9725( 4) - 06/26/03 06:39 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9725 Version: 4 Check-in Date: 26-Jun-2003 06:36:42 1.Proposal Title: The Long-term Observational Record of Uranus' Atmosphere, its Rings, and its Satellites: the WFPC2-ACS Link ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Erich Karkoschka University of Arizona CoI: Dr. Martin G. Tomasko University of Arizona N ------------------------------------------------------------------------------------ 5. Abstract Recording the seasonal change of Uranus is a key to understand seasonal changes in atmospheres due to Uranus' high obliquity. The best record to date comes from WFPC2 imaging of Uranus since 1994. We propose to image Uranus simultaneously with similar filters in WFPC2 and ACS so that this record can be extended with future ACS observations. Without such an observation, the long-term record of WFPC2 images cannot be linked with any future images because of Uranus' steep spectral features. Observations of the Uranian rings over a wide range of sub-solar latitudes allow powerful constraints on physical parameters, such as separation between ring particles. Our proposed observations will provide the necessary link between previous WFPC2 images and future ACS images near the ring-plane-crossing of 2007. The same reasoning applies to images of Uranian satellites, where a consistent record over a wide range of sub-solar latitudes yields information about satellite shape and albedo distribution. Since Cycle 12 is the last Cycle of WFPC2, there will be no other chance for the proposed observations. The investment of only two orbits will significantly enhance the scientific value of the previous 45 WFPC2 orbits on Uranus. Only HST has the spatial resolution and photometric stability for these studies. ------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 2] Observations Description ------------------------ We propose to observe Uranus one orbit with WFPC2 on PC1 and one orbit with ACS on HRC. For WFPC2, we choose ten filters which sample a wide range of wavelengths and methane absorption strengths. Uranus was imaged with one of these filters since 1994, with five filters since 1995, and with the remaining four filters since 1997. For ACS, we choose eleven filters. Nine of them almost match nine of the ten chosen WFPC2 filters in mean wavelength and width. Another ACS filter is also similar to one of the chosen WFPC2 filters. The last ACS filter is a ramp filter to sample specific wavelength regions to probe specific altitude levels in the atmosphere of Uranus. Filters and exposure times for WFPC2: F255W (160 s), F336W (100 s), F439W (35 s), F547M (10 s), FQCH4N-B-619nm (160 s), F658N (100 s), F673N (100 s), F791W (26 and 100 s), FQCH4N-D-893nm (160 s), and F850LP (160 s). Total exposure time is 19 minutes, total exposure overhead is 27 minutes, acquisition is 6 minutes, adding up to 52 minutes, which is about the available time in one orbit. Filters and exposure times for ACS: F250W (160 s), F330W (60 s), F435W (25 s), F550M (30 s), F658N (80 s), F660N (110 s), F775W (60 s), F814W (50 and 200 s), F892N (160 s), F850LP (160 s), and FR914M at 820, 883, and 1008 nm (160 s each). Total exposure time is 26 minutes, total exposure overhead is 20 minutes, and aquisition is 6 minutes, again adding up to 52 minutes. The selected exposure times yield signal-to-noise ratios of 50 or more per pixel except those of filters F255W/F250W and FQCH4N-D/F892N, where the selected exposure times are a compromise between sufficient signal and moderate spacecraft time. Exposures in all filters will not saturate on Uranus except for the second exposures in filters F791W and F814W which will intentionally saturate on Uranus in order to provide superior signals on faint rings and satellites. Since all selected WFPC2 filters have been used before on Uranus, including saturated exposures with F791W, we can predict with high confidence that the selected exposures will yield our intended goals. Considering the scale and sensitivity ratios between WFPC2 and ACS, we predict the same for the ACS exposures. Real Time Justification ----------------------- Timing constraints: The preferred time for the observations is within about two months of opposition, occurring Aug 24, 2003, in order to maximize the apparent size of Uranus, but this preference is not critical. For a better phase angle coverage of this observation in combination with GO 9823, the observations should start between 29.25 and 31.25 August, 2003. Since the rotational period of Uranus at mid-latitudes is 16-17 hours, we request a 15.5-17.5-hour interval between both orbits in order to image the same longitudes and to determine the rotational period of a few expected discrete features. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 3] 9725( 4) - 06/26/03 06:39 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET PLANET URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=URANUS | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | RANGE EARTH URANUS LT 19.5 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 6.0 | Window is within 60 days of | opposition to maximize apparent size | of Uranus. | ------------------------------------------------------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE ORIENT 70.0D TO 86.0 D ORIENT 250.0D TO 266.0 D BETWEEN 29- AUG-2003:06:00:00 AND 31-AUG-2003:06:00:00 On Hold Comments: Additional Comments: The requested timing is a coordinated effort with program GO 9823. This timing will benefit both programs by giving GO 9823 a better phase angle coverage and providing this program a better contect of discrete features of Uranus in combination with observations of GO 9823. The requested timing is not essential for the originally proposed goals. The requested orientation is the best for imaging of the outer satellites. This is not essential if it causes scheduling problems. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 URANUS WFPC2 IMAGE FQCH4P1 F850LP CR-SPLIT=NO,ATD-GAIN=15 1 160 S POS TARG 1, 0 5 ------------------------------------------------------------------------------------------------------------------------------------ 2 URANUS WFPC2 IMAGE FQCH4P1 F255W CR-SPLIT=NO,ATD-GAIN=7 1 160 S SAME POS AS 1 EXPAND MAX 5 DUR 400 S ------------------------------------------------------------------------------------------------------------------------------------ 3 URANUS WFPC2 IMAGE FQCH4P1 F336W CR-SPLIT=NO,ATD-GAIN=15 1 100 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 4 URANUS WFPC2 IMAGE FQCH4P1 F439W CR-SPLIT=NO,ATD-GAIN=15 1 35 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 5 URANUS WFPC2 IMAGE FQCH4P1 F547M CR-SPLIT=NO,ATD-GAIN=15 1 10 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 URANUS WFPC2 IMAGE FQCH4P1 FQCH4N15 6190 CR-SPLIT=NO,ATD-GAIN=15 1 160 S SAME POS AS 1 5 Comments: Spectral element needs to be changed to FQCH4N15 and Wavelength to 6190.0 ------------------------------------------------------------------------------------------------------------------------------------ 7 URANUS WFPC2 IMAGE FQCH4P1 F658N CR-SPLIT=NO,ATD-GAIN=15 1 100 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 URANUS WFPC2 IMAGE FQCH4P1 F673N CR-SPLIT=NO,ATD-GAIN=15 1 100 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 9 URANUS WFPC2 IMAGE FQCH4P1 F791W CR-SPLIT=NO,ATD-GAIN=15 1 26 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 10 URANUS WFPC2 IMAGE FQCH4P1 F791W CR-SPLIT=NO,ATD-GAIN=15 1 100 S SAME POS AS 1 5 ------------------------------------------------------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8930 CR-SPLIT=NO,ATD-GAIN=7 1 160 S SAME POS AS 1 EXPAND MAX 5 DUR 400 S ------------------------------------------------------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 7] Visit: 02 Visit Priority: Visit Requirements: PCS MODE FINE ORIENT 70.0D TO 74.0 D ORIENT 250.0D TO 254.0 D AFTER 01 BY 15.5 H TO 17.5 H On Hold Comments: Additional Comments: This visit is preferentially split by the SAA. It is scheduled one rotation of Uranus after Visit 1 in order to image the same longitudes as Visit 1. The orientation is same as in GO 9823 for a better consistentcy of both data sets. The orientation is not essential for the goals of this program. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 URANUS ACS/HR ACCUM HRC-FIX F775W CR-SPLIT=NO,GAIN=4 1 60 S C ------------------------------------------------------------------------------------------------------------------------------------ 2 URANUS ACS/HR ACCUM HRC-FIX F850LP CR-SPLIT=NO,GAIN=4 1 160 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 3 URANUS ACS/HR ACCUM HRC-FIX F250W CR-SPLIT=NO,GAIN=2 1 160 S SAME POS AS 1 EXPAND MAX C DUR 400 S ------------------------------------------------------------------------------------------------------------------------------------ 4 URANUS ACS/HR ACCUM HRC-FIX F330W CR-SPLIT=NO,GAIN=4 1 60 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 5 URANUS ACS/HR ACCUM HRC-FIX F435W CR-SPLIT=NO,GAIN=4 1 25 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 6 URANUS ACS/HR ACCUM HRC-FIX F550M CR-SPLIT=NO,GAIN=4 1 30 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 7 URANUS ACS/HR ACCUM HRC-FIX F658N CR-SPLIT=NO,GAIN=4 1 80 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 8 URANUS ACS/HR ACCUM HRC-FIX F660N CR-SPLIT=NO,GAIN=4 1 110 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 9 URANUS ACS/HR ACCUM HRC-FIX F814W CR-SPLIT=NO,GAIN=4 1 50 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 10 URANUS ACS/HR ACCUM HRC-FIX F814W CR-SPLIT=NO,GAIN=4 1 200 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 11 URANUS ACS/HR ACCUM HRC-FIX F892N CR-SPLIT=NO,GAIN=2 1 160 S SAME POS AS 1 EXPAND MAX C DUR 400 S ------------------------------------------------------------------------------------------------------------------------------------ 12 URANUS ACS/HR ACCUM HRC-FIX FR914M 8201 CR-SPLIT=NO,GAIN=4 1 160 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 8] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 13 URANUS ACS/HR ACCUM HRC-FIX FR914M 8828 CR-SPLIT=NO,GAIN=4 1 160 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 14 URANUS ACS/HR ACCUM HRC-FIX FR914M 10082 CR-SPLIT=NO,GAIN=4 1 160 S SAME POS AS 1 C ------------------------------------------------------------------------------------------------------------------------------------ 9725( 4) - 06/26/03 06:39 - [ 9] Summary Form for Proposal 9725 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures FQCH4P15 HRC-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=15 ATD-GAIN=7 GAIN=4 GAIN=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ORIENT 70.0D TO 86.0 D ORIENT 250.0D TO 266.0 D BETWEEN 29-AUG-2003 06 00 00 AND 31-AUG-2003 06 00 00 POS TARG 1, 0 SAME POS AS 1 EXPAND MAX DUR 400 S SAME POS AS 1 PCS MODE FINE ORIENT 70.0D TO 74.0 D ORIENT 250.0D TO 254.0 D AFTER 01 BY 15.5 H TO 17.5 H ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F850LP F255W F336W F439W F547M FQCH4N15 F658N F673N F791W FQCH4P15 F775W F250W F330W F435W F550M F660N F814W F892N FR914M ------------------------------------------------------------------------------------------------------------------------------------ Target Names URANUS ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 6190 8930 8201 8828 10082 ------------------------------------------------------------------------------------------------------------------------------------