Single Be stars as binary ejecta?

Among the mechanisms suggested for the creation of discs around Be stars is interaction with binary companions. This idea has largely been dismissed, because the majority of Be stars have no observed companion. This difficulty can be circumvented if single Be stars are actually ejected from binary systems (owing, for instance, to the supernova of the companion). Using Hipparcos data, we show that this explanation is not likely, by comparing the velocity distributions of Be stars with those of normal B stars. We find that the distributions are consistent to within 1 σ uncertainties, and thus do not support the formation of single Be stars through binary breakup.     

‘Swinging dipoles’ inmagnetic close binary stars

The recently discovered phenomena in polars — Magnetic Close Binary Stars (MCBS), are discussed. Asynchronous MCBS are on the propeller stage (which is analogous to the investigated one for neutron stars), and are synchronizing during t_S10³ yr, being during this stage rapidly evolving, mass ejecting systems. The accretion rate is largest when the angle between the magnetic axis and the line of centers is near zero. If 90°, then the magnetic field prevents the plasma flow, and the magnetic valve becomes closed. Near this position the oscillations of the orientation of the white dwarf's magnetic axis may be excited. This model of a swinging dipole has such observational properties: (a) the system's luminosity changes with characteristical times of some years; (b) the phase curves of light, polarization and radial velocities must be cyclically changing with a few year cycle; (c) one would observe the correlation between the phase shift of these curves, and the system's luminosity. The observational data on polars are briefly discussed. All these phenomena are observed in AM Herculis and some other polars, but subsequent studies are needed to investigate the orientation changes of the magnetic axis, and so the structure and evolution of this exotic class of our Galaxy population.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Orbital elements of the eclipsing binary ξ Phe

The elements of the orbit in the cases of elliptic orbit and the nonspherical form of the components were obtained on the basis of the published photoelectric and spectroscopic observations of the eclipsing binary system Phe.     

An EC 14026 pulsator in a reflection binary

During our campaign of acquiring follow-up photometric data to resolve short period pulsating sdB (EC14026 or V361 Hya) stars, we obtained data on the known pulsator KUV 04421+1416 and discovered that it is also in a reflection-effect binary. Here we present preliminary results of the pulsation analysis and provide some constraints on the companion, which is most likely an MV star. This makes KUV 04421+1416 only the second known system with an EC14026-type pulsator in a reflection-effect binary.     

“Constant” eclipsing binary in the instability strip

The eclipsing binary OO Peg consist of two late-A type stars in circular orbit with a period of 2.985 days. I use the high-resolution spectroscopic and extensive light curves from the ASAS and Hipparcos survey to measure the physical properties of the system. Previous attempts to model the light and radial velocity curves of the system have met with limited success, primarily because of the lack of a accurate photometric data. The system shows no signs of stellar activity, it is slowly rotating, has not been detected period changes, and there is no pulsational signs in the photometric data. I show the location of the components in effective temperature vs. luminosity diagram compared to the instability region limits established from eclipsing binary components. While more than 25 system have been plotted to diagram, about six single stars and OO Peg components do not show any pulsational frequencies. They are apparently constant stars lie within the pulsation instability region. I speculate as to the possible causes of this picture.     

Where are the binary source gravitational microlensing events? II

Despite the same multiplicity of lenses and sources, the frequency of detection of binary source events is relatively very low compared with that of binary lens events. Dominik pointed out that the rarity of binary source events is caused mainly by the large difference in amplification between the component stars. In this paper, we determine that the fraction of events with similar source star amplifications is as large as ∼8 per cent, and thus show that the very low detection rate for binary source events cannot be explained by this effect alone. By carrying out realistic simulations of binary source events, we find that a significant number of binary source events are additionally missed from detection for various other reasons. First, if the flux ratio between the component stars is very large, the light curve of the bright star is hardly affected by the light from the faint star. Secondly, if the separation is too small, the binary source stars behave like a single star, making it difficult to separate the binary source event from a single source event. Finally, although the probability of detecting binary source events increases as the source separation increases, some fraction of binary source events will still be missed because the light curves of these events will mimic those of single source events with longer time-scales and larger values of the impact parameter.     

A γ Doradus candidate in eclipsing binary BD And?

The BVR photometric light curves of the eclipsing binary BD And were obtained in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the photometric solutions were derived. The results show that BD And is a detached binary system, whose components have a little temperature difference of about 40 K. By analyzing photometric available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.011 days and a period of 9.6 years. The results indicate that the periodic oscillation could be caused by a third component physically attached to the eclipsing binary. After removing the light variations due to the eclipses and proximity effects, the light-curve distortions are further explained by the pulsation of the primary component with a dominant period of ∼1 day. In accordance with the position of the primary component on the Hertzsprung–Russell diagram and its pulsation period, the primary component of BD And could be an excellent γ Doradus candidate. It is rarely phenomenon that a component of the eclipsing binary system is a γ Doradus variable.     

Search for relativistic companions in ‘non-X-ray’ binary systems

Consideration is given to a search for relativistic objects in massive close binary systems without strong X-ray emission (L _x <10³⁴ erg s^–1). It is pointed out that, according to the present-day theory on the evolution of massive close binaries, the number of neutron stars and black holes in non-X-ray binary systems must be 100 times the number of the known X-ray binaries comprising OB supergiant stars; that is why, in studying non-X-ray binary systems, the chances are to detect about a hundred of black holes in the Galaxy.Criteria are formulated for the relativistic nature of companions in the binary systems, such as high spatial velocity values and height Z over the galactic plane for OB stars (runaway stars) and for Wolf-Rayet stars. As reported by Tutukov and Yungelson (1973), as well as by van den Heuvel (1976), the presence of ring-type nebulae can serve as another indication of a relativistic nature of companions in the case of Wolf-Rayet stars.Data are collected on Wolf-Rayet stars with low-mass companions (Table I), which can be relativistic objects accreting within a strong stellar wind from Wolf-Rayet stars. Presented are new findings in respect of spectral examination of the runaway OB-stars (Table II), bringing together data on eight OB stars which can represent binary systems with relativistic companions (Table III).A list of 28 OB-stars (Table IV) which offer a good chance for finding relativistic companions is given.     

CoRoT 102931335: a candidate γ Dor in an eclipsing binary

We present an on-going study of CoRoT 102931335. Our preliminary results indicate that the target is an eclipsing binary system with an orbital period of $3{.\!\!\vphantom{0}^{\mathrm{d}}}979$ and a primary component pulsating in the frequency range 0.6–0.8 c/d. The results of a ground-based follow-up program provided four-colour Strömgren photometry and allowed us to infer the spectral class and the primary effective temperature. We devised and applied an iterative procedure to disentangle the effects of binarity from those of pulsations and could test that a detailed binary modelling is essential for the purpose. Our results suggest that the pulsating component of CoRoT 102931335 could be a γ Dor variable, a rare occurrence in an eclipsing system.     

FRB 171019: an event of binary neutron star merger?

The fast radio burst, FRB 171019, was relatively bright when discovered first by ASKAP but was identified as a repeater with three faint bursts detected later by GBT and CHIME. These observations lead to the discussion of whether the first bright burst shares the same mechanism with the following repeating bursts. A model of binary neutron star merger is proposed for FRB 171019, in which the first bright burst occurred during the merger event, while the subsequent repeating bursts are starquake-induced, and generally fainter, as the energy release rate for the starquakes can hardly exceed that of the catastrophic merger event. This scenario is consistent with the observation that no later burst detected is as bright as the first one.     

A photometric study of an EW-type binary system： GV Leo

A photometric study of a contact binary system, GV Leo is presented. New observations were done using the B VR filter bands. We find that a revised orbital period is 0.26673171 d and the orbital period of this system is decreasing at a rate of dP/ dt = -4.95 × 10-7 d yr-1. The photometric solutions are fairly well fitted at a mass ratio of q = 0.1879, with a fillout factor of f = 17.74%. The results indicate that there exists mass transfer from the more massive component to the less massive one at a rate of relative mass exchange, 6zl/m = -1.09× 10-7 yr-1. It is possible that this weak- contact system, that shows a decreasing orbital period, may undergo contraction of the inner and outer critical Roche lobes and evolve into a deep-contact binary.     

Observational study of Hα in 31 RS CVn binary systems

90 spectral observations of the Hα regions of 31 RS CVn stars made with Reticon on the 2.1 metre McDonald Reflector in 1984 are reported here. Quantitative measurements were made on the Hα emission and absorption components. Combining with our previous observations in [1], we have now observed 70% of the systems in Hall's catalogue. On the basis of the combined data, a statistical discussion is presented.     

The contact binary AE phoenicis — An analysis from deconvoluted spectra

A method is described for an analysis of deconvoluted stellar spectra, and applied to new spectroscopic observations of the close eclipsing system AE Phuenicis, obtained with the 1.52 m telescope of the Southern European Observatory at La Silla, Chile, Results are presented for the rotational velocities of this variable, together with a proposed model of the system.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Young massive binary θ 1 OriC: Radial velocities of components

We succeeded in separating the absorption lines of both the primary C1 and the secondary C2 component in the spectra of the young massive binary θ ¹ OriC (O6Vp + B0V, mass sum 44 ± 7M _⊙), obtained during the period from November 1995 to February 2013 with different telescopes. These observations allowed us to derive, for the first time, the radial velocities of both components. The orbitalmotion of the secondary star is traced through its weak (the line depth is approximately 0.01–0.02) absorption lines of CII, NII, OII, Si III, which are broadened by fast rotation of the star. Silicon absorptions Si III λλ 4553, 4568, and 4575 are better suited for radial velocity measurements than the other lines. From the velocity curves, we obtained the systemic velocity of the system, γ = 31 ±2 kms^?1, and semi-amplitudes of the C1 and C2 velocities: K ₁ = 15 ± 2 kms^?1, K ₂ = 43 ± 3 kms^?1. This leads to individual component masses of M ₁ = 33 ± 5 M _⊙ and M ₂ = 11 ± 5 M _⊙, based on the adopted mass sum. At present, the combined spectroscopic-interferometric orbital solution cannot be obtained because of the large scatter of velocity measurements caused by chaotic line shifts in the spectrum of the primary star and by the weakness of wide absorptions from the secondary. New spectroscopy with a resolution of R ≥ 30000 and S/N ratio over 200 performed in the period close to the periastron passage in the second half of 2013, as well as additional long-baseline interferometry, will be decisive in refining the parameters of θ ¹ OriC. We expect that as a result of this campaign, masses and luminosities of the components will be determined with an accuracy of 2–3%.     

BI CVn – A spotted,overcontact, type-W eclipsing binary

We present photometric and spectroscopic observations of the eclipsing binary system BI CVn. Wilson–Devinney analysis of its light and radial velocity curves showed that the system is a W-subtype overcontact W-UMa type binary. We computed the absolute physical parameters of the system based on a mass ratio spectroscopically determined in this study. Though the orbital period had changed somehow in the past, it has remained constant for a long time since March 1999, contradicting the previous interpretations suggesting a cyclic variation superimposed on a quadratic change.     

Photometric study of the unusual binary system vsx j052807.9 + 725606

Results are reported from a three color (B, V, and R) photometric study of the recently discovered, unusual binary system VSX J052807.9 + 725606 = USNO-B1.0 1629–0064825. This system is extremely similar to the system V361 Lyr, which had previously been regarded as unique. We confirm the strong asymmetry of the phase curve and find that its amplitude depends on wavelength. This is interpreted using a model of a “direct impact” of the accretion flow with the atmosphere of the accreting component and the formation of a “hot spot.” The color temperatures are determined. The characteristics of the hot spot are estimated. We have also calculated new ephemerides for VSX J052807.9 + 725606.     

KIC 5197256: an eclipsing binary containing a δ Scuti variable star

This paper reports analysis of an eclipsing binary system KIC 5197256 with a δ Sct variable component.Utilizing light-curve modeling,several stellar parameters are derived,e.g.,temperature,mass,and mass ratio.The O-C diagram is a straight line with a negative slope which means that its period is almost constant for about 2 yr.Frequency analyses are performed for the residual light curve after subtracting the binary variations.The frequency spectrum reveals that one component star is a δ Scuti variable.Large frequency separation is cross-identified with the histogram graph and the Fourier transform method.Based on the large separation and density relationship,the mean density of the δ Sct component is estimated to be 0.05 g·cm~(-3).Five frequencies with the same frequency spacing in the range of 25 d~(-1)-34 d~(-1) are detected.Statistically,the pulsation amplitudes of δ Sct stars increase with decreasing of rotations,so we propose that KIC 5197256 might have a relatively large rotational velocity,and the frequency f_(10) might be the rotation frequency.