Rotation diagram for the CH₃CHO transitions reported in Table 1. The parameters N_up, g_up, and E_up are respectively the column density, the degeneracy, and the energy of the upper level. We note that the error bars on ln(N_up/g_up) are given by the vertical bar of the symbols. The g_up value is 74 for all the transitions used here (and reported in Table 1) with the exception of 17_2,15−16_2,14 A, where g_up = 70. The plot allows us to derive a rotational temperature of 87 ± 47 K and a total column density of 2 ± 1 × 10¹⁵ cm^-2.