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&

A Search for Pulsating, Mass-Accreting Components in Algol-Type Eclipsing Binaries

We present a status report on the search for pulsations in primary componants of Algols systems (oEA stars). Analysis of 21 systems with A0-F2 spectral type primaries revealed pulsations in two systems suggesting that of the order of ten persent of Algols primaries in this range are actually pulsators

UV Leo: The binary with the two suns

BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The elements of the two components of the system are calculated and the spot characteristics are given

A study of the binary GR Tauri from optical and infrared observations

Visual and infrared light curves of the noncontact, short period, close binary system GR Tauri were obtained in 1992 November. A new ephemeris of the binary is given using the times of minima inferred from all the observations of the system to date. New light and photometric data from the analysis of the B, V and J, K light curves via the Wilson-Devinney code are also given, resulting in a "near-contact" binary model for the system. The analysis of the colors of GR Tauri shows that the primary component's spectral type must be about A9 V, instead of A5 V according to a recent spectroscopic classification. © 1995 American Astronomical Society

Study of the contact binary AK Herculis: Light-curve analysis and orbital period investigation

AK Her is a very interesting contact binary exhibiting variable light curves and an obvious O'Connell effect, with max I greater than max II. In the present work an extensive study of this system is made covering not only its light curve analysis, but also its orbital period changes in an attempt to give a definite answer regarding the apsidal motion of AK Her. Photoelectric observations of AK Her, obtained between 1985-1987 at the National Observatory of Athens Greece, are presented, analysed and discussed. The light curve analysis was made with the W-D code and the geometric and photometric elements of the system were derived. The O'Connell effect was faced with a two dark spot model. Moreover, the orbital period of the system was examined and two periodicities were detected. Since the first one corresponds to the time interval for which observational data exist and the second was found to be half of the first, it turns out that none of them is true. Two other significant results that came from the present analysis are that the orbital period of AK Her does not follow a sinusoidal variation and that, from the times of minimum light at primary and secondary eclipses, it seems that there is no apsidal motion

Accretion disc in the massive V448 Cygni system

The UBV light curves of the early-type eclipsing binary V448 Cygni, obtained at the Abastumani Astrophysical Observatory from 1964 to 1967, are re-analysed here. The analysis was made assuming the presence of an accretion disc in the system, as inferred from the light-curve shape and spectroscopic characteristics of the system. The Roche model of a binary was used, containing a geometrically and optically thick accretion disc around the hotter and more massive star. By solving the inverse problem, the orbital elements and the physical parameters of the system components and of the accretion disc were estimated. This result is important for understanding the star formation and evolution processes in the systems with massive components. © 2009 RAS

Efficiency of O–C diagrams as diagnostic tools for long-term period variations

Context. The credibility of an O–C diagram analysis is investigated when long-term processes are examined in binary systems. The morphology of period and O–C diagrams is thoroughly explored when mass loss and magnetic braking, induced by stellar winds, drive the orbital evolution of late-type detached binaries. Conditions are specified that determine which process dominates. Aims. Our objective is to determine the minimum time intervals that observations are expected to span for a physical mechanism to be detectable by means of an O–C diagram analysis. Computations for various values that account for the noise level and the orbital period are performed to find out to which degree these affect the inferred intervals. Methods. Generalized \hbox{$\dot{J}-\dot{P}$} relations that govern the orbital evolution of a binary system are set and solved analytically to determine in a closed form the period and the function expected to represent the respective O–C variations. Semi-empirical relations adapting mass loss and magnetic braking processes for single cool stars are adopted and properly modified to be consistent with the latest observational constraints. A standard Newton-Raphson numerical procedure is then employed to estimate the minimum temporal range over which a specific mechanism is rendered measurable. Results. Mass loss rates comparable to or greater than −10-9 M⊙ yr-1 are measurable for typical noise levels of the O–C diagrams when the data span more than a century. Magnetic braking was proved to be very sensitive on the orbital period and on the braking law adopted for inference. It is expected to be detectable in current O–C diagrams of very short-period binaries only, for others it needs at least two centuries of observations to confirm its effects safely. Conclusions. Both wind driven mass loss and magnetic braking processes are able to drive the orbital evolution of short-period detached binaries (Porb1d) in amounts traced on human timescales. There are also special conditions under which their strength is equalized, locking the orbital period invariable in time. Several short-period RS CVn-type binaries are fine candidates where this regime is expected to prevail

Efficiency of ETV diagrams as diagnostic tools for long-term period variations: II. Non-conservative mass transfer, and gravitational radiation

Context. 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). Aims. Our primary objective concerns the traceability of each physical mechanism by means of an ETV diagram analysis. Also, possible critical mass ratio values are sought for those transfer modes that involve orbital angular momentum losses strong enough to dictate the secular period changes even when highly competitive mechanisms with the opposite direction act simultaneously. Methods. The J - P relation that governs the orbital evolution of a binary system is set to provide the exact solution for the period and the function expected to represent the subsequent eclipse timing variations. The angular momentum transport is parameterized through appropriate empirical relations, which are inferred from semi-analytical ballistic models. Then, we numerically determine the minimum temporal range over which a particular mechanism is rendered measurable, as well as the critical mass ratio values that signify monotonicity inversion in the period modulations. Results. Mass transfer rates comparable to or greater than 10-8 M⊙ yr-1 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 (qcr ≈ 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. Conclusions. The monotonicity of the period variations and the curvature of the respective ETV diagrams depend strongly on the accretion mode and the degree of conservatism of the transfer process. 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. © ESO, 2015

Efficiency of O-C diagrams as diagnostic tools for long-term period variations: I. Wind-driven mass loss and magnetic braking

Context: The credibility of an O-C diagram analysis is investigated when long-term processes are examined in binary systems. The morphology of period and O-C diagrams is thoroughly explored when mass loss and magnetic braking, induced by stellar winds, drive the orbital evolution of late-type detached binaries. Conditions are specified that determine which process dominates. Aims: Our objective is to determine the minimum time intervals that observations are expected to span for a physical mechanism to be detectable by means of an O-C diagram analysis. Computations for various values that account for the noise level and the orbital period are performed to find out to which degree these affect the inferred intervals. Methods: Generalized J-P relations that govern the orbital evolution of a binary system are set and solved analytically to determine in a closed form the period and the function expected to represent the respective O-C variations. Semi-empirical relations adapting mass loss and magnetic braking processes for single cool stars are adopted and properly modified to be consistent with the latest observational constraints. A standard Newton-Raphson numerical procedure is then employed to estimate the minimum temporal range over which a specific mechanism is rendered measurable. Results: Mass loss rates comparable to or greater than -10-9 M® yr-1 are measurable for typical noise levels of the O-C diagrams when the data span more than a century. Magnetic braking was proved to be very sensitive on the orbital period and on the braking law adopted for inference. It is expected to be detectable in current O-C diagrams of very short-period binaries only, for others it needs at least two centuries of observations to confirm its effects safely. Conclusions: Both wind driven mass loss and magnetic braking processes are able to drive the orbital evolution of short-period detached binaries (Porb1d) in amounts traced on human timescales. There are also special conditions under which their strength is equalized, locking the orbital period invariable in time. Several short-period RS CVn-type binaries are fine candidates where this regime is expected to prevail. © ESO, 2011

A search for pulsating, mass-accreting components in Algol-type eclipsing binaries

We present a status report on the search for pulsations in primary componants of Algols systems (oEA stars). Analysis of 21 systems with A0-F2 spectral type primaries revealed pulsations in two systems suggesting that of the order of ten persent of Algols primaries in this range are actually pulsators. © Springer Science+Business Media B.V. 2006