15490( 4) - 08-Feb-2019 20:43:29 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15490 Version: 4 Check-in Time: 08-Feb-2019 20:43:29 STScI Edit Number: 2 Title Titan at Opposite Seasons Using STIS Image Cubes ------------------------------------------------------------------------------------ Type Cycle GO 26 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Erich Karkoschka University of Arizona Y ------------------------------------------------------------------------------------ Abstract This proposal seeks to use STIS with one orbit each in 2017, 2018, and 2019 to map the full disk of Titan at 1024 wavelengths between 530 and 1000 nm and at 0.05 arc-sec sampling in both spatial dimensions. These observations repeat similar STIS observations between 1997 and 2004 in order to create data sets at opposite seasons. The comparison of the old and new data sets will characterize seasonal asymmetries as function of latitude and wavelength. STIS probes many altitude levels from the surface to the stratosphere eight scale heights higher. Radiative transfer models using previous STIS image cubes resulted in a seasonal model of Titan's haze based on the assumption that Titan is symmetric at opposite seasons. This is probably an approximation, and the proposed data are needed to characterize asymmetries. Cassini's mission is too short to observe Titan at opposite seasons. Ground-based adaptive optics systems do not provide a stable point spread function required to create a suitable data cube. HST is the only telescope that can achieve the goal until the next opportunity around 2047. Characterization of seasonal asymmetries provides one of the most sensitive tests for global circulation models. Titan's seasonal cycle is a vibrant current research topic due to 12 years of Cassini data. This proposal will expand STIS data to a range of 22 years. The opportunity is unique, and the required HST time is minimal. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations in Cycle 26 will use one orbit providing a full image cube of Titan. The orbit will be similar to the STIS/CCD orbit of GO 14612 taken in Cycle 24 and GO 15112 taken in Cycle 25. The orbit consists of 15 exposures with the grating G750L for wavelengths 530-1000 nm at 0.5 nm/pixel. Each successive exposure is offset by 0.051 arc-sec perpendicular to the slit orientation from the previous one. The aperture is 52X0.05E1. The saved part of the image is 140 spatial rows and all 1024 spectral columns. This avoids buffer dumps during the observation, but still provides plenty of background sky. Calibration exposures are a CCDFLAT and WAVECAL taken at start of Earth occultation. Acquisition is accomplished with a 1 sec exposure with the MIRROR and a F28X50LP aperture using ACQTYPE=DIFFUSE, CHECKBOX=19, DIFFUSE-CENTER=FLUX-CENTRIOD. The same acquisition found Titan's center to better than 0.05 arc-sec in GO 14612. Exposure times will be the longest possible to fit all Titan exposures into the orbit before occultation starts, about 83 sec each. Signal-to-noise levels will be about 50 per pixel in the red continuum. Titan's apparent diameter varies by 20 percent during each year. To optimize 15490( 4) - 08-Feb-2019 20:43:29 - [ 2] spatial resolution I request observations to be scheduled within about one month of opposition that occurs July 9, 2019 and Jul 20, 2020. This gives phase angles of Titan below 3 degrees , as was the case for previous STIS observations. I request to schedule observations during the optimal phase within Titan's 16-day orbit, which is within about two days of Titan's western elongation, when mostly dark terrain faces Earth, and when a STIS image cube was taken in every of the five years of observations. This request is not critical since other orbital longitudes give only a minor degradation of results. ------------------------------------------------------------------------------------ 15490( 4) - 08-Feb-2019 20:43:29 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: TITAN ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Satellite Titan ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=SATURN STD=TITAN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS SEP OF TITAN RHEA FROM EARTH GT 10" ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 8 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 15490( 4) - 08-Feb-2019 20:43:29 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-PERP-TO-SLIT Pattern_Purpose MOSAIC Number_Of_Points 15 Point_Spacing 0.051 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0.0 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 15490( 4) - 08-Feb-2019 20:43:29 - [ 5] Visit: 01 (Orbit1) Visit Requirements: SCHED 30%; BETWEEN 22-MAY-2019:03 AND 26-MAY-2019:11; BETWEEN 07-JUN-2019:01 AND 11-JUN-2019:09; BETWEEN 22-JUN-2019:20 AND 27-JUN-2019:06; BETWEEN 08-JUL-2019:19 AND 13-JUL-2019:03; BETWEEN 24-JUL-2019:17 AND 29-JUL-2019:01; BETWEEN 09-AUG-2019:14 AND 13-AUG-2019:22; BETWEEN 25-AUG-2019:12 AND 29-AUG-2019:20; BETWEEN 08-JUN-2020:08 AND 12-JUN-2020:16; BETWEEN 24-JUN-2020:06 AND 28-JUN-2020:13; BETWEEN 10-JUL-2020:03 AND 14-JUL-2020:10; BETWEEN 26-JUL-2020:00 AND 30-JUL-2020:08; BETWEEN 10-AUG-2020:21 AND 15-AUG-2020:05; BETWEEN 26-AUG-2020:19 AND 31-AUG-2020:03 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 TITAN STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=DIFFUSE, CHECKBOX=19, 1 1 S (1 S) GS ACQ SCENARIO BASE1BE DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 2 TITAN STIS/CCD ACCUM 52X0.05E1 G750L 7751 CR-SPLIT=NO, GAIN=1, 1 83 S (1245 PATTERN 1 2 SIZEAXIS2=140, WAVECAL=NO S) ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE STIS/CCD ACCUM 52X0.05 G750L 7751 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 CCDFLAT STIS/CCD ACCUM 52X0.05 G750L 7751 2 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ TITAN 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 1 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 2 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 3 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 4 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 5 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 6 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 7 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 8 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 9 none none none 1 N/A 1 15490( 4) - 08-Feb-2019 20:43:29 - [ 6] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 10 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 11 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 12 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 13 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 14 none none none 1 N/A 1 TITAN 2 STIS/CCD ACCUM 52X0.05E G750L 7751 15 none none none 1 N/A 1 WAVE 3 STIS/CCD ACCUM 52X0.05 G750L 7751 none none none none 1 N/A CCDFLAT 4 STIS/CCD ACCUM 52X0.05 G750L 7751 none none 1 none 1 N/A CCDFLAT 4 STIS/CCD ACCUM 52X0.05 G750L 7751 none none 2 none 1 N/A 15490( 4) - 08-Feb-2019 20:43:29 - [ 7] Summary Form for Proposal 15490 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.05, 52X0.05E1, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE, CHECKBOX=19, CR-SPLIT=NO, DIFFUSE-CENTER=FLUX-CENTROID, GAIN=1, SIZEAXIS2=140, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 07-JUN-2019:01 AND 11-JUN-2019:09, BETWEEN 08-JUL-2019:19 AND 13-JUL-2019:03, BETWEEN 08-JUN-2020:08 AND 12-JUN-2020:16, BETWEEN 09-AUG-2019:14 AND 13-AUG-2019:22, BETWEEN 10-AUG-2020:21 AND 15-AUG-2020:05, BETWEEN 10-JUL-2020:03 AND 14-JUL-2020:10, BETWEEN 22-JUN-2019:20 AND 27-JUN-2019:06, BETWEEN 22-MAY-2019:03 AND 26-MAY-2019:11, BETWEEN 24-JUL-2019:17 AND 29-JUL-2019:01, BETWEEN 24-JUN-2020:06 AND 28-JUN-2020:13, BETWEEN 25-AUG-2019:12 AND 29-AUG-2019:20, BETWEEN 26-AUG-2020:19 AND 31-AUG-2020:03, BETWEEN 26-JUL-2020:00 AND 30-JUL-2020:08, GS ACQ SCENARIO BASE1BE, PATTERN 1 2, SCHED 30% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G750L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names CCDFLAT, TITAN, WAVE ------------------------------------------------------------------------------------------------------------------------------------