P68	June 2001

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, Argentina

^* Postdoctoral Researcher FNRS, Belgium
^** Member of Carrera del Investigador Científico, CONICET, Argentina
^*** Member of Carrera del Investigador Científico, CICBA, Argentina
^**** Fellow of the Comisi&oacite;n de Investigaciones Científicas (CIC), Prov. de Buenos Aires, Argentina
^***** Research Associate FNRS, Belgium

⁺ Based on observations collected at the European Southern Observatory, La Silla (Chile) and the Complejo Astronómico El Leoncito (Argentina)

Abstract

     We discuss the orbital elements of the multiple system Tr 16-104 which is usually believed to be a member of the open cluster Trumpler 16 in the Carina complex. We show that Tr 16-104 could be a hierarchical triple system consisting of a short period (2.15 days) eclipsing O7V + O9.5V binary bound to a B0.2IV star. Our preliminary orbital solution of the third body indicates that the B-star most probably describes an eccentric orbit with a period of ~ 285 or ~ 1341 days around the close binary. Folding photometric data from the literature with our new ephemerides, we find that the light curve of the close binary exhibits rather narrow eclipses indicating that the two O-stars must be well inside their Roche lobes. Our analysis of the photometric data yields a lower limit on the inclination of the orbit of the close binary of i ≥ 77°. The stellar radii and luminosities of the O7V and O9.5V stars are significantly smaller than expected for stars of this spectral type. Our results suggest that Tr 16-104 lies at a distance of the order of 2.5kpc and support a fainter absolute magnitude for zero age main sequence O stars than usually adopted. We find that the dynamical configuration of Tr16-104 corresponds to a hierarchical system that should remain stable provided that it suffers no strong perturbation. Finally, we also report long-term temporal variations of high velocity interstellar Ca II absorptions in the line of sight towards Tr 16-104.