1999A&A...345..605J

We report the detection of infrared fine-structure lines of [Fe II] and [Si II] in the ISO-SWS spectra of two supergiants, α Ori and α Sco. From the observed intensities we infer that the emitting regions have temperatures in the range 1200-1800K and are located within about 20R_* from the star. This is interior to the region where dust is supposed to condense in the expanding envelope so that Fe and Si are not yet incorporated into the dust. The gas density required to thermalize these lines is of order 10⁶cm^–3 consistent with the expected density in the outflow at the adopted location. The total mass of gas being cooled through these atomic fine structure lines is of the order of 10^–4M_☉. Our calculation shows that cooling through the [OI] 63µm line extends over a larger radius than for both [Fe II] and [Si II].