ALMA Titan image cubes for CH3CN, HC3N and HNC observed August 2016 and May 2017

These 3D FITS files contain spectral line emission flux from Titan (in Janskys per beam) as a function of RA, dec. and frequency, observed using Atacama Large Millimeter/submillimeter Array (ALMA).

ALMA observations of Titan were obtained on 2017-05-08 and 2017-05-16 (as part of ALMA program 2016.A.00014.S; PI: Cordiner) and on 2016-08-18 and 2016-08-19 (as part of ALMA program 2015.1.01023.S; PI: Gurwell). The HNC (J=4-3), HC3N (J=40-39) and CH3CN (J=19-18) transitions were observed in 2017, whereas the HNC (J=4-3), HC3N (J=39-38) and CH3CN (J=19-18) were observed in 2016.

The raw observations were calibrated using standard scripts supplied by the observatory. The resulting measurement sets were continuum-subtracted using low-order polynomial fits to the line-free spectral regions adjacent to our lines of interest. The data were then imaged and cleaned (deconvolved) using the tclean algorithm in CASA 5.6. This routine implicitly corrects for the time-variability of Titan's position and radial velocity with respect to the observer, so the resulting image cubes are in the rest frame of Titan's center-of-mass. To facilitate meaningful intercomparisons, accounting for Titan's varying Geocentric distance, the 2016 and 2017 datasets were convolved to common circular beam dimensions, as projected in the plane of the sky. The image cubes were then cropped to isolate the emission lines of interest.