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 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Solar System GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Amanda S. Bosh Lowell Observatory CoI: Prof. James L. Elliot Massachusetts Institute of Technology N ------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------ 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 ------------------- ------------------------------------------------------------------------------------ 5825( 13) - 07/24/95 17:37 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5825( 13) - 07/24/95 17:37 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: TRITON ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE TRITON ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = NEPTUNE | STD = TRITON | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ 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. | ------------------------------------------------------------------------------------------------------------------------------------ 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: 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 ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 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). ------------------------------------------------------------------------------------------------------------------------------------ 30 TR148 FOS/RD ACQ 4.3 MIRROR 1 4S end orbit Comments: FOS ACQIMAGE OF FIELD OF VIEW ------------------------------------------------------------------------------------------------------------------------------------ 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). ------------------------------------------------------------------------------------------------------------------------------------ 5825( 13) - 07/24/95 17:37 - [ 7] Visit: 03 Visit Requirements: PCS MODE Fine On Hold Comments: Additional Comments: STAR-SPECTRA. Fine lock if possible; if not, coarse track is acceptable. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 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). ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 5825( 13) - 07/24/95 17:37 - [ 8] Visit: 04 Visit Requirements: PCS MODE Fine On Hold Comments: Additional Comments: BACK-SCANS. Fine lock if possible; if not, coarse track is acceptable. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 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). ------------------------------------------------------------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------------------------------------------------------------ 130 TRITON FOS/RD ACCUM 1.0 PRISM 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 5825( 13) - 07/24/95 17:37 - [ 9] Scan Paramters Form ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ 5825( 13) - 07/24/95 17:37 - [ 10] Summary Form for Proposal 5825 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACQ RAPID ACCUM ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Solar System ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR PRISM G650L ------------------------------------------------------------------------------------------------------------------------------------ Target Names TR148 TRITON ------------------------------------------------------------------------------------------------------------------------------------