Close Binary Stars Research Articles

A photometric study of V1193 Ori: Detection of orbital and negative superhump periods

We present the results obtained from unfiltered photometric CCD observations of V1193 Ori made during 24 nights between November 2002 and January 2003. We found periods of 0.1430 d , 0.1362 d and possibly 2.98 d in the data. The 0.1430 d period is consistent with the 1 d −1 alias of the proposed orbital period of P orb = 0.165 d (Ringwald, F.A., Thorstensen, J.R., Hamwey, R.M., 1994. MNRAS 271, 323; Papadaki, C., Boffin, H.M.J., Cuypers, J., Stanishev, V., Kraicheva, Z., Genkov, V., 2004. In: Hilditch, R.W., Hensberge, H., Pavlovski, K. (Eds.), Spectroscopically and Spatially Resolving the Components of Close Binary Stars, ASP Conference Series, vol. 318, Astronomical Society of the Pacific, San Francisco, p. 399.). Thus and using the known relation between the orbital and superhump periods, we interpret these periods as the orbital period of 0.1430 d , the negative superhump period of 0.1362 d and the precession period of 2.98 d . V1193 Ori can then be classified as a permanent superhump system.

The Structure of Close Binaries in Two Dimensions

The structure and evolution of close binary stars has been studied using the two-dimensional stellar structure algorithm developed by Deupree. We have calculated a series of solar composition stellar evolution sequences of binary models in which the mass of the two-dimensional model is 8 M☉ with a point-mass 5 M☉ companion. We have also studied the structure of the companion in two dimensions by considering the zero-age main sequence (ZAMS) structure of a 5 M☉ model with an 8 M☉ point-mass companion. This result suggests that treating the 5 M☉ star as a point source for the 8 M☉ evolution is reasonable. In all cases, the binary orbit was assumed to be circular and corotating with the rotation rate of the stars. We considered binary models with three different initial separations, a = 10, 14, and 20 R☉. These models were evolved through central hydrogen burning or until the more massive star expanded to fill its critical potential surface or Roche lobe. The model with a separation of 20 R☉ will be expected to go through case B-type mass transfer during the shell H-burning phase. The 14 R☉ model is expected to go through mass transfer much earlier, near the middle of core hydrogen burning, and the 10 R☉ model is very close to this situation at the ZAMS. The calculations show that evolution of the deep interior quantities is only slightly modified from those of single-star evolution. Describing the model surface as a Roche equipotential is also satisfactory until very close to the time of Roche lobe overflow, when the self-gravity of the model about to lose mass develops a noticeable aspherical component and the surface timescale becomes sufficiently short, so that it is conceivable that the actual surface is not an equipotential.

A parallel code for the analysis of light curves of close binary stars with surface inhomogeneities through the Astrocomp-grid portal

We present a parallel code for the analysis of sequences of light curves of magnetically active close binaries with brightness inhomogeneities on the surfaces of their component stars. The procedure allows us to search for the best values of the photometric parameters of the binary system as well as to obtain maps of the brightness inhomogeneities regularized by means of the Maximum Entropy and Tikhonov methods. The large amount of computational work is managed by means of a parallel application based on MPI. The code has been made available through the web-based portal Astrocomp ( http://www.astrocomp.it) that allows a registered remote user to run it on a set of high-performance computing resources in a completely transparent manner.

Eclipsing Spectroscopic Binaries in the SMC

The OGLE survey of the SMC has discovered ~1500 eclipsing binaries thereby providing an excellent platform to study the evolution of close binary systems through case A and case B mass-exchange processes. The complementary spectroscopic radial-velocity studies of these binaries are now in progress and are revealing many interesting systems which challenge current theoretical models of close binary star evolution. These studies also provide excellent direct determinations of distances to these binary stars leading to an improved understanding of the mean distance to the SMC and its 3-D structure. Comparisons between these binary-star distances and other methods of determining the mean distance to the SMC will also be made.

XMM-NewtonObservations of the Extremely Low Accretion Rate Polars SDSS J155331.12+551614.5 and SDSS J132411.57+032050.5

XMM-Newton observations of the polar SDSS J155331.12+551614.5 reveal that all the X-ray flux emerges at energies less than 2 keV. The best fit to the spectrum is with a thermal plasma with kT = 0.8 keV plus a 20–90 eV black body, yielding a thermal X-ray luminosity of (8.0–9.5) × 1028 ergs s-1. The low temperature and X-ray luminosity, together with the lack of variation of the X-ray flux during the observations, are all consistent with an extremely low accretion rate that puts the system in the bombardment regime of accretion, rather than accretion involving a standoff shock. It is likely that the observed X-rays originate from the M dwarf secondary star, thus providing a base activity level for late main-sequence stars in close binaries. SDSS J132411.57+032050.5 is detected by XMM-Newton at the faint EPIC pn count rate of 0.0012 ± 0.0003 counts s-1, giving an upper limit to the X-ray luminosity of ~7 × 1028 ergs s-1 for a distance of 300 pc, which is also consistent with the above scenario.

Statistical Properties of Solar-Type Close Binaries

AbstractTwo Coravel radial velocity surveys dedicated to F7-K field dwarfs and to open clusters are merged in order to investigate the statistical properties of binaries with periods up to 10 years. Thanks to the accurate trigonometric parallaxes provided by Hipparcos, an unbiased sample of spectroscopic binaries (SB) is selected. After correction for the uncertainties of the measurements, the following results are obtained: 1. The distribution of mass ratios exhibits a peak for equal-mass binaries (twins), which is higher for short-period binaries than for long-period binaries. 2. Apart from the twins, the distribution of mass ratios exhibits a broad peak from 0.2 to 0.6. 3. The orbital eccentricities of twins are slightly smaller than those of other binaries. 4. An excess of SB is observed with periods shorter than about 50 days in comparison with the Duquennoy and Mayor log-normal distribution of periods. These features suggest that close binary stars are generated by two different processes. A possible difference could come from the accretion onto the binary, for instance from a common envelope or from a circumbinary disk. Alternatively, twins could come from dynamic evolution of multiple systems. It is not clear whether the formation models are already sufficiently elaborated to reproduce our statistics.

The Impact of Large Databases on the Knowledge of Late-Type Close Binaries

AbstractThis paper presents some results of the analysis of the eclipsing binaries samples that came out as by-products of the OGLE microlensing surveys. These experiments monitored millions of stars in the direction of the galactic bulge (OGLE-I), and of the Small Magellanic Cloud (OGLE-II). Their completeness allowed the discovery of rare and interesting systems. An example is a new group of long period binaries in the SMC with presumably a giant component in contact with the critical lobe, which dominates the systemic light variation (“β -contacts”). These systems obey a period-luminosity-color relation and could be used as an auxiliary, but independent, tool for distance determination. Another very interesting object, for its implications in the studies of angular momentum loss processes by magnetic braking and of stellar activity, is the system of shortest known period with M dwarf components, discovered by OGLE-I, BW3 V38, that is the target of a spectroscopic follow-up. The perspectives for close binary star research in view of future space missions, such as COROT and Eddington are briefly discussed.

Guieloa: Adaptive Optics System for the 2.1-M SPM UNAM Telescope

AbstractGuieloa is the adaptive optics system project for the 2.1-m SPM telescope. This is a 19 sub-apertures curvature-type system. It corrects 8 Zernike terms. Guieloa is very similar to PUEO, the CFHT adaptive optics system and compensates the atmospheric turbulence from the R band to the K band. Among the planned applications of Guieloa are the study of OB binary systems, the detection of close binary stars, and the study of disks, jets and other phenomena associated with young stars.

Spot signatures of a solar‐type dynamo in close binary stars

AbstractMagnetic activity signatures in the atmosphere of active stars can be used to place constrains on the underlying processes of flux transport and dynamo operation in its convective envelope. The ‘solar paradigm’ for magnetic activity suggests that the magnetic field is amplified and stored at the base of the convection zone. Once a critical field strength is exceeded, perturbations initiate the onset of instabilities and the growth of magnetic flux loops, which rise through the convection zone, emerge at the stellar surface, and eventually lead to the formation of starspots and active regions. In close binaries, the proximity of the companion star breaks the rotational symmetry. Although the magnitude of tidal distortions is rather small, non‐linear MHD simulations have nevertheless shown in the case of main‐sequence binary components that they can cause non‐uniform surface distributions of flux tube eruptions. The present work extends the investigation to post‐mainsequence components to explore the specific influence of the stellar structure on the surface pattern of erupting flux tubes. In contrast to the case of main‐sequence components, where the consistency between simulation results and observations supports the presumption of a solar‐like dynamo mechanism, the numerical results here do not recover the starspot properties frequently observed on evolved binary components. This aspect points out an insufficiency of the applied flux tube model and leads to the conclusion that additional flux transport and possibly amplification mechanisms have to be taken into account. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Roche Problem: Some Analytics

Some exact analytical formulas are derived for the potential and mass ratio as a function of Lagrangian points position, in the classical Roche model of the close binary stars.

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

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

Doppler Tomography of the Massive Compact Binary Stars in the Multiple Star Systems δ Orionis and HD 206267

Cross-correlation techniques were applied separately to 60 International Ultraviolet Exporer (IUE) ultraviolet spectra and 20 ground-based optical spectra of the massive close binary star in the triple system d Orionis A, producing the first double-lined spectroscopic orbital elements for this binary. The resulting masses are and 3 m sin i p 8.7 1.4 M 1 , . Existing photometric orbits and 3 m sin i p 4.4 0.3 M 2 , Hipparcos photometry limit the central binary’s orbital inclination to the range , resulting in spectroscopic 67 –77 masses of, at most, and (Harvin m p 11.2 M m p 5.6 M 1 , 2 , et al. 2002, ApJ, 565, 1216). These masses are shockingly low—about one-third of the masses that would be expected based on the nonrotating stellar models of Schaller (1992, A&AS, 96, 269), given the component MK types. These masses are also less than one-half of those predicted by the more recent rotating stellar models of Meynet & Maeder (2000, A&A, 361, 101). Subsequent cross-correlation analysis of the 36 IUE ultraviolet spectra of the massive close binary star in the triple system HD 206267 A found masses of 3 m sin i p 28.0 1 and (J. Harvin et al. 2004, 3 1.8 M m sin i p 15.3 1.5 M , 2 , in preparation) for that binary, in general agreement with both the masses expected from evolutionary models and the masses found by Burkholder et al. (1997, ApJ, 490, 328), based on optical spectra. Hipparcos detected photometric variations in HD 206267 A, but they could not be definitely classified as eclipses, constraining only the upper limit of HD 206267 A’s orbital inclination. In view of the magnitude of the mass discrepancy found, the components of the central binary in d Orionis A may turn out to be post-Roche Lobe overflow objects of the very early case A variety. In this scenario, repeated close passes by the tertiary star would have robbed the central binary of its orbital energy, bringing the components into Roche Lobe overflow and resulting in two stars that are overluminous for their masses by a factor of 10, but somewhat underluminous for their respective MK types. The ultraviolet spectra and the optical He i line prol6678 files of the components of d Orionis A and the ultraviolet spectra of the components of HD 206267 A were reconstructed using a version of the Doppler tomography algorithm from Bagnuolo et al. (1994, ApJ, 423, 446), based on the new radial velocity orbits described above. Analysis of the reconstructed spectra revealed the component stars’ spectral morphology, rotational velocities, and relative flux contributions.

Are All Hot Subdwarf Stars in Close Binaries?

We discuss whether the hypothesis that “all (or most) subdwarfs are in close binaries” is supported by the frequently reported observations of photometrically or spectroscopically composite character of many hot subdwarf stars. By way of a possible counter-argument, we focus on resolved companions (optical pairs) of hot subdwarf stars. On a statistical basis, many of these are physically associated with the hot subdwarfs, i.e. they are common proper motion pairs. These resolved pairs make a several percent contribution to the catalog of hot subdwarf stars per decade in projected separation. If they are just the relatively wide members of a binary population similar to the local G-dwarf binary population (A&A, 248, 485), which has a very wide distribution of orbital separations, then many of the unresolved but composite hot subdwarf binaries may not be “close” in the astrophysical sense. In that case, binary channels for hot subdwarf formation may be less important than expected, or must involve companions (white dwarfs) that do not result in a composite spectrum system.

Close binary EHB stars from SPY

We present the results of a radial velocity (RV) survey of 46 subdwarf B (sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new sdB binary systems, but only one (4%) He-sdO binary. Orbital parameters of nine sdB and sdO binaries, derived from follow-up spectroscopy, are presented. Our results are compared with evolutionary scenarios and previous observational investigations.

Massive close binary stars and gamma-ray bursts

We analyze the observed parameters of massive extremely close binaries containing Wolf-Rayet stars and black holes, and identify those systems whose supernova outbursts lead to the formation of rapidly rotating Kerr black holes. It is proposed that the formation of such a black hole is accompanied by a strong gamma-ray burst. Several types of observed systems satisfy the conditions necessary for the formation of a Kerr black hole: BH+WR, BH+OB, WR+O, and BH+K,M.

WIYN Open Cluster Study: Tidal Interactions in Solar-Type Binaries

We present an ongoing study on tidal interactions in late-type close binary stars. New results on tidal circularization are combined with existing data to test and constrain theoretical predictions of tidal circularization in the pre-main-sequence (PMS) phase and throughout the main-sequence phase of stellar evolution. Current data suggest that tidal circularization during the PMS phase sets the tidal cutoff period for binary populations younger than ~ 1 Gyr. Binary populations older than ~ 1 Gyr show increasing tidal cutoff periods with age, consistent with active main-sequence tidal circularization.

The Role of Gas in the Merging of Massive Black Holes in Galactic Nuclei. I. Black Hole Merging in a Spherical Gas Cloud

Using high-resolution smoothed particle hydrodynamics numerical simulations, we investigate the effects of gas on the in-spiral and merger of a massive black hole binary. This study is motivated by both observational and theoretical work that indicate the presence of large amounts of gas in the central regions of merging galaxies. N-body simulations have shown that the coalescence of a massive black hole binary eventually stalls in a stellar background. However, our simulations suggest that the massive black hole binary will finally merge if it is embedded in a gaseous background. Here we present results in which the gas is assumed to be initially spherical with a relatively smooth distribution. In the early evolution of the binary, the separation decreases as a result of the gravitational drag exerted by the background gas. In the later stages, when the binary dominates the gravitational potential in its vicinity, the medium responds by forming an ellipsoidal density enhancement whose axis lags behind the binary axis, and this offset produces a torque on the binary that causes continuing loss of angular momentum and is able to reduce the binary separation to distances where gravitational radiation is efficient. Assuming typical parameters from observations of ultraluminous infrared galaxies, we predict that a black hole binary will merge within 107 yr; therefore, these results imply that in a merger of gas-rich galaxies, any massive central black holes will coalesce soon after the galaxies merge. Our work thus supports scenarios of massive black hole evolution and growth in which hierarchical merging plays an important role. The final coalescence of the black holes leads to gravitational radiation emission that would be detectable out to high redshift by LISA. We show that similar physical effects, which we simulate with higher resolution than in previous work, can also be important for the formation of close binary stars.

The collective mode and turbulent viscosity in accretion discs

The existence of a spiral-vortex structure is revealed by a numerical simulation of the dynamics of an accretion disc in close binary stars. This structure is not related to the tidal influence of a companion star. It is a density wave containing a one-armed spiral and an anticyclonic vortex. The formation of the structure is caused by a hydrodynamical instability. The latter results in a disc turbulence with a turbulent viscosity coefficient ν≃0.035 Ωh 2 ( h is a semithickness of the disc). This value is in accordance with both the value of a numerical viscosity in presented calculations and the results of observations. The period of the density wave rotation is in agreement with the typical periods of light curve variations observed in cataclysmic binary stars.

Accretion and dynamical interactions in small-Nstar-forming clusters:N= 5

We present results from high-resolution hydrodynamical simulations that explore the effects of small-scale clustering in star-forming regions. A large ensemble of small-N clusters with five stellar seeds have been modelled and the resulting properties of stars and brown dwarfs statistically derived and compared with observational data. Close dynamical interactions between the protostars and competitive accretion driven by the cloud collapse are shown to produce a distribution of final masses that is bimodal, with most of the mass residing in the binary components. When convolved with a suitable core mass function, the final distribution of masses resembles the observed initial mass function, in both the stellar and substellar regimes. Binaries and single stars are found to constitute two kinematically distinct populations, with about half of the singles attaining velocities 2k m s −1 , which might deprive low-mass star-forming regions of their lightest members in a few crossing times. The eccentricity distribution of binaries and multiples is found to follow a distribution similar to that of observed long-period (uncircularized) binaries. The results obtained support a mechanism in which a significant fraction of brown dwarfs form under similar circumstances as those of normal stars but are ejected from the common envelope of unstable multiple systems before their masses exceed the hydrogen burning limit. We predict that many close binary stars should have wide brown dwarf companions. Brown dwarfs, and, in general, very low-mass stars, would be rare as pure binary companions. The binary fraction should be a decreasing function of primary mass, with low-mass or substellar primaries being scarce. Where such binaries exist, they are expected either to be close enough (semimajor axis ∼10 au) to survive strong interactions with more massive binaries or to be born in very small molecular cloud cores.

Dynamics of magnetic flux tubes in close binary stars

Surface reconstructions of active close binary stars based on photometric and spectroscopic observations reveal non-uniform starspot distributions, which indicate the existence of preferred spot longitudes (with respect to the companion star). We consider the equilibrium and linear stability of toroidal magnetic flux tubes in close binaries to examine whether tidal effects are capable to initiate the formation of rising flux loops at preferred longitudes near the bottom of the stellar convection zone. The tidal force and the deviation of the stellar structure from spherical symmetry are treated in lowest-order perturbation theory assuming synchronised close binaries with orbital periods of a few days. The frequency, growth time, and spatial structure of linear eigenmodes are determined by a stability analysis. We find that, despite their small magnitude, tidal effects can lead to a considerable longitudinal asymmetry in the formation probability of flux loops, since the breaking of the axial symmetry due to the presence of the companion star is reinforced by the sensitive dependence of the stability properties on the stellar stratification and by resonance effects. The orientation of preferred longitudes of loop formation depends on the equilibrium configuration and the wave number of the dominating eigenmode. The change of the growth times of unstable modes with respect to the case of a single star is very small.