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Astron. Astrophys. 333, L63-L66 (1998)

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1. Introduction

The hydrogen recombination line maser in the peculiar emission line star MWC 349 is one of the rare astronomical masers originating in atomic transitions. Groundbased observations at millimeter and submillimeter wavelengths have shown that the [FORMULA] -line s (transitions [FORMULA]) are strongly amplified for quantum numbers [FORMULA] (wavelengths [FORMULA] mm), and that their flux increases toward shorter wavelengths down to 453 [FORMULA] m ([FORMULA]), the shortest wavelength submillimeter transition observed (Martín-Pintado et al. 1989a, 1989b; Thum et al. 1994a, 1994b). The [FORMULA] -line maser is therefore a very broad band phenomenon, and here we explore its range to still shorter wavelengths using the Infrared Space Observatory (ISO; Kessler et al. 1996).

The maser originates in the dense ionized corona of the circumstellar disk. Due to its brightness and the strong dependence of the amplification on electron density and other factors this maser is potentially an ideal tool for investigating the poorly known kinematics and physical conditions of disks around massive stars.

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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998