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The Algol paradox posed a serious challenge to the theory of evolution of close binaries. We indicate that it has been resolved by the collective efforts of a whole generation of astronomers rather than by anyone’s individual ingenious accomplishment. We discuss the role of illuminating ideas put forward by Zdeněk Kopal in solving the Algol paradox
Two basic problems of dynamics, one of which was tackled in the extensive work of Z. Kopal (see e.g. Kopal, 1978, Dynamics of Close Binary Systems, D. Reidel Publication, Dordrecht, Holland.), are presented with their approximate general solutions. The ‘penetration’ into the space of solution of these non-integrable autonomous and conservative systems is achieved by application of ‘The Last Geometric Theorem of Poincaré’...
A brief review of the physical mechanisms that could produce the observed orbital period changes in close binaries, the methods used to study them, and a general discussion is given.
The orbital period variations of the eclipsing binary BX And are examined analysing its (O-C) diagram 1) with the standard method, in which the minima times are fitted by the quadratic ephemeris combined with an assumed light-time effect, and 2) with the first continuous method. The results from the use of the two methods are, as was expected, different.
We present a new photoelectric light curve of α Coronae Borealis. The derived rate of apsidal motion differs from the theoretical prediction. A possible solution of the problem is suggested.
Several new times of minimum light recorded with photoelectric or CCD means have been gathered for the eccentric eclipsing binary V889 Aql (P = 11.1 days, e = 0.37). Its O-C diagram is presented, and improved elements of the apsidal motion and the light-time effect (LITE) are given. We found a long apsidal motion period of about 24 400 ± 2400 years and a period of the third body of about 52 ± 2 years.
The triple systems display several interesting effects; and are also important for understanding the origin and evolution of binaries. Namely mutual inclination of two orbits, changes of observed inclination, and problems with the third light will be discussed in this contribution.
We discuss implementation of light time effects in a general binary star program that solves for third body orbit parameters and binary star parameters together. The program combines radial velocities and light curves within a coherent analysis and can use data that are very unevenly distributed over time. By analyzing whole curves, the program has access to more information than only from eclipse...
Four eclipsing binaries, which show apparent changes of period, have been studied with respect to a possible presence of the light-time effect. With a least squares method we calculated new light elements of these systems, the mass function of the predicted third body, and its minimum mass. We discuss the probability of the presence of such bodies in terms of mass function, changes in radial velocity...
An astrometric solution, together with time of minimum analysis, has been made for the multiple system XY Leonis (HIP 49136) to identify the properties of the remote companion to the eclipsing pair (AB). From this solution, we derive the inclination of the wide orbit (AB-cd) as 94.4° ± 0.2°, angle of nodes as 247.3° ± 0.2°, and the mass of the wide component (the dwarf binary cd) as 0.98 ± 0.2 Mʘ...
UBV RI photometry and 4600–9000 Å spectroscopy of nova V475 Sct taken in the first 3 month after discovery is presented. The object can be classified as a Fe II type slow nova with t2,V = 48 days, t3,V = 53 days. The absolute magnitude of the nova at maximum, its colour excess and distance were determined. The observed 13.4 day periodicity of flares...
Photometric observations of the eccentric eclipsing binary V1143 Cyg were performed during Aug.–Sep. 2000 and July 2002, in Johnson B and V bands. The analysis of both light curves was made separately using the 1998 version of Wilson’s LC code. In order to find a new observed rate of apsidal motion, we followed the procedure described by Guinan and Maloney (1985). A new observed rate of apsidal motion...
I review the current knowledge on binarity accompanying intrinsic variability of different types, according to the existing classification scheme. In many cases, binary nature not only accompanies but causes intrinsic variability.
Light variations of a representative sample of 26 more or less periodically variable carbon stars were analyzed on the basis of 2220 individual observations made by the Hipparcos satellite and 33 544 visual observations listed in AFOEV and VSOLJ databases within the interval JD = 2 448 000 (1988) ±6 cycles. We found the osculating linear ephemerides of all stars and their mean light curves, as well...
Photometric observations of symbiotic stars in the blue and in the red spectral regions make it possible to reveal non-radial oscillations both of the cool and of the hot components. Light variations of red giants in the symbiotic systems CI Cyg and AG Peg show several periods in the 10–80d range, interpreted as p-mode pulsations. These modes are excited by a bright spot produced by radiation flux...
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.
oAnd is one of the most frequently observed Be stars, both in photometry and spectroscopy. It is a multiple system of at least four stars (a Be star, a close binary of spectral types B7 and B8, and an A star). For over a century, numerous observers report a highly variable spectrum, photometric changes, and a substantial range of radial velocity. The star has changed back and forth between...
Based on a new set of electronic spectra in a relatively wide spectral range (3500–8300 Å) and using the methods of spectrum disentangling (code KOREL) and solution of RV curves (code FOTEL), we determined new orbital elements of the binary star κ Dra. The solution of the radial velocity curves for Balmer and some other strong metallic lines suggested a circular orbit and led to the following orbital...
HD 6226 is a bright binary Be star at visual magnitude 6.81 (Hipparcos database). The emission and absorption phases occur in cycles, which are probably not periodic. The suspected period of about 630 days (derived from photometric measurements) is not confirmed by our spectroscopic survey. The latest emission phase developed in the beginning of 2003, then the emission strength systematically decreased...
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.
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