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Astron. Astrophys. 327, 1094-1106 (1997)

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1. Introduction

The eclipsing character of V 3903 Sgr was discovered by Cunha et al. (1990), the primary minimum having an amplitude of [FORMULA], [FORMULA] deeper than the secondary in the y passband. Cousins (1973) and Clariá (1976) both reported variations in the brightness of the system, classifying it as an irregular variable, but no light curve was published. Laurenti & Cerruti (1990) communicated UBVRI observations with very large scatter.

The system is a known spectroscopic binary (Conti & Alschuler 1971, Niemela & Morrison 1988), and very possibly a member of the R association Simeis 188 (Herbst et al. 1982, Cunha 1990, Vaz et al. 1993). High-precision photometric (uvby ) and spectroscopic observations are used in the present work. No sign of orbital eccentricity or period variation was found in our analysis. Information concerning V 3903 Sgr and the comparison stars is given in Table 1. The system is close to the Lagoon Nebula ([FORMULA]) and to Sagittarius OB1 association (centered at [FORMULA]).

[TABLE]

Table 1. Catalogue data and standard [FORMULA] indices for V 3903 Sgr and the comparison stars. The indices for V 3903 Sgr are for phases [FORMULA] (uvby ) and [FORMULA] ([FORMULA] ).

Responding to the lack of data on accurate masses and radii of O stars (Andersen 1993), we secured complete uvby light curves of V 3903 Sgr (Vaz et al. 1997), additional [FORMULA] photometry, and spectroscopic observations, that are presented here together with their analysis. Our results show that V 3903 Sgr is a well detached system, suited for precise determinations of masses and radii of its components. As the initial quality and distribution of our data obtained at PDO-LNA-CNPq were not adequate for very high precision determinations, we obtained more uvby observations at ESO, La Silla, with the SAT telescope. Both sets of photometric observations are analysed in this work (see Vaz et al. 1997 for a comparison between them).

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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