74 research outputs found
Efficiency of ETV diagrams as diagnostic tools for long-term period variations. II. Non-conservative mass transfer, and gravitational radiation
The credibility of an eclipse timing variation (ETV) diagram analysis is
investigated for various manifestations of the mass transfer and gravitational
radiation processes in binary systems. The monotonicity of the period
variations and the morphology of the respective ETV diagrams are thoroughly
explored in both the direct impact and the accretion disk mode of mass
transfer, accompanied by different types of mass and angular momentum losses
(through a hot-spot emission from the gainer and via the L2/L3 points). Mass
transfer rates comparable to or greater than 10^{-8} M_sun/yr are measurable
for typical noise levels of the ETV diagrams, regardless of whether the process
is conservative. However, the presence of a transient disk around the more
massive component defines a critical mass ratio q_cr ~ 0.83 above which the
period turns out to decrease when still in the conservative regime, rendering
the measurability of the anticipated variations a much more complicated task.
The effects of gravitational radiation proved to be rather undetectable, except
for systems with physical characteristics that only refer to cataclysmic
variables. Unlike the hot-spot effects, the Lagrangian points L2 and L3 support
very efficient routes of strong angular momentum loss. It is further shown that
escape of mass via the L3 point - when the donor is the less massive component
- safely provides critical mass ratios above which the period is expected to
decrease, no matter how intense the process is.Comment: 13 pages, 6 figures, 10 tables, published in A&
Photometric Observation And Period Study of GO Cygni
Photometric observations of GO Cyg were performed during the July-October
2002, in B and V bands of Johnson system. Based on Wilson's model, the light
curve analysis were carried out to find the photometric elements of the system.
The O-C diagram which is based on new observed times of minima suggests a
negative rate of period variation (dP/dt<0) for the system.Comment: 12 pages, 6 figures, 4 tables, submitted to Ap&S
Two new light curves of the eclipsing variable u Herculis
This paper presents two new light curves (in B and V) of the eclipsing variable star u Her which have been derived from photoelectric observations made at the National Observatory of Athens. General information of the system is given in the introduction, while Section 2 deals with some observational and reductional details. Section 3 gives the residuals O-C and Section 4 the normal points. © 1980 D. Reidel Publishing Co
The peculiar eclipsing star BD+13°3496 (V508 ophiuchi): New BV observations and light curve analysis
New BV photoelectric observations of the W UMa-type system V508 Ophiuchi, made in 1986 at the Kryonerion Astronomical Center of the National Observatory of Athens, Greece, are given. The corresponding mean light curves, as well as those obtained in 1981 at the same station using the same instruments, are analysed using frequency-domain techniques. The geometrical and photometric elements of the system have been found. These are combined with the now available spectroscopic data of the system to get its absolute elements. A general discussion for the light variations between the old and the new observations is made. From the light curve analysis it was found that V508 Oph is an A-type W UMa binary with both of its components to fill their corresponding Roche lobes. © 1989 Kluwer Academic Publishers
The system of DO cassiopeiae: Photoelectric observations and light curves analysis
The new B and V photoelectric observations of DO Cas, obtained during 1979 and 1980, are presented, analysed, and discussed. The observations were made at the National Observatory of Athens, Greece, and their analysis was based on the frequency domain, techniques. New geometric, photometric, and absolute elements for the system are given. © 1986 D. Reidel Publishing Company
BV photoelectric observations of V508 Ophiuchi
Photoelectric observations of V508 0ph in B and V made with the 48-inch Cassegrain reflector at the Kryonerion Astronomical Station of the National Observatory of Athens in 1981 are presented and discussed. © 1983 D. Reidel Publishing Company
New BV photoelectric observations of BX Andromedae
Photoelectric observations of BX Andromedae made with the 48 inch Cassegrain reflector at the Kryonerion Astronomical Station of the National Observatory of Athens during 1981 and 1982 are presented. © 1984 D. Reidel Publishing Company
Evaluation of the photometric perturbations in close binary systems - I. Tidal distortion
In the present study the photometric perturbations arising from the mututal tides of the two components in a close binary system are calculated and discussed. The evaluation is made for each star separately as well as for both stars together in the case of occulation eclipses terminating in totality. © 1983 D. Reidel Publishing Company
Two new light curves of the eclipsing variable u Herculis
This paper presents two new light curves (in B and V) of the eclipsing variable star u Her which have been derived from photoelectric observations made at the National Observatory of Athens. General information of the system is given in the introduction, while Section 2 deals with some observational and reductional details. Section 3 gives the residuals O-C and Section 4 the normal points. © 1980 D. Reidel Publishing Co
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