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Astron. Astrophys. 362, 158-168 (2000)

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CO band emission from MWC 349

I. First overtone bands from a disk or from a wind?

M. Kraus 1, E. Krügel 1, C. Thum 2 and T.R. Geballe 3

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Institut de Radio Astronomie Millimetrique, 38406 Saint Martin d'Hères, France
3 Gemini Observatory, 670 North A'ohoku Place, University Park, Hilo, HI 96720, USA

Received 16 December 1999 / Accepted 26 July 2000

Abstract

We have obtained spectra in the K band of the peculiar B[e]-star MWC 349. A 1.85-2.50 µm spectrum, measured at medium resolution, contains besides the strong IR continuum the first overtone CO bands, the hydrogen recombination lines of the Pfund series, and a number of other neutral atomic lines and ionic lines of low ionization, all in emission. Portions of the CO band and superposed Pfund series lines were observed at resolutions of 10-15 km s-1. The Pfund lines have gaussian profiles with FWHMs of [FORMULA] 100 km s-1, are optically thin, and are emitted in LTE. The CO band heads are formed in LTE at temperatures of 3500 to 4000 K. The width of the [FORMULA] band head indicates kinematic broadening of 50 to 60 km s-1. A number of CO emission geometries were investigated by spectral modeling. The emission may occur at the inner edge of the rotating circumstellar disk. In this case, the disk must have an outer bulge which partly blocks the radiation so that the observer sees only a sector on the far side where radial velocities are small. Alternatively, the CO emission originates in a wind and lines have gaussian profiles. Fits to both these geometries are of equally good quality. In a third alternative where the fit is less convincing, the CO emission is optically thin and comes from an extended Keplerian disk. In all successful fits the CO column density is [FORMULA] cm-2.

Key words: line: formation – stars: circumstellar matter – stars: emission-line, Be – infrared: stars – stars: individual: MWC 349

Send offprint requests to: M. Kraus (mkraus@mpifr-bonn.mpg.de)

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100
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