5834( 3) - 11/13/95 15:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5834 Version: 3 Check-in Date: ********** 1.Proposal Title: Distant Comet Nucleus Sizes ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Solar System GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Karen J. Meech Institute for Astronomy CoI: Olivier Hainaut Institute for Astronomy (as of 10-94) N ------------------------------------------------------------------------------------ 6. Abstract A subset of well-observed dynamically new comets will be between heliocentric distances of 19 to 28 AU during cycle 5 where it should be possible for the first time to detect their nuclei. These comets are part of a long-term ground-based program to search for physical and chemical differences between the comets entering the inner Solar System for the first time and those which have been thermally processed (the periodic comets). The gradual disappearance of their comae has been monitored for several years from the ground, but it has been impossible to observe the nuclei because of the presence of comae. The nucleus properties of these comets are not only essential to thermal sublimation models for the light-curve behavior, but also extremely important to models of the outer Solar System formation, in particular to the mass distribution in the nebula and the sizes of the protoplanetary bodies at large distances. Cycle 5 will be the only opportunity to obtain physical information about these nuclei before they become definitively too faint to be observed. The WFPC2 will be used to detect the nuclei to a limiting magnitude of R = 28. Non-detections are very improbable; however, the corresponding constraints (2.5-5.5 km) would be extremely strong, and equally important to the models. Small nucleus sizes, combined with thermal sublimation models, will rule out the hypothesis that distant, unusually active comets must be large, rather that they must have a greater abundance of highly volatile species. ------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 2] Observations Description ------------------------ Imaging of 2 of the 9 most distant comets in the program (ranging between heliocentric distances r = 18.7-26.4 AU) will be done through the F675W filter (R-band) on the WFC to get the highest S/N possible. Estimates for the nucleus sizes, hence V-band brightnesses for the targets have been obtained either from ground-based non-detection limits, or from detections when coma was present at r = 8-20AU. The brightnesses which range from 23.7-27.2 are bright limits. For limiting detections to 28th mag (at S/N = 5), very tight physical constraints may be placed on the nucleus sizes, ranging from RN = 2.5-4.8 km at the beginning of cycle 5 (3.0-5.5 km at the end of cycle 5). Using the WFPC2 Instrument Handbook, we calculate that this will require a total integration time of aroung 13,000 sec per comet nucleus (depending on the ecliptic latitude of each object). In addition, these exposure times will allow the detection (S/N = 3) of any residual comae to a limit of 24.7 mag arcsec^-2 in R. Because of the undersampling of the PSF in the wide field mode, and the need to go very faint, the telescope must be dithered between each exposure in order to avoid confusion between cosmic ray hits and hot pixels. This will add 1-2 min overhead per exposure. Exposure times will range from 6-8 minutes each, with 5 min overhead per pair in the CR-split mode. Optimal packing into orbits yields 7 orbits per object/visit. The wide field mode is preferred over the PC mode for greater coverage for astrometry, for greater ability to detect the low- surface-brightness comae, and to achieve the faintest limits on point sources. Real Time Justification ----------------------- None These comets are part of a database of objects which have been observed extensively from the ground during the past 8 years to follow the changes in the comae as a function of heliocentric distance. These observations will place final limits on the nucleus sizes which will constrain the models for the cometary activity. This program has been supported with approximately 10 nights on the CTIO 4m telescope, 20 nights on the CTIO 1.5m, 0.9m and Schmidt telescopes, 15 nights on the ESO NTT, 6 nights on the KPNO 4m and 2.1m telescopes, 3 nights on the Canada-France-Hawaii Telescope and 94 nights on the University of Hawaii 2.2m telescope. Related to this program, the co-I has been given 6 nights at ESO 3.6m to study the physical nature of Kuiper Belt objects. Owing to the faintness of the comets, we require low-sky conditions and are requesting that the observations be made when the zodiacal light contribution is minimum (although we are not using the formal "low-sky" option for scheduling as this shortens the time available per orbit. Further, we have also determined the periods of visibility when the comet observations will not be hindered by the presence of relatively "bright" field stars (v = 19). Calibration Justification ------------------------- None Additional Comments ------------------- None ------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 01 | TARGET NAME: COMET-SHOEMAKER-1984K1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET SHOEMAKER 84f-85XII ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=COMET , Q = 2.6993596 , E = | 0.9988181 , I = 116.84228 , O = | 49.71711 , W = 235.48967 , T = 06-SEP- | 85:08:03:14 , EPOCH = 29-DEC-95 , | EQUINOX = J2000 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | WND FROM 15-SEP-95 TO 11-OCT-95 WND FROM | 29-NOV-95 TO 27-DEC-95 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 28.33 +/- 0.0 V-R = 0.33 +/- 0.01 | R=28.0 is desired detection limit. | Comet might be as bright as V=26. | Ephemeris file spike_5834_1.trh was | constructed by A. Lubenow from | orbital elements provided by the PI. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 02 | TARGET NAME: COMET-SHOEMAKER-1987H1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET SHOEMAKER 87o-85XIV ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE = COMET , Q = 5.4787825 , E = | 1.0007255 , I = 132.55742 , O = | 268.21641 , W = 16.96193 , T = 14-NOV- | 86:00:13:07 , EPOCH = 29-DEC-95 , | EQUINOX = J2000 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | WND FROM 15-NOV-95 TO 30-DEC-95 WND FROM | 18-FEB-96 TO 21-MAR-96 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 28.33 +/- 0.0 V-R = 0.33 +/- 0.01 | R=28.0 is desired detection limit. | Comet might be as bright as V=26. | Ephemeris file spike_5834_2.trh was | constructed by A. Lubenow from | orbital elements provided by the PI. | ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Windows selected (file spike_5834_1.wnd made by A. Lubenow) so that field stars do not interfere with observation. These windows should be OR'ed. Added visit req. dates listed above (in target windows) constrain the S10 intensity of the zodiacal light to be below 120 and are the preferred dates. Either period is fine, but they should be ANDed with the window spike files. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET- WFPC2 IMAGE WF3 F675W 1 800S SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 2 COMET- WFPC2 IMAGE WF3 F675W 1 800S POS TARG 0.5, 0.5 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 3 COMET- WFPC2 IMAGE WF3 F675W 1 1000S SAME POS AS 2 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 4 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 2 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5 COMET- WFPC2 IMAGE WF3 F675W 1 350S SAME POS AS 2 END ORBIT SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 6 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 1.0, 1.0 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 7 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 6 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 8 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 6 END ORBIT SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 9 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 1.5, 1.5 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 10 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 9 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 11 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 9 END ORBIT SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 12 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 2.0, 2.0 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 13 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 12 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 14 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 12 END ORBIT SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 15 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 2.5, 2.5 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 16 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 15 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 17 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 15 END ORBIT SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 18 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 3.0, 3.0 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 19 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 18 SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 20 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 18 END ORBIT SHOEMAKER- 1984K1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 8] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Windows selected (file spike_5834_2.wnd made by A. Lubenow) so that field stars do not interfere with observation. These windows should be OR'ed. Added visit req. dates listed above (in target windows) constrain the S10 intensity of the zodiacal light to be at its minimum and are the preferred dates. Either period is fine, but they should be ANDed with the window spike files. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 21 COMET- WFPC2 IMAGE WF3 F675W 1 800S SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 22 COMET- WFPC2 IMAGE WF3 F675W 1 800S POS TARG 0.5, 0.5 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 23 COMET- WFPC2 IMAGE WF3 F675W 1 1000S SAME POS AS 22 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 24 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 22 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 25 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 22 END ORBIT SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 26 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 1.0, 1.0 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 27 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 26 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 28 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 26 END ORBIT SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 9] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 29 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 1.5, 1.5 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 30 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 29 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 31 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 29 END ORBIT SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 32 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 2.0, 2.0 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 33 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 32 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 34 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 32 END ORBIT SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 35 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 2.5, 2.5 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 36 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 35 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 37 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 35 END ORBIT SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 38 COMET- WFPC2 IMAGE WF3 F675W 1 1000S POS TARG 3.0, 3.0 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 10] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 39 COMET- WFPC2 IMAGE WF3 F675W 1 500S SAME POS AS 38 SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 40 COMET- WFPC2 IMAGE WF3 F675W 1 400S SAME POS AS 38 END ORBIT SHOEMAKER- 1987H1 Comments: None ------------------------------------------------------------------------------------------------------------------------------------ 5834( 3) - 11/13/95 15:47 - [ 11] Summary Form for Proposal 5834 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Solar System ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG 0.5, 0.5 SAME POS AS 2 SAME POS AS 2 END ORBIT POS TARG 1.0, 1.0 SAME POS AS 6 SAME POS AS 6 END ORBIT POS TARG 1.5, 1.5 SAME POS AS 9 SAME POS AS 9 END ORBIT POS TARG 2.0, 2.0 SAME POS AS 12 SAME POS AS 12 END ORBIT POS TARG 2.5, 2.5 SAME POS AS 15 SAME POS AS 15 END ORBIT POS TARG 3.0, 3.0 SAME POS AS 18 SAME POS AS 18 END ORBIT SAME POS AS 22 SAME POS AS 22 END ORBIT SAME POS AS 26 SAME POS AS 26 END ORBIT SAME POS AS 29 SAME POS AS 29 END ORBIT SAME POS AS 32 SAME POS AS 32 END ORBIT SAME POS AS 35 SAME POS AS 35 END ORBIT SAME POS AS 38 SAME POS AS 38 END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F675W ------------------------------------------------------------------------------------------------------------------------------------ Target Names COMET-SHOEMAKER-1984K1 COMET-SHOEMAKER-1987H1 ------------------------------------------------------------------------------------------------------------------------------------