! $Id: 23,v 5.1 1994/07/26 20:52:38 pepsa Exp $ coverpage: title_1: HETEROGENEITY OF DUST AND GAS EMISSIONS ON A COMETARY NUCLEUS sci_cat: SOLAR SYSTEM sci_subcat: COMET proposal_for: GO pi_title: DR. pi_fname: JOE pi_lname: ASTRONOMER pi_inst: STSCI pi_country: USA pi_phone: (301) 338-4700 keywords_1: COMET hours_pri: 0.45 num_pri: 1 wf_pc: Y time_crit: Y ! end of coverpage abstract: line_1: We propose to observe with the planetary camera (PC) of HST line_2: the short-period comet P/Faye at its closest approach to the line_3: Earth (0.6 AU). The high spatial resolution (40 km) over a line_4: large field will allow to image the dust and gas jets "down line_5: to the nucleus" and to follow their temporal evolution over line_6: a period of approximately 10 days. Combined with line_7: ground-based observations as a model of the dust/gas line_8: expansion, it will be possible to map the discrete sources line_9: of emission on the nucleus and study its rotational line_10: properties. HST will extend the present insight we have of line_11: comet Halley to another comet, an important step in the line_12: current exploration and understanding of primitive bodies in line_13: the solar system. ! ! end of abstract general_form_proposers: lname: Astronomer fname: Joe title: DR. inst: SPACE TELESCOPE SCIENCE INSTITUTE country: USA lname: UPPERCASE fname: JOSEPH title: DR. inst: SPACE TELESCOPE SCIENCE INSTITUTE country: USA ! ! end of general_form_proposers block general_form_text: question: 3 section: 1 line_1: Observation of a short-period comet of more than one line_2: apparition (to limit acquisition problems) coming line_3: sufficiently close to the Sun (q<1.6 AU) for activity and to line_4: the Earth (delta<0.6 AU) for resolution, having an elongation line_5: larger than 50 deg and apparent motion less than 0.21 arcsec line_6: per sec to satisfy HST conditions. An excellent opportunity line_7: exists in the proposed HST period: comet P/Faye 1984XI. The line_8: observational program consists in imaging the coma with PC line_9: and two filters: line_10: -F702W for the dust (this broad spectral region ensures a line_11: high signal for the continuum with only slight contamination line_12: by gas line_13: -F517N for C2. line_15: The PC/F702W observations are repeated 7 times at selected line_16: time intervals (96, 48, 24, 12, 6, 3 hours) to cover a broad line_17: range of possible rotational period of the nucleus. The line_18: PC/F517N observation is performed only one time, just line_19: following the seventh PC/F702W observation. ! question: 4 section: 1 line_1: HST high spatial resolution (40 km for comet P/Faye with PC) line_2: makes it possible to resolve jets in the immediate vicinity line_3: of the nucleus where rotational and radiation pressure line_4: effects are negligible. Therefore, confusion of jets is line_5: minimal and individual jets can be traced back to the line_6: nucleus. No restriction on observing time (due to elevation line_7: of target above local horizon and weather conditions) allow line_8: us to optimize the observation sequence for best sampling line_9: strategy. Finally, minimun sky back- ground (only zodiacal line_10: light and star background) improves detectability of low line_11: contrast features. Low level and time stability of background line_12: improve signal-to-noise ratio in the outer part of the coma line_13: considerably. Near nucleus studies of comets have been line_14: performed by ground- based observations using both line_15: photographic and CCD techniques. However, due to limited line_16: resolution and other problems, the results are not always line_17: firmly conclusive (c.f. Sekanina Z. and Larson S.M., 1986, line_18: Astron. J. 92, 462 and Nature 321, 357; Sekanina Z., 1987, line_19: Nature 325, 326).Even space probe observations which are line_20: not limited by resolution (Keller H.U. and Thomas N., 1988, line_21: Nature 333, 146) in conjunction with ground-based line_22: observations did not provide a unique solution due to line_23: insufficient observational coverage. ! question: 5 section: 1 line_1: One comet will be observed 7 times at specified time line_2: intervals with PC. The exposure time for the dust coma is line_3: calculated from a light curve based on total visual estimates line_4: by several observers after correcting for instrumental line_5: effects and normalizing at 1 AU. The observations during the line_6: last two apparitions (1976/77 and 1984) provide a very smooth line_7: flat curve. Then the total magnitude is predicted for the line_8: oct/nov 1991 period. A 1/r radial variation of the coma line_9: brightness is assumed and converted to absolute unit to match line_10: the predicted magnitude. A check is made with a calibrated line_11: image of the coma of P/Halley obtained with GIOTTO/HMC at a line_12: resolution similar to HST, adopting a realistic scaling of line_13: the dust production rate. Typical exposure times are 55s for line_14: F702W and 1400s for F517N (we consider that the brightness in line_15: the inner coma is still due mostly to the dust, C2 adding up line_16: further out). The brightness of the nucleus is based on line_17: Roemer et al.'s observations from the 1961 and 1969 line_18: apparitions after proper corrections. The derived absolute line_19: magnitude of 14.4 at zero phase angle implies a nucleus line_20: diameter of 8.6 km assuming a geometric albedo of 0.04. The line_21: nucleus is therefore a bright object for PC: the typical line_22: exposure time for F702W is 20s. In order to prevent signal line_23: chain saturation, the exposure times must be limited to 26s ! question: 5 section: 2 line_1: for F702W and 350s for F517N and repeated as necessary. The line_2: final strategy for the exposure times takes this into account line_3: as well as the possibility of a brighter or fainter object line_4: during the 1991 apparition. ! question: 6 section: 1 line_1: The observations are time critical from two aspects: line_2: they should take place during a period of about 15 days when line_3: the comet is closest to the Earth (maximum resolution); line_4: they should be sequenced to properly sample a wide range of line_5: possible rotational periods (time intervals are 96, 48, 24, line_6: 12, 6 and 3 hours). ! question: 7 section: 1 line_1: The plans for data reduction and analysis include the steps: line_2: 1)apply standard HST calibrations to generate corrected line_3: images in absolute units of brightness line_4: 2)check history of HST guiding of the comet line_5: 3)perform image processing enhancement to reveal the jets line_6: 4)study the temporal evolution of the jets and compare with line_7: ground-based images and a model of dust/gas expansion from line_8: the nucleus; compare the origin of dust and gas jets line_9: 5)map the active zones on the nucleus and study the line_10: rotational period and the orientation of the spin axis line_11: vector; failure to find a "simple" rotational solution would line_12: probably indicate a complex motion (e.g., rotation and line_13: precession). ! question: 8 section: 1 line_1: Early observations of comet P/Faye in 1990 and 1991 will be line_2: performed for astrometric positions. An updated ephemeris (or line_3: orbital elements) based on these observations will be sent to line_4: ST-SCI at least 2 months before the HST observations. This line_5: will give an accuracy of 1 to 3 arcsec appropriate for blind line_6: pointing. High-resolution ground-based images of the comet line_7: will be obtained over a period overlapping the HST line_8: observations in order to complement them and put them in a line_9: broader interval of cometary activity. ! question: 9 section: 1 line_1: A description of any previous HST data goes here. ! question: 10 section: 1 line_1: All participating investigators have extensive in-house image line_2: and data analysis capabilities. ! !end of general form text general_form_address: lname: ASTRONOMER fname: JOE title: DR. category: PI inst: STSCI addr_1: 3700 SAN MARTIN DRIVE city: BALTIMORE state: MD zip: 21218 country: USA phone: (301) 338-4700 ! ! end of general_form_address records ! No fixed target records found solar_system_targets: targnum: 1 name_1: COMET1 descr_1: COMET FAYE 1984XI lev1_1: TYPE = COMET, Q = 1.5933855, lev1_2: E = 0.5781845, I = 9.09095, lev1_3: O = 198.88006, W = 203.95376, lev1_4: T = 16-NOV-1991:04:38:54, lev1_5: EQUINOX = B1950, lev1_6: EPOCH = 31-OCT-1991, lev1_7: A1 = 0.45E-8, A2 = -0.49E-10, A3 = 0.0, lev1_8: ACQ = 3.0 wind_1: WND1 = 26-OCT-1991 TO 10-NOV-1991 comment_1: FLUXVAL_1 IS THE PREDICTED VISUAL comment_2: MAGNITUDE OF THE COMET NUCLEUS, comment_3: FLUXVAL_2 IS THE PREDICTED TOTAL comment_4: MAGNITUDE OF THE EXTENDED COMA comment_5: IN A CIRCULAR APERTURE OF 60" DIAM comment_6: DURING THE SPECIFIED WINDOW. comment_7: A RADIAL BRIGHTNESS VARIATION 1/R comment_8: IS ASSUMED IN THE COMA. fluxnum_1: 1 fluxval_1: V = 14.5 +/- 0.3 fluxnum_2: 2 fluxval_2: V = 9.2 +/- 0.5 fluxnum_3: 3 fluxval_3: SIZE = 60 ! ! end of solar system targets ! No generic target records found exposure_logsheet: linenum: 1.000 targname: COMET1 config: WFPC2 opmode: IMAGE aperture: WFALL sp_element: F555W num_exp: 1 time_per_exp: 26S s_to_n: 10 s_to_n_time: 4S fluxnum_1: 1 priority: 1 req_1: PERIOD 3D +/- 1D; req_2: ZERO-PHASE 23-JUN-1994; req_3: PHASE 0.3 +/- 0.1; req_4: CYCLE 3; comment_1: test of phase ! ! end of exposure logsheet ! No scan data records found