Rotational lines of SiC₂ observed with the IRAM 30 m telescope in the 25 target sources (black histograms). The spectral resolution of the observed lines is 1 MHz. The blue lines are the calculated emerging line profiles from the best-fit model using the LVG method. The red lines are the predicted line profiles assuming LTE excitation. Dashed lines correspond to calculated lines profiles for those sources where SiC₂ was not detected.