Evolution of Wolf-Rayet stars in binary systems: An analysis of the mass and orbital-eccentricity distributions

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 ～14^d for WR + O systems and ～2^d–3^d for OB + OB systems. The period range in which all WR + O orbits are circular \((1\mathop d\limits_. 6 \leqslant P \leqslant 14^d )\) is close to the range for SD systems with subgiants, \(0\mathop d\limits_. 7 \leqslant P \leqslant 15^d \). 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 \(P_{tr} = 12\mathop d\limits_. 4\), 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.     

The origin of the rotational and spatial velocities of radio pulsars

We analyze possible origins of the observed high rotational and spatial velocities of radio pulsars. In particular, these can be understood if all radio pulsars originate in close binary systems with orbital periods of 0.1–100 days, with the neutron star being formed by a type Ib,c supernova. The high spatial velocities of pulsars (v _p up to 1000 km/s) reflect the high Keplerian velocities of the components of these binaries, while their short periods of rotation (P _p < 4 s) are due to the rapid rotation of the presupernova helium-star components with masses of 2.5–10 M_⊙, which is synchronous with their orbital rotation. Single massive stars or components in wide binaries are likely to produce only slowly rotating (P _p > 4 s) neutron stars or black holes, which cannot be radio pulsars. As a result, the rate of formation of radio pulsars should be a factor of a few lower than the rate of type II and type Ib,c supernovae estimated from observations. This scenario for the formation of radio pulsars is supported by (i) the bimodal spatial velocity distribution of radio pulsars; (ii) the coincidence of the observed spatial velocities of radio pulsars with the orbital velocities of the components of close binaries with nondegenerate helium presupernovae; (iii) the correlation between the orbital and rotational periods for 22 observed radio pulsars in binaries with elliptical orbits; and (iv) the similarity of the observed rate of formation of radio pulsars and the rate of type Ib,c supernovae.     

Neutron stars in close binaries with elliptical component orbits

We consider the evolution of close binaries in which the initial secondary component is a nondegenerate helium star with mass M_He = 0.4–60 M_⊙, while the initially more massive primary has evolved into a black hole, neutron star, or degenerate dwarf. The neutron star is assumed to originate as a result of the evolution of a helium star with a mass of 2.5 M_⊙ ≤ M_He ≤ 10 M_⊙ after the explosion of a type Ib,c supernova. If the axial rotation of the helium star before the explosion is rigid-body and synchronized with the orbital rotation, for P_orb ≤ 0.16 day, the rotational energy of the young neutron star will exceed the energy of an ordinary supernova. If the magnetic field of the neutron star is sufficiently strong, the necessary conditions for a magnetic-rotational supernova are provided. The initial rotational period of a young neutron star originating in a system with an orbital period shorter than ～50 days is shorter than ～4 s, which, according to observations, is required for the appearance of a radio pulsar. A helium star whose mass exceeds ～10 M_⊙ in a close binary with an orbital period shorter than one day and with the axial rotation of the helium presupernova synchronous with the orbital rotation evolves into a Kerr black hole, whose formation is likely to be accompanied by a gamma-ray burst with a duration longer than two seconds. In particular, we consider close binaries in which the second supernova results in the formation of a neutron star that remains in the binary. The theoretical distribution of orbital periods and eccentricities for such systems is consistent with that observed for radio pulsars in the Galactic disk in binaries with compact components and orbital eccentricities exceeding ～0.09, providing an explanation for the observed correlation between the orbital eccentricities and orbital periods for these systems.     

Wolf-Rayet stars,black holes,and gamma-ray bursters in close binaries

We consider the evolutionary status of observed close binary systems containing black holes and Wolf-Rayet (WR) stars. When the component masses and the orbital period of a system are known, the reason for the formation of a WR star in an initial massive system of two main-sequence stars can be established. Such WR stars can form due to the action of the stellar wind from a massive OB star (M_OB≥50M_⊙), conservative mass transfer between components with close initial masses, or the loss of the common envelope in a system with a large (up to ～25) initial component mass ratio. The strong impact of observational selection effects on the creation of samples of close binaries with black holes and WR stars is demonstrated. We estimate theoretical mass-loss rates for WR stars, which are essential for our understanding the observed ratio of the numbers of carbon and nitrogen WR stars in the Galaxy \(\dot M_{WR} (M_ \odot yr^{ - 1} ) = 5 \times 10^{ - 7} (M_{WR} /M_ \odot )^{1.3} \). We also estimate the minimum initial masses of the components in close binaries producing black holes and WR stars to be ～25M_⊙. The spatial velocities of systems with black holes indicate that, during the formation of a black hole from a WR star, the mass loss reaches at least several solar masses. The rate of formation of rapidly rotating Kerr black holes in close binaries in the Galaxy is ～3×10^?6 yr^?1. Their formation may be accompanied by a burst of gamma radiation, possibly providing clues to the nature of gamma-ray bursts. The initial distribution of the component mass ratios for close binaries is dN～dq=dM₂/M₁ in the interval 0.04?q₀≤1, suggesting a single mechanism for their formation.     

A model for the population of helium stars in the Galaxy: Low-mass stars

We model the Galactic ensemble of helium stars using population synthesis techniques, assuming that all helium stars are formed in binaries. In this picture, single helium stars are produced by mergers of helium remnants of the components of close binaries (mainly, the merging of helium white dwarfs) or in the disruption of binaries with helium components during supernova explosions. The estimated total birthrate of helium stars in the Galaxy is 0.043 yr^?1; the total number is 4 × 10⁶; and the binarity rate is 76%. We construct a subsample of low-mass (M_He ? 2M_⊙) helium stars defined by observational selection effects: the limiting magnitude (V_He ≤ 16), ratio of the magnitudes of the components in binaries (V_He ≤ V_comp), and lower limit for the semiamplitude of the radial velocity required for detecting binarity (K_min = 30 km s^?1). The parameters of this subsample are in satisfactory agreement with observations of helium subdwarfs. In particular, the binarity rate in the selection-limited sample is 58%. We analyze the relations between the orbital periods and masses of helium subdwarfs and their companions in systems with various combinations of components. We predict that the overwhelming majority (～97%) of unobserved companions to helium stars will be white dwarfs, predominantly, carbon-oxygen white dwarfs.     

Late stages of the evolution of close compact binaries: Type I supernovae,gamma-ray bursts,and supersoft X-ray sources

We consider the evolution of close binaries resulting in the most intensive explosive phenomena in the stellar Universe—Type Ia supernovae and gamma-ray bursts. For Type Ia supernovae, which represent thermonuclear explosions of carbon-oxygen dwarfs whose masses reach the Chandrasekhar limit during the accretion of matter from the donor star, we derive the conditions for the accumulation of the limiting mass by the degenerate dwarf in the close binary. Accretion onto the degenerate dwarf can be accompanied by supersoft X-ray radiation with luminosity 1–10⁴ L _⊙. Gamma-ray bursts are believe to accompany the formation and rapid evolution of compact accretion-decretion disks during the formation of relativistic objects—black holes and neutron stars. The rapid (～1 M _⊙/s) accretion of matter from these disks onto the central compact relativistic star results in an energy release of ～0.1 M _⊙ c ² ～ 10⁵³ erg in the form of gamma-rays and neutrinos over a time of 0.1–1000 s. Such disks can form via the collapse of the rapidly rotating cores of Type Ib, Ic supernovae, which are components in extremely close binaries, or alternately due to the collapse of accreting oxygen-neon degenerate dwarfs with the Chandrasekhar mass into neutron stars, or the merging of neutron stars with neutron stars or black holes in close binaries. We present numerical models of the evolution of some close binaries that result in Type Ia supernovae, and also estimate the rates of these supernovae (～0.003/year) and of gamma-ray bursts (～10^?4/year) in our Galaxy for various evolutionary scenarios. The collimation of the gamma-ray burst radiation within an opening angle of several degrees “matches” the latter estimate with the observed rate of these events, ～10^?7–10^?8/year calculated for a galaxy with the mass of our Galaxy.     

Wolf-Rayet stars and relativistic objects: Distinctions between the mass distributions in close binary systems

The observed properties of Wolf-Rayet stars and relativistic objects in close binary systems are analyzed. The final masses M _CO ^f for the carbon-oxygen cores of WR stars in WR + O binaries are calculated taking into account the radial loss of matter via stellar wind, which depends on the mass of the star. The analysis includes new data on the clumpy structure of WR winds, which appreciably decreases the required mass-loss rates $\dot M_{WR}$ for the WR stars. The masses M _CO ^f lie in the range (1–2)M _⊙–(20–44)M _⊙ and have a continuous distribution. The masses of the relativistic objects M _x are 1–20M _⊙ and have a bimodal distribution: the mean masses for neutron stars and black holes are 1.35 ± 0.15M _⊙ and 8–10M _⊙, respectively, with a gap from 2–4M _⊙ in which no neutron stars or black holes are observed in close binaries. The mean final CO-core mass is $\overline M _{CO}^f = 7.4 - 10.3M_ \odot$ , close to the mean mass for the black holes. This suggests that it is not only the mass of the progenitor that determines the nature of the relativistic object, but other parameters as well-rotation, magnetic field, etc. One SB1R Wolf-Rayet binary and 11 suspected WR + C binaries that may have low-mass companions (main-sequence or subgiant M-A stars) are identified; these could be the progenitors of low-mass X-ray binaries with neutron stars and black holes.     

Radio pulsars in close binaries with neutron stars

The initial distribution of young radio pulsars, reconstructed from the observed distribution of their spatial velocities distorted by observational selection effects, taking into account the age and spatial distribution of radio pulsars with measured spatial velocities, appears to be bimodal. Most young pulsars are formed with velocities of ～100 km/s. Some fraction of young radio pulsars display an almost flat velocity distribution (dv/dv ≈ const) from 150 to 1000 km/s. Scenario modeling in the absence of an additional (kick) velocity acquired by the young neutron star during its formation in a supernova explosion can reproduce the initial velocity distribution of radio pulsars, but results in a higher fraction of radio pulsars in binaries than is observed. Assuming a random initial Maxwellian kick velocity of ～100 km/s makes it possible to reduce the fraction of radio pulsars in binaries to the observed value (<1%), while leaving the velocity distribution for radio pulsars close to the observed bimodal initial distribution. Such kick velocities are also able to explain the observed distribution of radio pulsars in close binaries in the eccentricity—orbital period plane.     

Evolution of close binaries and gamma-ray bursts

We analyze the late stages of evolution of massive (M ₀ ? 8 M _⊙) close binaries, from the point of view of possible mechanisms for the generation of gamma-ray bursts. It is assumed that a gamma-ray burst requires the formation of a massive (～1 M _⊙), compact (R ? 10 km) accretion disk around a Kerr black hole or neutron star. Such Kerr black holes are produced by core collapses of Wolf-Rayet stars in very close binaries, as well as by mergers of neutron stars and black holes or two neutron stars in binaries. The required accretion disks can also form around neutron stars that were formed via the collapse of ONeMg white dwarfs. We estimate the Galactic rate of events resulting in the formation of rapidly rotating relativistic objects. The computations were carried out using the “Scenario Machine.”     

Evolutionary connection between low-mass detached binaries,contact W UMa systems,and blue stragglers

We analyze the distribution of close binary stars in the orbital semimajor axis—primary mass plane. The reduced spatial density of stars with semimajor axes below 10R_⊙ is confirmed. We identify the area in this plane occupied by precursors of W UMa stars, assuming that the driving force causing the components to approach each other is their magnetic stellar wind. This scenario enables us to estimate the rate of formation (0.02/year) and lifetime (10⁸ yr) of W UMa stars. We derive a theoretical estimate of the ratio of the number of blue stragglers, N _BS , and of horizontal-branch stars, N _HB , in globular clusters based on the hypothesis that all blue stragglers are the result of component mergers in W UMa contact binaries. This ratio is N _BS /N _HB =0.4, close to the observed value for 62 Galactic globular clusters. We discuss possible reasons for the considerable dispersion of the observed estimates of this ratio for different clusters in our Galaxy.     

PG 1316+678: A young pre-cataclysmic binary with weak reflection effects

The PG 1316+678 star is classified as a pre-cataclysmic binary, as is evidenced by its photometric and spectroscopic observations. Its orbital period is determined to be P _orb = 3.3803^d, which coincides with the photometric period. The intensities of the emission HI and HeI lines are shown to vary synchronously with the brightness of the object (Δm _V = 0.065 ^m , Δm _R = 0.08 ^m ). These variations arise as the UV radiation from the DAO white dwarf is reflected from the surface of the cold companion. The parameters of the binary are estimated and the time of its evolution after the common-envelope phase is determined to be t ≈ 240 000 years. Thus, PG 1316+678 is a young pre-cataclysmic NN Ser variable with the smallest known photometric reflection effect.     

Three-dimensional hydrodynamical modeling of mass transfer in the close binary system β Lyr

We present a three-dimensional hydrodynamical modeling of mass transfer in the close binary system β Lyr taking radiative cooling into account explicitly. The assumed mass-transfer rate through the first Lagrangian point L₁ is 3.0 × 10^?5 M _⊙/yr. A flow with a radius of 0.14–0.16 (in units of orbital separation) is formed in the vicinity of L₁. This flow forms an accretion disk with a radius close to 23 R _⊙ and a thickness of about 10 R _⊙. The accretion disk is surrounded by an outer envelope that extends beyond the computational domain. A spiral shock forms at the outer boundary of the disk at orbital phase 0.25. Geometrically, the disk is toruslike, while the outer envelope is cylinder-like. In this model, which has low temperatures inside the computational domain, no jetlike structures form in the disk. It is possible that the jetlike structure in β Lyr arises due to the interaction of radiative wind from the accretor with the flow from L₁. In the model considered, a hot region exists over the poles of the accretor at a height of about 0.21. The amount of matter lost by the system is close to 10% of the mass flowing through L₁; i.e., the mass transfer in the system is almost conservative. For a mass-transfer rate of 3.0 × 10^?5 M _⊙/yr, the orbital period varies by 40.4 s/yr. This means that the observed variation of the orbital period of 19 s/yr should correspond to a mass-transfer rate close to 1.0 × 10^?5 M _⊙/yr.     

A dynamical study of 12 wide visual binaries

We have carried out the first dynamical studies of the relative motions of the components of 12 wide binaries: ADS 497, ADS 2427 (GL 130.1), ADS 3593, ADS 5436, ADS 6646, ADS 6783, ADS 9559 (δ Boo), ADS 10329, ADS 10759 (ψ Dra), ADS 14878, ADS 15229, and ADS 16558. The analysis is based on series of photographic observations made with the 26-inch refractor of Pulkovo Observatory, supplemented by data from the WDS Catalog, radial velocities and HIPPARCOS parallaxes. We used the parameters of the apparent motions, which can yield the orbit and mass of a binary from observations over a short arc of the orbit of the order of 5°–10°. The orbits and masses for six stars with orbital periods from 500 to 20 000 years have been reliably determined. For five stars with periods from 2000 to 100 000 years, we obtained probable orbits and mass estimates. For ADS 497 and ADS 10329, the mass excesses in their systems are 1 and 3 M _⊙, respectively, relative to the masses expected from the mass-luminosity dependence. In three cases, for ADS 3593, ADS 14878, and ADS 16558, the obtained estimates of the total mass of the components are 46, 25, and 7300 M _⊙, respectively, if the parallaxes are correct. A perturbation with amplitude 0.3″ and period 40 yrs has been detected in the orbital motion of the system ADS 10759, possibly indicating the presence of an invisible satellite with a mass of the order of 0.4 M _⊙. The orientations of the orbits in the Galactic reference frame have been determined for all 12 binaries. The planes of most of the obtained orbits are steeply inclined to the plane of the Galaxy, as was noted in previous studies.     

Evolution of close stellar binaries with black holes under the action of gravitational radiation and magnetic and induced stellar winds of the donor

We show that semi-detached close binary systems with massive (4–25M_⊙) black holes are formed in the evolution of massive stellar binaries in which the initial mass of the primary exceeds ～25M_⊙. The mass exchange in such systems is maintained by the nuclear evolution of the donor and by its magnetic and induced stellar winds. The donor in such systems can be a main-sequence star, subgiant, non-degenerate helium star, or white dwarf. The evolution of corresponding systems with black-hole masses of 10M_⊙ is investigated.     

Masses of stellar black holes and testing theories of gravitation

The paper analyzes the mass distribution of stellar black holes derived from the light and radial-velocity curves of optical stars in close binary systems using dynamical methods. The systematic errors inherent in this approach are discussed. These are associated primarily with uncertainties in models for the contribution from gaseous structures to the optical brightness of the systems under consideration. The mass distribution is nearly flat in the range 4–15M _⊙. This is compared with the mass distribution for black holes in massive close binaries, which can be manifest as ultrabright X-ray sources (L _x >10³⁹ erg/s) observed in other galaxies. If the X-ray luminosities of these objects correspond to the Eddington limit, the black-hole mass distribution should be described by a power law, which is incompatible with the flat shape derived dynamically from observations of close binaries in our Galaxy. One possible explanation of this discrepancy is the rapid evaporation of stellar-mass black holes predicted in recent multi-dimensional models of gravity. This hypothesis can be verified by refining the stellar black-hole mass spectrum or finding isolated or binary black holes with masses below ～3M _⊙.     

Dynamical evolution of multiple stars

We have modeled the dynamical evolution of small groups of N=3–18 stars in the framework of the gravitational N-body problem, taking into account possible coalescences of stars and the ejection of single and binary stars from the system. The distribution of states is analyzed for a time equal to 300 initial crossing times of the system. The parameters of the binaries and stable triple systems formed, as well as those of ejected single stars, are studied. In most cases, the evolution of the group results in the formation of a binary or stable triple system. The orbital eccentricities of the binaries formed are distributed according to the law f(e)=2e. As a rule, stable triple systems display pronounced hierarchy (the mean ratio of the semimajor axes of the outer and inner binaries is about 20:1). Stars are ejected with velocities from several km/s to several tens of km/s. The results of the modeling are compared with the parameters of observed wide binaries and triple systems.     

The evolutionary status of ultraluminous X-ray sources

We analyze models for quasi-stationary, ultraluminous X-ray sources (ULXs) with luminosities 10³⁸–10⁴⁰ erg/s exceeding the Eddington limit for a ～1.4M_⊙ neutron star. With the exception of relatively rare stationary ULXs that are associated with supernova remnants or background quasars, most ULXs are close binary systems containing a massive stellar black hole (BH) that accretes matter donated by a stellar companion. To explain the observed luminosities of ～10⁴⁰ erg/s, the mass of the BH must be ～40M_⊙ if the accreted matter is helium and ～60M_⊙ if the accreted matter has the solar chemical composition. We consider donors in the form of main-sequence stars, red giants, red supergiants, degenerate helium dwarfs, heavy disks that are the remnants of disrupted degenerate dwarfs, helium nondegenerate stars, and Wolf-Rayet stars. The most common ULXs in galaxies with active star formation are BHs with Roche-lobe-filling main-sequence companions with masses ～7M_⊙ or close Wolf-Rayet companions, which support the required mass-exchange rate via their strong stellar winds. The most probable candidate ULXs in old galaxies are BHs surrounded by massive disks and close binaries containing a BH and degenerate helium-dwarf, red-giant, or red-supergiant donor.     

The third body in the eclipsing system RR Lyn

Based on 70 years of published photoelectric observations, we have detected quasi-periodic cophased oscillations of the times of the primary and secondary minima of RR Lyn, one of the brightest and nearest eclipsing binaries in the northern sky ( $V = 5\mathop m\limits_. 54$ ; r=74 pc). Approximating these oscillations using the light equation yields estimates of the orbital parameters of the third body in the system and imposes constraints on its mass, M ₃. In the most probable case when the orbits of the eclipsing and triple systems are coplanar, M ₃=1.10±0.02M _⊙, and the semimajor axis of the orbit A ₃=17.4±3.5 AU, with a substantial eccentricity, e ₃=0.96±0.02. We have carried out a detailed study of the apsidal rotation of this eclipsing and now multiple system, which was suggested by Koch as a test of general relativity as far back as 1973. Our high-precision W BV R photoelectric photometry $(\sigma _{obs} \cong 0\mathop m\limits_. 0032)$ has removed some contradictions. At the same time, the proximity of the longitude of periastron ω 180°; the close correlation between the jointly estimated values of ω, e and the limb-darkening coefficients for the component disks, u ₁ and u ₂; and microfluctuations in the brightnesses of the stars prevent determination of the rate of rotation of the elliptical orbit in the system, even using the most accurate measurements.     

Wolf-Rayet stars with relativistic companions

The evolution of close binary systems containing Wolf-Rayet (WR) stars and black holes (BHs) is analyzed numerically. Both the stellar wind from the donor star itself and the induced stellar wind due to irradiation of the donor with hard radiation arising during accretion onto the relativistic component are considered. The mass and angular momentum losses due to the stellar wind are also taken into account at phases when the WR star fills its Roche lobe. It is shown that, if a WR star with a mass higher than ～10M _⊙ fills its Roche lobe in an initial evolutionary phase, the donor star will eventually lose contact with the Roche lobe as the binary loses mass and angular momentum via the stellar wind, suggesting that the semi-detached binary will become detached. The star will remain a bright X-ray source, since the stellar wind that is captured by the black hole ensures a near-Eddington accretion rate. If the initial mass of the helium donor is below ～5M _⊙, the donor may only temporarily detach from its Roche lobe. Induced stellar wind plays a significant role in the evolution of binaries containing helium donors with initial masses of ～2M _⊙. We compute the evolution of three observed WR-BH binaries: Cyg X-3, IC 10 X-1, and NGC 300 X-1, as well as the evolution of the SS 433 binary system, which is a progenitor of such systems, under the assumption that this binary will avoid a common-envelope stage in its further evolution, as it does in its current evolutionary phase.     

Physical parameters and dynamical properties of the multiple system ι UMa (ADS 7114)

We analyze the physical parameters, orbital elements, and dynamic stability of the multiple system ?? UMa (HD 76644 = ADS 7114). We have used the positions from the WDS catalog and our own observations on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the 1.5-m Russian-Turkish Telescope (Antalya, Turkey). We have obtained more precise orbital parameters of the subsystems, and spectral types, absolute magnitudes, and masses of the components. The primary has Sp = F0 V?CIV, M = 1.7 ± 0.1M _??, T _eff = 7260 ± 70 K, and log g = 4.30 ± 0.07. The companion in the close Aa subsystem is most likely a white dwarf with a mass of approximately 1.0 ± 0.3M _??. The spectral types and masses of the components in the BC subsystem are M3V, M4V and 0.35 ± 0.05M _??, 0.30 ± 0.05M _??, respectively. The total mass is 3.4 ± 0.4M _??. The Aa subsystem probably has an orbital period of 4470^d = 12.2^y and an eccentricity of approximately 0.6. The outer subsystem seems to have a period of approximately 2084 yrs and an eccentricity of approximately 0.9. We have carried out simulations using the stability criteria and shown that for all possible variations in the component parameters, the multiple system is unstable on a time scale of less than 10⁶ years with a probability exceeding 0.98. Possible reasons for this instability are discussed.