! File: 1137C.PROP ! Database: PEPDB ! Date: 16-FEB-1994:03:08:00 coverpage: title_1: COMPOSITION AND STRUCTURE OF COMETARY COMAE (WF/PC-33): title_2: CYCLE 3 AND FUTURE-CYCLE CONTINUATION sci_cat: SOLAR SYSTEM proposal_for: GTO/WFC targ_of_opp: Y pi_title: PROF. pi_fname: JAMES pi_mi: A. pi_lname: WESTPHAL pi_inst: CALTECH pi_country: USA pi_phone: (818) 356-4900 keywords_1: COMETS, HALLEY'S COMET hours_pri: 7.20 num_pri: 2 time_crit: X pi_position: PROF OF PLANETARY SC ! end of coverpage abstract: line_1: A "target of opportunity" comet will be imaged to resolve the profile shape line_2: and comet coronal properties of this nearby comet. The observations will line_3: be planned to allow the sublimation process to be monitored for comparison line_4: to other comet coronae and with coronal models. ! ! end of abstract general_form_proposers: lname: WESTPHAL fname: JAMES mi: A. inst: CALTECH country: USA ! ! end of general_form_proposers block general_form_text: question: 2 section: 1 line_1: Gas and grains released from the nucleus of a comet flow outward forming the line_2: coma. While near the nucleus, the grains are accelerated by the rapidly line_3: expanding gas, after which they should coast at roughly constant velocity, line_4: except for their interaction with the solar wind. A constant velocity flow of line_5: long-lived grains would result in a coma luminosity profile in which surface line_6: brightness falls inversely with projected radius. However, observations yield line_7: profiles in which brightness typically falls faster than that, implying that line_8: the grains are "fading" as they coast. The observed rate of fading appears line_9: statistically to have an inverse correlation with heliocentric distance, as one line_10: might expect if the sublimation of partly volatile grains were taking place. line_11: The heliocentric distance at which this postulated sublimation cuts off is line_12: difficult to determine from ground-based observation, but it appears to be line_13: somewhere between 6 and 9 AU. line_14: STWF/PC imaging of cometary comae can be helpful in constraining cometary line_15: grain models. Imaging of an unusually nearby comet (as a Target of line_16: Opportunity) to resolve the profile shape near the nucleus so as to probe line_17: the scale of the acceleration domain. WFC exposures with Filter F702W would line_18: yield profiles dominated by the continuum, while similar exposures with line_19: Filter F517N would yield the inner part of the profile of Csub2 (a daughter line_20: product) after suitable continuum subtraction. To aid the latter and to line_21: measure the color of the grains, ! question: 2 section: 2 line_1: exposures with Filters F555W and F439W will also be made in some cases. line_3: In order to probe the domain near the nucleus where grains are undergoing line_4: gas-dynamical acceleration, we need to obtain profile data at a resolution of line_5: 10 km or less. With suitable processing of PC images, that resolution can be line_6: expected out to nearly 0.3 AU. Closer is, of course, better. Statistics line_7: predict (ASTRON. J. 89, 154, 1984) five such comets per decade, but only about line_8: half of those may be favorably situated for ST observation. There is thus a line_9: reasonable chance that a favorable target of opportunity may occur during GTO line_10: time. If it does, we propose to observe it. ! question: 3 section: 1 line_1: COMET X: A comet passing unusually near the earth will be observed line_2: (prefereably more than once) as a target of opportunity with the PC, using the line_3: narrowband Csub2 filter plus three wideband filters. In order to result in line_4: significant new science, this "Comet X" should be observed as close to the line_5: earth as possible: line_6: There is no way of knowing in advance what cycle these Comet X observations ! question: 3 section: 2 line_1: will fall in. ! question: 5 section: 1 line_1: See the scheduling requirements outlines under Item 3 above. ! question: 8 section: 1 line_1: Observations of Comet X may need to be scheduled under the procedures used for line_2: targets of opportunity. ! question: 13 section: 1 line_1: PC frames of an unusually nearby comet will be processed to yield line_2: information about the inner coma where grains are accelerated by expanding line_3: gas. ! !end of general form text general_form_address: lname: GUNN fname: JAMES mi: E. category: CON inst: PRINCETON UNIVERSITY addr_1: ASTROPHYSICAL SCIENCE addr_2: PEYTON HALL city: PRINCETON state: NJ zip: 08540 country: USA phone: (609) 452-3802 ! lname: DANIELSON fname: G. EDWARD category: CON inst: CALTECH addr_1: M/S 170-25 addr_2: DIVISION OF GEOLOGICAL & PLANETARY SCIENCE city: PASADENA state: CA country: USA phone: (818) 356-6861 ! lname: BAUM fname: WILLIAM category: CON inst: LOWELL OBSERVATORY addr_1: PLANETARY RESEARCH LAB addr_2: 1400 WEST MARS HILL ROAD city: FLAGSTAFF state: AZ zip: 86002 country: USA phone: (602) 774-3358 ! lname: WESTPHAL fname: JAMES mi: A. title: PROF. category: PI inst: CALTECH addr_1: M/S 170-25 addr_2: DIVISION OF GEOLOGICAL addr_3: & PLANETARY SCIENCES city: PASADENA state: CA zip: 91125 country: USA phone: (818) 356-4900 ! ! end of general_form_address records ! No fixed target records found ! No solar system records found generic_targets: targnum_1: 1 name_1: COMET-X descr_1: NEAR EARTH COMET criteria_1: AS NEAR EARTH AS ALLOWED BY POINTING CONSTRAINTS. criteria_2: MUST BE LESS THAN 0.3 AU criteria_3: TARGET OF OPPORTUNITY ! ! end of generic targets exposure_logsheet: linenum: 10.000 targname: COMET-X config: PC opmode: IMAGE aperture: PC6 sp_element: F555W num_exp: 1 time_per_exp: 1S priority: 2 param_1: CR-SPLIT=NO,PRE-FLASH=YES req_1: SAME ORIENT FOR 11-17 AS 10; req_2: NON-INT / 10-21; req_3: CYCLE 3 / 10-21 comment_1: CYCLE 3-9 VERSION comment_2: JEG/RML 3/25/92 20:18. ! linenum: 11.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F555W num_exp: ^ time_per_exp: 10S priority: ^ param_1: ^ req_1: GROUP 10-17 NO GAP ! linenum: 12.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F702W num_exp: ^ time_per_exp: 1S priority: ^ param_1: ^ ! linenum: 13.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F702W num_exp: ^ time_per_exp: 10S priority: ^ param_1: ^ ! linenum: 14.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F439W num_exp: ^ time_per_exp: 10S priority: ^ param_1: ^ ! linenum: 15.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F439W num_exp: ^ time_per_exp: 100S priority: ^ param_1: ^ ! linenum: 16.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F517N num_exp: 1 time_per_exp: 10S priority: ^ param_1: ^ ! linenum: 17.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: ^ num_exp: 1 time_per_exp: 100S priority: ^ param_1: ^ ! linenum: 18.000 targname: COMET-X config: PC opmode: IMAGE aperture: PC6 sp_element: F555W num_exp: 1 time_per_exp: 1S priority: 2 param_1: CR-SPLIT=NO,PRE-FLASH=YES req_1: SAME ORIENT FOR 18-21 AS 10; req_2: GROUP 18-21 NO GAP; req_3: AFTER 10 BY 7D +/- 1D; ! linenum: 19.000 targname: COMET-X config: PC opmode: IMAGE aperture: PC6 sp_element: F702W num_exp: 1 time_per_exp: 1S priority: 2 param_1: CR-SPLIT=NO,PRE-FLASH=YES ! linenum: 20.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F439W num_exp: ^ time_per_exp: 10S priority: ^ param_1: ^ ! linenum: 21.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F517N num_exp: ^ time_per_exp: 10S priority: ^ param_1: ^ ! ! end of exposure logsheet ! No scan data records found