Long‐term orbital period behaviors of the neglected Algol type binaries: CC Herculis and XZ Aquilae

Orbital period variations of two neglected Algol type binaries, CC Her and XZ Aql, are studied based on all available times of minima. In the case of CC Her, it is found that the O –C curve displays a tilted sinusoidal variation with an eccentricity of 0.54 ± 0.03 and a period of 52.4 ± 0.4 yr, which can be explained by the light‐time effect due to the presence of an unseen component. The course of the orbital period change in XZ Aql appears less reliable but its O –C curve can be represented by a periodic variation with a period of 36.7 ± 0.6 yr superimposed on an upward parabola. The parabolic variation indicates a secular period increase with a rate of dP /dt = 7.1 s per century. The corresponding conservative mass transfer from less massive component to the more massive one is about 3.26 × 10^–7 M_⊙ yr^–1. It is interesting to see that the O –C variation of CC Her displays no evidence (as upward parabola) on the mass transfer characteristic for Algols. The periodic change of the orbital period of XZ Aql, like CC Her, may be caused by the presence of the thirdbody. The lower limits of the masses of the hypothetical unseen components for CC Her and XZ Aql are found to be 2.69 M_⊙ and 0.47 M_⊙, respectively. The third body of CC Her should be detectable not only spectroscopically but also photoelectrically, if it exists. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An absolute clock of the cosmos?

In 1968–2005 different observers (mainly, one of the authors—V.M. Lyuty) performed numerous measurements of luminosity of the nucleus of the Seyfert galaxy NGC 4151. It is shown that (a) luminosity of the object pulsated over 38 years with a period of 160.0106(7) min coinciding, within the error limits, with the well-known period P ₀ = 160.0101(2) min of the enigmatic “solar” pulsations, and (b) when registering oscillations of luminosity of NGC 4151 nucleus with the P ₀ period, time moments of observations must be reduced to the earth instead of the sun, i.e., to the reference frame of the observer. The coherent P ₀ oscillation is characterized, therefore, by invariability of both frequency and phase with respect to redshift z and the earth’s orbital motion, respectively. From these results it, thus, follows that the coherent P ₀ oscillation seems to be of a true cosmological origin. The P ₀ period itself might represent a course of the “cosmic clock” related to the existence of an absolute time of the Universe in Newton’s comprehension.     

New CCD photometry for the extreme lower mass-ratio binary AW Ursae Majoris

This paper presents charge-couple device (CCD) photometric observations for the eclipsing binary AW UMa. The V-band light curve in 2007 was analyzed using the 2003 version of the Wilson–Devinney code. It is confirmed that AW UMa is a total eclipsing binary with a higher degree of contact f=80.2% and a lower mass ratio of q=0.076. From the (O−C) curve, the orbital period shows a continuous period decrease at a rate of dP/dt=−2.05×10⁻⁷ d yr⁻¹. The long-term period decrease suggested that AW UMa is undergoing the mass transfer from the primary component to the secondary one, accompanied by angular momentum loss due to mass outflow L ₂. Weak evidence indicates that there exists a cyclic variation with a period of 17.6 yr and a small amplitude of A=0. ^d 0019, which may be attributed to the light-time effect via the third body. If the existence of an additional body is true, it may remove a great amount of angular momentum from the central system. For this kind of contact binary, as the orbital period decreases, the shrinking of the inner and outer critical Roche lobes will cause the contact degree f to increase. Finally, this kind of binary will merge into a single rapid-rotation star.     

Parametric instabilities in relativistic plasma

Parameteric instabilities in the relativistic plasma are considered. It is shown that in the electron relativistic plasma (T _em _0e c ²) the electron mass oscillation in the external electrical field leads to the instability of Langmuir and low frequency aperiodic oscillations as well. In the case of the hot electron ion plasma with relativistic electron temperature the low frequency aperiodic and periodic oscillations are studied. The wave increments for all considered cases are obtained.     

CK Bootis: a W UMa system with a small mass ratio

We present an analysis of BV R light curves of an eclipsing binary CK Bootis, a system with a very small mass ratio. The light curves appear to exhibit a typical O'Connell effect. The light curves are analyzed by means of the latest version of the WD program. The asymmetry of the light curves is explained by a cool star spot model. The simultaneous BV R synthetic light curve analysis gives a tiny mass ratio of 0.12, an extremely large fill‐out factor of 0.65, and a very small difference between the component temperatures of 90 K. The absolute parameters of the system were also derived by combining the photometric solutions with the radial velocity data. The mass of the secondary is very low (0.15 M_⊙) and it continues losing mass. Thirty seven new times of minimum are reported. It is found that the orbital period of the system has a quasi periodic variation, superimposed on a period increase. The long‐term period increase rate is deduced to be dP/dt = 3.54x10^–7 d yr^–1, which can be interpreted as being due to mass transfer from the less massive star to the more massive component. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measurement of the orbital period of the X-ray burster GS 1826-238 based on observations of its optical brightness variations

The variability of the optical and X-ray fluxes from the binary GS 1826-238 is investigated. An epoch-folding analysis of the optical data obtained with the RTT-150 telescope in 2003–2004 has revealed periodic brightness variations in the source with a period P _orb = 2.24940 ± 0.00015 h with a high statistical significance. When estimating the detection significance of the periodic signal, we have specially taken into account the presence of a powerful aperiodic component (“red noise”) in the source’s brightness variability. The source’s power density spectra in the frequency range ∼10⁻⁵–0.01 Hz have been obtained. We have detected a statistically significant break in the power density spectrum of GS 1826-238 at a frequency ν _br ≈ (8.48 ± 0.14) × 10⁻⁵ Hz in both optical and X-ray energy bands. We have estimated the orbital period of the binary GS 1826-238 using the correlation between the break frequency in the power density spectrum and the orbital period of binaries, P _orb ∝ 1/ν _br, found by Gilfanov and Arefiev (2005): P _orb = 3.7 ± 0.8 h and P _orb = 11.3 ± 5.9 h when using Sco X-1 and 1H 16267-273, respectively, as reference sources. It seems to us that the method for estimating the orbital periods of low-mass X-ray binaries using the correlation P _orb ∝ 1/ν _br may turn out to be very promising, especially for persistent low-luminosity X-ray binaries.     

Period Changes in Four Algol-Type Binaries: SX Dra, AV Del, CU Peg and DK Peg

Orbital period changes of four neglected short-period semidetached Algols, SX Dra, AV Del, CU Peg and DK Peg, are presented based on the analysis of their O–C observations. It is found that the three systems, AV Del, CU Peg and DK Peg, show rapid period increase at rates of dP/dt =+3.15 × 10^-6, +2.00 × 10^-6 and +4.88 × 10^-7days/year respectively. For the other system, SX Dra, a possible periodic variation in the orbital period is discovered to superimpose on a very rapid period increase (dP/dt = +1.09 × 10^-5 days/year). The period increases of the four Algols can be explained by a mass transfer from the secondary to the more massive primary, which is in agreement with the semi-detached configurations of these systems. However, since the period increases are rather rapid, the mass transfer should be on a dynamical time scale. The cyclic period change in SX Dra suggests that there may exist a third body in this system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Astronomical constraints on properties of sterile neutrino dark matter

We consider sterile neutrinos as a component of dark matter in the Milky Way and clusters, and compare their rest mass, decay rate and the mixing angle. A radiative decaying rate of order Γ∼10⁻¹⁹ s⁻¹ for sterile neutrino rest mass m _s =18–19 keV can satisfactorily account for the cooling flow problem and heating source in Milky Way center simultaneously. Also, these ranges of decay rate and rest mass match the prediction of the mixing angle sin ²2θ∼10⁻³ with a low reheating temperature in the inflation model, which enables the sterile-active neutrino oscillation to be visible in future experiments. However, decaying sterile neutrinos have to be ruled out as a major component of dark matter because of the high decay rate.     

Bi-periodic variation in the BL Lac AO 0235+164

High resolution VLBI hybrid map of the BL Lacertae object AO 0235+164 has been produced at a wavelength of 6 cm. The map shows that the object's radio structure is dominated by a strong, nearly unresolved core with a weak and clear component in northeast direction and a faint one in southwest direction. The positional angle of its jet component are equal to66.4^°, which is the biggest one in comparison with previous results. Based on the variation of its flux density with time at three different frequencies, we find that the flux density of AO 0235+164 shows bi-periodic variation, i.e., the shorter periodic variation of ∼ 1.81 years and a longer periodic variation of ∼ 3.63 years. The later is essentially in agreement with our earlier predicted results that the existence of the periodic variation of ∼ 3.63 years may be caused by the precession of its `central engine'. This bi-periodic variation is probably the results of the joint action of jet outbursts and jet rotation. With the binary black hole models of Kaastra and Roos, we get the minimum total mass of the binary system of 1.46 × 10⁸ M _⊙. This revised version was published online in July 2006 with corrections to the Cover Date.     

The most resonant pulsation frequency of δ Scuti stars

Pulsation of the Sun with a period of P₀ ≈ 160 min discovered about two decades ago, is still waiting explanation. In view of the hypothesis about its cosmological origin, and attempting to find signature of this P₀ periodicity among other (short-period variable) stars, the pulsation frequencies of δ Sct stars are subjected to specific analysis. With a confidence level ≈ 3.8σ it is found that the frequency v₀ = P₀⁻¹ ≈ 104 m̈Hz, within the error limits, appears indeed to be the most “resonant” one for the total sample of 318 pulsating stars of δ Sct type (the most commensurable, or “synchronizing”, period for all these stars occurs to be 162 ± 4 min). We conjecture that a) the P₀ oscillation might be connected with periodic fluctuations of gravity field (metrics), and b) the primary excitation mechanism of pulsations of δ Sct stars, reffected by this “ubiquitous” P₀ resonance, must be attributed perhaps to superfast rotation of their inner cores (their rates tend to be in near-resonance with the “universal” v₀ frequency). The arguments are given favouring a cosmoogical nature of the P₀ oscillation.     

The bolometric light curve of SN 1993J and the nature of its progenitor

We have constructed the bolometric light curve of SN 1993J based on UBVRI(JHK) photometric data obtained from various sources and assumingA _V = 0 and a distance modulus of 27.6. Effective temperatures and photosphere radius at various times have been obtained from detailed blackbody fits. The bolometric light curve shows two maxima. The short rise time to the second maximum, and the luminosities at the minimum and the second maximum are used to constrain the properties of the progenitor star. The total mass of the hydrogen envelope M_H, in the star is found to be ≲ 0.2 M_⊙ at the time of explosion, and the explosion ejected about 0.05 M_⊙ of Ni⁵⁶. Thin hydrogen envelope combined with a sufficient presupernova luminosity suggest that the exploding star was in a binary with a probable period range of 5yr ≤P _orb ≤ 11yr.     

Motion close to the Hopf Bifurcation Of the vertical family of periodic orbits of L4

The paper deals with different kinds of invariant motions (periodic orbits, 2D and 3D invariant tori and invariant manifolds of periodic orbits) in order to analyze the Hamiltonian direct Hopf bifurcation that takes place close to the Lyapunov vertical family of periodic orbits of the triangular equilibrium point L₄ in the 3D restricted three-body problem (RTBP) for the mass parameter, μ greater than (and close to) μ_R (Routh’s mass parameter). Consequences of such bifurcation, concerning the confinement of the motion close to the hyperbolic orbits and the 3D nearby tori are also described.     

Classical and relativistic node precessional effects in WASP-33b and perspectives for detecting them

WASP-33 is a fast rotating, main sequence star which hosts a hot Jupiter moving along a retrograde and almost polar orbit with semi-major axis a=0.02 au and eccentricity provisionally set to e=0. The quadrupole mass moment J₂^*J_{2}^{\star} and the proper angular momentum S _⋆ of the star are 1900 and 400 times, respectively, larger than those of the Sun. Thus, huge classical and general relativistic non-Keplerian orbital effects should take place in such a system. In particular, the large inclination Ψ_⋆ of the orbit of WASP-33b to the star’s equator allows to consider the node precession [(W)\dot]\dot{\Omega} and the related time variation dt _d /dt of the transit duration t _d . The WASP-33b node rate due to J₂^*J_{2}^{\star} is 9×10⁹ times larger than the same effect for Mercury induced by the Sun’s oblateness, while the general relativistic gravitomagnetic node precession is 3×10⁵ times larger than the Lense-Thirring effect for Mercury due to the Sun’s rotation. We also consider the effect of the centrifugal oblateness of the planet itself and of a putative distant third body X. The magnitudes of the induced time change in the transit duration are of the order of 3×10⁻⁶,2×10⁻⁷,8×10⁻⁹ for J₂^*J_{2}^{\star}, the planet’s rotational oblateness and general relativity, respectively. A yet undiscovered planet X with the mass of Jupiter orbiting at more than 1 au would induce a transit duration variation of less than 4×10⁻⁹. A conservative evaluation of the accuracy in measuring dt _d /dt over 10 yr points towards ≈10⁻⁸. The analysis presented here will be applicable also to other exoplanets with similar features if and when they will ne discovered.     

Numerical simulations of pulsationally unstable accretion disks around supermassive black holes

The innermost region of slim accretion disks with standard viscosity is unstable against axisymmetric radial inertial acoustic perturbations under certain conditions. Numerical simulations are performed in order to demonstrate behaviors of such unstable disks. It is shown that oscillations with the period of 10^–3 (M _BH/M ) s can be excited near the inner edge of the disks, whereM _BH is the mass of the central object. This kind of unstable disks is a possible origin of the periodic X-ray time variabilities with period of 10⁴s observed in a Seyfert galaxy NGC 6814.     

IGR J16547-1916/1RXS J165443.5-191620—a new intermediate polar from the INTEGRAL galactic survey

We present the results of our optical identification of the X-ray source IGR J16547-1916 detected by the INTEGRAL observatory during a deep all-sky survey. Analysis of the spectroscopic data from the SWIFT and INTEGRAL observatories in the X-ray energy band and from the BTA (Special Astrophysical Observatory) telescope in the optical band has shown that the source is most likely an intermediate polar—an accreting white dwarf with the mass ofM _WD μ 0.85M _⊙ binary system. Subsequent studies of the object’s rapid variability with the RTT-150 telescope have confirmed this conclusion by revealing periodic pulsations of its optical emission with a period of ≈550 s.     

Changes in the Sun’s mass and gravitational constant estimated using modern observations of planets and spacecraft

More than 635 thousand positional observations of planets and spacecraft of various types (mostly radiotechnical ones, 1961–2010) were used to estimate possible changes in the gravitational constant, Sun’s mass, and semi-major axes of planetary orbits, as well as the associated value of the astronomical unit. The observations were analyzed based on the EPM2010 ephemerides constructed at the Institute of Applied Astronomy (Russian Academy of Sciences) in a post-Newtonian approximation as a result of simultanious numerical integration of the equations of motion of nine major planets, the Sun, the Moon, asteroids, and trans-Neptunian objects. The heliocentric gravitational constant GM _⊙ was found to vary with a rate of (GṀ _⊙/GM _⊙ = (−5.0 ± 4.1)) × 10⁻¹⁴ per year (at the 3σ level). The positive secular changes in the semimajor axes ȧ _i /a _i were found for Mercury, Venus, Mars, Jupiter, and Saturn provided by high-precision observations. These changes also correspond to the decrease in the heliocentric gravitational constant. The changing of GM _⊙, itself is probably caused by the loss of the mass M _⊙ of the Sun due to its radiation and solar wind; these effects are partly compensated by the material falling onto the Sun. Allowing for the maximum bounds on the possible change in the Sun’s mass M _⊙, it has been found from the change obtained in GM _⊙ that the annual change Ġ/G of the gravitational constant G falls within the interval −4.2 × 10⁻¹⁴ < ȧ/G < +7.5 × 10⁻¹⁴ with a 95% probability. The astronomical unit (AU) is connected by its definition only with the heliocentric gravitational constant. The decrease of GM _⊙ obtained in this paper should correspond to a secular decrease in the AU. It is shown, however, that the modern level of accuracy does not allow us to determine a change in the AU. The attained posibility of determining changes in GM _⊙ using high-accuracy observations encourages us to have a relation between GM _⊙ and the AU fixed for a certain moment in time, since it is inconvenient to have a time-dependent length for the AU.     

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.     

On the evolution of the ‘f’ family in the restricted three-body problem

Poincaré surface of section technique is used to study the evolution of a family ‘f’ of simply symmetric retrograde periodic orbits around the smaller primary in the framework of restricted three-body problem for a number of systems, actual and hypothetical, with mass ratio varying from 10⁻⁷ to 0.015. It is found that as the mass ratio decreases the region of phase space containing the two separatrices shrinks in size and moves closer to the smaller primary. Also the corresponding value of Jacobi constant tends towards 3.     

Possible Evidence of Time Variation of Weak Interaction Constant from Double Beta Decay Experiments

A comparison is made of the probability of the process of two neutrino double beta decay for ⁸²Se in direct (counter) and geochemical experiments. It is shown that the probability is systematically lower in geochemical experiments, which characterize the probability of ββ(2ν) decay a few billion years ago. The experimental data for ¹³⁰Te are also analyzed. It is shown that geochemical measurements on young minerals give lower values of T _1/2 (¹³⁰Te) and T _1/2 (⁸²Se) as compared to measurements on old minerals. It is proposed that this could be due to a change in the weak interaction constant with time. Possibilities of new, precise measurements performed with the aid of counters and geochemical experiments are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Periodic orbits under combined effects of oblateness and radiation in the restricted problem of three bodies

In this paper, we study the existence of libration points and their linear stability when the three participating bodies are axisymmetric and the primaries are radiating, we found that the collinear points remain unstable, it is further seen that the triangular points are stable for 0<μ<μ _c , and unstable for where , it is also observed that for these points the range of stability will decrease. In addition to this we have studied periodic orbits around these points in the range 0<μ<μ _c , we found that these orbits are elliptical; the frequencies of long and short orbits of the periodic motion are affected by the terms which involve parameters that characterize the oblateness and radiation repulsive forces. The implication is that the period of long periodic orbits adjusts with the change in its frequency while the period of short periodic orbit will decrease.