2017ApJ...843..119R

New distances to the supernova remnants (SNRs) G31.9+0.0 and G54.4-0.3 have been found. The analysis method uses H I absorption spectra and CO channel maps. Individual H I channel maps are used to verify absorption features in the H I absorption spectrum or to determine if they have noise. Both of the SNRs are associated with molecular clouds so accurate kinematic velocities are determined. The H iabsorption is used to resolve the kinematic distance ambiguity. The resulting new distance for G31.9+0.0 is 7.1 ± 0.4 kpc and for G54.4-0.3 it is 6.6 ± 0.6 kpc. These are significant revisions to the previous values.