COMET C/2004 Q2 (MACHHOLZ): PARENT VOLATILES, A SEARCH FOR DEUTERATED METHANE, AND CONSTRAINT ON THE CH{sub 4} SPIN TEMPERATURE

Journal Article · Fri Jul 10 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/699/2/1563; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21333718

Bonev, Boncho P; Villanueva, Geronimo L ^[1]; Mumma, Michael J; DiSanti, Michael A ^[2]; Gibb, Erika L ^[3]; Magee-Sauer, Karen ^[4]

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1. Department of Physics, Catholic University of America, Washington, DC 20064 (United States)
2. Solar System Exploration Division, Mailstop 693, NASA's Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Department of Physics and Astronomy, University of Missouri - St. Louis, St. Louis, MO 63121 (United States)
4. Department of Physics and Astronomy, Rowan University, Glassboro, NJ 08028-1701 (United States)

High-dispersion ({lambda}/{delta}{lambda} {approx} 25,000) infrared spectra of Comet C/2004 Q2 (Machholz) were acquired on 2004 November 28-29, and 2005 January 19 (UT dates) with the Near InfraRed echelle SPECtrograph (NIRSPEC) at the Keck-2 telescope on Mauna Kea. We detected H{sub 2}O, CH{sub 4}, C{sub 2}H{sub 2}, C{sub 2}H{sub 6}, CO, H{sub 2}CO, CH{sub 3}OH, HCN, and NH{sub 3} and we conducted a sensitive search for CH{sub 3}D. We report rotational temperatures, production rates, and mixing ratios (with respect to H{sub 2}O) at heliocentric distances of 1.49 AU (2004 November) and 1.21 AU (2005 January). We highlight three principal results. (1) The mixing ratios of parent volatiles measured at 1.49 AU and 1.21 AU agree within confidence limits, consistent with homogeneous composition in the mean volatile release from the nucleus of C/2004 Q2. Notably, the relative abundance of C{sub 2}H{sub 6}/C{sub 2}H{sub 2} is substantially higher than those measured in other comets, while the mixing ratios C{sub 2}H{sub 6}/H{sub 2}O, CH{sub 3}OH/H{sub 2}O, and HCN/H{sub 2}O are similar to those observed in comets, referred to as 'organics-normal'. (2) The spin temperature of CH{sub 4} is >35-38 K, an estimate consistent with the more robust spin temperature found for H{sub 2}O. (3) We obtained a 3{sigma} upper limit of CH{sub 3}D/CH{sub 4} < 0.020 (D/H < 0.005). This limit suggests that methane released from the nucleus of C/2004 Q2 is not dominated by a component formed in extremely cold (near 10 K) environments. Formation pathways of both interstellar and nebular origin consistent with the measured D/H in methane are discussed. Evaluating the relative contributions of these pathways requires further modeling of chemistry including both gas-phase and gas-grain processes in the natal interstellar cloud and in the protoplanetary disk.

• OSTI ID: 21333718
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 699; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
AMMONIA
CARBON MONOXIDE
COMETS
DIMETHYL SULFIDE
ETHANE
HYDROCYANIC ACID
INFRARED SPECTRA
METHANE
METHANOL
MIXING RATIO
PROTOPLANETS
SIMULATION
SOLAR SYSTEM
SPIN
TELESCOPES
VOLATILITY
WATER