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We present a detailed study based on infrared (IR) photometry of all Galactic RV Tauri stars from the General Catalogue of Variable Stars (GCVS). RV Tauri stars are the brightest among the Population II Cepheids. They are thought to evolve away from the asymptotic giant branch (AGB) towards the white dwarf domain. IRAS detected several RV Tauri stars because of their large IR excesses and it was found that they occupy a specific region in the [12] - [25], [25] - [60] IRAS two-colour diagram. We used the all sky survey of Wide-field Infrared Survey Explorer to extend these studies and compare the IR properties of all RV Tauri stars in the GCVS with a selected sample of post-AGB objects with the goal to place the RV Tauri pulsators in the context of post-AGB evolution. Moreover, we correlated the IR properties of both the RV Tauri stars and the comparison sample with other observables like binarity and the presence of a photospheric chemical anomaly called depletion. We find that Galactic RV Tauri stars display a range of IR properties and we differentiate between disc sources, objects with no IR excess and objects for which the spectral energy distribution (SED) is uncertain. We obtain a clear correlation between disc sources and binarity. RV Tauri stars with a variable mean magnitude are exclusively found among the disc sources. We also find evidence for disc evolution among the binaries. Furthermore our studies show that the presence of a disc seems to be a necessary but not sufficient condition for the depletion process to become efficient. [ABSTRACT FROM AUTHOR]

We present new radial velocities and UBV photometric observations of three eclipsing binaries, V799 Cas, BX Psc and HD 172189, in order to increase the number of close binaries with absolute parameters determined accurately. Standard wide-band indices for the systems and comparison stars were determined accurately. Using the times of mid-eclipses, new ephemerides are calculated for three systems. V799 Cas and HD 172189 consist of two well-detached components in eccentric orbits. BX Psc is a single-lined eclipsing binary which consists of a late-A and an early-K star. The effective temperatures of the hotter components and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. The UBV photometric data and radial velocities were analysed simultaneously for the systems' parameters using Wilson–Devinney code. The masses have been found to be for the primary and secondary stars of V799 Cas, BX Psc and HD 172189, respectively. The radii of the components are derived in the case of V799 Cas: . We have calculated the distances to the systems of V799 Cas, BX Psc and HD 172189 as 607 ± 35, 213 ± 6 and 432 ± 12 pc, respectively, using bolometric magnitudes and empirical bolometric corrections for the component stars. The model predictions match the measured properties of V779 Cas, BX Psc and HD 172189 for an age of 250 Myr, 1 Gyr and 890 Myr, respectively. A subsolar fractional metal abundance, , provides a better match to the absolute parameters of all three systems. [ABSTRACT FROM AUTHOR]

We present new radial velocities and photometric observations of three double-lined eclipsing binaries LL Aqr, MP Del and NSV 20913. This paper is the third in the planned series of investigations. Standard wide-band indices for the systems and comparison stars were determined accurately. Using the times of mid-eclipses, new ephemerides are calculated for the three systems. These systems consist of two well-detached components in eccentric orbits. The effective temperatures of the hotter components and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. New UBV photometric data and radial velocities were analysed simultaneously for the systems' parameters using Wilson–Devinney (WD) code. The masses have been found to be and for the primary and secondary stars of LL Aqr, MP Del and NSV20913, respectively. The radii of the components are derived in the case of LL Aqr: ; in those of MP Del: ; and NSV20913: . The masses, radii and effective temperatures of the component stars have been determined with an accuracy of 5–8, 2–3 and 1–3 per cent, respectively. We have calculated the distances to the systems of LL Aqr, MP Del and NSV 20913 as and , respectively, using bolometric magnitudes and empirical bolometric corrections for the component stars. The stellar model prediction match the measured properties of LL Aqr for an age of about 1.78 Gyr, indicating the components near the half of their core-hydrogen-burning lifetimes. However, the components of MP Del have an age of 1.59 Gyr, the primary component being turn off from the main sequence. The age of the NSV20913's components is about 1 Gyr, indicating the primary component seems to have evolved just slightly off the main sequence but the less massive secondary component is still close to the zero-age main sequence. A subsolar fractional metal abundance, , provides a better match to the absolute parameters of all three systems. [ABSTRACT FROM AUTHOR]

This paper is the second in the planned series of investigations. We present new radial velocities and photometric observations of V2080 Cyg and V2365 Oph. New UBV photometric data and radial velocities were analysed for the systems' parameters. While V2080 Cyg consists of two nearly equal F-type main-sequence stars, V2365 Oph has two different components, namely an early A-type primary and a G-type secondary star. New ephemerides are calculated for both systems. The masses of the component stars have been derived as and for V2080 Cyg and and for V2365 Oph. The effective temperatures and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. The radii have been measured by simultaneous fitting the UBV light curves using Wilson–Devinney code and are for both components of V2080 Cyg and and for V2365 Oph. The absolute parameters of the stars in both systems lie within the same ranges in the mass–radius, mass–effective temperature, mass–luminosity and luminosity–effective temperature planes as in detached Algol systems. A comparison between the properties of the systems of interest and the predictions of theoretical evolutionary models is undertaken in the and radius–log age diagrams. The model predictions match the measured properties of V2080 Cyg for an age of about 5.6 Gyr and a ‘solar’ metal abundance , indicating the components near the end of their core hydrogen-burning phases. However, the position of the components of V2365 Oph on the Hertzsprung–Russell (HR) diagram is best reproduced with evolutionary models for somewhat metal-deficient stars. We found an age of about 700 Myr, with the primary component slightly evolved off the zero-age main-sequence and the secondary one still very close to it. From the basic stellar parameters we have also redetermined the distances to V2080 Cyg and V2365 Oph as and , which are in agreement with, and more accurate than, Hipparcos values. The observations show that at least one of the components of V2365 Oph is an intrinsic variable with a period and peak-to-peak amplitude of 0.07 d and 0.05 mag, respectively. In accordance with its position in the HR diagram, the primary component should be considered as a δ Scuti star and it is believed to be the variable star in the system. [ABSTRACT FROM AUTHOR]

We present the first radial velocities and ground-based photometric observations of V1665 Aql and AG Ari. These double-lined eclipsing binaries have eccentric orbits with eccentricities of 0.24 and 0.09, respectively. New UBV photometric data and radial velocities were analysed using a modified version of the Wilson–Devinney program for the parameters of the systems. Good phase coverage and relatively small scatter both in the light and in the radial-velocity curves meant that the eccentricity and the argument of periastron as well as orbital and stellar parameters could be determined. Our solutions indicate that AG Ari includes a third light with a considerable amount of 5.6 per cent in U, 6.4 per cent in B, and 9 per cent in V. By comparing its light contribution with the total light we classified it as an F-type star. The components in each system are of very nearly equal mass, temperature, and luminosity. Their absolute parameters were compared with those of stars belonging to well-studied detached eclipsing binaries. The components lie well inside the main-sequence band. In addition, the apsidal motion rates of the system have been determined from an analysis of all the photometric observations obtained by space missions and by us. We determined the preliminary apsidal motion periods of the systems to be 449 ± 34 yr for V1665 Aql and 155 ± 6 yr for AG Ari. Because well-detached eclipsing binaries are optimal distance indicators, we estimated the distances to V1665 Aql and AG Ari to be 477 ± 40 and 292 ± 18 pc from the determined absolute visual magnitudes and interstellar extinction. A comparison with evolutionary tracks indicates that the primary component of V1665 Aql has an age of about 1.6 × 108 yr and is near the main-sequence terminal age. The components of AG Ari are intermediate-mass main-sequence stars with an age of about 5.6 × 108 yr. [ABSTRACT FROM AUTHOR]

Binary systems showing both apsidal motion and light travel time (LTT) effects which cause orbital period changes in close binaries were studied. 15 triple systems showing apsidal motion were found by searching the literature, and a table including the important parameters of these systems was constructed. Six of the systems given in this table were selected and observed photometrically. Existence of both apsidal motion and LTT effects in all selected systems was investigated by means of the analysis of their eclipse times. The mean observed internal structure constants, , and contributions to the apsidal motion from the theory of General Relativity and the third/fourth bodies were calculated. The masses of the third/fourth bodies and some characteristics of their orbits were also calculated. [ABSTRACT FROM AUTHOR]

We investigate the Alfvén wave propagation characteristics in the inner zone (r < 1.35R...) of the North Polar Coronal Hole. The linear, incompressible magnetohydrodynamic (MHD) approximation reveals two wave modes with different phase velocities. Alfvén wave with the slower phase velocity is quickly damped; in other words it cannot propagate in the coronal plasma. On the other hand, the higher phase velocity Alfvén waves can propagate along the magnetic field lines. Mechanical energy flux density of these waves is found to be high enough to replace the coronal energy which is lost via optically thin emission and through heat conduction to the chromosphere below. We show that Alfvén waves propagating along the magnetic flux tubes go through refraction and get damped via viscous dissipation and resistivity. The energy flux density of the waves is of the order of 10[sup 6] erg cm[sup -2] s[sup -1]. The radial profile of the energy flux density in the region 1.05-1.35 R shows a rise until about 1.15 R where it peaks and further on declines less steeply than rising arm. This result is used to interpret Si viii data taken by the Solar Ultraviolet Measurements of Emitted Radiation instrument on board Solar and Heliospheric Observatory. Si VIII lines like many other ionic lines show nonthermal broadening. The observed radial profile of the non-thermal line-of-sight velocity of Si viii shows a plateau which coincides with the peak of the energy flux density we derived. We claim that this coincidence is not accidental but indicates the fact that the decrease in the energy flux density of damped Alfvén waves causes the plateau formation in Si viii non-thermal line-of-sight velocity profile. [ABSTRACT FROM AUTHOR]