Formation Conditions of Icy Materials in Comet C/2004 q2 (Machholz). I. Mixing Ratios of Organic Volatiles

Details Formation Conditions of Icy Materials in Comet C/2004 q2 (Machholz). I. Mixing Ratios of Organic Volatiles Formation Conditions of Icy Materials in Comet C/2004 q2 (Machholz). I. Mixing Ratios of Organic Volatiles

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009apj...703..121k&link_type=abstract

The Astrophysical Journal, Volume 703, Issue 1, pp. 121-130 (2009).

Astronomy and Astrophysics

Astronomy

6

Comets: General, Comets: Individual: C/2004 Q2 Machholz, Solar System: Formation

Scientific paper

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 H2O, HCN, C2H2, NH3, CH4, C2H6, CH3OH, and H2CO with high-signal-to-noise ratios. Based on our observations, we determined the mixing ratios of the molecules relative to H2O 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 C2H2/H2O and C2H6/H2O in C/2004 Q2 are lower than typical Oort Cloud comets. Especially, C2H2/H2O 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 (C2H2+C2H6)/H2O ratios and C2H6/(C2H6+C2H2) ratios in comets from the viewpoint of conversion from C2H2 to C2H6 in the precometary ices. We found that (C2H2+C2H6)/H2O ratio in C/2004 Q2 is lower than the ratio in typical Oort Cloud comets while C2H6/(C2H6+C2H2) 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 H2O, CH4, and C2H2 formed similar environment, the C2H6/(C2H6+C2H2) ratio might not be sensitive in the temperature range where hydrogen-addition reactions occurred and cometesimals formed (~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).

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