The distribution and excitation of CH3OH in comet C/2012 K1 (PanSTARRS) from ALMA

We present measurements of spatially and spectrally resolved CH₃OH emission from the coma of comet C/2012 K1 (PanSTARRS) observed using the Atacama Large Millimeter/submillimeter Array (ALMA) in June 2014. The CH3OH emission is centrally peaked, with a spatial profile consistent with production from the sublimation of ices from the nucleus. From the detection of multiple lines of CH₃OH in the J=7-6 and K=3-2 bands around 339 and 252 GHz, respectively, the line-of-sight average rotational excitation temperatures (T_rot) have been derived as a function of spatial position across the coma. At the CH₃OH peak, we find Trot=92 K, falling to about 40 K at a distance of 1000 km. The temperature does not fall monotonically but shows a double-peaked structure, indicative of a heating source at distances >=500 km from the nucleus.