6634( 19) - 07/25/96 11:29 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6634 Version: 19 Check-in Date: 25-Jul-1996 11:26:46 1.Proposal Title: The nucleus of comet 46P/Wirtanen ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: PHILIPPE LAMY LABORATOIRE D'ASTRONOMIE SPATIALE CoI: Michael F. A'HEARN University of Maryland N CoI: Eberhard GR"U N Max-Planck-Institut fur Kernphysik N CoI: Laurent JORDA Observatoire de Meudon N CoI: Uwe KELLER Max-Planck-Institut fur Aeronomie N CoI: Zdenek SEKANINA Jet Propulsion Laboratory N CoI: Imre T'O TH Konkoly Observatory N CoI: Harold A. WEAVER Applied Research Corporation N ------------------------------------------------------------------------------------ 6. Abstract We propose Planetary Camera observations of comet 46P/Wirtanen, which is the target of the approved ROSETTA rendezvous mission, the third cornerstone of the ESA Horizon 2000 program. Except for a few photographic "nuclear" magnitudes which suggest a radius of 1.6 km (assuming an albedo of 0.04), little is known about the properties of its nucleus and it is of utmost importance to attempt to characterize it to the fullest possible extent. Unfortunately, comet 46P/Wirtanen will not come close to the Earth during the next decade so that the only possible approach to studying the nucleus consists in observing it at large heliocentric distances when the activity is very low. The high spatial resolution offered by the Planetary Camera ( 100 km for 2 pixels) and its high sensitivity will allow us to detect any faint coma and substract it with minimal assumptions. We propose to measure the V and R magnitudes of the nucleus in order to derive its color, and we plan to study its rotational properties by measuring its projected cross sections as a function of time. We have an approved program to observe the nucleus of comet 46P/Wirtanen with ISOCAM in the thermal infrared so that we shall derive its albedo and in turn its size with very minimal asumptions by combining HST and ISO observations. Should structures be detected in the faint coma, we shall map the sources of dust on the nucleus. The determination of these basic properties is essential for the preparation of the ROSETTA mission. ------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 2] Observations Description ------------------------ The proposed sequence of observations results from a compromise between the scientific requirements of an adequate temporal coverage, and the necessarily limited time available on the HST. We request 8 near-contiguous orbits for comet 46P/Wirtanen (the exact scheduling will be worked out and optimized with the STScI staff as done for our observations of comet Borrelly). This will give a time coverage of approximately 12 to 18 hours (depending upon whether orbits are contiguous or nearly contiguous), well adapted to the presently observed mean value of 10 hours for the rotation period of short-period comets. Each orbit includes three F675W images and two F555W images. We have treated each orbit as a separate visit, even though it may be possible to support several orbits with the same pair of guide stars. Each visit consists of one orbit with the following exposure sequence in each orbit: F675W, two 300 sec images F555W, two 300 sec images F675W, one 200 sec image The above sequence will be used a total of 8 times = 8 orbits. We want all of the orbits to be completed within ~10 HST orbits, which means that a 1 or 2 orbit gap within the sequence is acceptable. We enforce this timing by using the visit special requirement: SEQ WITHIN 960M. This program should be executed sometime between 31-JUL-96 and 20- AUG-96. We have used the REQ EPHEM CORR on all exps in order to leave open the possibility of uplinking an ephemeris correction in case it's needed. Please note that we intend to update the comet's orbital elements during the last available opportunity (i.e., prior to final SMS generation). Real Time Justification ----------------------- As it is entirely excluded to perform simultaneous observations with HST and ISO because of very different operational constraints, the best approach consists in optimizing the two programs separately. Subsequent matching of the visible and infrared light curves during the analysis should not introduce any major uncertainty in the determination of the properties of the nucleus (our proposed plans call for just a few weeks between the two campaigns). For the HST observations, the optimization led to choosing a window of 20 days centered on 10 August 1996. In addition, the 8 requested orbits must be taken over a period of about 10 HST orbits (i.e., there can be a couple orbit gap). We have an approved program to observe cometary nuclei with ISOCAM and comet 46P/Wirtanen is number 1 on our target list (the referees recommended that this comet "must be done"). Thanks to the high sensitivity and good spatial resolution of ISOCAM, it will be possible to detect the thermal emission (8 -15 microns) of the nuclei above the contribution of the coma. Due to different constraints, it is entirely excluded to consider simultaneous HST-ISO observations. However, with only a few weeks between the ISOCAM observations and the HST observations, it will be possible to determine the relative phases of the two datasets and thus to compare the visible (HST) and the infrared (ISO) light curves so as to derive the albedo of the nucleus following a method extensively used on asteroids and on a few cometary nuclei ( e.g., P/Arend- Rigaux). Ground-based CCD images will be secured before the HST observations in order to refine the ephemerides of the comet. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: *Dr. Harold Weaver*48 Bellchase Court*Pikesville, MD 21208 Ship Via: UPS Email: weaver@ari.net , ------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: WIRTANEN ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET 46P/WIRTANEN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=COMET,Q=1.06397530,E=0.65677159,I=1 | 1.722697,O=82.208922,W=356.321837,T = 14 | -Mar- | 1997:03:22:18.0,EQUINOX=J2000,EPOCH=18- | Aug-1996,A1=3.20814603395E-09,A2=- | 1.75045585208E-09 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 20.1+/-0.5 | New elements from Hal Weaver; B-V = 0.65 | 7/23/96. | Ephemeris Uncertainty: 6000 KM | Acquisition Uncertainty: 5 " | ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 5] Visit: 01 Visit Requirements: SEQ 1-8 WITHIN 10 ORBITS BETWEEN 10-AUG-96 AND 02-SEP-96 On Hold Comments: Additional Comments: Each visit should take 1 orbit. We want to complete the entire program within 10 orbits, if possible. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 11-12 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 12 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 6] Visit: 02 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 21 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 21-22 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 22 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 7] Visit: 03 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 31 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 31-32 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 32 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 8] Visit: 04 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 41 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 41-42 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 42 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 9] Visit: 05 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 51 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 51-52 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 52 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 10] Visit: 06 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 61 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 61-62 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 62 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 11] Visit: 07 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 71 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 71-72 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 72 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 12] Visit: 08 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 81 WIRTANEN WFPC2 IMAGE PC1 F675W CR-SPLIT = NO 2 600 S REQ EPHEM CORR WIRT1 SEQ 81-82 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 82 WIRTANEN WFPC2 IMAGE PC1 F555W CR-SPLIT = NO 1 500 S REQ EPHEM CORR WIRT1 ------------------------------------------------------------------------------------------------------------------------------------ 6634( 19) - 07/25/96 11:29 - [ 13] Summary Form for Proposal 6634 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT = NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 1-8 WITHIN 10 ORBITS BETWEEN 10-AUG-96 AND 02-SEP-96 REQ EPHEM CORR WIRT1 SEQ 11-12 NON-INT REQ EPHEM CORR WIRT1 REQ EPHEM CORR WIRT1 SEQ 21-22 NON-INT REQ EPHEM CORR WIRT1 SEQ 31-32 NON-INT REQ EPHEM CORR WIRT1 SEQ 41-42 NON-INT REQ EPHEM CORR WIRT1 SEQ 51-52 NON-INT REQ EPHEM CORR WIRT1 SEQ 61-62 NON-INT REQ EPHEM CORR WIRT1 SEQ 71-72 NON-INT REQ EPHEM CORR WIRT1 SEQ 81-82 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F675W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names WIRTANEN ------------------------------------------------------------------------------------------------------------------------------------