6621( 7) - 07/08/96 11:12 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6621 Version: 7 Check-in Date: 08-Jul-1996 11:09:10 1.Proposal Title: 55P/Tempel-Tuttle and the Leonid Meteors ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Michael F. A'Hearn University of Maryland CoI: Martin Beech University of Western Ontario N CoI: Peter Brown University of Western Ontario N CoI: Philippe L. Lamy Laboratoire d'Astronomie Spatiale N CoI: Harold A. Weaver Applied Research Corp. N CoI: Donald K. Yeomans Jet Propulsion Laboratory N ------------------------------------------------------------------------------------ 6. Abstract Comet 55P/Tempel-Tuttle, the parent of the Leonid meteor stream, provides a very rare opportunity to study the relationship of cometary ejection processes to a meteor stream. The comet comes to perihelion (P = 33 yr) in cycle 7 with an unusually close approach to Earth (Delta = 0.35 AU in January 1998). There is a reasonable probability that this will lead to a major meteor storm in the Leonid shower and modeling of the shower to predict the storm requires knowledge of the comet's nuclear properties. There is no reliable estimate of even the size of the nucleus. We propose to observe the comet at very large heliocentric distance in cycle 6 to obtain an estimate of the size and rotational period, the factors that have the largest effect on the predictions of the meteor stream. During cycle 7 we propose to observe the nucleus and circum-nuclear region at closest approach to Earth as part of Lamy's ongoing program of observing comets within 0.7 AU of Earth. This will enable us to estimate the active fraction of the nucleus, obtain the color of the nucleus for comparison with the colors of other Near-Earth objects, and to determine the relationship of the nuclear outgassing to the nuclear rotation. This will also enable us to directly compare the two approaches for determining nuclear sizes - observation at small geocentric distance with explicit removal of the coma and observation at large heliocentric distance assuming negligible coma, while simultaneously learning about the possible activity at large heliocentric distance. ------------------------------------------------------------------------------------ 6621( 7) - 07/08/96 11:12 - [ 2] Observations Description ------------------------ We propose to image the comet for one orbit early in cycle 6 (August 1996, r_H ~ 6 AU) with F606W and CR-SPLIT to obtain with maximum sensitivity a preliminary estimate of the size and to determine the apparent magnitude with sufficient precision to optimize subsequent observations. The position and rate (of order 15 arcsec per hour) will be calculated by co-I Yeomans and these will be accurate enough that interactive acquistion is not required. The observation should be obtained before the comet is lost in the solar avoidance zone in late 1996 in order to ensure that there is minimal coma. During this period, the comet's heliocentric motion is negligible but Earth is moving away from the comet so the comet is getting somewhat fainter. Thus the observation should be made as soon in Cycle 6 as possible. The tactics for the single observation in cycle 6 are straightforward. Co-I Yeomans will provide the best estimate of the orbital elements shortly before the observation is to be carried out. This can be done before the SMS is sent to GSFC, i.e. several weeks before the observation. The orbital elements included in the Target List were obtained from the IAU Central Bureau for Astronomical Telegrams (i.e. from Brian Marsden) on 15 Feb 1996. We will point blind so as to put the nucleus near the center of the PC chip, actual position is not important except that it should avoid any known bad rows or columns. We will track on the comet's rate for the orbit and make two exposures through F606W for the full orbit. This should result in two exposures of approximately 800 seconds each. The actual exposure times should be adjusted to fill the orbit and they need not be of equal duration, although they should probably not differ by as much as a factor 2. Additional observations have been approved by the Cycle 6 TAC for Cycle 7 but these must be reviewed by the Cycle 7 TAC and will not be described until the time of phase 2 submission for Cycle 7. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6621( 7) - 07/08/96 11:12 - [ 3] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 01 | TARGET NAME: C-TEMPEL-TUTTLE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET 55P/Tempel-Tuttle ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=COMET,Q=0.9751862,E=0.9055453,I=162 | .47504,O=235.22530,W=172.50522,T = 27- | Feb- | 1998:11:05:28.0,EQUINOX=J2000,EPOCH=27- | Apr-1996 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 26 | B-V = 0.7 | | Ephemeris Uncertainty: 600 S | ------------------------------------------------------------------------------------------------------------------------------------ 6621( 7) - 07/08/96 11:12 - [ 4] Visit: 10 Visit Requirements: BEFORE 30-SEP-96 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 C-TEMPEL-TU WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 1300 S REQ EPHEM CORR TTLE ------------------------------------------------------------------------------------------------------------------------------------ 12 C-TEMPEL-TU WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 700 S END ORBIT TTLE ------------------------------------------------------------------------------------------------------------------------------------ 6621( 7) - 07/08/96 11:12 - [ 5] Summary Form for Proposal 6621 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 30-SEP-96 REQ EPHEM CORR END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names C-TEMPEL-TUTTLE ------------------------------------------------------------------------------------------------------------------------------------