5825( 13) - 07/24/95 17:37  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      5825
                                                       Version: 13
                                                       Check-in Date: **********

1.Proposal Title:
The Structure of Triton's Lower Atmosphere
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2. Scientific Category   3. Proposal For  4. Cycle
Solar System                GO               5
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5. Investigators
                                                                                     Contact?
    PI: Dr. Amanda S. Bosh                Lowell Observatory
   CoI: Prof. James L. Elliot             Massachusetts Institute of Technology         N

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6. Abstract

With the occultation of Tr148 (McDonald and Elliot, submitted) in August 1995, we
have the opportunity to distinguish between two competing models for Triton's lower
atmosphere (Tyler  et al. 1989; Strobel and Summers 1994). Additionally, we will be
acquiring data on an atmosphere that has been predicted to be changing quite rapidly
(Hansen and Paige 1992; Spencer and Moore 1992).  High quality occultation data sets
are crucial for testing these theories and establishing the changing state of
Triton's atmosphere.
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                                                5825( 13) - 07/24/95 17:37  - [  2]

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

     (1) Within 48 hours before or after the occultation observation, obtain
     spectrum of star with G650L/RD and PRISM (to be used during the occultation
     observation). This determines the spectrum of the star for later use in data
     analysis.  (2) At least one orbit before the start of the occultation
     observations, acquire an ``offset- acquisition" star:  one that is within 1.5
     arcmin of the star to be occulted but further from Triton and Neptune than the
     target star.  This offset acquisition technique has been successfully
     implemented before (GTO/HSP1081) to avoid problems with target acquisition in
     the bright scattered light background near Triton and Neptune.  A suitable
     offset acquisition candidate will be chosen after ground-based astrometric
     frames are obtained and analyzed.  (3) Blind offset to Tr148.  Prior astrometry
     will have determined the relative positions of these two stars to better than
     0.1 arcsec, assuring accurate placement of the target star in the science
     aperture.  Obtain confirmatory ACQ exposure to verify placement of Tr148 in
     science aperture.  (4) Track on Tr148 while Triton's atmosphere passes in front
     of it (1 orbit). The one atmosphere observation will last about 15 minutes.  We
     will be using only 374 diodes in the PRISM to increase our temporal resolution.
     (5) Within 48 hours before or after the occultation observation, obtain spectra
     of Triton. This observation establishes the spectra of Triton separately,
     without any stellar component.  This will be used in later analyses. Cycle 5:
     Primary Orbits:  4 Exposures:  13

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

     Time-critical:  stellar occultations by solar system bodies are inherently time
     -critical observations.  They occur at a particular time, determined by the
     planetary ephemeris and star position; therefore, no other dates/times are
     acceptable. We will provide ground-based astrometry prior to the event. With
     this astrometry we will locate an offset acquisition target and determine its
     position relative to Tr148 with an accuracy of better than 0.1 arcsec. We will
     also use this astrometry to refine the predicted impact time. If astrometry
     indicates that the HST will not be in the occultation shadow, we will not
     observe this event, but will choose another event instead.  We also plan to
     apply for observing time at ground-based stations to acquire the necessary
     multiple chords across Triton.  The S/N and resolution from such a site will be
     inferior to that from HST, but will be sufficient to constrain the impact
     parameter.

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


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

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                                                5825( 13) - 07/24/95 17:37  - [  3]

  Data Distribution

  Media:           8MM
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:        UPS
  Email:                                                              ,
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                                                5825( 13) - 07/24/95 17:37  - [  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   TR148        STAR                    RA=19H 41M 00.376S +/- 0.01S,    J2000             V=12.9 +/- 0.1
                                         DEC=-20D 51' 41.20" +/- 0.1"                       B-V=0.7 +/- 0.1
                                                                                            V-R=0.4 +/- 0.1
                                                                                            V-I=0.8 +/- 0.1
    Comments: Star position will be updated >=2 months before
              observation is performed.  If occultation shadow zone
              will not be in HST observability, we will not observe
              this target. Contact:  Amanda S. Bosh, Lowell
              Observatory.

                                                5825( 13) - 07/24/95 17:37  - [  5]

TARGET LIST    b)Solar System Targets
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TARGET NUMBER:    3    |    TARGET NAME: TRITON
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TARGET DESCRIPTION: SATELLITE TRITON
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           TARGET POSITION LEVEL 1                            |            TARGET POSITION LEVEL 2
                                                              |
    STD = NEPTUNE                                             |    STD = TRITON
                                                              |
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           TARGET POSITION LEVEL 3                            |            WINDOWS
                                                              |
                                                              |
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DATA                                                          |            COMMENTS
                                                              |
V = 13.52 +/- 0.05                                            |    Triton along the apparent path of
B-V=0.72 +/- 0.05                                             |    the occulted star. Scan starting
                                                              |    position parameters will be updated
                                                              |    after final astrometry and revised
                                                              |    occultation prediction.
                                                              |
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                                                5825( 13) - 07/24/95 17:37  - [  6]

Visit: 01
     Visit Requirements:  PCS MODE Fine GROUP 1-4 WITHIN 48H BETWEEN 14-AUG-95:04:00 AND 14-AUG-
                          95:05:40
     On Hold Comments:    <none>
     Additional Comments: OCC-ACQ.  Fine lock if possible; if not, coarse track is acceptable.  The
                          BETWEEN time is computed to be the beginning of the target acq sequence.
                          The actual event is observed in exp 40, and occurs at 7:48+/-2m, and is of
                          aprox 200 sec durration.   The data-taking exposure time should cover the
                          time between 7:40 and 7:55.


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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10       TR148       FOS/RD ACQ/BIN 4.3     MIRROR           bright=168000   1   1S      ONBOARD ACQ FOR 20
                            ARY                              faint=420
   Comments:  Time_per_exposure will change after offset
              acquisition star is chosen.
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20       TR148       FOS/RD ACQ/PEA 0.3     PRISM            SCAN-STEP-X =   1   1S      ONBOARD ACQ FOR 30-40
                            K                                0.11, SCAN-STEP
                                                             -Y = 0.11,
                                                             SEARCH-SIZE-X =
                                                             5, SEARCH-SIZE-
   Comments:  Time_per_exposure will change after offset     Y = 5
              acquisition star is chosen.  Using Binary &
              Peak acquisitions to achieve 0.08" pointing
              accuracy (sequence Z+D2 from CAL/FOS-132).
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30       TR148       FOS/RD ACQ     4.3     MIRROR                           1   4S      end orbit
   Comments:  FOS ACQIMAGE OF FIELD OF VIEW
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40       TR148       FOS/RD RAPID   1.0     PRISM            READ-TIME =     1   900S    EXPAND MIN DUR MAX DUR END ORBIT
                                                             0.231, SUB-STEP
                                                             = 1, COMB = NO,
                                                             STEP-TIME = 0.2
   Comments:  IGNORE SAA.  Can split exposure across SAA.
              Event occurs at 14-AUG-95:07:48 +/- 2M and
              has duration aprox 200 seconds. USE DIODES
              139-512 ONLY I.S. (Dahlem) recomends:   USE
              DIODES 124-497 (partial scattered light
              correction).
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                                                5825( 13) - 07/24/95 17:37  - [  7]

Visit: 03
     Visit Requirements:  PCS MODE Fine
     On Hold Comments:    <none>
     Additional Comments: STAR-SPECTRA.  Fine lock if possible; if not, coarse track is acceptable.


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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50       TR148       FOS/RD ACQ/BIN 4.3     MIRROR           bright=168000   1   1S      ONBOARD ACQ FOR 60
                            ARY                              faint=420
   Comments:  Time_per_exposure may change after photometry
              of star is obtained.  Do not execute within
              +/- 72M of Visit 2.
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60       TR148       FOS/RD ACQ/PEA 0.3     PRISM            SCAN-STEP-X =   1   1S      ONBOARD ACQ FOR 70-90
                            K                                0.17, SCAN-STEP
                                                             -Y = 0.17,
                                                             SEARCH-SIZE-X =
                                                             4, SEARCH-SIZE-
   Comments:  Time_per_exposure may change after photometry  Y = 4
              of star is obtained.  Using Binary & Peak
              acquisitions to achieve 0.12" pointing
              accuracy (sequence Z+E1 from CAL/FOS-132).
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70       TR148       FOS/RD RAPID   1.0     PRISM            READ-TIME =     1   23.1S
                                                             0.231, SUB-STEP
                                                             = 1, COMB = NO,
                                                             STEP-TIME = 0.2
   Comments:  USE DIODES 139-512 ONLY I.S. (Dahlem)
              recomends:   USE DIODES 124-497 (partial
              scattered light correction). Get spectrum of
              occulted star when it is away from
              Triton/Neptune.  Same parameters as
              occultation.
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80       TR148       FOS/RD ACCUM   1.0     PRISM                            1   60S
   Comments:  Get spectrum of occulted star when it is away
              from Triton/Neptune.  Parameters set to
              optimize signal, calibration ability.
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90       TR148       FOS/RD ACCUM   1.0     G650L                            1   60S
   Comments:  Get spectrum of occulted star when it is away
              from Triton/Neptune.  Parameters set to
              optimize signal, calibration ability.
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                                                5825( 13) - 07/24/95 17:37  - [  8]

Visit: 04
     Visit Requirements:  PCS MODE Fine
     On Hold Comments:    <none>
     Additional Comments: BACK-SCANS.  Fine lock if possible; if not, coarse track is acceptable.


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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100      TRITON      FOS/RD ACQ/BIN 4.3     MIRROR                           1   0.93S   ONBOARD ACQ FOR 110
                            ARY
   Comments:  Do not execute within +/- 72M of Visit 2.
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110      TRITON      FOS/RD ACQ/PEA 0.3     PRISM            SCAN-STEP-X =   1   0.94S   ONBOARD ACQ FOR 120-130
                            K                                0.17, SCAN-STEP
                                                             -Y = 0.17,
                                                             SEARCH-SIZE-X =
                                                             4, SEARCH-SIZE-
   Comments:  Using Binary & Peak acquisitions to achieve    Y = 4
              0.12" pointing accuracy (sequence Z+E1 from
              CAL/FOS-132).
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120      TRITON      FOS/RD RAPID   1.0     PRISM            READ-TIME =     1   66.99S  SPATIAL SCAN 1 SINGLE-EXP
                                                             0.231, SUB-STEP
                                                             = 1, COMB = NO,
                                                             STEP-TIME = 0.2
   Comments:  USE DIOES 139-512 ONLY I.S. (Dahlem)
              recomends:   USE DIODES 124-497 (partial
              scattered light correction).  Scan parameters
              and Time_Per_Exposure will change with final
              geometric track prediction.
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130      TRITON      FOS/RD ACCUM   1.0     PRISM                            1   60S
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                                                5825( 13) - 07/24/95 17:37  - [  9]

Scan Paramters Form
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Data ID: 1
Exposure Logsheet lines:
FGS Scan:                        C      Dwell Only: dwell points/line:         0   Seconds per dwell:                    0.00
Scan width (arc-secs):      0.0000      Scan length (arc-secs):           5.0000   Angle between sides (degrees)        90.00
Number of lines:                 1      Scan rate (arc-sec/sec):          0.0750   PA of first scan line (degrees)     79.400
Scan frame (CEL or S/C):       CEL      Length Offset (arc-sec):          2.5000   Width Offset (arc-sec):             0.0000
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                                                5825( 13) - 07/24/95 17:37  - [ 10]

            Summary Form for Proposal  5825

  Item                         Used in this proposal
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  Configurations               FOS/RD
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  Opmodes                      ACQ/BINARY ACQ/PEAK ACQ RAPID ACCUM
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  Optional Parameters          bright=168000 faint=420 SEARCH-SIZE-Y = 5 STEP-TIME = 0.2 SEARCH-SIZE-Y = 4 COMB = NO SEARCH-SIZE-X
                               = 4 SUB-STEP = 1
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  Proposal Category            GO
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  Scientific Category          Solar System
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  Special Requirements         PCS MODE Fine GROUP 1-4 WITHIN 48H BETWEEN 14-AUG-95 04 00 AND 14-AUG-95 05 40 ONBOARD ACQ FOR 20
                               ONBOARD ACQ FOR 30-40 end orbit EXPAND MIN DUR MAX DUR END ORBIT PCS MODE Fine ONBOARD ACQ FOR 60
                               ONBOARD ACQ FOR 70-90 ONBOARD ACQ FOR 110 ONBOARD ACQ FOR 120-130 SPATIAL SCAN 1 SINGLE-EXP
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  Spectral Elements            MIRROR PRISM G650L
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  Target Names                 TR148 TRITON
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