Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003arep...47...38c&link_type=abstract
Astronomy Reports, Volume 47, Issue 1, pp.38-58
Astronomy and Astrophysics
Astronomy
4
Scientific paper
We have undertaken a statistical study of the component mass ratios and the orbital eccentricities of WR + O close binary, detached main-sequence (DMS), contact early-type (CE), and semidetached (SD) systems. A comparison of the characteristics of WR + O systems and of DMS, CE, and SD systems has enabled us to draw certain conclusions about the evolutionary paths of WR + O binaries and to demonstrate that up to 90% of all known WR + O binaries formed as a result of mass transfer in massive close O + O binary systems. Since there is a clear correlation between the component masses in SD systems with subgiants, the absence of an anticorrelation between the masses of the WR stars and O stars in WR + O binaries cannot be considered evidence against the formation of WR + O binaries via mass transfer. The spectroscopic transitional orbital period P {tr/sp} corresponding to the transition from nearly circular orbits ( e sp<0.1) to elliptical orbits ( e sp≥0.1) is ˜14d for WR + O systems and ˜2d-3d for OB + OB systems. The period range in which all WR + O orbits are circular (1mathop dlimits_. 6 ≤slant P ≤slant 14^d ) is close to the range for SD systems with subgiants, 0mathop dlimits_. 7 ≤slant P ≤slant 15^d . The large difference between the P {tr/sp} values for WR + O and OB + OB systems suggests that a mechanism of orbit circularization additional to that for OB + OB systems at the DMS stage (tidal dissipation of the orbital energy due to radiative damping of the dynamical tides) acts in WR + O binaries. It is natural to suggest mass transfer in the parent O + O binaries as this supplementary orbit-circularization mechanism. Since the transitional period between circular and elliptical orbits for close binaries with convective envelopes and ages of 5×109 years is P_{tr} = 12mathop dlimits_. 4, the orbits of most known SD systems with subgiants had enough time to circularize during the DMS stage, prior to the mass transfer. Thus, for most SD systems, mass transfer plays a secondary role in circularization of their orbits. In many cases, the initial orbital eccentricities of the O + O binary progenitors of WR + O systems are preserved, due to the low viscosity of the O-star envelopes and the short timescale for their nuclear evolution until the primary O star fills its Roche lobe and the mass transfer begins. The mass transfer in the parent O + O systems is short-lived, and the number of orbital cycles during the early mass-transfer stage is relatively low (lower than for the progenitors of SD systems by three or four orders of magnitude). The continued transfer of mass from the less massive to the more massive star after the component masses have become equal leads to the formation of a WR + O system, and the orbit's residual eccentricity increases to the observed value. The increase of the orbital eccentricity is also facilitated by variable radial mass loss via the wind from the WR star in the WR + O system during its motion in the elliptical orbit. The result is that WR + O binaries can have considerable orbital eccentricities, despite their intense mass transfer. For this reason, the presence of appreciable eccentricities among WR + O binaries with large orbital periods cannot be considered firm evidence against mass transfer in the parent O + O binary systems. Only for the WR + O binaries with the longest orbital periods (4 of 35 known systems, or 11 %) can the evolution of the parent O + O binaries occur without filling of the Roche lobe by the primary O star, being governed by radial outflow in the form of the stellar wind and possibly by the LBV phenomenon, as in the case of HD 5980.
Cherepashchuk Anatol M.
Karetnikov V. G.
No associations
LandOfFree
Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1525984