High Resolution Submillimeter Observations of Stratospheric CH3CN on Titan

Abstract

Pilot observations of submillimeter transitions of methyl cyanide (CH3CN) in the stratosphere of Titan were performed on March 23, 2009 using the eSMA, combining the three submillimeter facilities on Mauna Kea (the SMA, JCMT, and CSO). Tuning to the J=19-18 rotational line ladder near 349.4 GHz, seven of the K-component transitions were detected. The eSMA provided a spatial resolution 0.2" by 0.35"; Titan was near 0.85" in diameter. Images created from the spectral line data show that the methyl cyanide emission is strongest at northern high latitudes, while nearly undetectable at southern high latitudes. This is in qualitative agreement with Cassini CIRS observations of the stratospheric distribution of other nitriles with latitude (e.g. Coustenis et al. 2007; Teanby et al 2008). A full inversion of the line data will be presented, providing a three dimensional view of CH3CN in the Titan stratosphere for comparison with CIRS data on other species. In addition, time evolution of the latitudinal distribution will be explored via comparison with lower ( 0.5" resolution) CH3CN images from 2000 obtained with the OVRO MM Array. The eSMA data for the K=0 through 3 components were obtained with a spectral resolution of 200 kHz, or 170 m/s. With further calibration and removal of velocity tracking errors, there is the possibility of directly detecting the sense and to some extent magnitude of the stratospheric wind field with these data.