CO(2−1) intensity distribution at the systemic velocity as a function of radius for three M-star models from Saberi et al. (2019). The models were normalized to the peak of the fitted Gaussian and scaled to the FWHM radius of that Gaussian for each model separately. The normalized Gaussian is indicated by the solid red line in the figure. For each model, the vertical lines indicate the photodissociation radius R_p, which was also scaled to the Gaussian FWHM radius for each model. See text for a further explanation.