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Affected by the Earth's atmosphere, the image of a primary and satellite system may appear unresolved, such as the dwarf planet Haumea system. It is found by experiments that neither the two-dimensional Gaussian nor modified moment centering algorithms can accurately measure the photocenter of an image of unresolved primary and satellite system observed. This work investigates a specific centering algorithm to accurately measure the photocenter, which would be helpful to derive some physical parameters (e.g. orbital parameters and mass). Taking the dwarf planet Haumea and its brighter satellite Hi'iaka as an example, we simulate the motion of the photocenter with different seeings. We find that the photocenter of system changes significantly with seeings (∼0.074″ with the different seeings of 1″ and 3″) when using the two-dimensional Gaussian centering algorithm. However, the modified moment centering algorithm can accurately measure the photocenter of system without noises, but when noises are added its accuracy will be greatly influenced by noises. In this work, a new centering algorithm is proposed, which can accurately measure the photocenter with less influence of seeings and noises. Observations of dwarf planet Haumea taken over 25 nights are used to test the effectiveness of our proposed method. Compared with using two-dimensional Gaussian centering algorithm, the fitted parameter is slightly more accurate with less positional fitting errors when using the proposed method in this work. This method can also be applied to the centering of binary stars. [ABSTRACT FROM AUTHOR]

In this study, we present the results obtained from the analysis of KOI-7234's photometric data obtained by the Kepler satellite. For the first time in the literature, the light curve analysis of the system was carried out and it seems that the system was composed of two low mass components with the masses of 0.574 M ⊙ and 0.442 M ⊙ in radii of 0.598 R ⊙ and 0.529 R ⊙ with the semi-major axis of 17.390 R ⊙ . In total, 195 flares have been detected from the short cadence data. Over these parameters, two different OPEA models were obtained for the system, and P l a t e a u values were calculated as 1.578 ± 0.117 s for the first model and 1.735 ± 0.099 s for the second, while the half-time values were calculated as 1826.87 s and 1138.10 s. The general flare frequency of the system was calculated as 0.02345 h − 1 . [ABSTRACT FROM AUTHOR]

The current consensus is that at least half of the OB stars are formed in binary or multiple star systems. The evolution of OB stars is greatly influenced by whether the stars begin as close binaries, and the evolution of the binary systems depend on whether the mass transfer is conservative or nonconservative. FUV/NUV spectropolarimetry is poised to answer the latter question. This paper discusses how the Polstar spectropolarimetry mission can characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase, and quantify its amount. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision, and polarimetry can resolve linear polarization with 10 − 3 precision or better. The spectroscopy will identify absorption by mass streams and other plasmas seen in projection against the stellar disk as a function of orbital phase, as well as scattering from extended splash structures, including jets. The polarimetry tracks the light coming from material not seen against the stellar disk, allowing the geometry of the scattering to be tracked, resolving ambiguities left by the spectroscopy and light-curve information. For example, nonconservative mass streams ejected in the polar direction will produce polarization of the opposite sign from conservative transfer accreting in the orbital plane. Time domain coverage over a range of phases of the binary orbit are well supported by the Polstar observing strategy. Special attention will be given to the epochs of enhanced systemic mass loss that have been identified from IUE observations (pre-mass reversal and tangential gas stream impact). We show how the history of systemic mass and angular momentum loss/gain episodes can be inferred via ensemble evolution through the r–q diagram. Combining the above elements will significantly improve our understanding of the mass transfer process and the amount of mass that can escape from the system, an important channel for changing the final mass and ultimate supernova of a large number of massive stars found in binaries at close enough separation to undergo interaction. [ABSTRACT FROM AUTHOR]

The winds of massive stars are important for their direct impact on the interstellar medium, and for their influence on the final state of a star prior to it exploding as a supernova. However, the dynamics of these winds is understood primarily via their illumination from a single central source. The Doppler shift seen in resonance lines is a useful tool for inferring these dynamics, but the mapping from that Doppler shift to the radial distance from the source is ambiguous. Binary systems can reduce this ambiguity by providing a second light source at a known radius in the wind, seen from orbitally modulated directions. From the nature of the collision between the winds, a massive companion also provides unique additional information about wind momentum fluxes. Since massive stars are strong ultraviolet (UV) sources, and UV resonance line opacity in the wind is strong, UV instruments with a high resolution spectroscopic capability are essential for extracting this dynamical information. Polarimetric capability also helps to further resolve ambiguities in aspects of the wind geometry that are not axisymmetric about the line of sight, because of its unique access to scattering direction information. We review how the proposed MIDEX-scale mission Polstar can use UV spectropolarimetric observations to critically constrain the physics of colliding winds, and hence radiatively-driven winds in general. We propose a sample of 20 binary targets, capitalizing on this unique combination of illumination by companion starlight, and collision with a companion wind, to probe wind attributes over a range in wind strengths. Of particular interest is the hypothesis that the radial distribution of the wind acceleration is altered significantly, when the radiative transfer within the winds becomes optically thick to resonance scattering in multiple overlapping UV lines. [ABSTRACT FROM AUTHOR]

We present our observational results of AM CVn star CR Boo in the UBVR bands. Our observational campaign includes data obtained over 5 nights with the National Astronomical Observatory Rozhen, Belogradchik, and the AS Vidojevica telescopes. During the whole time of our observations the brightness of the system varied between 13.95 – 17.23 in the B band. We report the appearance of humps during the period of quiescence and superhumps during the active state of the object, (where the latter are detected on two nights). We obtain the superhumps periodicity for two nights, P s h ≈ 24.76 − 24.92 min. The color during maximum brightness is estimated as − 0.107 < (B − V) 0 < 0.257 and the corresponding temperature is in the range as 7700 [K] < T (B − V) 0 < 11 700 [K]. We found that CR Boo varies from bluer to redder in the nights with outbursts activity. The star becomes bluer during the times of superhumps. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the problem of clustering 1318 new variable stars found in the Milky way. Our recent work distinguishes these stars based on their light curves which are univariate series of brightness from the stars observed at discrete time points. This work proposes a new approach to look at these discrete series as continuous curves over time by transforming them into functional data. Then, functional principal component analysis is performed using these functional light curves. Clustering based on the significant functional principal components reveals two distinct groups of eclipsing binaries with consistency and superiority compared to our previous results. This method is established as a new powerful light curve-based classifier, where implementation of a simple clustering algorithm is effective enough to uncover the true clusters based merely on the first few relevant functional principal components. Simultaneously we discard the noise from the data study involving the higher order functional principal components. Thus the suggested method is very useful for clustering big light curve data sets which is also verified by our simulation study. [ABSTRACT FROM AUTHOR]

We present the first evidence for the pulsations of primary components of four eclipsing binary systems. The TESS light curves of the targets are analyzed, the light and the absolute parameters are derived. Fourier analyses are applied to the residual data subtracted from the binary models to reveal the pulsational characteristics of the primaries. The components of the systems are compared to well-known binary systems of the same morphological type. The types of pulsational classes for the primaries are also discussed. Results show that CPD-30 740 and V1637 Ori are oscillating eclipsing Algol type binary stars, while HD 97329 and TYC 683-640-1 are found to be detached systems with pulsating primary components. We conclude that the primary components of the systems are pulsating stars. [ABSTRACT FROM AUTHOR]

Many exoplanets are discovered in binary star systems in internal or in circumbinary orbits. Whether the planet can be habitable or not depends on the possibility to maintain liquid water on its surface, and therefore on the luminosity of its host stars and on the dynamical properties of the planetary orbit. The trajectory of a planet in a double star system can be determined, approximating stars and planet with point masses, by solving numerically the equations of motion of the classical three-body system. In this study, we analyze a large data set of planetary orbits, made up with high precision long integration at varying: the mass of the planet, its distance from the primary star, the mass ratio for the two stars in the binary system, and the eccentricity of the star motion. To simulate the gravitational dynamics, we use a 15th order integration scheme (IAS15, available within the REBOUND framework), that provides an optimal solution for long-term integration. In our data analysis, we evaluate if an orbit is stable or not and also provide the statistics of different types of instability: collisions with the primary or secondary star and planets ejected away from the binary star system. Concerning the stability, we find a significant number of orbits that are only marginally stable, according to the classification introduced by Musielak et al. (Astron. Astrophys. 434:355, 2005). For planets of negligible mass, we estimate the critical semi-major axis a c as a function of the mass ratio and the eccentricity of the binary, in agreement with the results of Holman and Wiegert (Astron. J. 117:621, 1999). However we find that for very massive planets (Super-Jupiters) the critical semi-major axis decrease in some cases by a few percent, compared to cases in which the mass of the planet is negligible. [ABSTRACT FROM AUTHOR]

A dynamical model has been developed to envisage the star formation scenario in filamentary molecular clouds. In the present work a double well potential has been considered to find the number of stable stationary points as the origin of field star, binary stars or stellar associations. It is found that low density structure can lead to the formation of field stars while an intermediate density structure is favourable for formation of binary stars. Stellar associations are generally prevalent in dense filamentary molecular clouds. [ABSTRACT FROM AUTHOR]

The V R I passbands light curves of V344 Lac were presented and analyzed by using the latest version of the W-D code. The observed spectrum reveals that V344 Lac is not an A3 type but would be a later F type star according to the yielded temperature. The results of solution show that V344 Lac is an A-subtype contact binary, with a moderate photometric mass ratio of 0.387 ± 0.003 and a moderate contact factor of 44.6 ± 3.0 % . Based on the parallax given by Gaia, the parameters of the components are estimated as: M 1 = 1.16 M ⊙ , M 2 = 0.45 M ⊙ , R 1 = 1.31 R ⊙ , R 2 = 0.88 R ⊙ , L 1 = 2.512 L ⊙ , L 2 = 1.057 L ⊙ . The period investigation indicates that V344 Lac may have an eccentric orbital oscillation, with P 3 = 12.4 ± 0.5 yr , A 3 = 0.0020 ± 0.0002 d , and e = 0.38 ± 0.16 . Analysis shows such oscillation would be caused by a magnetic activity which can be explained by the Applegate mechanism. Meanwhile, according to the value of l 3 and the estimated physical parameters of V344 Lac, the mass of the third companion may be 0.79 M ⊙ . This third body could be a wide company. [ABSTRACT FROM AUTHOR]

It is well known that the equation of state (EoS) of compact objects like neutron and quark stars is not determined despite there are several sophisticated models to describe it. From the electromagnetic observations, summarized in Lattimer and Prakash (2001), and the recent observation of gravitational waves from binary neutron star inspiral GW170817 Abbott et al. (2017) and GW190425 The LIGO Scientific Collaboration et al. (2020), it is possible to make an estimation of the range of masses and so constraint the mass of the neutron and quark stars, determining not only the best approximation for the EoS, but which kind of stars we would be observing. In this paper we explore several configurations of neutron stars assuming a simple polytropic equation of state, using a single layer model without crust. In particular, when the EoS depends on the mass rest density, p = K ρ 0 Γ , and when it depends on the energy density p = K ρ Γ , considerable differences in the mass-radius relationships are found. On the other hand, we also explore quark stars models using the MIT bag EoS for different values of the vacuum energy density B . [ABSTRACT FROM AUTHOR]

The results of the investigation of the core-envelope model presented in Negi et al. (Gen. Relativ. Gravit. 22:735, 1990) have been discussed in view of the reference (Negi et al. in Gen. Relativ. Gravit. 51:131, 2019). It is seen that there are significant changes in the results to be addressed. In addition, I have also calculated the gravitational binding energy, causality and pulsational stability of the structures which were not considered in Negi et al. (Gen. Relativ. Gravit. 22:735, 1990). The modified results have important consequences to model neutron stars and pulsars. The maximum neutron star mass obtained in this study corresponds to the mean value of the classical results obtained by Rhoades and Ruffini (Phys. Rev. Lett. 32:324, 1974) and the upper bound on neutron star mass obtained by Kalogera and Baym (Astrophys. J. 470:L61, 1996) and is much closer to the most recent theoretical estimate made by Sotani (Phys. Rev. C 95:025802, 2017). On one hand, when there are only few equations of state (EOSs) available in the literature which can fulfil the recent observational constraint imposed by the largest neutron star masses around 2 M ⊙ (Demorest et al. in Nature 467:1081, 2010; Antoniadis et al. in Science 340:6131, 2013; Cromartie et al. in Nat. Astron. 4:72, 2020), the present analytic models, on the other hand, can comfortably satisfy this constraint. Furthermore, the maximum allowed value of compactness parameter u (≡ M / a ; mass to size ratio in geometrized units) ≤ 0.30 obtained in this study is also consistent with an absolute maximum value of u max = 0.333 − 0.005 + 0.001 resulting from the observation of binary neutron stars merger GW170817 (see, e.g. Koliogiannis and Moustakidis in Astrophys. Space Sci. 364:52, 2019). [ABSTRACT FROM AUTHOR]

We present accurate physical parameters of the eccentric binary system V889 Aql using its new spectroscopic data. According to our solutions, the system consists of two nearly identical components with primary slightly evolved. The parameters of the components are T e f f 1 = 10000 ± 250 K, T e f f 2 = 10500 ± 250 K, M 1 = 2.12 ± 0.14 M ⊙ , M 2 = 2.11 ± 0.14 M ⊙ , R 1 = 1.93 ± 0.02 R ⊙ , R 2 = 1.74 ± 0.02 R ⊙ , log L 1 = 1.52 ± 0.05 L ⊙ , log L 2 = 1.52 ± 0.04 L ⊙ . We verify the apsidal motion in the system and investigate the presence of a third body discussed in the literature. The internal structure constants of the components are derived for the first time. According to the O–C analysis, high rate of relativistic contribution to the apsidal motion given in the literature is confirmed and a value of the relativistic contribution of 68 per cent is obtained. [ABSTRACT FROM AUTHOR]

We carried out high-precision photometric observations of three eclipsing ultrashort-period contact binaries (USPCBs). Theoretical models were fitted to the light curves by means of the Wilson-Devinney code. The solutions suggest that the three targets have evolved to a contact phase. The photometric results are as follows: (a) 1SWASP J030749.87−365201.7, $q=0.439\pm0.003$ , $f=0.0\pm3.6\%$ ; (b) 1SWASP J213252.93−441822.6, $q=0.560\pm0.003$ , $f=14.2\pm1.9\%$ ; (c) 1SWASP J200059.78+054408.9, $q=0.436\pm0.008$ , $f=58.4\pm1.8\%$ . The light curves show O'Connell effects, which can be modeled by the assumed cool spots. The cool spots models are strongly supported by the night-to-night variations in the $I$ -band light curves of 1SWASP J030749.87−365201.7. For a comparative study, we collected the whole set of 28 well-studied USPCBs with $P < 0.24$ day. Thus, we found that most of them (17 of 28) are in shallow contact (i.e. fill-out factors $f<20\%$ ). Only four USPCBs have deep fill-out factors (i.e. $f>50\%$ ). Generally, contact binaries with deep fill-out factors are going to merge, but it is believed that USPCBs have just evolved to a contact phase. Hence, the deep USPCB 1SWASP J200059.78+054408.9 seems to be a contradiction, making it very interesting. Particularly, 1SWASP J030749.87−365201.7 is a zero contact binary in thermal equilibrium, implying that it should be a turn-off sample as predicted by the thermal relaxation oscillation (TRO) theory. [ABSTRACT FROM AUTHOR]

The eclipsing symbiotic binary BF Cyg has had five orbital minima during its last optical outburst after 2006. The second minimum is much shallower than the first one and after that the minimum get deeper again. We determined the parameters of the accretion structure surrounding the compact object in two minima and traced its evolution until 2014. Moreover, we analysed the continuum of the system in the region of the $UBVR_{\mathrm{C}}I_{\mathrm{C}}$ photometric bands to derive the parameters of its components at two times orbital maximum and calculated the mass-loss rate of the compact object. The results obtained allow us to conclude about the mechanism of fading of the optical light of the system until 2014. These results show that the optical flux of the outbursted compact object decreases because of 'contraction' of its observed photosphere (pseudophotosphere) which, on its side, is due to increase of the velocity of its stellar wind, and the optical flux of the circumbinary nebula decreases mainly because of reduction of its mean density, which, on its side, is due to destruction of the accretion structure. [ABSTRACT FROM AUTHOR]

In the present study we have analysed Chandra Observational data of 2 galaxies: NGC 5643 and NGC 7457. Four point sources from NGC 5643 and two point sources from NGC 7457 with net counts ${\ge} 100$ were considered for the present study. The spectra of these sources were fitted using two spectral models- an absorbed powerlaw and an absorbed disk blackbody. The spectrum of all the sources can be explained almost equally by both the models. We report here the discovery of 3 Ultraluminous X-ray sources (ULXs), X-1, X-2 and X-3 in the galaxy NGC 5643 and one ULX, X-5 in the galaxy NGC 7457. The spectral parameters suggest that all the above four ULX sources are in hard state ( $\varGamma \sim 1.42\mbox{--}1.86$ ), which may be due to thermal comptonization. If explained by absorbed diskblackbody model, the Black Hole (BH) mass of these sources are estimated to be stellar mass BHs with X-2, & X-5 accreting at super-Eddington rate while X-1 and X-3 at sub-Eddington rate. Another ULX, X-4 in NGC 5643 which is also accreting at super-Eddington rate is found to be a variable ULX with its luminosity reducing from $4.4 \times 10^{40}~\mbox{ergs}\,\mbox{s}^{-1}$ to $2.27 \times 10^{40}~\mbox{ergs}\,\mbox{s}^{-1} $ in the 0.3-10.0 keV energy range within a period of 11 years. [ABSTRACT FROM AUTHOR]

Asteroids that follow similar orbits may have a dynamical connection as their current paths could be the result of a past interaction with a massive perturber. The pair of extreme trans-Neptunian objects or ETNOs (474640) 2004 VN-2013 RF exhibits peculiar relative orbital properties, including a difference in longitude of the ascending node of just 1 $\stackrel {\circ }{\text{.}}$ 61 and 3 $\stackrel {\circ }{\text{.}}$ 99 in inclination. In addition, their reflectance spectra are similar in the visible portion of the spectrum. The origin of these similarities remains unclear. Neglecting observational bias, viable scenarios that could explain this level of coincidence include fragmentation and binary dissociation. Here, we present results of extensive direct $N$ -body simulations of close encounters between wide binary ETNOs and one trans-Plutonian planet. We find that wide binary ETNOs can dissociate during such interactions and the relative orbital properties of the resulting unbound couples match reasonably well those of several pairs of known ETNOs, including 474640-2013 RF. The possible presence of former binaries among the known ETNOs has strong implications for the interpretation of the observed anisotropies in the distributions of the directions of their orbital poles and perihelia. [ABSTRACT FROM AUTHOR]

This paper investigates the periodic motion of a particle in the doubly synchronous binary asteroid systems. Two typical doubly synchronous systems, 809 Lundia and 3169 Ostro, are discussed in detail. Under the Roche figure assumption, the two bodies of doubly synchronous system can be modeled as two triaxial ellipsoids. The Ivory's theorem is used to derive the gravitational potential of the system. Then, a global numerical method, which combines grid searching and differential correction, is developed for systematically searching periodic orbits in the doubly synchronous systems. A total of 30 and 28 families of periodic orbits around Lundia and Ostro are found, respectively. Furthermore, on the basis of the analysis of morphology, stabilities and invariant manifolds, the potential applications of these periodic orbit families are studied. Several quasi-circular orbit families with low instability index are found to be suitable for the observation of the two typical binary systems. The invariant manifolds of some periodic orbits near the equilibrium points can provide the fuel-free trajectories to achieve the ballistic landing to the surface of the asteroids and transfer between the binary asteroids. [ABSTRACT FROM AUTHOR]

Stellar membership determination of an open cluster is an important process to do before further analysis. Basically, there are two classes of membership determination method: parametric and non-parametric. In this study, an alternative of non-parametric method based on Binned Kernel Density Estimation that accounts measurements errors (simply called BKDE- e) is proposed. This method is applied upon proper motions data to determine cluster's membership kinematically and estimate the average proper motions of the cluster. Monte Carlo simulations show that the average proper motions determination using this proposed method is statistically more accurate than ordinary Kernel Density Estimator (KDE). By including measurement errors in the calculation, the mode location from the resulting density estimate is less sensitive to non-physical or stochastic fluctuation as compared to ordinary KDE that excludes measurement errors. For the typical mean measurement error of 7 mas/yr, BKDE- e suppresses the potential of miscalculation by a factor of two compared to KDE. With median accuracy of about 93 %, BKDE- e method has comparable accuracy with respect to parametric method (modified Sanders algorithm). Application to real data from The Fourth USNO CCD Astrograph Catalog (UCAC4), especially to NGC 2682 is also performed. The mode of member stars distribution on Vector Point Diagram is located at μcos δ=−9.94±0.85 mas/yr and μ=−4.92±0.88 mas/yr. Although the BKDE- e performance does not overtake parametric approach, it serves a new view of doing membership analysis, expandable to astrometric and photometric data or even in binary cluster search. [ABSTRACT FROM AUTHOR]

The equilibrium points and the curves of zero-velocity (Roche varieties) are analyzed in the frame of the regularized circular restricted three-body problem. The coordinate transformation is done with Levi-Civita generalized method, using polynomial functions of n degree. In the parametric plane, five families of equilibrium points are identified: $L_{i}^{1}, L_{i}^{2}, \ldots, L_{i}^{n}$, $i\in\{ 1,2,\ldots,5 \}, n \in\mathbb{N}^{*}$. These families of points correspond to the five equilibrium points in the physical plane L, L,..., L. The zero-velocity curves from the physical plane are transformed in Roche varieties in the parametric plane. The properties of these varieties are analyzed and the Roche varieties for n∈{1,2,...,6} are plotted. The equation of the asymptotic variety is obtained and its shape is analyzed. The slope of the Roche variety in $L_{1}^{1}$ point is obtained. For n=1 the slope obtained by Plavec and Kratochvil () in the physical plane was found. [ABSTRACT FROM AUTHOR]

The aim of the present work is to find the secular solution around the triangular equilibrium points and reduce it to the periodic solution in the frame work of the generalized restricted thee-body problem. This model is generalized in sense that both the primaries are oblate and radiating as well as the gravitational potential from a belt. We show that the linearized equation of motion of the infinitesimal body around the triangular equilibrium points has a secular solution when the value of mass ratio equals the critical mass value. Moreover, we reduce this solution to periodic solution, as well as some numerical and graphical investigations for the effects of the perturbed forces are introduced. This model can be used to examine the existence of a dust particle near the triangular points of an oblate and radiating binary stars system surrounded by a belt. [ABSTRACT FROM AUTHOR]

Reflection effect phenomenon is studied on the formation of spectral lines in a close binary system when primary component has an extended atmosphere and the secondary component is a point source. Irradiation effect is calculated using one dimensional rod model and self radiation is calculated using continuum radiative transfer equation in spherically symmetric atmosphere. The total radiation is the sum of the radiation of the individual components and the mutually reflected light. Line profiles are also computed along the line of sight observer at infinity for irradiation, self radiation and total radiation and compared in order to study the reflection effect on spectral lines. It is found that the radiation field varies on the primary component when angle of incidence changes from the secondary component. The contour maps show that the radiative interaction makes the outer surface of the primary star warm when its companion illuminates the radiation. The effect of reflection on spectral lines is studied and noticed that the flux in the lines increases at all frequency points and the cores of the lines received more flux than the wings and equivalent width changes accordingly. [ABSTRACT FROM AUTHOR]

We report the results of our population synthesis for post common-envelope binaries by following the evolution of each system in detail. Our main focus is a comparison with the white dwarf mass distribution of post common-envelope systems from the Sloan Digital Sky Survey. We employ a Monte Carlo method to choose the initial parameters of the progenitors (primary mass, mass ratio and orbital period). Then the evolution of the progenitor binary system is followed up to the onset of the common-envelope phase, which usually occurs near the tip of the giant branch or asymptotic giant branch. An approximate post-Helium flash evolution for primary masses ${\leq}2.25 \mathrm{M_{\odot}}$ is included. The binary parameters before and after common-envelope phase are calculated using the energy budget argument. In this paper we address the case of α=1.0, which is the commonly adopted value to calculate the common-envelope ejection. We consider a hydrogen-exhausted core to define the core mass of the primary (white dwarf mass, M) at the onset of common envelope phase. To obtain the present-day M distributions, we assumed a constant star formation rate. The distribution resulting from our population synthesis shows a double peak profile for M, similar to previous population syntheses and recent observational data. Our present synthesis result could not reproduce the location of the low and high mass peaks from the observations, but shows how a future synthesis can be made to produce an M distribution which is closer to observational data. [ABSTRACT FROM AUTHOR]

We present ultraviolet spectra of two eclipsing interacting binary systems, W Ser and UX Mon, with good coverage over the 14.16-day and 5.9-day orbital periods, respectively, using observations taken by the International Ultraviolet Explorer ( IUE) during the period between 1978-1993 and 1981-1991. Two profiles of W Ser and UX Mon showing variations of line fluxes at two orbital phases are presented. This paper focuses on the N V emission line at 1240 Å, C II emission line at 1336 Å, C IV emission line at 1550 Å, O III emission line at 1666 Å and the Si III emission line at 1892 Å, produced in an extended gaseous envelope around the mass-gaining component by calculating spectral line fluxes. Our results show that there are variations of line fluxes with time, similar to the light curves found for both W Ser and UX Mon. We attribute these spectral variations to eclipse effects and to variations in the mass transfer rate. These results from the IUE observations support the thick disk model around the primary star in which variations of mass transfer affect the observed radiation from the gaseous envelope around the hot star. Future, high-resolution imaging is recommended to confirm the inferred asymmetrical circumstellar envelopes. [ABSTRACT FROM AUTHOR]

We present low and high resolution ultraviolet spectra of the Capella spectroscopic binary system from the observations taken by the International Ultraviolet Explorer (IUE) during the period between 1978-1990 and 1978-1995. Thirteen profile of Capella showing variations of line fluxes at different orbital phases are presented. This paper focuses on the C IV emission line at 1550 Å produced in the transition region of the secondary star and Mg II emission lines at 2800 Å produced in the stellar chromosphere of the secondary star by calculating spectral line fluxes. Our results show that there are significant variations of line fluxes with time. These spectral variations are similar to that found in the EUV by Dupree and Brickhouse (in Int. Astron. Union Symp. 176P:184D, ) in the UV for H 1 Ly α by Ayres et al. (in Astrophys. J. 402:710A, ), and in the near IR by Katsova (in Astrophys. Space Sci. 252:427K, ). We attribute these variations in line fluxes to the variations of both density and temperature in the line emitting regions as a result of the intermediate-scale magnetic fields responsible for stellar activity leading to these spectral variations. [ABSTRACT FROM AUTHOR]

We locate and examine the stability of the 'out of plane' equilibrium points, L of an infinitesimal body in the field of stellar-oblate binary systems moving in elliptic orbits around their common center of mass. Their positions and stability depend on the oblateness as well as radiation coefficients of the primaries and the eccentricity of their orbits. A numerical application of this problem for the systems: Gamma Leporis and Altair are given. [ABSTRACT FROM AUTHOR]

This paper investigates the motion of an infinitesimal body in the generalized restricted three-body problem. It is generalized in the sense that both primaries are radiating, oblate bodies, together with the effect of gravitational potential from a belt. It derives equations of the motion, locates positions of the equilibrium points and examines their linear stability. It has been found that, in addition to the usual five equilibrium points, there appear two new collinear points L, L due to the potential from the belt, and in the presence of all these perturbations, the equilibrium points L, L come nearer to the primaries; while L, L, L, L move towards the less massive primary and L moves away from it. The collinear equilibrium points remain unstable, while the triangular points are stable for 0< μ< μ and unstable for $\mu_{c} \le\mu\le\frac{1}{2}$, where μ is the critical mass ratio influenced by the oblateness and radiation of the primaries and potential from the belt, all of which have destabilizing tendency. A practical application of this model could be the study of the motion of a dust particle near the oblate, radiating binary stars systems surrounded by a belt. [ABSTRACT FROM AUTHOR]

This paper deals mainly with the application of the mixed leapfrog symplectic integrators with adaptive timestep to a conservative post-Newtonian Hamiltonian formulation with canonical spins for spinning compact binaries. The adaptive timestep depends on the two body separation r and the magnitude of the spins. Various numerical tests including a chaotic high-eccentricity orbit show that the fixed step symplectic integrators lost drastically the good long term behaviour in the test cases with large eccentricity, the adaptive timestep integrator is always superior to the constant step in the integral precision. [ABSTRACT FROM AUTHOR]

We take the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron star (NS) low-mass X-ray binaries (LMXBs) as the samples, and investigate the morphology of the samples, which focuses on the quality factor, peak frequency of kHz QPOs, and try to infer their physical mechanism. We notice that: (1) The quality factors of upper kHz QPOs are low (2∼20 in general) and increase with the kHz QPO peak frequencies for both Z and Atoll sources. (2) The distribution of quality factor versus frequency for the lower kHz QPOs are quite different between Z and Atoll sources. For most Z source samples, the quality factors of lower kHz QPOs are low (usually lower than 15) and rise steadily with the peak frequencies except for Sco X-1, which drop abruptly at the frequency of about 750 Hz. While for most Atoll sources, the quality factors of lower kHz QPOs are very high (from 2 to 200) and usually have a rising part, a maximum and an abrupt drop. (3) There are three Atoll sources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high quality factors for lower kHz QPOs. These three sources have been detected with the spin frequencies and sidebands, in which the source with higher spin frequency presents higher quality factor of lower kHz QPOs and lower difference between sideband frequency and lower kHz QPO frequency. [ABSTRACT FROM AUTHOR]

In this paper, the rms-flux (root mean square-flux) relation along the Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e. positive, negative, and 'arch'-like correlations are found in different branches. The rms is positively correlated with flux in normal branch (NB), but anti-correlated in the vertical horizontal branch (VHB). The rms-flux relation shows an 'arch'-like shape in the horizontal branch (HB). We also try to explain this phenomenon using existing models. [ABSTRACT FROM AUTHOR]

The ESA Gaia mission will bring a new era to the domain of standard candles. Progresses in this domain will be achieved thanks to unprecedented astrometric precision, whole-sky coverage and the combination of photometric, spectrophotometric and spectroscopic measurements. The fundamental outcome of the mission will be the Gaia catalogue produced by the Gaia Data Analysis and Processing Consortium (DPAC), which will contain a variable source classification and specific properties for stars of specific variability types. We review what will be produced for Cepheids, RR Lyrae, Long Period Variable stars and eclipsing binaries. [ABSTRACT FROM AUTHOR]

The regularization of a new problem, namely the three-body problem, using 'similar' coordinate system is proposed. For this purpose we use the relation of 'similarity', which has been introduced as an equivalence relation in a previous paper (see Roman in Astrophys. Space Sci. doi:, ). First we write the Hamiltonian function, the equations of motion in canonical form, and then using a generating function, we obtain the transformed equations of motion. After the coordinates transformations, we introduce the fictitious time, to regularize the equations of motion. Explicit formulas are given for the regularization in the coordinate systems centered in the more massive and the less massive star of the binary system. The 'similar' polar angle's definition is introduced, in order to analyze the regularization's geometrical transformation. The effect of Levi-Civita's transformation is described in a geometrical manner. Using the resulted regularized equations, we analyze and compare these canonical equations numerically, for the Earth-Moon binary system. [ABSTRACT FROM AUTHOR]

In literature, there is no exact analytical solution available for determining the radius of Roche equipotential surfaces of distorted close binary systems in synchronous rotation. However, Kopal (Roche Model and Its Application to Close Binary Systems, Advances in Astronomy and Astrophysics, Academic Press, New York ) and Morris (Publ. Astron. Soc. Pac. 106:154, ) have provided the approximate analytical solutions in the form of infinite mathematical series. These series expressions have been commonly used by various authors to determine the radius of the Roche equipotential surfaces, and hence the equilibrium structures of rotating stars and stars in the binary systems. However, numerical results obtained from these approximating series expressions are not very accurate. In the present paper, we have expanded these series expressions to higher orders so as to improve their accuracy. The objective of this paper is to check, whether, there is any effect on the accuracy of these series expressions when the terms of higher orders are considered. Our results show that in most of the cases these expanded series give better results than the earlier series. We have further used these expanded series to find numerically the volume radius of the Roche equipotential surfaces. The obtained results are in good agreement with the results available in literature. We have also presented simple and accurate approximating formulas to calculate the radius of the primary component in a close binary system. These formulas give very accurate results in a specified range of mass ratio. [ABSTRACT FROM AUTHOR]

Detailed analyses by independent research groups over several decades reveal a significant discrepancy between the observed rate of periastron advance in the detached eclipsing binary star systems DI Herculis and V541 Cygni and the values theoretically predicted from the combined classical and general relativistic effects. A modification to Newton's gravitational theory is proposed in this investigation to account for these discrepancies, and is represented by where G is a second gravitational constant. The two body problem is solved analytically in closed form, resulting in a retrograde contribution to the advance of periastron. Numerical values of G were calculated from an analysis of the available data for each of these binary star systems, resulting in a value of G=(1.5±0.3)×10 m kg s from the analysis of V541 Cygni, and $G_{o} = (1.5_{ - 1.5}^{ + 0.3}) \times 10^{-27}~\mbox{m}^{2}\,\mbox{kg}^{-1}\,\mbox{s}^{-2}$ from an analysis of DI Herculis. The level of agreement between these values supports the assumption that the rotational axes of the stars in V541 Cygni are oriented perpendicular to the orbital plane, as opposed to the highly inclined orbits of the stars observed in DI Herculis. An independently determined value of G was calculated through an analysis of the Pioneer anomaly data, resulting in G=(3.00±0.37)×10 m kg s. Within a factor of two, this value of G agrees with the results obtained from DI Herculis and V541 Cygni. The proposed theory predicts the 'turn on' of the Pioneer anomaly to occur at a heliocentric distance of 10.0 AU, in good agreement with observation. [ABSTRACT FROM AUTHOR]

A new equivalence relation, named relation of 'similarity' is defined and applied in the restricted three-body problem. Using this relation, a new class of trajectories (named 'similar' trajectories) are obtained; they have the theoretical role to give us new details in the restricted three-body problem. The 'similar' coordinate systems allow us in addition to obtain a unitary and an elegant demonstration of some analytical relations in the Roche geometry. As an example, some analytical relations published by Seidov (in Astrophys. J. 603:283, ) are demonstrated. [ABSTRACT FROM AUTHOR]

We present results of 3D numerical simulations of the matter flow in the disk of a binary T Tauri star. It is shown that two bow-shocks caused by the supersonic motion of the binary components in the gas of the disk are formed in the system having parameters typical for T Tauri stars. These bow-shocks significantly change the flow pattern. In particular, for systems with circular orbits they determine the size and shape of the inner gap. We also show that the redistribution of the angular momentum due to the bow-shocks leads to occurrence of two matter flows propagating from the inner edge of the circumbinary disk to the components. Further redistribution of this matter between the components is considered. [ABSTRACT FROM AUTHOR]

Detection of a composite flux in photometry can serve as an indication of a photometrically unresolved binarity and can contribute to the parameterization of the components of binary systems. A main goal of the present study is to develop a method of automatic photometric detection of binaries, based on multi-color photometry, theoretical stellar spectral energy distributions and general understanding of binary evolution. In particular, we consider an ultraviolet photometry where, in combination with optical and infrared photometry, interstellar reddening can be easier distinguished from temperature reddening. The following procedure is applied to achieve the declared goal. One can compose possible pairs of components, based on evolution concept. This can be done for various stages of binary evolution. Theoretical spectral energy distributions and response functions of ultraviolet photometric bands in appropriate sky surveys allow us to compute color-indices of such pairs, when they are unresolved, as well as of single stars. Usage of an interstellar extinction law gives us theoretical color-indices of reddened objects, both single stars and unresolved binaries. When plotted on a multidimensional color space, they allow us to indicate areas, where unresolved binaries can be easily separated from single stars, and identify binaries among objects, cross-matched in photometric surveys. [ABSTRACT FROM AUTHOR]

We obtained several epochs of light minima and a complete R light curve of the W-type contact binary V1128 Tau in 2009. Two cool spots on the massive component are used to model the photometric light curve. Using all available data we find evidence for a long-term period variation with an amplitude of 0.0050±0.0012 days and a period of 16.7±0.9 years. Using parameters derived from a photometric model of the 2009 light curve we show that this period change could be explained by the Applegate mechanism on one of the components. [ABSTRACT FROM AUTHOR]

High speed photometric observations of the dwarf nova VSX J074727.6 + 065050 made in December 2009 during quiescence show an orbital modulation at P=85.6 min. They also show that the star is a member of the relatively rare CV/ZZ group, i.e. the accreting white dwarf primary has non-radial pulsations. The two regions of oscillating power are at 684 s and 238 s. There is some evidence for hidden ∼1 µHz fine structure splitting, which has been seen in three other CV/ZZ stars. [ABSTRACT FROM AUTHOR]

We discuss the possibility to obtain an electromagnetic emission accompanying the gravitational waves emitted in the coalescence of a compact binary system. Motivated by the existence of black hole configurations with open magnetic field lines along the rotation axis, we consider a magnetic dipole in the system, the evolution of which leads to (i) electromagnetic radiation, and (ii) a contribution to the gravitational radiation, the luminosity of both being evaluated. Starting from the observations on magnetars, we impose upper limits for both the electromagnetic emission and the contribution of the magnetic dipole to the gravitational wave emission. Adopting this model for the evolution of neutron star binaries leading to short gamma ray bursts, we compare the correction originated by the electromagnetic field to the gravitational waves emission, finding that they are comparable for particular values of the magnetic field and of the orbital radius of the binary system. Finally we calculate the electromagnetic and gravitational wave energy outputs which result comparable for some values of magnetic field and radius. [ABSTRACT FROM AUTHOR]

The interest in the study of the Algol binary system Y Leonis is justified not only by its light curve having a very deep primary minimum, and pulsating character of its primary component, but also by the complex behavior of its O- C curve which is featured by the presence of long and short time scale modulations. Taking into account the previously inferred K spectral type of the secondary component, one may expect that one of the involved periodicities could be related to magnetic cycles of this star. We gave the Wilson-Devinney solution of the eclipse light curve using our observational data obtained during 2009. The long- and short-term photometric variability of Y Leo is approached both through literature data and new CCD data. Even though these data are scarce, they revealed significant variability in the maximum and minimum brightness of this binary system at long time-scale. The nature of the rapid photometric variations during the deepest phase of primary minima can hardly be explained only by weak δ Scuti pulsations of the primary component which is still visible in partial eclipses. [ABSTRACT FROM AUTHOR]

We present spectroscopic orbits for the active stars HD 82159 (GS Leo), HD 89959, BD +39° 2587 (a visual companion to HD 112733), HD 138157 (OX Ser), HD 143705, and HD 160934. This paper is a sequel to one published in this journal in 2006, with similar avowed intention, by Gálvez et al. They showed only graphs, and gave no data, and no orbital elements apart from the periods (only two of which were correct) and in some cases the eccentricities. Here we provide full information and reliable orbital elements for all the stars apart from HD 160934, which has not completed a cycle since it was first observed for radial velocity. [ABSTRACT FROM AUTHOR]

We present the first-look analysis of the high-speed multicolour photometry of the bright V361 Hya-type star EO Ceti ( m=12.3). The observations were gathered with the three-channel ULTRACAM instrument attached to the 4.2-m William Herschel Telescope. The data set has a total time span of 6.2 d and consists of 31 h simultaneous three colour photometry. The main power regions in all three colours are the same as previously reported in the white light photometric campaigns on EO Ceti. We calculate the frequencies, amplitudes and phases of the significant modes in three colours of the SDSS system, r′, g′ and u′. The amplitudes of the detected modes are the highest in the u′ lightcurve, and the phases are the same in all three colours within the measurement accuracy. The amplitudes of the highest signal-to-noise modes show time variability in all three colours. We analyse the amplitude and phase variations of the five highest signal-to-noise modes in different colours. Even though the amplitudes show variations from night to night, the amplitude ratios are found to be constant to within 2 σ level. This result is promising as it allows us to compare the observed amplitude ratios with theoretically calculated amplitude ratios. This may further constrain the mode identification of the highest amplitude modes in EO Ceti and let us test the proposed seismic and binary evolution models. [ABSTRACT FROM AUTHOR]

SDSS J160043.6+074802.9 appears to be a binary consisting of a subwarf-O (sdO) star and a late-type Main Sequence companion; the sdO is the only known pulsator in this class of stars and some modes have pulsation amplitude and frequency variations. Surface gravity and helium abundance determinations in the literature do not agree within quoted error limits; these appear to have unidentified systematic errors which, once accounted for, should show that surface gravity and helium abundance determinations to date are not as discordant as is currently supposed. Non-linear pulsation effects are proposed as a possible interpretation of pulsation amplitude and frequency variations observed in some modes. [ABSTRACT FROM AUTHOR]

In this talk, we will simply show the consequences of binary population synthesis for blue stragglers, such as the integrated spectral energy distribution (ISED), the color-magnitude diagram, the specific frequency, and the influences on colors. Blue stragglers have been found in all stellar populations and they are an important population component in both stellar evolution and star clusters. Much evidence shows that blue stragglers are relevant to primordial binaries. The binary population synthesis study shows that primordial binary evolution may produce blue stragglers at any given times. The specific frequency in this way decreases with time first, then increases when the age is larger than 10 Gyr, while that from angular momentum loss induced by magnetic braking in low-mass binaries increases with time and exceeds that of primordial binary evolution in a population older than 3 Gyr. Meanwhile, blue stragglers resulting from primordial binary evolution are dominant contributors to the ISEDs in ultraviolet and blue bands in a population between 0.3 and 2.0 Gyr. The mass fraction of the lost matter from the primary accreted by the secondary, β, significantly affects on the final results, e.g. the specific frequency of blue stragglers decreasing with β, blue stragglers produced from a high value of β being more massive, then contributing more to the ISEDs of the host clusters. For old open clusters, it is appropriate to adopt a higher value of β when the primary is in HG at the onset of mass transfer. Our study also shows that, for most Galactic open clusters, the specific frequency of blue stragglers obtained from our simulations is much lower than that of observations, which has been discussed in this talk. [ABSTRACT FROM AUTHOR]

In this contribution, we explore some open questions about Extreme Horizontal Branch (EHB) stars in globular clusters. In particular, we present the current status of the search for rapid pulsators, He-depleted stars, and close binaries, three kind of objects very common among field EHB stars, but which first surveys failed to detect in clusters. We also analyze how the lack of cluster EHB binaries can reconcile with theoretical expectations. We give special attention to the first close EHB binary discovered in a globular cluster, whose characteristics point to a very rare or even unique object. Finally, we analyze some recent puzzling results about spectroscopically derived masses, that could point to the presence of two distinct families of EHB's in clusters. For all these topics, we present the recent advancement in knowledge, the results requiring more investigation, and what has still to be done to fix the unsolved problems, showing the main points of our studies, the aims of our works, and what we expect to obtain from them. [ABSTRACT FROM AUTHOR]

I briefly review the method of population synthesis of binary stars and discuss the preliminary results of a study of the Galactic population of subdwarf B stars. In particular I focus on the formation of (apparently) single sdB stars and their relation to (apparently) single helium-core white dwarfs. I discuss the merits of mergers of two helium white dwarfs and interactions with sub-stellar companions for explaining these single objects. A preliminary conclusion is that the current observations suggest both mechanisms may contribute, but that the helium white dwarfs are likely formed in majority from interactions with sub-stellar companions. [ABSTRACT FROM AUTHOR]

In the last decade or so, there have been numerous searches for hot subdwarfs in close binaries. There has been little to no attention paid to wide binaries, however. The advantages of understanding these systems can be many. The stars can be assumed to be coeval, which means they have common properties. The distance and metallicity, for example, are both unknown for the subdwarf component, but may be determinable for the secondary, allowing other properties of the subdwarf to be estimated. With this in mind, we have started a search for common proper motion pairs containing a hot subdwarf component. We have uncovered several promising candidate systems, which are presented here. [ABSTRACT FROM AUTHOR]

The HYPER-MUCHFUSS (HYPER-velocity stars or Massive Unseen Companions of Hot Faint Underluminous Stars from SDSS) project targets a population of high-velocity subluminous B stars to discover either close binaries with massive unseen companions or hyper-velocity stars. We re-observed high-velocity subdwarf selected candidates from the SDSS spectroscopic Data Release 6. Starting in 2007 we used several instruments and have now reached a completion level of 33% (from 265 targets), whereas we found at least 16 close binaries. Here we present results for two of our 39 hyper-velocity star candidates. From the available Digitized Sky Surveys photographic plates we measured a significant proper motion for 14 stars. Combining this information with a detailed spectroscopic analysis allows for the first time a complete determination of the 3D-trajectories for a high-velocity sample. We present our preliminary results for the two subdwarfs J1644+4523 and J1211+1437. Assuming the Standard Allen and Santillan (Rev. Mex. Astron. Astrofis. 22:255, ) potential the first one is bound and originates in the central region of the Galaxy. The subdwarf B star J1211+1437 is possibly unbound and seems to originate in the Galactic rim. We also performed numerical kinematical experiments with increased dark matter halo mass. and found that the origin of J1644+4523 in the central region is not changed but the time-of-flight is drastically shortened. J1211+1437 would be bound and probably belongs to population II. [ABSTRACT FROM AUTHOR]

The HYPER-MUCHFUSS project targets a population of high velocity subluminous B stars to discover either close binaries with massive unseen companions or hyper-velocity stars. Our starting point is the enormous database of SDSS. We preselected sdO/B candidates by colour and classified them by visual inspection of their spectra. We measured the radial velocity from the coadded SDSS spectra, which serves as first epoch measurement. Stars with high Galactic rest-frame velocities were selected and second epoch observations were obtained starting in 2007 at several sites. For the brighter targets we also included the SDSS individual spectra as additional information. In the course of our survey we observed 88 out of 265 stars from our target list. We discovered 39 HVS candidates as well as 49 close binaries. In addition we analysed all single spectra of sdBs from SDSS and found 120 close binaries. For the targets with constant RVs we performed a proper motion analysis with the highest possible accuracy from the available digitised photographic plates. Together with the analysed spectra and the calculation of the spectroscopic distance, we calculated complete trajectories and deduced the origins of these stars. Targets with high RV variability on short timescales were selected for follow-up. Numerical simulations based on the period and companion mass distribution of the known sdB binary sample were carried out to optimise the target selection and single out candidate binaries with massive companions. The follow-up campaign using WHT/ISIS and CAHA-3.5m/TWIN started in 2009. [ABSTRACT FROM AUTHOR]