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Astron. Astrophys. 349, 573-587 (1999)

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On the nature of the H II infrared emission lines of [FORMULA] Scorpii *

P.A. Zaal 1, A. de Koter 1, L.B.F.M. Waters 1,2, J.M. Marlborough 3, T.R. Geballe 4, J.M. Oliveira 5,6 and B.H. Foing 5

1 Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 SRON Laboratory for Space Research Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
3 Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7, Canada
4 Joint Astronomy Center, 660 N A'ohoku Place, Hilo, Hawaii 96720, USA
5 ESA Space Science Department, SCI-SO/ESTEC, PB 299, 2200 AG Noordwijk, The Netherlands
6 Centro de Astrofísica da Universidade do Porto, Rua das Estrelas s/n, P-4150 Porto, Portugal

Received 17 December 1998 / Accepted 13 July 1999

Abstract

We present H[FORMULA], He I  [FORMULA] 2.058 µm and 6 hydrogen Brackett and Pfund lines of [FORMULA] Sco (B0.2V) obtained using the ground-based INT and UKIRT instruments as well as satellite data from ISO. The infrared lines all show core emission. We have investigated the formation of these lines using sophisticated non-LTE models.

The observed emission in the most pronounced hydrogen lines, such as Br[FORMULA] and Pf[FORMULA], is stronger than predicted by our models. The velocities of peak emission are blue-shifted by 5-10 km s-1 with respect to the stellar velocity. This together with the surprisingly strong width of Br[FORMULA] and the peculiar profile of He I  [FORMULA] 2.058 suggests that shock-induced turbulent velocity fields may be present in or somewhat above the stellar photosphere, as has already been suggested from analysis of optical and ultraviolet data. We derive [FORMULA] = 32[FORMULA]2 kK from the infrared data alone, a value consistent with previous optical analysis. The good agreement indicates that quantitative analysis of infrared lines alone (e.g. for hot stars in regions of high extinction) can be used to characterize photospheres accurately. We also investigate the mass loss of [FORMULA] Sco and find an upper-limit of 6 10-9 [FORMULA].

A parameter study of the infrared hydrogen and helium lines indicates that emission may be expected in Br[FORMULA] and Pf[FORMULA] for stars with [FORMULA] [FORMULA] 16 kK and will dominate the profiles of these lines for [FORMULA] [FORMULA] 31 and 26 kK, respectively. He I  [FORMULA] 2.058 will be in emission for 20 [FORMULA] [FORMULA] [FORMULA] 33 kK and He II line profiles will contain emission at [FORMULA] [FORMULA] 33 kK. The effect of surface gravity on these values is small.

Key words: stars: atmospheres – stars: early-type – stars: emission-line, Be – infrared: stars – line: formation – radiative transfer

* based on data obtained with the ESA Infrared Space Observatory (ISO), with the UK infrared telescope (UKIRT, Hawaii) and with the Isaac Newton Telescope (INT, La Palma)

Send offprint requests to: P.A. Zaal

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© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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