The eclipsing hypergiant R 81 (B2.5Ia-O) in the Large Magellanic Cloud ^*,**

System properties from spectroscopic and photometric monitoring

¹ Landessternwarte Königstuhl, 69117 Heidelberg, Germany
² European Southern Observatory, 85748 Garching, Karl-Schwarzschild-Str. 2, Germany
³ Institut für Astronomie, ETH Zentrum, 8092 Zürich, Switzerland
⁴ Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany
⁵ Astronomy Group, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

Corresponding author: O. Stahl, O.Stahl@lsw.uni-heidelberg.de

Received: 25 March 2002
Accepted: 30 April 2002

Abstract

The eclipsing P Cygni-type star R 81 (HDE 269128, HIP 24080) of spectral type B2.5 Ia-0 in the Large Magellanic Cloud was studied on the basis of a long continuous time series with simultaneous high-resolution Feros spectra and photometric measurements in the Strömgren system. The stellar parameters derived for the primary are  K and . The orbital period of the binary is 74.566 days. The mean light curve shows two eclipses, a brightness maximum just after the eclipse of the hypergiant and a slow decline of brightness between the two minima. For the first time, the orbital motion of the primary has been detected. The system is close and eccentric () and both components nearly fill their Roche volumes. A spectral signature of the companion of the hypergiant has not been found. We suspect that the secondary is embedded in a shell or disk of material accreted from the primary. In addition, line profile variations with a period of about 11 days, probably caused by non-radial pulsation, were observed. The line profiles indicate a strong wind from the primary with an outflow velocity of about 150 km s^-1. Near primary eclipse, strong absorptions in low excitation lines emerge abruptly that point to an outflow of enhanced density and higher velocity in the direction towards and beyond the secondary.