HIGHLY DEPLETED ETHANE AND MILDLY DEPLETED METHANOL IN COMET 21P/GIACOBINI-ZINNER: APPLICATION OF A NEW EMPIRICAL {nu}{sub 2}-BAND MODEL FOR CH{sub 3}OH NEAR 50 K

Journal Article · Sun Jan 20 04:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/763/1/1· OSTI ID:22167208

DiSanti, M. A.; Bonev, B. P.; Villanueva, G. L.

We obtained infrared spectra of Comet 21P/Giacobini-Zinner (hereafter 21P/GZ) using NIRSPEC at Keck II on UT 2005 June 3, approximately one month before perihelion, that simultaneously sampled H{sub 2}O, C{sub 2}H{sub 6}, and CH{sub 3}OH. Our production rate for H{sub 2}O (3.885 {+-} 0.074 Multiplication-Sign 10{sup 28} molecules s{sup -1}) was consistent with that measured during other apparitions of 21P/GZ as retrieved from optical, infrared, and radio observations. Our analysis also provided values for rotational temperature (T {sub rot} = 51 {+-} 3 K) and the abundance ratio of ortho and para spin populations for water (OPR = 2.99 {+-} 0.23, implying a spin temperature exceeding 50 K). Six Q-branches in the {nu}{sub 7} band of C{sub 2}H{sub 6} provided a production rate (5.27 {+-} 0.90 Multiplication-Sign 10{sup 25} s{sup -1}) that corresponded to an abundance ratio of 0.136 {+-} 0.023 Multiplication-Sign 10{sup -2} relative to H{sub 2}O, confirming the previously reported strong depletion of C{sub 2}H{sub 6} from IR observations during the 1998 apparition, and in qualitative agreement with the depletion of C{sub 2} known from optical studies of 21P/GZ. For CH{sub 3}OH, we applied our recently published quantum model for the {nu}{sub 3} band to obtain a rotational temperature (48{sup +10}/{sub -7} K) consistent with that obtained for H{sub 2}O. In addition, we developed a new empirical model for the CH{sub 3}OH {nu}{sub 2} band, based on observations of Comet 8P/Tuttle with NIRSPEC. The application of our {nu}{sub 2} model to 21P/GZ yielded a production rate in agreement with that obtained from the {nu}{sub 3} band. Combining results from both {nu}{sub 2} and {nu}{sub 3} bands provided a production rate (47.5 {+-} 4.4 Multiplication-Sign 10{sup 25} s{sup -1}) that corresponded to an abundance ratio of 1.22 {+-} 0.11 Multiplication-Sign 10{sup -2} relative to H{sub 2}O in 21P/GZ, indicating mild depletion of CH{sub 3}OH. Together with observations of 21P/GZ in 1998, our study provides a measure of primary volatile production rates for this Jupiter family comet over multiple apparitions using high-resolution IR spectroscopy.

• OSTI ID: 22167208
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 763; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
APPROXIMATIONS
ASTRONOMY
ASTROPHYSICS
COMETS
ETHANE
INFRARED SPECTRA
JUPITER PLANET
METHANOL
MOLECULES
RESOLUTION
SPIN
VOLATILITY
WATER