Ultraviolet Studies Of Interacting Binaries

Interacting Binaries consist of a variety of stellar objects in different stages of evolution and those containing accreting compact objects still represent a major challenge to our understanding of not only close binary evolution but also of the chemical evolution of the Galaxy. These end-points of binary star evolution are ideal laboratories for the study of accretion and outflow processes, and provide insight on matter under extreme physical conditions. One of the key-questions of fundamental relevance is the nature of SN Ia progenitors. The study of accreting compact binary systems relies on observations over the entire electromagnetic spectrum and we outline here those unresolved questions for which access to the ultraviolet range is vital, as they cannot be addressed by observations in any other spectral region.An erratum to this article can be found at     

Bimodal Structure of Gas Streams in Interacting Binaries

There are two modes of gas streams in close binary systems: geometrically thick for low mass transfer rate or geometrically thin for higher mass transfer. Geometrical thickness of the streams is not proportional to the amount of transferred mass. The limit between the two possibilities is discussed.     

On the Asynchronous Rotation of Accretors in Interacting Binaries

We show that the gaining component in interacting binaries can rotate faster than its orbital revolution as a consequence of the accretion process. We derive an approximative analytical formula for the Roche lobe radius of asynchronously rotating accretors. We present the case of the semi-detached interacting binary TX UMa, for which we measured directly asynchronous rotation of its accretor. We suggest a method to detect indirectly a fast spinning of accretors in symbiotic binaries based on the the X-ray luminosity of the boundary layer. We demonstrate this possibility for the case of EG And.     

Star-Spots Studies for Three Short Period RS CVn-Type Binaries

Light curve analysis for three short-period RS CVn-type binaries were performed, using: a) Fourier analysis techniques for light curve changes in the frequency domain; b) photometric curve fit by means of numerical quadratures to develop theoretical light curves appropriate to RS CVn stars. The two methods were applied to the systems ER Vul, BH Vir, and UV Psc. Improved physical and geometrical parameters are found by taking the average of the results measured by the above two methods.     

Transneptunian Binaries

The discovery of binaries among the population of transneptunian objects isa landmark advance in the study of this remote region of the solar system.Determination of binary orbits will enable direct determination of systemmasses, fundamental for determination of density, internal structure, and bulkcomposition. The mere existence of binaries with the observed separations andapparent masses constrains models of planetary formation.     

Studies of Stars in the Ultraviolet

Solar System Research - In this paper we describe scientific problems of stellar astrophysics that require observational data in the ultraviolet domain of the electromagnetic spectrum. These...     

密近双星中的驼峰现象

本文首先介绍激变变星SU UMa型星的驼峰现象和最近发现的X射线新星中各类光变,再从理论上探讨这些光变与驼峰现象的关系,推测驼峰现象不仅出现于光学波段,而且可能出现于紫外和X射线波段.最后,建立一种由驼峰现象判断主星是否为黑洞的可能方法.     

Be Stars in Binaries

A brief review of Be stars in binaries is presented. Attention is paid to systems, where the Be phenomenon is clearly connected to the duplicity, but is not a simple consequence of mass transfer.     

黑洞双星的形成

目前,观测证认的黑洞双星在黑洞质量分布上存在一峰值,但是还没有比较完备的理论可以解释,试图对该分布规律给出较合理的解释．鉴于恒星的氦(He)核在黑洞形成中所扮演角色的重要性,将He核质量与黑洞初始质量联系起来．根据Fryer等人的二维核塌缩模拟的结果,找到了一拟合关系,从而根据He核大小可以估算黑洞的初始质量．采用PPE恒星演化程序计算确定He核质量．最后得到星族Ⅱ和星族Ⅰ黑洞双星的黑洞初始质量的分布,并结合观测给出了相应的解释．     

The Evolution of Massive Close Binaries

We present results of evolutionary computations for massive close binaries with the Brussels simultaneous evolution code for conservative and non-conservative Roche lobe overflow (RLOF). We discuss mass transfer in massive close binaries during phases of RLOF, common envelope, spiral-in and merging. We examine the effects of stellar wind during successive stellar evolution phases and the final fate of primaries. We show how our library can be used to explain well-known binaries such as the WR + OB system V444 Cyg, HMXBs Vela X-1 and Wray 977, LMXBs like Her X-1, and binary pulsars. More details on the evolution of massive close binaries can be found in “The Brightest Binaries” (Vanbeveren et al., 1998).     

Companions of Post-Common Envelope sdB Binaries

Preliminary results are presented from two ongoing complementary surveys intended to investigate the nature and characteristics of the optically invisible secondaries in post-common envelope subdwarf B (sdB) binary stars. We obtain precise radial velocities to derive periods and minimum companion masses for bright field sdB stars. These data are combined with light curves to search for eclipses, reflection effects, or ellipsoidal variations. We emphasize the importance of using complete unbiased samples, without which it will not be possible to understand the details of the multiple processes that produce these stars. It remains true that all known secondary companions in short-period sdB binaries are nearly invisible, thus they must be either low mass main sequence (MS) stars or compact objects, e.g., white dwarfs. In our small, nearly-complete sample, white dwarf secondaries outnumber MS secondaries by about a factor of five. Known MS masses in short-period sdB binaries are all surprisingly low, indicating a possible bimodal mass distribution for all MS secondaries in sdB binaries.     

Eclipsing Binaries in Open Clusters

The study of detached eclipsing binaries in open clusters can provide stringent tests of theoretical stellar evolutionary models, which must simultaneously fit the masses, radii, and luminosities of the eclipsing stars and the radiative properties of every other star in the cluster. We review recent progress in such studies and discuss two unusually interesting objects currently under analysis. GV Carinae is an A0 m + A8 m binary in the Southern open cluster NGC 3532; its eclipse depths have changed by 0.1 mag between 1990 and 2001, suggesting that its orbit is being perturbed by a relatively close third body. DW Carinae is a high-mass unevolved B1 V + B1 V binary in the very young open cluster Collinder 228, and displays double-peaked emission in the centre of the Hα line which is characteristic of Be stars. We conclude by pointing out that the great promise of eclipsing binaries in open clusters can only be satisfied when both the binaries and their parent clusters are well-observed, a situation which is less common than we would like.     

X-Ray Binaries in Nearby Galaxies

In the last few years Chandra observations have revolutionized the study of X-ray binaries by extending observed samples to extragalactic distances and stellar environments of varied star formation history. Here we summarize some of our results related to the interpretation of current observations of young star clusters and of elliptical galaxies.     

Post-Common-Envelope Binaries with Distorted Secondaries

We will examine the properties of binary systems which have Roche lobe filling secondaries and white dwarf primaries as well as systems where the secondary is only partially filling its Roche lobe. We will also discuss observational properties such as ellipsoidal variations, light reprocessing and radial velocity measurements of the close binary systems BPM 71214, EC 13471-1258 and GD 245. The properties of BPM 71214 and EC 13471-1258 show that these systems may be pre-cataclysmic variables just prior to the onset of mass transfer or they may be hibernating novae. GD 245 is a pre-cataclysmic variable.     

Hot Subdwarfs in Precataclysmic Binaries

We present a brief review of the recent results in modeling physical processes in strongly irradiated atmospheres of unevolved companions in precataclysmic binary systems (PCB) and their light curves. Constraints on physical parameters of the hot sdws primaries, thermal instability in upper irradiated atmosphere, monochromatic albedos, the deficit of the total emergent flux compared to the incoming flux from hot sdw primary are briefly discussed.     

Infrared Observations of High-Mass X-Ray Binaries

We present the first results of our ISO program on High-Mass X-ray Binaries (HMXBs). Infrared photometry, obtained at different aspect angles of the systems, is used to investigate the massive star's disrupted stellar wind and the accretion flow towards the compact X-ray source. Scenarios for massive binary evolution predict that HMXBs receive a large kick velocity during the supernova explosion of the compact star's progenitor. One might, therefore, expect to observe wind bow shocks around these systems such as observed around many OB-runaway stars. Such a wind bow shock has recently been discovered around the system Vela X-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Formation of Black Hole Binaries

A peak exists in the distribution of observed black hole masses and no satisfactory explanation has been forthcoming so far. Here, we attempt an interpretation. We first establish a link between the helium core mass and the initial black hole mass, based on the result of 2-dimensional simulation of stellar core collapse by Fryer et al. Then the helium core masses are computed by using the PPE stellar evolution code, and the distribution of initial black hole masses for black hole binaries in stellar populations II and I is obtained. These are then compared with observations.     

Active Longitudes in Close Binaries

We obtain a class of transformations between Brans–Dicke (BD) scalar field conformal factor of the metric and the Klein–Gordon (KG) wave (its amplitude and phase), such that the BD action described by conformaly flat (CF) metrics is reduced to the KG action. We then present a modified theory as a causal Bohmian quantum gravity by using the quantum potential back reaction effects on the Minkowski background spacetime. We also derive Hamilton–Jacobi equations of the modified theory which is useful for obtaining its de Broglie pilot wave.     

Disks Around Post-Main Sequence Binaries

We propose that at least two stars on or near the AGB have long-lived orbiting disks: HD 44179, the central star in the Red Rectangle, and BM Gem, a carbon-rich star with an oxygen-rich circumstellar envelope. The CO emission from both of these disks has a spike with a width near ∼2 km s⁻¹, indicating disk radii of ∼10¹⁶ cm. The dust in such disks is therefore quite cold (near T ∼ 50 K for the Red Rectangle) and may emit primarily at submillimeter wavelengths. The disks around stars where there is also substantial mass loss may not be easily observable; there could be many as yet undiscovered disks around AGB stars This revised version was published online in September 2006 with corrections to the Cover Date.     

Wide Binaries from Few-Body Interactions

The orbital properties of wide binaries are modified by stellar encounters during their lifetimes as field stars. The few body process is particularly efficient right after the star formation in star clusters. In this article we review the orbital parameters which we expect from the few-body process. First, the solutions of the General Three-Body Problem are described, and then a detailed discussion of the theory relevant to binaries follows. Among other things, Öpik's law of the distribution of semi- major axes of the binaries is derived. In addition, we summarize recent results from the few-body problem of extended bodies which may be relevant to the early dynamical evolution of protostellar clouds.