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标题：Observations of Jupiter Family Comet 252P/LINEAR During a Close Approach to Earth Reveal Large Abundances of Methanol and Ethane
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作者：L. Paganini ; M. N. Camarca ; M. J. Mumma 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2019
卷号：158
期号：3
页码：1-9
DOI：10.3847/1538-3881/ab289c
语种：English
出版社：American Institute of Physics
摘要：We observed short-period comet 252P/LINEAR post-perihelion during its 2016 passage, which presented a favorable opportunity to survey its chemical composition at a close Earth approach (∼0.14 au). We characterized the cometʼs chemical composition on four dates (UT 2016 April 12, 19, 26, and 29) using spectroscopic measurements with the Near-infrared Spectrograph (NIRSPEC) at the Keck Observatory on Maunakea, HI. Our high-resolution infrared spectra yielded production rates for four species (H 2 O, CH 3 OH, C 2 H 6 , and HCN) and upper limits for five species (NH 3 , H 2 CO, C 2 H 2 , CO, and CH 4 ). We measured water at an average production rate of 4.9±0.1×10 27 molec s −1 . The chemical properties of 252P suggest a rather typical composition, yet somewhat enriched in methanol and ethane but low in formaldehyde (upper limit) compared to other short-period comets surveyed at infrared wavelengths. Analysis of the ortho/para ratio in water indicates a nuclear spin temperature larger than∼38 K, consistent with statistical equilibrium (2σ). Spatial distributions of gases, which are representative of possible heterogeneity in the nucleus and/or gas dynamics upon sublimation, showed rather symmetric profiles, with subtle enhancements of the more volatile species C 2 H 6 and HCN toward the sunward hemisphere, while water showed spatial distributions that were extended toward the anti-sunward hemisphere. The continuum was characterized by a narrow distribution. We place our infrared results in the context of observations with the Discovery Channel Telescope, the James Clerk Maxwell submillimeter Telescope, and the Hubble Space Telescope.
关键词：comets: general;comets: individual (252P/LINEAR);infrared: planetary systems;techniques: spectroscopic