Mass transfer and loss of the massive semi-detached binary AI Crucis

AI Crucis is a short-period semi-detached massive close binary (P = 1.41771d, Sp.=B1.5) in the open cluster NGC 4103. It is a good astrophysical laboratory for investigating the formation and evolution of massive close binary stars via case A mass transfer. Orbital period variations of the system were analyzed based on one newly determined eclipse time and the others compiled from the literature. It is discovered that the orbital period of the binary is continuously increasing at a rate of dP/dt = +1.00(±0....     

Mass loss and orbital period decrease in detached chromospherically active binaries

The secular evolution of the orbital angular momentum (OAM), the systemic mass  ( M = M ₁+ M ₂)  and the orbital period of 114 chromospherically active binaries (CABs) were investigated after determining the kinematical ages of the subsamples which were set according to OAM bins. OAMs, systemic masses and orbital periods were shown to be decreasing by the kinematical ages. The first-order decreasing rates of OAM, systemic mass and orbital period have been determined as     per systemic OAM,     per systemic mass and     per orbital period, respectively, from the kinematical ages. The ratio of d log  J /d log  M = 2.68, which were derived from the kinematics of the present sample, implies that there must be a mechanism which amplifies the angular momentum loss (AML)     times in comparison to isotropic AML of hypothetical isotropic wind from the components. It has been shown that simple isotropic mass loss from the surface of a component or both components would increase the orbital period.     

Mass transfer in tidally unstable compact binaries

The 2001 outburst of WZ Sagittae has shown the most compelling evidence yet for an enhancement of the mass-transfer rate from the donor star during a dwarf nova outburst in the form of hotspot brightening. I show that, even in this extreme case, the brightening can be attributed to tidal heating near the interaction point of an accretion stream with the expanding edge of an eccentric accretion disc, with no need at all for an increase in the mass-transfer rate. Furthermore, I confirm previous suggestions that an increase in mass-transfer rate through the stream damps any eccentricity in an accretion disc and suppresses the appearance of superhumps, in contradiction to observations. Tidal heating is expected to be most significant in systems with small mass ratios. It follows that systems like WZ Sagittae – which has a tiny mass ratio – are those most likely to show a brightening in the hotspot region.     

Evolution in semi-detached binary systems

The evolutionary process of semi-detached binary systems is examined on the basis of non-conservation of orbital angular momentum. We conclude that the semi-detached binary systems follow Type B evolution.     

Mass transfer in double white dwarf binaries

I review the implications of our recent numerical simulations of the hydrodynamics of Roche lobe overflow in double white dwarf binaries, with special emphasis on the stability and survival of such systems after the onset of dynamically unstable mass transfer. We find that some of these systems may survive and enter a secular phase of orbital expansion, driven by gravitational radiation, undergoing slow and decreasing mass transfer, and be observable as AM Canum Venaticorum binaries.     

Mass loss and spin

The evolution of spin in a star undergoing adiabatic mass loss is considered. It is established that adiabatic mass loss cannot drive spin. If such a mass loss is due to a binary component overflowing its Roche lobe then this result rules out the possibility of asynchronous rotation in close contact systems. If the mass loss is driven by some other mechanism then a spin up of the star is also not possible.     

Mass loss mechanisms in evolved stars

Summary Mass loss is a very important phenomenon for stellar evolution. In the late stages of stars it becomes fairly high (up to 10^–4 M/yr) though with a much decreased expansion velocity (about 30 kms^–1). It can also be variable, sporadic. Now, though the first observational evidence for mass loss from cool stars is usually attributed to Adams and McCormak in 1935 and though a lot of observational and theoretical papers have been devoted to it since this discovery, we only know mechanisms which are probably efficient under the dominant physical conditions, but neither one mechanism nor a combination of mechanisms is able to produce the observed effects. Those most invoked (thermal gas pressure, radiation pressure, acoustic waves, shock waves, Alfvén waves, ) will be described and criticized, with emphasis on the radiation pressure on dust grains at work at least in the outer part of cool atmospheres. The geometry and the content of expanding atmospheres are also discussed together with the mechanisms that may be important at small scales. Both theory and observations are taken into accout.     

Mass transfer in eccentric binaries: the new oil-on-water smoothed particle hydrodynamics technique

To measure the onset of mass transfer in eccentric binaries, we have developed a two-phase smoothed particle hydrodynamics (SPH) technique. Mass transfer is important in the evolution of close binaries, and a key issue is to determine the separation at which mass transfer begins. The circular case is well understood and can be treated through the use of the Roche formalism. To treat the eccentric case, we use a newly developed two-phase system. The body of the donor star is made up from high-mass water particles, whilst the atmosphere is modelled with low-mass oil particles. Both sets of particles take part fully in SPH interactions. To test the technique, we model circular mass-transfer binaries containing a  0.6 M_⊙  donor star and a  1 M_⊙  white dwarf; such binaries are thought to form cataclysmic variable (CV) systems. We find that we can reproduce a reasonable CV mass-transfer rate, and that our extended atmosphere gives a separation that is too large by approximately 16 per cent, although its pressure scale height is considerably exaggerated. We use the technique to measure the semimajor axis required for the onset of mass transfer in binaries with a mass ratio of   q = 0.6  and a range of eccentricities. Comparing to the value obtained by considering the instantaneous Roche lobe at pericentre, we find that the radius of the star required for mass transfer to begin decreases systematically with increasing eccentricity.     

The semi-detached binary system RZ draconis

The 1978 photoeletric observations of the late type close binary RZ Dra were reanalyzed with the Wilson and Devinney approach. Photometric parameters were determined (in Tab. 1.). The system is found to be semi-detached where the less massive component fills its Roche surface, whereas the other component almost does so. The configuration of the system is shown in Fig. 1. The absolute dimensions of the system are found to be M₁ = 0.61M⊙, $\text{M}{}_2\text{= 0.41}\text{M}\text{⊙}\text{R}{}_1\text{= 1.15}\text{R}\text{,}\text{?}\text{and}\text{R}{}_2\text{= 0.96}\text{R}\text{⊙}$. Both components appear to be overluminous and oversized for their masses and spectral types. Its evolutionary stage is also discussed. The variability in the brightness of the primary mlnimum(Fig. 4) indicates mass loss from the vicinity of L₂, which would be mainly responsible for the long-term decrease in its period.     

Mass loss from solar-type stars

Winds are directly detected from solar-type stars only when they are very young. At ages 10⁶ yr, these stars have mass loss rates 10⁶ times the mass flux of the present solar wind. Although these young T Tauri stars exhibit ultraviolet transition-region and X-ray coronal emission, the large particle densities of the massive winds lead to efficient radiative cooling, and wind temperatures are only 10⁴ K. In these circumstances thermal acceleration is unlikely to play an important role in driving the mass loss. Turbulent energy fluxes may be responsible for the observed mass loss, particularly if substantial magnetic fields are present.The presence of stellar mass loss is indirectly shown by the spindown of low-mass stars as they age. It appears that many solar-mass stars spin up as they contract toward the Main-Sequence, reaching a maximum equatorial velocity of 50 to 100 km s^–1. These stars spin down rapidly upon reaching the Main Sequence. Spindown may be enhanced by a decoupling or lag between convective envelope and radiative core. Because this spindown occurs fairly early in a solar-type star's history, the internal structure of old stars like the Sun may not depend upon initial conditions.     

Mass loss from Wolf-Rayet stars

Mass loss rates for 9 LMC WR stars are determined using IUE, UV, and visible spectrophotometric observations. A good correlations of mass loss rate with effective temperature and luminosity is indicated by the data, in agreement with the theoretical predictions.     

Mass loss from Wolf-Rayet stars

The observed times of minimum light derived from the photometry of the Wolf-Rayet eclipsing binary stars CQ Cep and V444 Cyg are used to estimate the mass-loss rate of the Wolf-Rayet components in several modes of mass-loss and mass-exchange.     

Mass loss from viscous advective disc

Rotating transonic flows are long known to admit standing or oscillating shocks. The excess thermal energy in the post-shock flow drives a part of the in falling matter as bipolar outflows. We compute mass loss from a viscous advective disc. We show that the mass outflow rate decreases with increasing viscosity of the accretion disc, since viscosity weakens the centrifugal barrier that generates the shock. We also show that the optical depth of the post-shock matter decreases due to mass loss which may soften the spectrum from such a mass losing disc.     

AI Cru: A semi-detached system?

The only existing photoelectric light curve of AI Cru has been re-analysed using the Wilson and Devinney (1971) direct method of solution. The system is found to be a semi-detached system of spectral type (B5 v+B8 v), with a mass ratioq=m _c /m _h =0.6. This solution differs somewhat from that obtained by Giuricinet al. (1980), using Wood's (1972) method, but seems more realistic because of the smaller value ofq and the reduced temperature difference between the components, which amounts to about 3300 K.     

Variable binaries and variables in binaries in the Binary star DataBase

The Binary star DataBase(BDB, http://bdb.inasan.ru) combines data from catalogs of binary and multiple stars of all observational types. There is a number of ways for variable stars to form or to be a part of binary or multiple systems. We describe how such stars are represented in the database.     

Revised photometric elements of three semi-detached binary systems

TheV andB light curves of three Algol-type eclipsing binaries (UZ Cyg, VW Cyg, AQ Peg), observed by Ammanet al. (1979), have been analysed using the Wilson and Devinney (1971) model. We find that all of them are semi-detached systems, with A-type primary components and K-type evolved secondary which fill the corresponding lobe, although VW Cyg should perhaps be considered as an sd-d system.     

Gravity-darkening in eclipsing binaries

A quantitative analysis of the ellipticity effect in close binary systems of the W Ursae Maioris type with spectroscopically known mass-ratios discloses that the photometric ellipticities of these variables are, in general, more than twice as large as the dynamical ellipticities (due to the geometrical distortion alone) computed for contact models of centrally condensed stars. If, moreover, this excess of the photometric over dynamical ellipticity is attributed to the phenomenon of gravity-darkening over distorted surfaces of the constituent components, this darkening must be present to a considerablylarger degree than that predicted by the theory of radiative transfer — a result difficult to reconcile with the existence of extensive sub-surface convection zones in late-type Main-Sequence stars. If, on the other hand, gravity-darkening is present in W UMa-type systems in the amount predicted by the theory (let alone in the presence of sub-surface convection), the only effective way of reconciling the theory with the observations would be to assume that the mean fractional radii of their constituent components are appreciablylarger than those appropriate for contact models in which the two components just fill the largestclosed Roche equipotentials capable of containing their mass. In other words, it would appear that the W UMa-type stars considered in this paper may constitute a single dumb-bell figure rather than two distinct components; and that the observed variations of light, colour or radial velocity are invoked by the axial rotation (and consequent variable cross-section) or this dumb-bell figure rather than to the contribution of individual stars.     

Supernovae in close binaries

The impact of a supernova shell onto 2.82M _⊙ and 20.0M _⊙ main-sequence stars is investigated for various initial orbital separations, and various supernova shell masses and velocities. The inelastic collision between the star and the supernova shell, the shock propagation into the companion star, and other forms of momentum transfer such as the rocket effect are considered. The total momentum transfer due to the supernova is insufficient to eject the companion from the binary as long as the companion retains most of its mass, regardless of the initial orbital separation. Ejection of the companion may occur if the companion is nearly destroyed. Even in contact binaries destruction does not necessarily occur, and if the orbital separation exceeds 10¹² cm, destruction of the companion becomes quite unlikely.