DPS 42nd Meeting Abs..

formed by the dimerizaon of CH 3 in CH 4 -rich ice by irradiaon of energec protons (Hadson and Moore, 1997). So the existence of ethylene (C 2 H 4 ) is a key todisnguish these hypothesizes. The abundance of C 2 H 4 is clue to contribuon of C 2 H 6 formaon by hydrogen addion reacons.If we can confirm the existence of ethylene, conversion efficiency from acetylene to ethane and ethylene would provide clear view to the hydrogen addionreacons in the early solar nebula or in the pre-solar molecular cloud, because H atom can sck on cold grains under low temperature condions (< ~20 K) only.However, fluorescence excitaon model for ethylene in comets have never been proposed to date. In this work, we will present the fluorescence excitaon modelof ethylene and we will determine C 2 H 4 /H 2 O raos (or its upper limits) for the comets in our database.28.10: Fluorescence Excitaon Model of Ammonia in Low-Acvity CometsAuthor Block: Hideyo Kawakita 1 , H. Kobayashi 11 Kyoto Sangyo University, Japan.Presentaon Time: 10/4/2010 4:18 PM - 4:20 PMLocaon: Exhibit HallAbstract: Ammonia is one of the major N-bearing molecules in cometary ices. Ammonia can be observed by radio (inversion transions), far-infrared (rotaonaltransion) and near-infrared regions (vibraonal transions). In the near-infrared regions, not only ammonia but also water and other organic volales can beobserved as emission lines simultaneously by the high-dispersion spectroscopy. Therefore, it is easy to determine mixing raos of various organic volales fromthe near-infrared high-dispersion spectra of comets.The fluorescence efficiencies for the emission lines are necessary to determine the gas producon rate from the observaons, and there are a few studies for thefluorescence excitaon model of ammonia in comets. The populaon distribuon in the vibraonal ground state is assumed to follow the Boltzmann distribuonin these models. This assumpon is valid in the case of inner coma of producve comets (i.e., frequent inter-molecular collisions can maintain the Boltzmanndistribuon). In the low-acvity comets, however, the inter-molecular collisions are not so frequent enough to maintain the Boltzmann distribuon in thevibraonal ground state. In the case of ammonia, the populaon will favor the metastable states if the collision me scale is much longer than the decay mescales ~10 s for the non-metastable states.We developed the fluorescence excitaon model of cometary ammonia by involving collisional transions explicitly. Transions by the collision with water and bythe collision with electron are taken into account. We will apply our model to the observaons of Jupiter family comets.28.11: OP Rs Of Ammonia versus. 14N/15N Raos In CN In 15 CometsAuthor Block: Yoshiharu Shinnaka 1 , H. Kawakita 1 , H. Kobayashi 1 , E. Jehin 2 , J. Manfroid 2 , D. Hutsemékers 2 , C. Arpigny 21 Kyoto Sangyo University, Japan, 2 Instut d’Astrophysique et de Géophysique, Université de Liège, Belgium, Belgium.Presentaon Time: 10/4/2010 4:20 PM - 4:22 PMLocaon: Exhibit HallAbstract: The solar system was formed from interstellar maer 4.6 Gyrs ago and comets are considered as remnants of icy planetesimals formed in the earlysolar system. One of interesng primordial characters of cometary ice is an ortho-to-para abundance rao (OPR) of molecules such as H2O, NH3, etc. The OPRprobably indicates the molecular formaon temperatures in the solar nebula or in the pre-solar molecular cloud.We determined the OPRs of ammonia by using the high dispersion opcal spectra of NH2 in 15 comets: C/1995 O1 (Hale-Bopp), C/1999 S4 (LINEAR), C/2001 A2(LINEAR), C/2000 WM1 (LINEAR), 153P/Ikeya-Zhang, C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 Y1 (Juels-Holvorcem), C/2001 Q4 (NEAT), C/2002 T7(LINEAR), C/2003 K4 (LINEAR), 8P/Tule, 88P/Howell, 9P/Tempel 1, and 73P-B and -C/Schwassmann-Wachmann 3. The observaons were mainly carried out bythe Ultraviolet and Visual Echelle Spectrograph (UVES) mounted on the Very Large Telescope (VLT) in Chile. Other telescopes/instruments were also used in somecases. The OPRs of ammonia are determined from OPRs of NH2 (0,9,0) ro-vibronic band around 600 nm. Although absorpon lines (by the telluric atmosphere)and cometary C2 emission lines blended affected to NH2 emission lines in this region, we removed them in our analysis. The determined OPRs of ammoniaclustered around ~30K but not in the cases of 73P-B and -C. This situaon is very similar to that of 14N/15N raos in CN (i.e., 73P-B and -C are quite peculiarrelave to other comets). We discuss about the relaonship between the OPRs of ammonia and 14N/15N raos in CN in these 15 comets. Our results indicate theformaon of materials at relavely higher temperatures for 73P-B and -C than other comets.28.12: Observaons of Water in Comet 81P/Wild 2 by Subaru Telescope / IRCSAuthor Block: Mio Hashimoto 1 , H. Kobayashi 2 , H. Kawakita 2 , Y. Shinnaka 21 Saga Pref. Space Science Museum, Japan, 2 Kyoto Sangyo Univ., Japan.Presentaon Time: 10/4/2010 4:22 PM - 4:24 PMLocaon: Exhibit HallAbstract.Abstract: Comet 81P/Wild 2 was the target of the STARDUST sample return mission by NASA, and the results of ground-based analysis of sampled dustgrains provided us the details of cometary dusts. However, it is lile known about gaseous species in the comet 81P/Wild 2. The most abundant gaseous speciesin the coma is H2O that controls physical processes in the coma. Water producon rate is one of important parameter to evaluate the acvity of the comet. Todetermine the water producon rate of comet 81P/Wild 2, we performed near-infrared high-dispersion spectroscopic observaons by Subaru telescope/IRCS. Ourobservaons were carried out on both January 31 and February 1, 2010. We concentrate on the data taken on February 1 because S/N rao of spectra taken onJanuary 31 was not so good. The brightness of the comet was about 10th magnitude at our observaons. We could detect the strong water emission lines; X(1,0,1) 202 --- X (1,0,0) 303 at 3526.5 cm-1 and X (1,0,1) 211 --- X (1,0,0) 312 at 3514.4 cm-1. We will present the water producon rate of comet 81P/Wild 2determined from those emission lines.28.13: Crystalline Silicate Grains Of Comet 17P/Holmes Ejected At Its Outburst Observed With Subaru/COMICSAuthor Block: Mitsuru Yamaguchi 1 , T. Ootsubo 2 , J. Watanabe 3 , M. Honda 4 , I. Sakon 5 , M. Ishiguro 6 , Y. Sarugaku 7 , Y. Shinnaka 1 , H. Kobayashi 1 , H. Kawakita 11 Kyoto Sangyo University, Japan, 2 Tohoku University, Japan, 3 NAOJ, Japan, 4 Kanagawa University, Japan, 5 University of Tokyo, Japan, 6 Seoul Naonal University,Korea, Republic of, 7 JAXA/ISAS, Japan.Presentaon Time: 10/4/2010 4:24 PM - 4:26 PMLocaon: Exhibit HallAbstract: Comets had formed from dust and icy materials in the solar nebula 4.6 Gyrs ago. The cometary materials are considered as the most prisne in thesolar system and both dust grains and icy materials in comets have been used to invesgate the formaon condions of the solar system. Furthermore, it isconsidered that the existence of crystalline silicate in comets indicates the radial mixing of materials in the early solar nebula.Crystalline silicate is formed in high temperature environment. Then, it is clue to understand the difference between thermal and dynamical evoluon of dust inproto-solar nebula.A large outburst of comet 17P/Holmes has occurred in late October 2007. Just aer the outburst began, we carried out low-dispersion spectroscopic observaonin mid-infrared region (8 -13 µm) with COMICS mounted on the 8.2-m Subaru Telescope on October 25th-28 th, 2007 UT, when the comet was at a heliocentricdistance of 2.44 -2.45 AU.