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Astron. Astrophys. 326, 271-276 (1997)

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1. Introduction

The irregular variable UX Orionis (= BD -4 1029 = HD 293782 = IRAS 05020-0351) belongs to the evolutionarily young stars of the Orion population (Herbig & Bell 1988). It is, however, not a typical member of Herbig Ae/Be stars as it is not associated with a nebulosity.

UX Ori belongs to a subclass of irregular variables originally suggested by Hoffmeister (1949). More recently, UX Ori is often considered as the prototype of this subclass (Voshchinnikov 1989, Herbst et al. 1994). Its light curve seems to consist of several components. In addition to long-term wave-like variations, there are irregularly occurring short-lasting deep Algol-like minima.

Discussing UBV measurements of SV Cep, another member of this subclass, Wenzel (1969) suggested occultations by circumstellar dust clouds as a reason for the Algol-like minima. This hypothesis was subsequently further developed by many authors (Wenzel et al. 1971; Gahm et al. 1974; Zaytseva & Chugainov 1984; Voshchinnikov 1989; Grinin et al. 1991; Graham 1992; Friedemann et al. 1992, 1993, 1995, Herbst et al. 1994) and got increasing acceptance. The detection of infrared excesses by IRAS confirmed the presence of circumstellar dust and led to the construction of quantitative models of circumstellar dust shells.

UX Ori has been studied intensively in recent years. It is associated with the IRAS point source 05020-0351. The infrared radiation of the circumstellar dust shell was modelled by Bibo & Thé (1990), Hillenbrandt et al. (1992), and Hartmann et al. (1993). Grinin et al. (1994) discussed photometric, polarimetric and spectroscopic observations of a very deep minimum in some detail.

In this paper we will present the first infrared spectrum of the circumstellar dust in the wavelength region 8-13 µ m. The spectrum is compared with laboratory data of silicate dust. The physical conditions within the circumstellar shell are estimated by means of a spherically symmetric model providing an acceptable fit of the observed spectral energy distribution.

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998