Spectra of ¹²CO 2−1 (thin line) and ¹³CO 2−1 (thick line) on the locations of CO spirals. The alphabet order labels the distance to the stellar location: A is the closest, while J is the most distant one. The separations between the spectra is 056. The shaded Gaussian indicates the integration area used to estimate the spiral mass. The dotted vertical line marks V_sys of 5.85 km s^-1.