7489( 17) - 10/01/97 11:11 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7489 Version: 17 Check-in Date: 01-Oct-1997 11:10:52 1.Proposal Title: Triton's Atmospheric Structure: Problems with Present Models ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JAMES L. ELLIOT MIT CoI: Catherine B. Olkin Lowell Observatory N CoI: Otto G. Franz Lowell Observatory N CoI: Mary A. Agner Massachusetts Institute of Technology N ------------------------------------------------------------------------------------ 6. Abstract Models of Triton's atmosphere based on Voyager data and known physical processes predict a positive temperature gradient above Triton's troposphere. However, Earth- based stellar occultation probes in 1995 (Olkin et al. 1997) do not confirm this model prediction, but find the thermal gradient to be consistent with an isothermal or adiabatic profile. Data of higher signal-to-noise are needed to establish the thermal structure of Triton's middle atmosphere more accurately, as a guide to fundamental revisions of the models. Occultations of two bright stars may be visible with HST occur in 1997. We propose to observe these events (should they prove visible with HST), using the FGS both as a high-speed photometer and in its normal role for occultation astrometry before and after each event. The HST is needed because (i) it may be the only large telescope in the occultation path and would yield thermal profiles much more accurate than any obtained previously, (ii) the FGS is the best way to examine the candidates for multiplicity prior to the events, and (iii) HST astrometry (much more accurate than ground-based astrometry) will be essential if only one chord can be observed for these events. ------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 2] Observations Description ------------------------ All observations are carried out with FGS-3 and filter F583W. Orbit #1 (Tr176): In this orbit we accomplish three goals: (i) Determine whether Tr176 is a double with one set of TRANS mode exposures; (ii) determine the position of Tr176 relative to a local network with POS mode exposures of it and some nearby stars; (iii) calibrate the photometry of the TRANS mode (to be used for the occultation in Orbit #2) by taking long scans. Results from (i) may affect the final occultation prediction and the deployment of ground stations, so the results are needed as early in Cycle 7 (or before) as practical. Orbit #2 (Tr176): In this orbit we we will be carrying out astrometry of Triton and Tr176 as Triton moves closer to Tr176 and hopefully occults it. The astrometry and photometry will be obtained from the same set of TRANS exposures. The second TRANS exposure is begun after Triton closes within 2 arcsec of Tr176 (so that centering on the common center of light should be good). The time when the second exposure starts will have to be adjusted later, when the occultation prediction has been refined and we know the phase of the HST orbit (two weeks prior to the observations). The orbit has been selected to include our best estimate of the midtime of the occultation. Orbit #3 (Tr180): In this orbit we accomplish three goals: (i) Determine whether Tr180 is a double with one set of TRANS mode exposures; (ii) determine the position of Tr180 relative to a local network with POS mode exposures of it and some nearby stars; (iii) calibrate the photometry of the TRANS mode (to be used for the occultation in Orbit #4) by taking long scans. Orbit #4 (Tr180): In this orbit we we will be carrying out astrometry of Triton and Tr180 as Triton moves closer to Tr180 and hopefully occults it. The astrometry and photometry will be obtained from the same set of TRANS exposures. Only a single TRANS exposure is needed because the relative velocity of Triton and Tr180 is slow enough that the objects should always be within 2 arcsec of each other for the entire orbit. The orbit has been selected to include our best estimate of the midtime of the occultation. 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 and times are acceptable. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Otto Franz*1400 W. Mars Hill Rd.*Flagstaff, AZ 86001 Ship Via: Email: ogf@lowell.edu ------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 TR176 STAR RA=20H 2M 51.240S +/- 0.02S, J2000 V = 13.88+/-0.2 DEC=-20D 0' 57.22" +/- 0.1" 2 TR176-1-REF CALIBRATION, RA= 300.73375D +/- 0.00014D, J2000 V = 14.90+/-0.2 ASTROMETRIC DEC= -20.004400D +/- 0.00014D 3 TR176-2-REF CALIBRATION, RA= 300.70248D +/- 0.00014D, J2000 V = 12.33+/-0.2 ASTROMETRIC DEC= -20.02849D +/- 0.00014D 4 TR176-3-REF CALIBRATION, RA= 300.66547D +/- 0.00014D, J2000 V = 14.02+/-0.2 ASTROMETRIC DEC= -20.01533D +/- 0.00014D 5 TR180 STAR RA= 19H 57M 32.204S +/- 0.02S, J2000 V = 11.29+/-0.2 DEC= -20D 18' 18.75" +/- 0.1" 6 TR180-1-REF CALIBRATION, RA= 299.48689D +/- 0.00014D, J2000 V = 14.89+/-0.2 ASTROMETRIC DEC= -20.27601D +/- 0.00014D 7 TR180-2-REF CALIBRATION, RA= 299.42515D +/- 0.00014D, J2000 V = 14.45+/-0.2 ASTROMETRIC DEC= -20.29942D +/- 0.00014D 8 TR180-3-REF CALIBRATION, RA= 299.28774D +/- 0.00014D, J2000 V = 14.98+/-0.2 ASTROMETRIC DEC= -20.31563D +/- 0.00014D 9 TR180-T STAR RA= 19H 57M 32.933S +/- 1.0", J2000 V = 13.0+/-0.5 DEC= -20D 17' 7.14" +/- 1.0" 7489( 17) - 10/01/97 11:11 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENTation 256D TO 258D SCHEDulability 70% BETWEEN 1-JUL-97 AND 15-JUL-97 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TR176 FGS TRANS 3 F583W SCANS=21,STEP-SIZE=1 1 450 S POS TARG 0.0, 0.0;SEQ 10-80 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 20 TR176 FGS TRANS 3 F583W SCANS=18,STEP-SIZE=2 1 668 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 30 TR176 FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 35 TR176-2-REF FGS POS 3 F583W 1 10 S MAX DUR 10S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 40 TR176-1-REF FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 60 TR176-3-REF FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 70 TR176-2-REF FGS POS 3 F583W 1 10 S MAX DUR 10S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 80 TR176 FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENTation 256D TO 260D SCHEDulability 70% BETWEEN 18-JUL-97:10:16:00 AND 18-JUL-97:11:46:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TR176 FGS TRANS 3 F583W SCANS=42,STEP-SIZE=2 1 1575 S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENTation 90D TO 91D BETWEEN 11-SEP-97:17:00:00 AND 11-SEP-97:19:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TR180 FGS TRANS 3 F583W SCANS=21,STEP-SIZE=1 1 458 S POS TARG 0.0,0.0; SEQ 10-80 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 30 TR180-T FGS TRANS 3 F583W SCANS=50,STEP-SIZE=2 1 540 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 45 TR180 FGS POS 3 F583W 1 2 S MAX DUR 2S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 50 TR180-1-REF FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 60 TR180-2-REF FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 70 TR180-3-REF FGS POS 3 F583W 1 60 S MAX DUR 60S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 80 TR180 FGS POS 3 F583W 1 2 S MAX DUR 2S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 8] Visit: 04 Visit Priority: Visit Requirements: BETWEEN 4-NOV-97:4:45:00 AND 4-NOV-97:6:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TR180 FGS TRANS 3 F583W SCANS=42,STEP-SIZE=1 1 1050 S POS TARG 0.0, 0.0 SEQ 10-20 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 20 TR180 FGS TRANS 3 F583W SCANS=17,STEP-SIZE=2 1 850 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 7489( 17) - 10/01/97 11:11 - [ 9] Summary Form for Proposal 7489 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TRANS POS ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCANS=21 STEP-SIZE=1 STEP-SIZE=2 SCANS=42 SCANS=50 SCANS=17 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENTation 256D TO 258D SCHEDulability 70% BETWEEN 1-JUL-97 AND 15-JUL-97 POS TARG 0.0, 0.0;SEQ 10-80 NON-INT SAME POS AS 10 MAX DUR 20S; SAME POS AS 10 MAX DUR 10S; SAME POS AS 10 MAX DUR 40S; SAME POS AS 10 ORIENTation 256D TO 260D SCHEDulability 70% BETWEEN 18-JUL-97 10 16 00 AND 18-JUL-97 11 46 00 POS TARG 0.0, 0.0 ORIENTation 90D TO 91D BETWEEN 11-SEP-97 17 00 00 AND 11-SEP-97 19 00 00 POS TARG 0.0,0.0; SEQ 10-80 NON-INT MAX DUR 2S; SAME POS AS 10 MAX DUR 60S; SAME POS AS 10 BETWEEN 4-NOV-97 4 45 00 AND 4-NOV-97 6 00 00 POS TARG 0.0, 0.0 SEQ 10-20 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F583W ------------------------------------------------------------------------------------------------------------------------------------ Target Names TR176 TR176-2-REF TR176-1-REF TR176-3-REF TR180 TR180-T TR180-1-REF TR180-2-REF TR180-3-REF ------------------------------------------------------------------------------------------------------------------------------------