V505 Mon -An early-type binary with a disk^*

¹ Astronomical Institute of the Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
² Astronomical Institute of the Slovak Academy of Sciences, 09 056 Tatranská Lomnica, Slovakia
³ Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
⁴ Department of Astronomy, University of California, Los Angeles, California 90025 1562, USA
⁵ Dominion Astrophysical Observatory, 5071 W. Saanich Road, Victoria, B.C., V8X4M6 Canada

Corresponding author: P. Mayer, mayer@mbox.cesnet.cz

Received: 10 April 2001
Accepted: 7 June 2001

Abstract

New spectra of the eclipsing binary V505 Mon (usually classified as B5 Ib) were obtained in the optical and UV regions. Only spectral lines of one component are visible, with K = 93 km s^-1. According to arguments based on the extent of the disk the mass ratio might be about 0.30. The star with the visible spectral lines would then have a mass of 2.3, the other component of 7.7 , i.e. their supergiant nature can be ruled out. The distance to the system appears to be about 1 kpc. Together with published photometric data, the spectroscopy provides clear evidence for the presence of a disk around the secondary component. The profiles of the C ii 1335/6 doublet lines are used to derive the rotational velocity of the disk. The structure of the disk can be characterized by a central ionized zone surrounded by neutral outer parts. Additional matter of cloudy nature has to be present, and both components are embedded in an extended atmosphere. Abundance of carbon was found to be very low. Similarity with some other non-eclipsing binaries is discussed.