The long-term binary system VV Cep

Abstract

VV Cep is an eclipsing binary with a period of about 20.4 years that is comprised of an M2Iab primary star and an early B secondary star. A preliminary orbit was announced in 1933 by Harper & Christie (1936), and McLaughlin (1934) described the behaviour of the wide emission lines of Hydrogen and those of ionized CaII, the H & K lines, which were divided by sharp absorption and shifted in velocity, and presented the V/R (violet to red component) ratio for the Hydrogen Balmer lines. In October 1936, McLauglin (1936) announced that the hot star in VV Cep had been eclipsed, establishing the system as an eclipsing binary. Goedicke (1939a,b) carried out the first detailed spectroscopic analysis of this system. Wright (1977) inferred the existence of intermittent mass transfer and an H[alpha] emitting disk. Kawabata et al. (1981) and Moellenhoff & Schaifers (1978, 1981) further described what appeared to be an accretion disk around the B star. The dimension of the disk around the Be star was determined by Peery (1966) to be less than 1/18 of the diameter of the M supergiant’s photosphere, and according to investigations of Hutchings & Wright (1971) it is not spherically symmetrical, but rather is more dense in the direction of the stellar equator, as in the case of a normal Be star. This seems to be quite logical in view of the remarkable stream of gas in this system. Long-term monitoring of the intensity variations of the V and R emission peaks (the so-called V/R ratio) delivers important information about the peak strength as measure or the mass and/or density of the gas in the disk, expressed as equivalent width (EW) of the emission, and the direction of movement of the corresponding gas region within the disk (Figure 1). The violet and the red (V and R) components into which the emission line of the VV Cep spectrum is split can be linked to the radiation of the gas disk around the Be star. Due to its counterclockwise rotation around the central star, in relation to the line of sight of the observer, it results in a blueshift by moving towards the observer (V component) and a redshift by moving away (R component) from the observer.