       Q0107-0232  FOS/RD ACQ/BIN 4.3     MIRROR                           1   100.6S  ONBOARD ACQ FOR 11,13,15,17,19,21,23,25
                            ARY
------------------------------------------------------------------------------------------------------------------------------------
11       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   24M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
12       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 11
------------------------------------------------------------------------------------------------------------------------------------
13       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
14       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 13
------------------------------------------------------------------------------------------------------------------------------------
15       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
16       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 15
------------------------------------------------------------------------------------------------------------------------------------
17       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
18       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 17
------------------------------------------------------------------------------------------------------------------------------------
19       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
20       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 19
------------------------------------------------------------------------------------------------------------------------------------
21       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
22       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 21
------------------------------------------------------------------------------------------------------------------------------------
23       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
24       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 23
------------------------------------------------------------------------------------------------------------------------------------
25       Q0107-0232  FOS/RD ACCUM   1.0     G190H    1590-                   1   37M
                                                     2312
------------------------------------------------------------------------------------------------------------------------------------
26       Q0107-0232  WFPC2  IMAGE   WFALL   F606W            CR-SPLIT=NO     1   15M     PAR WITH 25
------------------------------------------------------------------------------------------------------------------------------------
                                                6100(  7) - 04/09/96 10:55  - [  7]

Exposures
------------------------------------------------------------------------------------------------------------------------------------
Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|   Optional    |Num|  Time |               Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|  Parameters   |Exp|       |             Requirements
------------------------------------------------------------------------------------------------------------------------------------
27       WAVE        FOS/RD ACCUM   1.0     G190H    1590-                   1   DEF
                                                     2312
   Comments:  DO NOT CHANGE GRATING POSITION BETWEEN
              EXPOSURES
------------------------------------------------------------------------------------------------------------------------------------
                                                6100(  7) - 04/09/96 10:55  - [  8]

            Summary Form for Proposal  6100

  Item                         Used in this proposal
------------------------------------------------------------------------------------------------------------------------------------
  Configurations               FOS/RD WFPC2
------------------------------------------------------------------------------------------------------------------------------------
  Opmodes                      ACQ/BINARY ACCUM IMAGE
------------------------------------------------------------------------------------------------------------------------------------
  Optional Parameters          CR-SPLIT=NO
------------------------------------------------------------------------------------------------------------------------------------
  Proposal Category            GO
------------------------------------------------------------------------------------------------------------------------------------
  Scientific Category          Quasars
------------------------------------------------------------------------------------------------------------------------------------
  Special Requirements         ONBOARD ACQ FOR 2-5 ONBOARD ACQ FOR 7-9 ONBOARD ACQ FOR 11,13,15,17,19,21,23,25 PAR WITH 11 PAR
                               WITH 13 PAR WITH 15 PAR WITH 17 PAR WITH 19 PAR WITH 21 PAR WITH 23 PAR WITH 25
------------------------------------------------------------------------------------------------------------------------------------
  Spectral Elements            MIRROR G270H G190H F606W
------------------------------------------------------------------------------------------------------------------------------------
  Target Names                 Q0107-025A Q0107-025B Q0107-0232 WAVE
------------------------------------------------------------------------------------------------------------------------------------