Highly Depleted Ethane and Slightly Depleted Methanol in Comet 21P/Giacobini-Zinner: Application of Empirical g-factors for CH3OH near 50 K
Abstract
We report results from high resolution (λ/Δλ 24,000) infrared spectra of Comet 21P/Giacobini-Zinner (21P/GZ) using NIRSPEC at Keck II on UT 2005 June 03, approximately one month before perihelion. We simultaneously sampled emissions from the ν7 band of C2H6, the ν2 and ν3 bands of CH3OH, and several hot bands of H2O, permitting a direct measure of parent volatile abundances in 21P/GZ. Our production rate for H2O was consistent with that measured from previous apparitions as retrieved from optical, infrared, and mm-wavelength observations. Our analysis of C2H6 confirmed its previously reported strong depletion from IR observations during the 1998 apparition [1,2], similar to the depletion of C2 in 21P/GZ known from optical studies [3]. For CH3OH, we applied our recently published quantum model for ν3 [4], obtaining Trot consistent with that for H2O ( 50 K) and a high abundance ratio CH3OH/C2H6 ( 9). We observed similar Trot and CH3OH/C2H6 in Comet 8P/Tuttle [5,6], and used these to produce effective (empirical) ν2 g-factors for 157 lines [7]. Application of our empirical ν2 model to 21P/GZ provided a production rate consistent with that from ν3, and an abundance ratio CH3OH/H2O in agreement with that measured previously [1,8]. We present a summary of our results for 21P/GZ and compare with abundances obtained for other Jupiter family comets. Our study provides the first measure of primary volatile production rates for any JFC over multiple apparitions using high resolution ground-based IR spectroscopy. We acknowledge support from the NASA Planetary Atmospheres, Planetary Astronomy, and Astrobiology Programs and from the NSF Astronomy and Astrophysics Research Grants Program. References [1] Weaver et al. 1999 Icarus 142:482 [2] Mumma et al. 2000 ApJ 531:L155 [3] A’Hearn et al. 1995 Icarus 118:223 [4] Villanueva et al. 2012 ApJ 747:37 [5] Bonev et al. 2008 ApJ 680:L61 [6] Boehnhardt et al. 2008 ApJ 683:L71 [7] DiSanti et al. 2012 ApJ (in press) [8] Biver et al. 2002 EMP 90:323
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #44
- Pub Date:
- October 2012
- Bibcode:
- 2012DPS....4431420D