7439( 17) - 08/14/98 11:35 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7439 Version: 17 Check-in Date: 14-Aug-1998 11:34:27 1.Proposal Title: H-Lyman Alpha Emission from the Upper Atmosphere of Uranus ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Gilda Ballester University of Michigan CoI: John Clarke University of Michigan N CoI: Lotfi Ben Jaffel Institut D'Astrophysique de Paris N CoI: Randy Gladstone Southwest Research Institute N CoI: Steve Miller University College London N CoI: Larry Trafton University of Texas, Austin N CoI: John Trauger Jet Propulsion Laboratory N ------------------------------------------------------------------------------------ 5. Abstract An excess of H-LyAlpha emission from Uranus' sunlit hemisphere has been detected by the IUE satellite since 1982, and some excess was confirmed with the Voyager 2 UVS during the 1986 encounter with Uranus. This emission is additional to the scattered solar and IPM H-LyAlpha, and must be produced by internal processes in the upper atmosphere, such as aurora or other unidentified mechanisms. IUE has observed very large short- and long-term intensity variations that support an auroral source. However, although Voyager detected UV auroral emissions by H2 in the sunlit hemisphere, it did not detect a large H-LyAlpha auroral emission there, making it impossible to provide conclusive evidence that the H-LyAlpha enhancements are due to aurora. Auroral emissions are spatially confined, and resolution of the emission spatial distribution could yield the needed evidence, or could alternatively provide observational clues to other possible causes of these variations. Uranus' intrinsically weak H-LyAlpha emission (~1600 R on average) has not allowed for such an experiment in the past. This program will image Uranus H-LyAlpha emission with STIS, which will have the high sensitivity in the far-UV (STIS/FUV MAMA) required to perform this experiment. The 6 allotted orbits have been re-organized, due to MAMA SAA restrictions, into a set of two orbits that will provide basic spatial information, and a more complete 4-orbit set that will fully map the emissions over two Uranus rotations. ------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 2] Observations Description ------------------------ Each of the 6 allotted orbits will constitute a visit. In each visit, there will be a guide star acquisition, a 1000 sec STIS/FUV MAMA image with the F25SRF2 filter for background information, followed by a 1000 sec (or longer) H -LyAlpha image with the STIS/FUV MAMA clear of filters, 25MAMA. TIMETAG mode will be used to characterize temporal changes in the emissions and background. The BUFFER-TIME for the 25MAMA exposure includes a high 4000 R geocoronal H- LyAlpha background. Taking the 25MAMA image at the end of the HST orbit applies to post-opposition observing, as for 1997, since this minimizes the geocoronal H-LyAlpha contamination. If the observing dates are moved to 1998 pre- opposition (before August 1988), it is then crucial to move the 25MAMA exposure to the beginning of the orbit. The observing should be done close to opposition, within at most about two months. The 6 visits have been re- organized into two sets, in order to accommodate the new STIS MAMA restriction for observing during the five consecutive HST orbits completely free of SAA passage that occur every 24 hours. Set #1: This set consists of a pair of visits to simply image Uranus for basic spatial and temporal information of Uranus in the far-UV. Any separation of the visits will do. But a three-orbit separation within a free-SAA window would be preferred, since this would provide some spatial mapping, increasing the chances of detecting the aurora. Set #2: This set consists of four visits grouped into two pairs that will map Uranus over two planetary rotations, preserving the main purpose of the program to spatially resolve the components of Uranus' H-LyAlpha emission. Fortunately, Uranus' rotational period of 17.24-hr allows for making comparative mapping on two consecutive days. The last rotational phase viewed on day 1 is picked-up on day 2, thus measuring temporal changes, and the mapping is then completed on day 2: day 1 - visit 3/one orbit on, three orbits off, visit 4/one orbit on day 2 - visit 5/one orbit on, three orbits off, visit 6/one orbit on where the rotational phase (cml) would be day 1 - visit 3/cml=xx, three orbits off, visit 4/cml=xx+134 day 2 - visit 5/cml=xx+140, three orbits off, visit 6/cml=xx+274. [The staff at STScI have found possible dates in 1997 with blank or nearly blank fields complying with the bright object MAMA restriction. The dates identified so far are 9/11, 9/27, 9/28, 10/3 and 10/4, and provide two opportunities for consecutive days, 9/27-9/28 and 10/3-10/4.] Another possible combination of days appropriate for comparative mapping consists of scheduling the second pair of visits six days after the beginning of the first pair. This is based on the maximum uncertainty in the separation of the 5-free-SAA-orbit periods of 24 hours being 10 minutes, as we have been informed, which gives an acceptable maximum uncertainty of 21 degrees of Uranus rotation. (The 0.01-hr uncertainty in Uranus' rotational period translates only to 1.2 degrees in six days.) An alternative set #2 is then: day 1 - visit 3/one orbit on, three orbits off, visit 4/one orbit on day 7 - visit 5/one orbit on, three orbits off, visit 6/one orbit on corresponding to day 1 - visit 3/cml=xx, three orbits off, visit 4/cml=xx+134 day 7 - visit 5/cml=xx+126, three orbits off, visit 6/cml=xx+260. [Coincidentally, there are two possible alternative combinations for the identified dates for 1997, namely 9/27-10/3 and 9/28-10/4.] Early information on the possible observing days will be helpful for planning of ground-based near-IR observations of Uranus' H3+ emissions the closest possible in time by co-I's S. Miller and L. Trafton (to help identify the excitation processes of these ionospheric emissions). Real Time Justification ----------------------- The observations should be scheduled close to opposition, within about two months, because it is important to minimize the geocoronal H-LyAlpha background signal to less than about 3 kR, given Uranus' low H-LyAlpha emission (average~1.6 kR). The time restrictions in the observation Set #2 are explained above, and have been devised to attempt to preserve the main science goal of mapping Uranus' far-UV emissions. Calibration Justification ------------------------- Additional Comments ------------------- AUGUST 1998 - REQUESTED MODIFICATION TO EXPOSURES IN VISITS 3-6 TO IMPROVE THE S/N BASED ON RESULTS FROM VISITS 1-2: A new method will be used for Visits 3-6 in order to decrease the large noise contribution from the disk-reflected sunlight above 1500 Ang in the H-LyAlpha signal from Uranus. For Visits 1-2 this was done by subtracting a F25SRF2 image from a 25MAMA image. The data show that improvement is clearly needed. From a talk by B. Woodgate and detailed conversation with C. Bowers (STIS GTOs), a new approach was devised that should be much more favorable approach. We will do slitless spectroscopy with the G140L and 25MAMA aperture, which will disperse out the signal above 1216 Ang, thus yielding a monochromatic image of Uranus at LyAlpha. The signal in nearby wavelengths should be minimal. Since Uranus is only 3.7 arcsec in diameter, the disk-reflected light will be well separated from the Uranus LyAlpha image. (The geocoronal background will still be present.) A POS TARG of +3 arcsec in AXIS1 will move Uranus LyAlpha signal away from the short-wavelength cutoff of the spectrum. POS TARG +2 arcsec in AXIS2 will move Uranus away from the repeller wire shadow. (In this spectroscopy mode, the local bright object limits should be more relaxed than in the imaging mode.) ------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: University of Michigan, AOSS - Space Physics Research Lab, 2455 Hayward St., Ann Arbor, MI 48109-2143 Ship Via: Email: ------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=URANUS | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF URANUS BETWEEN 295 75 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = +5.5+/-0.5 | Observe Uranus close to opposition, B-V = 0.56 | within about two months, to minimize SURF-LINE(1216)=5.0+/-2.5e-14 | geocorona. SIZE=3.6+/-0.2 | | ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 5] Visit: 01 Visit Priority: Visit Requirements: SCHED 100% BETWEEN 28-Jul-1998:03:00:00.0 AND 29-Jul-1998:06:30:00.0 BETWEEN 30-Jul-1998:08:00:00.0 AND 30-Jul-1998:10:30:00.0 On Hold Comments: Additional Comments: BETWEENs represent intersection of times that meet coordinated ground based observing requirements and STIS MAMA bright object protection times. Ground Based Observing---------------------- July 27, 1998 6-11 UT July 29, 1998 6- 11 UT July 30, 1998 6-11 UT July 31, 1998 6-11 UT STIS MAMA Bright Object Protection---------------------------------- July 28, 1998 3 UT - July 29, 1998 7 UT July 30, 1998 8-18 UT Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 URANUS STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=200 1 1000 S SEQ 101-102 NON-INT UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 102 URANUS STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=7000 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SCHED 100% BETWEEN 28-Jul-1998:03:00:00.0 AND 29-Jul-1998:06:30:00.0 BETWEEN 30-Jul-1998:08:00:00.0 AND 30-Jul-1998:10:30:00.0 On Hold Comments: Additional Comments: BETWEENs represent intersection of times that meet coordinated ground based observing requirements and STIS MAMA bright object protection times. Ground Based Observing---------------------- July 27, 1998 6-11 UT July 29, 1998 6- 11 UT July 30, 1998 6-11 UT July 31, 1998 6-11 UT STIS MAMA Bright Object Protection---------------------------------- July 28, 1998 3 UT - July 29, 1998 7 UT July 30, 1998 8-18 UT Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 201 URANUS STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=200 1 1000 S SEQ 201-202 NON-INT UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 202 URANUS STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=7000 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 7] Visit: 03 Visit Priority: Visit Requirements: SCHED 100% On Hold Comments: Additional Comments: The pairs of visits 3 and 4 and visits 5 and 6 are coordinated in time. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 300 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S POS TARG 3.0, 2.0 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 310 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S SAME POS AS 300 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 8] Visit: 04 Visit Priority: Visit Requirements: SCHED 100% AFTER 03 BY 6 H TO 7 H On Hold Comments: Additional Comments: This visit should be separated from visit 3 by three HST orbits, that is, visits 3 and 4 should be made at the beginning and end of a free-SAA period. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 400 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S POS TARG 3.0, 2.0 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 410 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S SAME POS AS 400 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 9] Visit: 05 Visit Priority: Visit Requirements: SCHED 100% AFTER 03 BY 23.5 H TO 25.5 H On Hold Comments: Additional Comments: This visit should be separated from visit 3 by 1 day, BUT NOTE THAT THERE IS AN ALTERNATIVE SEPARATION OF 6 DAYS. See text for more details. The purpose is to view the same rotational phase of Uranus in visits 4 and 5. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 500 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S POS TARG 3.0, 2.0 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 510 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S SAME POS AS 500 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 10] Visit: 06 Visit Priority: Visit Requirements: SCHED 100% AFTER 05 BY 6 H TO 7 H On Hold Comments: Additional Comments: This visit should be separated from visit 5 by three HST orbits, that is, visits 5 and 6 should be made at the beginning and end of a free-SAA period. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 600 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S POS TARG 3.0, 2.0 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 610 URANUS STIS/F TIME-TA 25MAMA G140L 1425 BUFFER-TIME=200 1 1030 S SAME POS AS 600 UV-MAM G A Comments: Expand exposure time if possible. ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 11] Visit: 07 Visit Priority: Visit Requirements: AFTER 05 BY 2.75 Orbits TO 3.25 Orbits On Hold Comments: Additional Comments: This visit is linked to take place in the orbit before visit 6. If there is not a STIS MAMA observation in one of the two orbits before visit 6, then visit 6 cannot schedule. Once the MAMAs are turned on, they must stay on for a minimum of two hours. If the MAMAs are turned on at the beginning of visit 6, they would still have to be on in the orbit after visit 6, but that orbit crosses the SAA, and the MAMAs must not be on in an orbit that crosses the SAA. This visit may not be needed if a MAMA observation from another program is scheduled in one of the two orbits preceeding visit 6. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 700 DARK STIS/F ACCUM DEF DEF 1 1 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7439( 17) - 08/14/98 11:35 - [ 12] Summary Form for Proposal 7439 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 25MAMA F25SRF2 DEF ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TIME-TAG ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=200 BUFFER-TIME=7000 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 100% BETWEEN 28-Jul-1998 03 00 00.0 AND 29-Jul-1998 06 30 00.0 BETWEEN 30-Jul-1998 08 00 00.0 AND 30-Jul-1998 10 30 00.0 SEQ 101-102 NON-INT SEQ 201-202 NON-INT SCHED 100% POS TARG 3.0, 2.0 SAME POS AS 300 SCHED 100% AFTER 03 BY 6 H TO 7 H SAME POS AS 400 SCHED 100% AFTER 03 BY 23.5 H TO 25.5 H SAME POS AS 500 SCHED 100% AFTER 05 BY 6 H TO 7 H SAME POS AS 600 AFTER 05 BY 2.75 Orbits TO 3.25 Orbits ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L DEF ------------------------------------------------------------------------------------------------------------------------------------ Target Names URANUS DARK ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------