<=== observer ===> "EGRUEN",\ "Gruen, E.",\ "",\ "Max-Planck-Institut fuer Kernphysik",\ "Saupfercheckweg 1",\ "103980",\ "D-69029",\ "Heidelberg",\ "Germany",\ "49 6221 516478",\ "49 6221 516324",\ "GRUEN@KOVA.MPI-HD.MPG.DE" <=== proposal ===> "COMETS3",1,1,\ {"abundances","comets","dust properties"},\ {"Leinert, Ch.", "Campins, H.", "Crovisier, J.", "Cruikshank, D.",\ "Encrenaz, T.", "Hanner, M.S.", "Knacke, R.", "Kraetschmer, W.", "Lamy, P.",\ "Lemke, D.", "Solc, M.", "Sykes, M.", "Vanysek, V."} <=== title ===> Comet observations with ISOPHOT: Study of bare nuclei, onset of activity, composition of comets and dust production Part 3 <=== abstract ===> SCIENTIFIC ABSTRACT Comets comprise the most primitive material in the solar system. Observations of their composition are diagnostic of the environment during their formation. Phenomena to be studied are bare cometary nuclei and onset of activity at large heliocentric distances and gas and dust emissions in the inner solar system. Objectives of observations of gas and dust are to characterize the physical parameters of the dust (total production, sizes and surface properties) and to analyze the chemical composition of both volatile and refractory constituents with special emphasis on organic compounds. The first priority target, P/Kopff, is most productive among the here proposed comets: not only in dust, but also in gas production (OH up to 5x10^28). Also, a cometary trail of this comet was observed by IRAS. Results from this observational programme have to be compared with the results from the programme "Properties of Solar System Dust" and other CP-comet observations by CAM, SWS and LWS. OBSERVATION SUMMARY Observations of active comets (P/Kopff and P/Churyumov-Gerasimenko or P/Wild 2) should be made through 4 apertures (13.8 to 120 arcsec at three wavelengths between 12.8 and 25 microns) centered on maximum brightness and through 9 filters (3.6 to 160 microns) to obtain thermal energy spectrum of the dust emission. Spectra in the 2-12 micron range will be obtained with PHT-S, in order to determine the strength and shape of features due to organic grains, silicate grains and various molecular species (H2CO, CO, CO2, CH-X, etc.). Observations of cometary nuclei and onset of activity (Chiron and P/Schwassmann-Wachmann 1) should be made in several sets of flux measurements from 25 to 160 microns with PHT-P and PHT-C. Observations through 3 different apertures (52 to 99 arcsec) with the 60 micron filter may allow separation of a dust coma from the nucleus. LINKED OBSERVATIONS: Active comets have high proper motion. They are tracked in the solar system objects mode. No ephemeris are given here. The astrometric observation of the target objects shortly before launch and during the ISO operation should be used for ephemeris improvement. Background is determined by a subsequent (a few days later) staring observation at the mid-term position of the previous observation ("shadow" object). Targets for observations of bare nuclei are in the outer solar system and hence have slow proper motion (< 0.1'/h). They are observed as solar system objects with staring mode. In order to determine the background, the method of "shadow" object is also used. FIXED TIME OBSERVATIONS: The active comet observations are time-critical (within a few days) because of the time-variable activity. It is planned to specify the accurate observation time after the exact ephemeris are known and an analysis of the background has been made. CONCATENATION: Each comet observation starts with a peaking-up of the tracked comet. For time-economy this is done only once per observation which includes several filters-, apertures- and one spectrometer-observation. In addition the 3.6 micron observation has to be concatenated with the PHT-S observation in order to provide absolute calibration of the spectra. <=== scientific_justification ===> DETAILED OBSERVATION INFORMATION The estimation of the infrared flux of comets is a most difficult task. Data is only available for relatively bright comets. Therefore, the assumptions for brightness calculations are based on comparison of various activity parameters of comets determined mostly from observations in the visual and near infrared spectral range. The best candidate, chosen as the first priority target, comet P/Kopff, according the photometric visual data has about 0.03 of the dust production of P/Halley. Thus, no more than 100 to 200 kg/sec can be expected. Comparable with comet Kopff are for instance P/Wild 2 (also in our target list). Other periodic comets observable in the proposed period of ISO observation are less active in the dust production. The expected infrared flux in continuum has been estimated with an assuption that a dust coma with radius of 10000 km and with "grey" optical thickness tau, radiates as "grey" body with albedo 0.2. Thus the flux of the coma at heliocetric and geocetric distances r and D is proportional to Planck function B(T,r,D) x tau. The optical thickness for given coma radius is a function of dust particles effective cross-section and their density, dust production and the dust velocity. For micron size patricles with density 1000 kg/m^3 and velocity about 0.3 km/sec is tau about 10^-6 to 10^-5 for the dust production between 10 to 100 kg/sec. The temperature of black body at r = D = 1 AU is assumed to be 330 K (the dust particles are somewhat superheated). The calculted coma flux in the case P/Kopff (r = 2 AU, D = 1.6 AU) at 25 microns wavelength is 3 to 30 Jy. The flux from nuclei is computed for spherical body with the albedo 0.05. Nucleus radius has been estimated from the minimal observed brigthness taken from The Comet Light Curve Atlas (Kamel 1992). Almost all nuclei radii are in range 2 to 3 km with exception of Chiron (radius 150 km) and of comet P/Schwassmann-Wachmann 1 (20 km). The fluxes of nuclei are at 25 microns about 10 mJy with exception of Chiron and P/S-W-1 (650 mJy, and 80 mJy, respectively). Visibility for ISO observation of P/Kopff, P/S-W-1, were provided by Dr. Salama. For other comets the visibility plots (computed for 93/94 launch !) were used. It must be noted, that actualized visibility plots were not available at the time of prepration of this proposal. Therefore, more information is vital for more precise determination of the observing period for the individual targets and should be distributed as soon as possible. Comet P/Honda-Mrkos-Pajdusakova, which will be bright early 1996, must be deleted from the observation programme. The daily motion of this comet is greatly over the limit 2'/day. Also comets P/Churyomov-Gerasimenko, and P/Wild 2 are about at this daily motion limit, but still in the range of acceptability. The integration times for various modes of observations and instruments were silmulated with the AOT simulator programme. After many tests and variations of imput parameters, the targets were divided in 3 categories. Relatively bright (more than 1 Jy at 25 microns), medium bright (more than 0.5 Jy) and fainter comets than 500 mJy. For each group of comets the integration times are estimated, so that at 25 microns the S/N should be about 100, for bright targets, 20 to 60 for medium bright and about 10 to 5 for faint targets. Time distribution for autumn launch targets: Team top 40% second 30% last 30% PHT : 0 0 5582 total : 0 0 5582 Time distribution for spring launch targets: Team top 40% second 30% last 30% PHT : 0 0 5582 total : 0 0 5582 <=== autumn_launch_targets ===> 1, "PHT05", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 1344, 2 2, "PHT05", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 418, 3 3, "PHT05", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 420, 4 4, "PHT25", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 190, 5 5, "PHT04", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 609, 0 6, "PHT05", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 1344, 7 7, "PHT05", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 418, 8 8, "PHT05", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 420, 9 9, "PHT25", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 190, 10 10, "PHT04", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 609, 0 <=== spring_launch_targets ===> 1, "PHT05", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 1344, 2 2, "PHT05", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 418, 3 3, "PHT05", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 420, 4 4, "PHT25", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 190, 5 5, "PHT04", 3.0, "Y", "P/Schwassmann-W. 1 220001", 0., 0., 2000, 0., 0., 609, 0 6, "PHT05", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 1344, 7 7, "PHT05", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 418, 8 8, "PHT05", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 420, 9 9, "PHT25", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 190, 10 10, "PHT04", 3.0, "N", "P/Schwassmann-W. 1 sha 220001", 0., 0., 2000, 0., 0., 609, 0