Orbital-period variations of the Algol-type eclipsing binaries RW CrB and AO ser

Orbital-period variations of the Algol-type eclipsing binaries RW CrB and AO Ser are analyzed. It is shown that the period variations of these systems are due mainly to the light-time effect due to the eclipsing binary’s motion in its long-period orbit. The period variations of RW CrB are reproduced by motion of the eclipsing binary with a period of 55.8 years around a third body with the mass M ₃ > 0.36M⊙. The period variations of AO Ser can be reproduced either solely with the light-time effect, or by a superposition of the light-time effect and a slow secular decrease in the period. In the former case, the period of the long-period orbit is 111.5 years; in the latter case, it is 108 years. Both cases imply the same mass for the third body in the AO Ser system: M ₃ > 0.35M⊙. The residual small-amplitude orbitalperiod variations of the two systems can be due to magnetic cycles.     

The eclipsing variable CM Dra: Surface activity and orbital elements

A long series of observations of the low-mass eclipsing system CM Dra (M ₁, M _⊙<0.25M _⊙, dM4.5e, V=12.9^m, P _orb=1.27^d) was obtained in 1996–1997 as part of the international TEP (Search for Transits of Extrasolar Planets) project. The observations were obtained on the 70-cm telescope of the Astronomical Observatory of Ural State University with an automatic two-star photometer. The total duration of the data series was 155 h. We construct and analyze a master light curve, including calculation of the photometric and absolute orbital elements. Evidence for surface activity was detected. The light curve of CM Dra outside eclipses shows low-amplitude (0.024^m) brightness variations, suggesting the presence of a starspot on one of the components. The amplitude of these variations stayed the same over 20 years, but the phase of the brightness maximum shifted by one-third of the orbital period, possibly reflecting changes in the longitude or asymmetry of a single large polar spot. We detected four flares whose energies were factors of several hundred higher than those of solar flares. The derived flare rate agrees with data for CM Dra in the literature but is much lower than is typical for Population I stars in our Galaxy.     

Age and metallicity estimates for moderate-mass stars in eclipsing binaries

We estimate the ages and metallicities for the components of 43 binary systems using a compilation of accurate observational data on eclipsing binaries for which lines of both components are visible in their spectra, together with two independent modern sets of stellar evolution models computed for a wide range of masses and chemical abundances. The uncertainties of the resulting values are computed, and their stability is demonstrated. The ages and metallicity are compared with those derived in other studies using different methods, as well as with independent estimates from photometric observations and observations of clusters. These comparisons con firm the reliability of our age estimates. The resulting metallicities depend significantly on the choice of theoretical model. Comparison with independent estimates favors the estimates based on the evolutionary tracks of the Geneva group.     

Long-term starspot activity of the eclipsing binaries BH Vir and WY Cnc

We present the results of multicolor photometry of the two spotted, short-period, late-type RS CVn stars BH Vir and WY Cnc. We have derived the parameters of the binaries’ components, and refined their masses, radii, and luminosities. A strong flare of WY Cnc was detected for the first time, and pre-flare variations of the star’s activity studied. Our observations and published data spanning 40 years are analyzed using a zone starspot model. We demonstrate that the spots are always concentrated near the equators and at intermediate latitudes, with maximum spotted areas as large as 29% for BH Vir and 21% for WY Cnc. The temperature differences between spotted regions and the quiet photosphere were 2300 K (BH Vir) and 1800 K (WY Cnc). The detected long-term brightness variations of BH Vir suggest the existence of an activity cycle with a probable period of 22 years. Both stars have starspots concentrated at two active longitudes separated by approximately half of the orbital period during all the studied seasons; these longitudes remained the same (0° and 184°) for BH Vir over 40 years, whereas they migrated in the direction of the stellar rotation at a rate of 3.8°/yr for WY Cnc, suggesting a cycle of 47 years for the migration of the active longitudes.     

Apsidal motion and physical parameters of the eclipsing binary system AR Cas

Using the four-channel automatic photoelectric photometer of the Sternberg Astronomical Institute’s Tien Shan Mountain Observatory, we have acquired accurate (σ_obs≈0.004^m) W BV R brightness measurements for the eclipsing binary AR Cas during selected phases before eclipse ingress and after egress, as well as at the center of minima. A joint analysis of these measurements with other published data has enabled us to derive for the first time a self-consistent set of physical and geometrical parameters for the star and the evolutionary age of its components, t=(60±3)×10⁶ years. We have found the period of the apsidal motion (U_obs=1100±160 years, \(\dot \omega _{obs} = 0^\circ .327 \pm 0^\circ .049\) years^?1) and the apsidal parameter of the primary, logk _2,1 ^obs =?2.41±0.08, with the apsidal parameter being in good agreement with current models of stellar evolution. There is an ultraviolet excess in the primary’s radiation, Δ(U?B)=?0.12^m and Δ(B?V)=?0.06^m, possibly due to a metal deficiency in the star’s atmosphere.     

Orbital period variations of the eclipsing binaries TU Cnc,VZ Leo,and OS Ori

Variations of the orbital periods of the eclipsing binaries TU Cnc, VZ Leo, and OS Ori are analyzed. Secular period decreases were earlier believed to occur in these systems. It is demonstrated that the period variations of TU Cnc can be represented using the light-time effect corresponding to the orbital motion of the eclipsing binary with a period of 78.6 years around the center ofmass of the triple system, with the mass of the third body being M ₃ > 0.82M _⊙. With the same accuracy, the period variations of VZ Leo and OS Ori can be represented either solely using the light-time effect, or a superposition of a secular period decrease and the light-time effect. For VZ Leo, the period of the long-term orbit is 63.8 years in the former case and 67.9 years in the latter case. Similar masses for the third body are indicated in both cases: M ₃ > 0.55M _⊙ and M ₃ > 0.61M _⊙. For OS Ori, the period of the long-term orbit is 46 years and M ₃ > 0.5M _⊙ in the former case, and the period is 36 years and M ₃ > 0.6M _⊙ in the latter case.     

Atmospheric lithium abundances of the carbon giants AQ And,HK Lyr,UX Dra,and WZ Cas

The LTE lithium abundances, logN (Li), have been determined for the atmospheres of the four carbon giants AQ And, HK Lyr, UX Dra, and WZ Cas, applying the synthetic-spectrum technique to the LiI λ670.8 nm resonance doublet. We used estimates of the effective temperatures T _eff, metallicities, elemental abundances, and carbon-isotope ratios for these stars from the literature [12C/13C]. The resulting lithium abundances depend significantly on the adopted T _eff, so that we can find each star’s range of possible logN(Li) values for a given range of effective temperatures (ΔT _eff = 200−300 K). The uncertainty in the derived logN(Li) values is 1.3 for AQ And and UX Dra, 0.5 for HK Lyr, and 0.8 for WZ Cas. Our most probable logN(Li) values (or ranges) are −1.25 for AQ And, −1.2 for HK Lyr, −1.0 ≤ logN(Li) ≤ +0.3 for UX Dra, and 4.3 ≤ logN(Li) ≤ 4.8 for WZ Cas. The derived C/O ratios for the stellar atmospheres also depend on T _eff. Possible uncertainties in other atmospheric parameters do not change logN(Li) by more than 0.2.     

Multiperiodicity in the Orbital Period Variations of the Eclipsing Binary System Z Per

Astronomy Reports - The variations in the orbital period of the eclipsing binary system Z Per have been analyzed. It has been shown that the variations in the period can be represented as a...     

Variations in solar and geomagnetic activity with periods near to 1.3 year

It is known that solar wind velocity fluctuates regularly with a period of about 1.3 years. This periodicity (and other signals with periods near to 1.1 and 0.9 years) has also been observed in biological data. The variation is a temporary feature, mostly being observed in the early 1990s. Here, the occurrence of these periodic signals in solar and geomagnetic activity between 1932 and 2005 has been investigated. The signal with 1.3 year period is present in geomagnetic activity only in a short interval after 1990 and to a lesser extent around 1942. At other times the signal is very weak or not present at all. Other periods are much lower amplitude and appear only sporadically throughout the time investigated. A connection between these periods and solar cycles (e.g. different even or odd cycles) has not been proven. It is possible that there is a long-term periodicity in the occurrence of the 1.3 year period but the time series data available is insufficient to confirm this. There are no such periodicities in solar activity. In order to gain a greater understanding of these periodic signals, we should search for their origin in interplanetary space.     

Long-term variations in the spottedness of BY Dra M dwarfs

The results of a spottedness study for twelve red dwarf stars covering several decades and based on a vast amount of photometric observations are presented. The analysis makes use of multicolor (UBV RI) photometric monitoring of ten of these stars since 1991 at the Crimean Astrophysical Observatory, as well as data from the literature. The spottedness parameters for selected active BY Dra red dwarfs have been refined using an improved zonal model for the spotted stellar atmospheres to allow for the possible presence of two active longitudes on the stars. Time variations in the spot activity of these systems are analyzed in order to look for possible cycles. Three of the stars show a drift of their spots in the latitude towards the stellar poles; however, the magnitude of this latitude drift is a factor of two to three lower than the analogous value for sunspots. All the stars except for YZ CMi display relationships between the area of the spots and their latitude, with correlation coefficients R from 0.67 to 0.97. Evidence for the presence of activity cycles with durations from 25 to 40 years is found for six stars, which are characterized by synchronous variations in the areas and latitudes of their spots, as well as of the overall photometric brightness.     

Orbital-Period Variations of the Eclipsing Binaries RY Aur,GG Cas,RS Lep,and RV Tri

Variations of the orbital periods of the eclipsing binaries RY Aur, GG Cas, RS Lep, and RV Tri are analyzed. The period variations in all of these systems can be represented as a superposition of a secular period decrease and cyclic variations that can be explained with the light-time effect due to the presence of a third body in the system. The secular period decrease could be due to magnetic braking.

     

Multiplicity and apsidal motion in the eclipsing binary EQ Boo

We present the first estimates of the relative and absolute parameters of the eclipsing binary EQ Boo based on a light-curve analysis (P = 5.43^d, V = 8.8 ^m ). This star is simultaneously Component A of the visual binary ADS 9422 (spectral types F7V + G0V; separation of the components 1.3″; magnitude difference 0.7 ^m ). The derived disagreement between the components’ physical parameters and the assumption that they have the same age can be removed if there is a fourth, late-type star in the system. This is also able to explain the observed anomaly in the behavior of the O-C residuals at times of minima.     

Over-reflection instability and the developed turbulence in accretion disks in close binaries

The results of studies of the over-reflection mechanism for the development of hydrodynamical instability in the accretion disks of close binary stars are presented. The driving of this instability is shown to result in the generation of regular, large-scale, spiral-vortex structures and the development of turbulence in the disk. The derived estimates of the coefficient of turbulent viscosity are in good agreement with the observations, and are able to explain the high rate of angular-momentum transfer and the measured accretion rate. The developed theoretical model is used with the observational data to derive a power-law spectrum for the developed turbulence.     

Studies of the evolutionary relationship between detached and contact binaries

We estimate the extent to which there is an evolutionary relationship between detached main-sequence binaries and ～KW, KW, and KP contact binaries in the first mass-exchange phase. The current and initial distributions of close binaries of these types are calculated per unit volume of space in the vicinity of the Sun and used to demonstrate evolutionary transitions from low-mass, short-period, detached systems to contact binaries.     

Photometric elements and apsidal motion of the eclipsing binary ES Lac

We have obtained high-accuracy photoelectric measurements of ES Lac, an eclipsing binary with an elliptical orbit (B9III + B9III; P = 4.459^d, e = 0.198) in 1985–2004 at the Sternberg Astronomical Institute’s Tien Shan High-Altitude Observatory. Our detailed analysis of the 19-year uniform series of measurements has yielded the first photometric elements for this system, as well as a self-consistent set of physical and geometrical parameters for the binary. The virtually identical components (M ₁ = M ₂ = 3.0 M _⊙; R ₁ = R ₂ = 4.12 R _⊙) are appreciably separated from the main sequence, and are located on the giant branch: their age is t = (3.5 ± 0.2) × 10⁸ yrs. An analysis of our observations together with previously published times of minima has enabled a considerable refinement of the period of the apsidal motion, U = 355 ± 20 years, and a first determination of the apsidal parameter reflecting the radial density distributions for the components stars: k ₂ ^obs = 0.00213(18). This value is in a good agreement with the value expected theoretically for current evolutionary models of such stars: k ₂ ^th = 0.00257(15).     

Impact of the magnetic field on the structure of accretion disks in semi-detached binaries

We discuss characteristic features of the magnetic gas-dynamical structure of the flows in a semi-detached binary system obtained from three-dimensional simulations, assuming that the intrinsic magnetic field of the accreting star is dipolar. The turbulent diffusion of the magnetic field is taken into account. The SS Cyg system is considered as an example. Including the magnetic field can alter the basic parameters of the accretion disk, such as the accretion rate and the characteristic density. The magnetic field in the disk is primarily toroidal.     

Disk wind in young binaries and its impact on the infrared excesses of young stars

We consider the effect of binarity of young stars on the spectral energy distribution of the IR radiation from circumstellar dust. The formation of a common dust envelope in a binary system with a low-mass secondary component is strongly affected by the disk wind from the secondary. The small velocities in peripheral areas of the wind are such that it can be partially or entirely captured by the primary, even when the distance between the components is up to several astronomical units. As a result, an envelope with a rather complex spatial and kinematic structure is formed. Its mass is many orders of magnitude smaller than that of the accretion disk around the binary. However, the thermal radiation emitted by dust particles of the envelope can be comparable to the total radiation of the accretion disk. This result is discussed in the context of the deficit at near-IR wavelengths (2–10µm) in current models for accretion disks around young stars.     

A photometric study of the eclipsing dwarf nova GY Cnc in quiescence and during an outburst

The results of photometric observations of the dwarf nova GY Cnc in the Rc filter acquired in 2013–2015 (~3900 orbital cycles, 19 nights in total) are presented, including observations during its outburst in April 2014. The binary’s orbital elements have been refined. The orbital period has changed only insignificantly during the ~30 000P_orb since the earlier observations; no systematic O–C variations were detected, only fluctuations within 0.004^d on time scales of 1500–2000P_orb. A “combined” model is used to solve for the parameters of GY Cnc during two states of the system. The flux from the white dwarf is negligible due to the star’s small size. The temperature of the donor star, T₂ ~ 3667 K (Sp M0.2 V), varies between 3440 and 3900 K (Sp K8.8–M1.7 V). The semi-major axis of the disk is a ~ 0.22a₀, on average. In quiescence, a varies within ~40%. The disk has a considerable eccentricity (e ~ 0.2?0.3) for a < 0.2a₀. The disk shape becomes more circular (e < 0.1) with increasing a. The outburst of GY Cnc was associated with increased luminosity of the disk due to the parameter α_g (related to the viscosity of the disk material) decreasing to 0.1–0.2 and the temperature in the inner parts of the disk increasing twofold, to T_in ~ 95 000 K. These changes were apparently due to the infall of matter onto the surface of the white dwarf as the outburst developed. All parameters of the accretion disk in quiescence display considerable variations about their mean values.     

Climate and the orbital parameters of the Earth

The discovery of glacial ages in the 19th century triggered the first scientific questions on the evolution of climate through time, and thus corresponds to the dawn of palaeoclimatology. Since then, scientists have attempted to reconstruct past climatic changes and to understand their physical basis. Two competing theories have been suggested to explain the sequence of glacial–interglacial epochs: either the variations of the Earth orbital elements, or the atmospheric composition in carbon dioxide. If the astronomical theory has been largely confirmed since the last 30 years, a physical modeling of the climatic processes at work is still in its infancy. Besides, the most recent results of palaeoclimatology are clearly demonstrating that, more than never, a synthesis of these two old hypotheses is needed.     

Photometric elements,apsidal motion,and the third body in the eclipsing binary V974 Cyg

We have derived the first photoelectric light curve of the eclipsing binary V974 Cyg from our own photoelectric observations. Analysis of the light curve has yielded the system’s photometric elements (r ₁ ≈ r ₂ = 0.1192, e = 0.058, L ₁ ≈ L ₂ = 0.486, and L ₃ = 0.028) and absolute parameters (M ₁ ≈ M ₂ = 2.2M _⊙, T _eff,1 ≈ T _eff,2 = 9500 K, a = 15.0R _⊙, distance d = 1.29 kpc, age log t = 8.0, t/tMS = 0.11). We have detected apsidal motion with the period U _obs = (1140 ± 170) yrs, and the presence of a third body in the system. The orbital parameters derived for the third body are P ₃ = 26.5 yrs, e ₃ = 0.78, and a ₃ sin i ₃ = 1.5 AU; and the lower limit for its mass is M ₃ > 0.58M _⊙. The observed apsidal-motion rate is higher than is expected theoretically by a factor of 1.5. The axial rotation of the system’s components is not yet synchronized with the orbital motion, probably because V974 Cyg is relatively young and detached.