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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Observations Description
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(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
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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
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Additional Comments
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Data Distribution
Media: 8MM
Blocking Factor: 10
Ship To: PI_Address
Ship Via: UPS
Email: ,
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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.
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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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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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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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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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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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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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