Top: SD spectra (black, from left to right: SEST ¹²CO(1−0), IRAM ¹²CO(1−0), APEX ¹²CO(2−1), and APEX ¹²CO(3−2)) with the best-fit shell model convolved with the respective beams (red). The green spectra show the shell emission extracted from the ALMA data and convolved with the respective SD beams. Bottom: SD spectra after subtracting the best-fit shell models. The red lines show the best-fit model fit to the shell-subtracted SD observations to constrain the average mass-loss rate since creation of the shell.