ALMA C¹⁷O J = 6−5 observations of the Red Rectangle. The resulting beam size (HPBW) is 0.′′31 × 0.′′26 (shown in the insert) and the chosen velocity resolution is 0.45 km s^-1. The contours are −0.075, 0.075, 0.225, and 0.675 Jy/beam (logarithmic spacing by a factor 3, equivalent to 2.54, 7.62, and 22.9 K). The emission is weak compared with the ¹²CO J = 6−5 emission shown in Bujarrabal et al. (2013b) and Fig. B.1, which reaches a peak of ~200 K. The continuum has been subtracted.