Properties and nature of Be stars

Abstract

Reliable determination of the basic physical properties of hot emission-line binaries with Roche-lobe filling secondaries is important for developing the theory of mass exchange in binaries. It is a very hard task, however, which is complicated by the presence of circumstellar matter in these systems. So far, only a small number of systems with accurate values of component masses, radii, and other properties are known. Here, we report the first detailed study of a new representative of this class of binaries, BR CMi, based on the analysis of radial velocities and multichannel photometry from several observatories, and compare its physical properties with those for other well-studied systems. BR CMi is an ellipsoidal variable seen under an intermediate orbital inclination of ∼51• , and it has an orbital period of 12.d 919059(15) and a circular orbit. We used the disentangled component spectra to estimate the effective temperatures 9500(200) K and 4655(50) K by comparing them with model spectra. They correspond to spectral types B9.5e and G8III. We also used the disentangled spectra of both binary components as templates for the 2D cross-correlation to obtain accurate radial velocities and a reliable orbital solution. Some evidence of a secular period increase at a rate of (1.1 ± 0.5) s per year was found. This, together with a very low mass ratio of 0.06 and a normal mass and radius of the mass gaining component, indicates that BR CMi is in a slow phase of the mass exchange after the mass-ratio reversal. It thus belongs to a still poorly populated subgroup of Be stars for which the origin of Balmer emission lines is safely explained as a consequence of mass transfer between the binary components.

A dynamo mechanism as the potential origin of the long cycle in double periodic variables

“…Particularly interesting are the objects where no long cycle has been found to date, including V448 Cyg and BR CMi (Harmanec et al 2015). These objects are at the extreme ends for the masses of the donor stars, with 13.7 M ⊙ for V448 Cyg and 0.14 M ⊙ for BR CMi.…”

“…The presence of such cycles is known since a long time, as Gaposchkin (1944) inferred the presence of a long cycle in RX Cas, Lorenzi (1980a,c) demonstrated the presence of a long cycle in AU Mon, and Guinan (1989) inferred it for β Lyr. Nowadays, much larger samples of binaries with long cycles are known, and the above mentioned systems as well as other binaries with well-known physical parameters were for instance recently revisited by Harmanec et al (2015).…”

Physical properties of seven binary and higher-order multiple OB systems

“…3. Following the experience of Harmanec et al (2015), we first disentangled the spectra using KOREL and made the preliminary orbital solution based on the RVs from the Gaussian fitting of line profiles. Then we used the disentangled spectra as templates for asTODCOR.…”

V346 Centauri: Early-type eclipsing binary with apsidal motion and abrupt change of orbital period

“…Following Harmanec et al (2015) we adopted the spectra disentangled by KOREL as the templates for the 2D cross-correlation. The spectral region 4460-4486 Å was used.…”