期刊
ICARUS
卷 220, 期 1, 页码 277-285出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.icarus.2012.04.030
关键词
Comets; Comets, Coma; Comets, Composition; Comets, Nucleus; Ices
资金
- NASA ESPCoR [NNX08AV85A]
- NMSU
We present observations and analysis of the forbidden oxygen lines in Comets C/2006 W3 (Christensen) and C/2007 Q3 (Siding Spring) at heliocentric distances of 3.13 and 2.96 AU, respectively. We obtained the observations using the ARCES echelle spectrometer, which is mounted on the Astrophysical Research Consortium 3.5-m telescope at Apache Point Observatory. We detected the 5577, 6300, and 6364 angstrom atomic oxygen lines in Christensen and we calculated the ratio of the green (5577 angstrom) line flux to that of the red doublet (6300 and 6364 angstrom). We obtained a ratio of 0.24 +/- 0.08, a number higher than previous measurements for other comets at smaller heliocentric distance. This shows that CO and/or CO2 made detectable contributions to the O I population in the coma of Christensen. We only detected the 6300 angstrom line in Siding Spring, resulting in an upper limit for the oxygen line ratio of 0.20. Based on the derived flux for the 6300 angstrom line, we constrain the CO2 and H2O production rate in Siding Spring. A comparison of our results at similar to 3 AU to previous findings for comets at this approximate heliocentric distance suggests that a heliocentric distance of 3 AU is a transition region between H2O and CO2 dominated activity in comets. (C) 2012 Elsevier Inc. All rights reserved.
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