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Methanol (CH3OH) radiates efficiently at infrared wavelengths, dominating the C--H stretching region in comets, yet inadequate quantum-mechanical models have imposed limits on the practical use of its emission spectra. Accordingly, we constructed a new line-by-line model for the v3 fundamental band of methanol at 2844 cm-1 (3.52μm) and applied it to interpret cometary fluorescence spectra. The new model permits accurate synthesis of line-by-line spectra for a wide range of rotational temperatures, ranging from 10 K tomore than 400 K.We validated the model by comparing simulations of CH3OH fluorescent emission with measured spectra of three comets (C/2001 A2 LINEAR, C/2004 Q2 Machholz and 8P/Tuttle) acquired with high-resolution infrared spectrometers at high-altitude sites. The new model accurately describes the complex emission spectrum of the v3 band, providing distinct rotational temperatures and production rates at greatly improved confidence levels compared with results derived from earlier fluorescence models. The new model reconciles production rates measured at infrared and radio wavelengths in C/2001 A2 (LINEAR). Methanol can now be quantified with unprecedented precision and accuracy in astrophysical sources through high-dispersion spectroscopy at infrared wavelengths. [ABSTRACT FROM AUTHOR]

The Jupiter-family comet 103P/Hartley 2 (103P) was the target of the NASA EPOXI mission. In support of this mission, we conducted observations from radio to submillimeter wavelengths of comet 103P in the three weeks preceding the spacecraft rendezvous on UT 2010 November 4.58. This time period included the passage at perihelion and the closest approach of the comet to the Earth. Here, we report detections of HCN, H2CO, CS, and OH and upper limits for HNC and DCN toward 103P using the Arizona Radio Observatory Kitt Peak 12 m telescope (ARO 12 m) and submillimeter telescope (SMT), the James Clerk Maxwell Telescope (JCMT), and the Green Bank Telescope (GBT). The water production rate, = (0.67-1.07) × 1028 s–1, was determined from the GBT OH data. From the average abundance ratios of HCN and H2CO relative to water (0.13 ± 0.03% and 0.14 ± 0.03%, respectively), we conclude that H2CO is depleted and HCN is normal with respect to typically observed cometary mixing ratios. However, the abundance ratio of HCN with water shows a large diversity with time. Using the JCMT data, we measured an upper limit for the DCN/HCN ratio <0.01. Consecutive observations of ortho-H2CO and para-H2CO on November 2 (from data obtained at the JCMT) allowed us to derive an ortho:para ratio (OPR) of ≈2.12 ± 0.59 (1σ), corresponding to Tspin > 8 K (2σ). [ABSTRACT FROM AUTHOR]

We report production rates, rotational temperatures, and related parameters for gases in C/2013 R1 (Lovejoy) using the Near InfraRed SPECtrometer at the Keck Observatory, on six UT dates spanning heliocentric distances (Rh) that decreased from 1.35 AU to 1.16 AU (pre-perihelion). We quantified nine gaseous species (H2O, OH*, CO, CH4, HCN, C2H6, CH3OH, NH3, and NH2) and obtained upper limits for two others (C2H2 and H2CO). Compared with organics-normal comets, our results reveal highly enriched CO, (at most) slightly enriched CH3OH, C2H6, and HCN, and CH4 consistent with “normal”, yet depleted, NH3, C2H2, and H2CO. Rotational temperatures increased from ∼50 K to ∼70 K with decreasing Rh, following a power law in Rh of –2.0 ± 0.2, while the water production rate increased from 1.0 to 3.9 × 1028 molecules s–1, following a power law in Rh of –4.7 ± 0.9. The ortho-para ratio for H2O was 3.01 ± 0.49, corresponding to spin temperatures (Tspin) ⩾ 29 K (at the 1σ level). The observed spatial profiles for these emissions showed complex structures, possibly tied to nucleus rotation, although the cadence of our observations limits any definitive conclusions. The retrieved CO abundance in Lovejoy is more than twice the median value for comets in our IR survey, suggesting this comet is enriched in CO. We discuss the enriched value for CO in comet C/2013 R1 in terms of the variability of CO among Oort Cloud comets. [ABSTRACT FROM AUTHOR]