Ground-based multiwavelength observations of comet 103P/Hartley 2

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) × 10²⁸s^-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 T_spin> 8 K (2σ).