Dust temperature map of CB 26 (color scale), overlaid with contours of the hydrogen column density (white: 10²¹ and 10²² cm^-2, black: 0.5, 2, 4, 6, and 8 × 10²¹ cm^-2). Yellow contours mark N_out (Eq. (3)) and N_1′ (Eq. (10), referring to the starless core SMM2). Dotted yellow ellipses mark the N_1′ approximations for the two subcores described in Sect. 5.3. The yellow square marks the column density peak and position of CB 26-SMM2; the asterisk marks the position of CB 26-SMM1 (Table 5).