The HD5980 multiple system: Masses and evolutionary status

Gloria Koenigsberger, Nidia Morrell, D. John Hiller, Fabian R.N. Schneider, Nicolas Gonzalez-Jimenez,
Norbert Langer, and Rodolfo Barba

1) Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico; 2) Las Campanas Observatory, The Carnegie Observatories; 3) Department of Physics and Astronomy, & Pittsburgh Partile Physis, Astrophysics and Cosmology Center, University of Pittsburgh; 4) Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, and Instituto de Astrofisica de La Plata; 5) Argelander-Institut fur Astronomie; 6) Departamento de Fisica, Universidad de la Serena

New spectroscopic observations of the LBV/WR multiple system HD5980 in the Small Magellanic Cloud are used to address the question of the masses and evolutionary status of the two very luminous stars in the 19.3d eclipsing binary system. Two distinct components of the N V 4944 A line are detected in emission and their radial velocity variations are used to derive masses of 61 and 66 Mo, under the assumption that binary interaction effects on this atomic transition are negligible. We propose that this binary system is the product of quasi-chemically homogeneous evolution with little or no mass transfer. Thus, both of these binary stars may be candidates for gamma-ray burst progenitors or even pair instability supernovae. Analysis of the photospheric absorption lines belonging to the third-light object in the system confirm that it consists of an O-type star in a 96.56d eccentric orbit (e=0.82) around an unseen companion. The 5:1 period ratio and high eccentricities of the two binaries suggest that they may constitute a hierarchical quadruple system.

Reference: Astronomical Journal (in press)
Status: Manuscript has been accepted