FORMATION CONDITIONS OF ICY MATERIALS IN COMET C/2004 Q2 (MACHHOLZ). I. MIXING RATIOS OF ORGANIC VOLATILES

Journal Article · Sun Sep 20 00:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/1/121· OSTI ID:21372016

Kobayashi, Hitomi; Kawakita, Hideyo ^[1]

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1. Department of Physics, Faculty of Science, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan)

We observed comet C/2004 Q2 (Machholz) with the Keck II telescope in late 2005 January and we obtained the spectra of C/2004 Q2 including many emission lines of volatile species such as H{sub 2}O, HCN, C{sub 2}H{sub 2}, NH{sub 3}, CH{sub 4}, C{sub 2}H{sub 6}, CH{sub 3}OH, and H{sub 2}CO with high-signal-to-noise ratios. Based on our observations, we determined the mixing ratios of the molecules relative to H{sub 2}O in C/2004 Q2. Since C/2004 Q2 is one of Oort Cloud comets, it is interesting to compare our results with other Oort Cloud comets. The mixing ratios of C{sub 2}H{sub 2}/H{sub 2}O and C{sub 2}H{sub 6}/H{sub 2}O in C/2004 Q2 are lower than typical Oort Cloud comets. Especially, C{sub 2}H{sub 2}/H{sub 2}O ratio in C/2004 Q2 is as lower as Jupiter Family comets. However, mixing ratios of other molecules in C/2004 Q2 are similar to typical Oort Cloud comets. C/2004 Q2 might be the intermediate type between Oort Cloud and Jupiter Family comets. To investigate the formation conditions of such intermediate type comet, we focused on the (C{sub 2}H{sub 2}+C{sub 2}H{sub 6})/H{sub 2}O ratios and C{sub 2}H{sub 6}/(C{sub 2}H{sub 6}+C{sub 2}H{sub 2}) ratios in comets from the viewpoint of conversion from C{sub 2}H{sub 2} to C{sub 2}H{sub 6} in the precometary ices. We found that (C{sub 2}H{sub 2}+C{sub 2}H{sub 6})/H{sub 2}O ratio in C/2004 Q2 is lower than the ratio in typical Oort Cloud comets while C{sub 2}H{sub 6}/(C{sub 2}H{sub 6}+C{sub 2}H{sub 2}) ratio in C/2004 Q2 is consistent with the ratio of the typical Oort Cloud comets and Jupiter family comets. If we assume that the cometary volatiles such as H{sub 2}O, CH{sub 4}, and C{sub 2}H{sub 2} formed similar environment, the C{sub 2}H{sub 6}/(C{sub 2}H{sub 6}+C{sub 2}H{sub 2}) ratio might not be sensitive in the temperature range where hydrogen-addition reactions occurred and cometesimals formed ({approx}30 K). We employed the dynamical-evolutional model and the chemical-evolutional model to determine the formation region of C/2004 Q2 more precisely. We found that comet C/2004 Q2 might have formed in relatively inner region of the solar nebula than the typical Oort Cloud comet (but slightly further than 5 AU from the proto-Sun).

• OSTI ID: 21372016
• Journal Information: Astrophysical Journal, Vol. 703, Issue 1; Other Information: DOI: 10.1088/0004-637X/703/1/121; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
AMMONIA
CLOUDS
COMETS
DIMETHYL SULFIDE
ETHANE
HYDROCYANIC ACID
HYDROGEN ADDITIONS
ICE
JUPITER PLANET
METHANE
METHANOL
MIXING RATIO
SIGNAL-TO-NOISE RATIO
SOLAR NEBULA
SOLAR SYSTEM
SUN
TELESCOPES
VOLATILITY
WATER
ALCOHOLS
ALKANES
CHALCOGENIDES
DIMENSIONLESS NUMBERS
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
MAIN SEQUENCE STARS
NEBULAE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
PLANETS
STARS
SULFIDES
SULFUR COMPOUNDS