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Astron. Astrophys. 345, 605-610 (1999)

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Atomic fine-structure lines in the ISO-SWS spectra of the supergiants [FORMULA] Orionis and [FORMULA] Scorpii *

K. Justtanont 1, A.G.G.M. Tielens 2,3, T. de Jong 4,5, J. Cami 2,5, L.B.F.M. Waters 5,2 and I. Yamamura 5

1 Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden
2 SRON-Groningen, P.O.Box 800, 9700 AV Groningen, The Netherlands
3 Kapteyn Institute, P.O.Box 800, 9700 AV Groningen, The Netherlands
4 SRON-Utrecht, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
5 Astronomical Institute `Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received 27 August 1998 / Accepted 1 March 1999

Abstract

We report the detection of infrared fine-structure lines of [Fe II] and [Si II] in the ISO-SWS spectra of two supergiants, [FORMULA] Ori and [FORMULA] Sco. From the observed intensities we infer that the emitting regions have temperatures in the range 1200-1800 K and are located within about 20 R* 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 106 cm-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 10-4 M[FORMULA]. Our calculation shows that cooling through the [O I] 63 µm line extends over a larger radius than for both [Fe II] and [Si II].

Key words: stars: chromospheres – stars: circumstellar matter – stars: individual: ff Ori – stars: individual: ff Sco – stars: late-type – infrared: stars

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.

Send offprint requests to: K. Justtanont (kay@astro.su.se)

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© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999
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