Close Binary Stars Research Articles

The relation between the ADF and the ionized nebular mass in PNe

Abstract In this work we analyze the proposed relation between ADFs and ionized masses in planetary nebulae. For this, we have collected from the literature the ADFs and other parameters such as heliocentric distances, Hβ luminosities, logarithmic reddening correction at Hβ, c(Hβ), electron densities and others and we calculated the ionized mass for a sample of 132 PNe, 27 of which possess a binary central star (14 are close binaries). In addition the distribution of these objects in the Galaxy is analyzed. The ionized masses were calculated considering two different electron densities, the one provided by the [S ii] density sensitive lines ratio and the one provided by the [Cl iii] lines ratio. No relation was found between ionized masses and ADFs for this sample, although it is confirmed than the PNe with the largest ADFs correspond in general to objects with a close binary central star, although it is important to say that about 20 per cent of these objects have an ADF larger than 5 but smaller than 10. Therefore a PN having a close binary central star does not necessarily exhibit an extremely large ADF. We also have searched for possible relations between the ADFs and the stellar atmospheres, divided in H-rich and H-poor stars. No particular relation was found. Interestingly, several PNe with a [WR] H-poor CSPN present an ADF larger than 10, but so far they have not been reported as having a binary central star.

TIC 435850195: The Second Triaxial Tidally Tilted Pulsator

The Transiting Exoplanet Survey Satellite (TESS) has enabled the discovery of numerous tidally tilted pulsators (TTPs), which are pulsating stars in close binaries where the presence of a tidal bulge has the effect of tilting the primary star’s pulsation axes into the orbital plane. Recently, the modeling framework developed to analyze TTPs has been applied to the emerging class of triaxial pulsators, which exhibit nonradial pulsations about three perpendicular axes. In this work, we report on the identification of the second-ever discovered triaxial pulsator, with 16 robustly detected pulsation multiplets, of which 14 are dipole doublets separated by 2ν orb. We jointly fit the spectral energy distribution and TESS light curve of the star, and find that the primary is slightly evolved off the zero-age main sequence, while the less massive secondary still lies on the zero-age main sequence. Of the 14 doublets, we associate eight with Y 10x modes and six with novel Y 10y modes. We exclude the existence of Y 11x modes in this star and show that the observed pulsation modes must be Y 10y . We also present a toy model for the triaxial pulsation framework in the context of this star. The techniques presented here can be utilized to rapidly analyze and confirm future triaxial pulsator candidates.

On the Value of High Precision Radial Velocity Observations and Astrometric Orbits for Binary Stars Hosting Exoplanets

Observations have concluded that exoplanet hosting binary stars appear to have wider mean separations than a definitive sample of “field binaries” as well as an apparent deficit of very close pairs. Many exoplanets orbit near their host stars equatorial plane, especially for close-in, small planets. Precision radial velocities of exoplanets in close binary stars are sparse but badly needed in order to provide statistical samples revealing the host stars spin axis and determinations of the masses and orbital planes of their planets. Astrometric orbits of the stars can provide precise binary orbital elements. In the quest for occurrence rates, the detection of planets is biased against transit recognition of small planets in binary systems. Together the measurements of binary host stars and their planets are required to yield robust tests of planet formation, stability, and evolution mechanisms as well as provide correct small planet occurrence rates.

Suggested magnetic braking prescription derived from field complexity fails to reproduce the cataclysmic variable orbital period gap

Magnetic wind braking drives the spin-down of low-mass stars and the evolution of most interacting binary stars. A magnetic braking prescription that was claimed to reproduce both the period distribution of cataclysmic variables (CVs) and the evolution of the rotation rates of low-mass stars is based on a relation between the angular momentum loss rate and magnetic field complexity. The magnetic braking model based on field complexity has been claimed to predict a detached phase that could explain the observed period gap in the period distribution of but has never been tested in detailed models of evolution. Here we fill this gap. We incorporated the suggested magnetic braking law in MESA and simulated the evolution of for different initial stellar masses and initial orbital periods. We find that the prescription for magnetic braking based on field complexity fails to reproduce observations of The predicted secondary star radii are smaller than measured, and an extended detached phase that is required to explain the observed period gap (a dearth of non-magnetic with periods sim 2$ and $ sim 3$ hours ) is not predicted. Proposed magnetic braking prescriptions based on a relation between the angular momentum loss rate and field complexity are too weak to reproduce the bloating of donor stars in derived from observations and, in contrast to previous claims, do not provide an explanation for the observed period gap. The suggested steep decrease in the angular momentum loss rate does not lead to detachment. Stronger magnetic braking prescriptions and a discontinuity at the fully convective boundary are needed to explain the evolution of close binary stars that contain compact objects. The tension between braking laws derived from the spin-down of single stars and those required to explain and other close binaries containing compact objects remains.

The improved component masses and parallaxes for the two close binary stars: HD 80671 and HD 97038

We present the fundamental stellar parameters, including the individual component masses, as well as the orbital parameters, and dynamical parallaxes of the two close binary stars; HD80671, and HD97038. The stellar parameters are spectrophotometrically estimated via Al-Wardat’s method for analyzing binary and multiple stellar systems, which is having a combination of the spectroscopic analysis and the photometric analysis to build the combined and individual synthetic spectral energy distributions of the individual components of the systems and so to estimate their fundamental parameters, metallicities, and ages. It employs Kurucz’s model atmospheres of single stars, while the orbital parameters are estimated using Tokovinin’s method. The individual spectrophotometric component masses are inferred with good accuracy, and found to be MSphA = 1.47±0.10M⊙ and MSphB=1.29±0.09M⊙ with an age of 1.0±0.09 Gyr for HD80671, and MSphA=1.17±0.09M⊙ and MSphB=1.12±0.08M⊙ with an age of 3.981±0.35 Gyr for HD97038. The improved dynamical parallaxes are given as πdyn=28.305±0.45 mas for HD80671, and πdyn=16.26±0.30 mas for HD97038. The evolutionary status of two binaries is discussed depending on the positions of the components on the isochrones and evolutionary tracks.

Binary central stars of planetary nebulae in the Large Magellanic Cloud

Context. Close binary central stars of planetary nebulae (PNe) must have formed through a common envelope evolution during the giant phase experienced by one of the stars. Transfer of the angular momentum from the binary system to the envelope leads to the shortening of the binary separations from the radius of red giant to the radius of the order of few tenths of AU. Thus, close binary central stars of planetary nebulae are laboratories to study the common envelope phase of evolution. The close binary fraction in the Galaxy has been measured in various sky surveys, but the close binary fraction is not yet well constrained for the Magellanic Clouds, and our results may help the study of common envelope evolution in low-metallicity environments. Aims. This paper presents a continuation of our study of variability in the Magellanic Cloud planetary nebulae on the basis of data from the OGLE survey. Previously, we had analysed the OGLE data in the Small Magellanic Cloud. Here, the study is extended to the Large Magellanic Cloud (LMC). In this paper we search for close binary central stars with the aim to constrain the binary fraction and period distribution in the LMC. Methods. We identified 290 counterparts of PNe in the LMC in the I-band images from the OGLE-III and OGLE-IV surveys. However, the light curves of ten objects were not accessible in the OGLE database, and thus we analysed the time series photometry of 280 PNe. Results. In total, 32 variables were found, but 5 of them turned out to be foreground objects. Another 18 objects show irregular or regular variability that is not attributable to the binarity of their central stars. Their status and the nature of their variability will be verified in the follow-up paper. Nine binary central stars of PNe with periods between 0.24 and 23.6 days were discovered. The obtained fraction for the LMC PNe is 3.3-1.6+2.6% without correcting for incompleteness. This number is significantly lower than the 12–21% derived in the analogous search in the Galactic bulge. We discuss this difference, taking into account observational biases. The lower binary fraction suggests a lower efficiency of the common envelope phase in producing close binaries in the LMC compared to the Galaxy.

Close Binary Stars Modeled by Two Prolate Ellipsoids in Synchronous Rotation

The presence of tidal deformations in close binary stars has already been confirmed by astronomical observations. The present paper aims to simply address an astronomy problem, studying the relative movement of close binaries disturbed by their mutual deformation through some basic concepts and tools of celestial mechanics. For this purpose, the tidal effect is modeled by considering that each star is an elongated revolution ellipsoid in such a way that axes of revolution are coincident, and their largest axes point toward each other along the motion. The potential for mutual attraction is then obtained, resulting in a perturbed Keplerian system with perturbation proportional to the inverse of the cubic distance between the stars, thus being a one-degree-of-freedom problem and, therefore, integrable. The effective potential, the integrals of energy and angular momentum, and the Laplace vector are used to obtain qualitative information about the dynamics before integrating it. The motion describes a rosette-like orbit with periodic osculating elements, or a circle when the energy is a local minimum. Finally, an analytical solution is presented in terms of elliptic functions by using a regularizing and linearizing function.

Observational Constraints on Close Binary Star Evolution. I. Putative Contact Binaries with Long Periods and High Mass Ratios

Evolutionary and structural models for contact binary stars make quantitative predictions about the distribution of systems in the mass ratio (q)–orbital period (P) plane. Specifically, contact binaries containing primaries with convective envelopes are predicted to be absent at mass ratios larger than a critical threshold that is a function of orbital period and total mass. We test this prediction by characterizing candidate contact binaries that appear to have mass ratios in violation of this threshold. We obtained quadrature-phase echelle spectra (R ≈ 31,000) for 18 close binaries (0.65 day < P < 2.00 days) in the Kepler field, from which we extracted radial velocity profiles for each system. Use of a joint Markov Chain Monte Carlo fitting routine on the Kepler light curves and the radial velocity profiles allows us to retrieve all fundamental system and component parameters. Of the 18 systems, only one is a contact binary, and both components likely have radiative—not convective—envelopes. The 17 remaining systems are detached binaries (eight) or semidetached binaries (four) with ellipsoidal variations, rotating variables (four), or pulsating variables (one). Therefore, none of the systems are in violation of the theoretical mass ratio thresholds for low-mass contact binaries. The 12 noncontact binaries follow a T 2/T 1–q relation significantly weaker than expected for main-sequence components, suggesting radiative heating of the secondaries. Most of the secondaries have radii larger than main-sequence expectations, a possible consequence of heating. Four secondaries fill their Roche lobes, while none of the primaries do, possibly indicating prior mass-ratio reversal.

Slowly rotating close binary stars in Cassini states

ABSTRACT Recent asteroseismic measurements have revealed a small population of stars in close binaries, containing primaries with extremely slow rotation rates. Such stars defy the standard expectation of tidal synchronization in such systems, but they can potentially be explained if they are trapped in a spin-orbit equilibrium known as Cassini state 2 (CS2). This state is maintained by orbital precession due to an outer tertiary star, and it typically results in a very sub-synchronous rotation rate and high degree of spin-orbit misalignment. We examine how CS2 is affected by magnetic braking and different types of tidal dissipation. Magnetic braking results in a slower equilibrium rotation rate, while tidal dissipation via gravity waves can result in a slightly higher rotation rate than predicted by equilibrium tidal theory, and dissipation via inertial waves can result in much slower rotation rates. For seven binary systems with slowly rotating primaries, we predict the location of the outer tertiary predicted by the CS2 theory. In five of these systems, a tertiary companion has already been detected, although it is closer than expected in three of these, potentially indicating tidal dissipation via inertial waves. We also identify a few new candidate systems among a population of eclipsing binaries with rotation measurements via spot modulation.

Super slowly spinning stars in close binaries

ABSTRACT Stars in short-period binaries typically have spins that are aligned and synchronized with the orbit of their companion. In triple systems, however, the combination of spin and orbital precession can cause the star’s rotation to evolve to a highly misaligned and sub-synchronous equilibrium known as a Cassini state. We identify a population of recently discovered stars that exhibit these characteristics and which are already known to have tertiary companions. These third bodies have a suitable orbital period to allow the inner binary to evolve into the sub-synchronous Cassini state, which we confirm with orbital evolution models. We also compute the expected stellar obliquity and spin period, showing that the observed rotation rates are often slower than expected from equilibrium tidal models. However, we show that tidal dissipation via inertial waves can alter the expected spin–orbit misalignment angle and rotation rate, potentially creating the very slow rotation rates in some systems. Finally, we show how additional discoveries of such systems can be used to constrain the tidal physics and orbital evolution histories of stellar systems.

THE ROLE OF BINARY STARS IN UNDERSTANDING THE PHYSICS AND EVOLUTION OF STARS

The diversity of close binary stars (CBS) and the rich manifestation of their activity as a result of the interaction of stellar components have turned their observed family into a very developed and effective tool for studying the evolution of stars. This review presents the main features of modern ideas about the evolution of CBS from their origin to the formation of finite compact remnants of components: degenerate dwarfs, neutron stars and stellar black holes. The main phenomena related to their interaction with each other and accompanying the process of fusion of compact components of the CBS are also listed, taking into account the effect of common envelopes, radiation of gravitational waves in cataclysmic and X-ray binaries, supernovae (SN Ia, SN Ib), gamma-bursters and other systems. The paper is based on a talk presented at the astrophysical memorial seminar “Novelties in Understanding the Evolution of Binary Stars”, dedicated to the 90th anniversary of Professor M.A. Svechnikov.

MASS RATIO AND ECCENTRICITY DISTRIBUTIONS OF YOUNG SPECTROSCOPIC BINARY STARS

We collected the information about 83 pre-main sequence double-lined spectroscopic binaries. Among them there are Ae/Be Herbig stars, T Tauri stars and red dwarfs. The eccentricity – period relation, the mass ratio and eccentricity distributions of young spectroscopic binaries are constructed and analyzed. The overwhelming majority of close binaries with \(P {{10}^{d}}\) have eccentricity near to zero, the stars less than 1 million years old are rare among them. The mass ratio distribution of systems with \(P {{10}^{d}}\) has a prominent maximum in a range of \(q = 0.9{\kern 1pt} - {\kern 1pt} 1.0\). The number of young spectroscopic binaries with \(P {{10}^{d}}\) does not decrease with decreasing mass ratio as sharply as in the case of close binary stars, about 12% of these stars have \(q 0.5\). The paper is based on a talk presented at the astrophysical memorial seminar “Novelties in Understanding the Evolution of Binary Stars”, dedicated to the 90th anniversary of Professor M.A. Svechnikov.

Tidal Angular Momentum in Close Binary Systems in presence of Wind Driven Non-conservative Mass Transfer with Uniform Mass Accretion Rate

A very well-known property of close binary stars is that they usually rotate slowly than a similar type single star. Massive stars in close binary systems are supposed to experience an exchange of mass and angular momentum via mass transfer and tidal interaction, and thus the evolution of binary stars becomes more complex than that of individual stars. In recent times, it has become clear that a large number of massive stars interact with binary companions before they die. The observation also reveals that in close pairs the rotation tends to be synchronized with the orbital motion and the companions are naturally tempted to invoke tidal friction. We here introduce the effect of tidal angular momentum in the model of wind driven non-conservative mass transfer taking mass accretion rate as uniform with respect to time. To model the angular momentum evolution of a low mass main sequence companion star can be a challenging task. So, to make the present study more interesting, we have considered initial masses of the donor and gainer stars at the proximity of bottom-line main sequence stars and they are taken with lower angular momentum. We have produced a graphical profile of the rate of change of tidal angular momentum and the variation of tidal angular momentum with respect to time under the present consideration.

Merger Conditions of Population III Protostar Binaries

Massive close binary stars with extremely small separations have been observed, and they are possible progenitors of gravitational-wave sources. The evolution of massive binaries in the protostellar accretion stage is key to understanding their formation process. We, therefore, investigate how close the protostars, consisting of a high-density core and a vast low-density envelope, can approach each other but not coalesce. To investigate the coalescence conditions, we conduct smoothed particle hydrodynamics simulations following the evolution of equal-mass binaries with different initial separations. Since Population (Pop) I and III protostars have similar interior structures, we adopt a specific Pop III model with the mass and radius of 7.75 M ⊙ and 61.1 R ⊙ obtained by the stellar evolution calculations. Our results show that the binary separation decreases due to the transport of the orbital angular momentum to spin angular momentum. If the initial separation is less than about 80% of the sum of the protostellar radius, the binary coalesces in a time shorter than the tidal lock timescale. The mass loss up to the merging is ≲3%. After coalescence, the star rotates rapidly, and its interior structure is independent of the initial separation. We conclude that there must be some orbital shrinking mechanism after the protostars contract to enter the zero-age main-sequence stage.

Spectroscopic and evolutionary analyses of the binary system AzV 14 outline paths toward the WR stage at low metallicity

Context. The origin of the observed population of Wolf-Rayet (WR) stars in low-metallicity galaxies, such as the Small Magellanic Cloud (SMC), is not yet understood. Standard, single-star evolutionary models predict that WR stars should stem from very massive O-type star progenitors, but these are very rare. On the other hand, binary evolutionary models predict that WR stars could originate from primary stars in close binaries. Aims. We conduct an analysis of the massive O star, AzV 14, to spectroscopically determine its fundamental and stellar wind parameters, which are then used to investigate evolutionary paths from the O-type to the WR stage with stellar evolutionary models. Methods. Multi-epoch UV and optical spectra of AzV 14 are analyzed using the non-local thermodynamic equilibrium (LTE) stellar atmosphere code PoWR. An optical TESS light curve was extracted and analyzed using the PHOEBE code. The obtained parameters are put into an evolutionary context, using the MESA code. Results. AzV 14 is a close binary system with a period of P = 3.7058 ± 0.0013 d. The binary consists of two similar main sequence stars with masses of M1, 2 ≈ 32 M⊙. Both stars have weak stellar winds with mass-loss rates of log Ṁ/(M⊙ yr−1) = −7.7 ± 0.2. Binary evolutionary models can explain the empirically derived stellar and orbital parameters, including the position of the AzV 14 components on the Hertzsprung-Russell diagram, revealing its current age of 3.3 Myr. The model predicts that the primary will evolve into a WR star with Teff ≈ 100 kK, while the secondary, which will accrete significant amounts of mass during the first mass transfer phase, will become a cooler WR star with Teff ≈ 50 kK. Furthermore, WR stars that descend from binary components that have accreted significant amount of mass are predicted to have increased oxygen abundances compared to other WR stars. This model prediction is supported by a spectroscopic analysis of a WR star in the SMC. Conclusions. Inspired by the binary evolutionary models, we hypothesize that the populations of WR stars in low-metallicity galaxies may have bimodal temperature distributions. Hotter WR stars might originate from primary stars, while cooler WR stars are the evolutionary descendants of the secondary stars if they accreted a significant amount of mass. These results may have wide-ranging implications for our understanding of massive star feedback and binary evolution channels at low metallicity.

A Dynamical Systems Approach to the Theory of Circumbinary Orbits in the Circular Restricted Problem

To better understand the orbital dynamics of exoplanets around close binary stars, i.e., circumbinary planets (CBPs), we applied techniques from dynamical systems theory to a physically motivated set of solutions in the Circular Restricted Three-Body Problem (CR3BP). We applied Floquet theory to characterize the linear dynamical behavior—static, oscillatory, or exponential—surrounding planar circumbinary periodic trajectories (limit cycles). We computed prograde and retrograde limit cycles and analyzed their geometries, stability bifurcations, and dynamical structures. Orbit and stability calculations are exact computations in the CR3BP and reproducible through the open-source Python package pyraa. The periodic trajectories (doi.org/10.5281/zenodo.7532982) produce a set of noncrossing, dynamically cool circumbinary orbits conducive to planetesimal growth. For mass ratios μ ∈ [0.01, 0.50], we found recurring features in the prograde families. These features include (1) an innermost near-circular trajectory, inside which solutions have resonant geometries, (2) an innermost stable trajectory (a c ≈ 1.61 − 1.85 a bin) characterized by a tangent bifurcating limit cycle, and (3) a region of dynamical instability (a ≈ 2.1 a bin; Δa ≈ 0.1 a bin), the exclusion zone, bounded by a pair of critically stable trajectories bifurcating limit cycles. The exterior boundary of the exclusion zone is consistent with prior determinations of a c around a circular binary. We validate our analytic results with N-body simulations and apply them to the Pluto–Charon system. The absence of detected CBPs in the inner stable region, between the prograde exclusion zone and a c , suggests that the exclusion zone may inhibit the inward migration of CBPs.

High-precision broadband linear polarimetry of early-type binaries

Aims. The fact that the O-type close binary star system AO Cassiopeiae exhibits variable phase-locked linear polarization has been known since the mid-1970s. In this work, we re-observe the polarization arising from this system more than 50 yr later to better estimate the interstellar polarization and to independently derive the orbital parameters, such as inclination, i, orientation, Ω, and the direction of the rotation for the inner orbit from the phase-folded polarization curves of the Stokes q and u parameters. Methods. The Dipol-2 polarimeter was used to obtain linear polarization measurements of AO Cassiopeiae in the B, V, and R passbands with the T60 remotely controlled telescope at an unprecedented accuracy level of ~0.003%. We have obtained the first proper quantification of the interstellar polarization in the direction heading towards AO Cas by observing the polarization of three neighboring field stars. We employed a Lomb-Scargle algorithm and detected a clear periodic signal for the orbital period of AO Cas. The standard analytical method based on a two-harmonics Fourier fit was used to obtain the inclination and orientation of the binary orbit. Results. Our polarimetric data exhibited an unambiguous periodic signal at 1.76 days, thus confirming the orbital period of the binary system of 3.52 days. Most of the observed polarization is of interstellar origin. The de-biased values of the orbital inclination are i = 63° + 2°/−3° and orientation of Ω = 29º(209º) ± 8°. The direction of the binary system rotation on the plane of the sky is clockwise.

Formation of Fast-spinning Neutron Stars in Close Binaries and Magnetar-driven Stripped-envelope Supernovae

Formation of Fast-spinning Neutron Stars in Close Binaries and Magnetar-driven Stripped-envelope Supernovae

MHD Modeling of Mass Transfer Processes in Close Binary Stars

A three-dimensional numerical model has been developed to study the flow structure in close binary systems with a magnetic field. The model uses a system of equations of modified magnetic hydrodynamics, which allows describing all the main dynamic effects associated with the magnetic field. It takes into account the processes of radiation heating and cooling, heating due to current dissipation, as well as magnetic field diffusion. The model allows calculations in a wide range of magnetic field values. Comparison of the calculation results with observational data confirms the reliability and high efficiency of the model. The paper presents the calculation results of the flow structure in a typical intermediate polar. It is shown that an accretion disk is formed in such a binary system, which has the following characteristic features: “hot line”, tidal shock waves, precession density wave, magnetospheric region, and accretion columns. In this case, the magnetic field in the disk is predominantly toroidal. The paper also presents the results of calculations for typical polars. In such systems, instead of an accretion disk, a collimated stream of matter is formed, moving along the magnetic field lines to the magnetic poles of the white dwarf. It is shown that in synchronous polars, variations of the mass transfer rate lead to a change in the spatial configuration of the flow. In asynchronous polars, changes in the flow structure for different phases of the beat period are observed as well as the processes of switching the flow between the magnetic poles of the accretor. Numerical calculations of the asynchronous system are performed under the assumption of the dipole configuration of the magnetic field for different values of the dipole offset relative to the center of the white dwarf. The paper presents a method for estimating this offset from observational light curves.

Close Binary Stars. IX: Statistical Studies of Close Binary Systems

Close Binary Stars. IX: Statistical Studies of Close Binary Systems