FIGURE 3. Comparison of spectra for the metastable isomers HCN and HNC in VY CMa.

The J = 3  2 rotational transitions of both species are shown in the figure. The HNC spectrum is displayed in red, whereas that for HCN is plotted in black. HNC shows only the red- and blue-shifted flows, whereas HCN has a contribution from the spherical wind as well. The HNC/HCN ratio is roughly 0.001 for the directed flows, indicating high temperature formation²⁶, perhaps due to shocks. The spectra were measured in the 1-mm wavelength band using the SMT. The scale on the left-hand side of the spectra applies to the HCN data, whereas that on the right is for HNC. Spectral resolution for both lines is 1 MHz.