E. Antonopoulou

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 u J − u 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.

Infrared photometry of the RS CVn binary HR 1099 (V711 Tau)

Infrared observations inJ, H andK of the RS CVn-type binary HR 1099 (V711 Tau) show apparent light variations similar to those in the visible. The phase shift towards increasing phase is confirmed. There is no conspicuous infrared excess attributable to circumstellar emission. The amplitudes of the infrared variation are compatible with the spot model proposed for RS CVn and enable plausible limits on a characteristic spot temperature and effective spot area to the set.

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.

The UV spectrum of the binary system TY Pyx

A detailed list and analysis of line identifications of five UV spectra of the RS CVn-type binary system TY Pyxidis are presented. These spectra are recorded at different phases with the International Ultraviolet Explorer (IUE). Two of them are in the wavelength rangeλλ1235–1950 Å while the other three in the rangeλλ2700–3110 Å.The far-UV spectrum of TY Pyx is mainly an emission spectrum dominated by the emission lines of the ions:Ci, Oi, Cii, Siii, Heii, Alii, and Feiii. We also pointed out the existence of a Feiii [34] line in absorption.The UV spectrum between 2700–3110 Å is dominated by weak absorption lines. Two satellite components are indicated for many lines, which correspond to the two stars of the system, in the two out of the three spectra (LWP 13386 and LWP 13347).Violet emission wings are observed for Fei [1], Tii [1],Oiv [1], and Siiii [1]. The UV spectrum of TY Pyx is also characterized by the multi-structure of Mgii [1] resonance lines.

Infrared photometry of UV Piscium

The eclipsing binary system UV Psc was observed in the near-infrared (JHK), and a wave-like distortions have been observed similar to those in the visible. The out-of-eclipse observations have shown real large amount of scatter. This cannot be attributed to the existence of spots on one of the components, which can explain the wave-like distorition of the light curves, but probably to the intrinsic variability of one of them.

Energy estimation of ultra high energy cosmic particles by lateral distribution functions of extensive air showers

Energy is among the characteristics of Ultra High Energy Cosmic Rays (E > 5 ×1019eV) which could be estimated experimentally based on simulations. This paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of extensive air showers, vertical and inclined, are simulated to derive the lateral distribution functions of the shower particles. The scenario of simulations is adapted to the P. Auger Observatory site.

Detection of MHD waves in the solar chromosphere

One of the main features of the quiet solar chromosphere is the Network Bright Points (NBP), formed by emerging magnetic flux at the boundaries of supergranular cells. Using SSW IDL routines and wavelet analysis of series of images in four bandpasses (CaIIK3, Mgb1, Mgb2 and Hα core) we have detected MHD wave modes in the Network Bright Points of the solar chromosphere. The observations have been analyzed using cross‐correlation techniques and we have drawn conclusions on wave propagation and mode‐coupling.

An investigation of the tidally driven period changes in detached binary systems through O – C time series analysis: the case of RT And and WY Cnc

Detached binary systems are subjected to a variety of physical mechanisms which are able to change their period in a continuous way and in a broad band of timescales. Assuming that these changes should be detectable in O–C diagrams in a way specified by the physical theory of the underlying mechanisms, we carry out a preliminary study in a properly selected sample of detached binaries, where no mass transfer is expected. We are primarily interested in finding traces of tidal moments in observed orbital period changes (possibly coupled with stellar wind angular momentum losses). We focus our attempts on two short-period chromospherically active binaries (RT And and WY Cnc), whose expected period changes rates are found to be close to those derived by means of time series analysis. Emphasis is also given to systems which show a remarkably constant orbital period, in disagreement with the values expected by theory. †This paper was originally due to be published in the Special Issue: Close Binary Stars in Mod...

Line Broadening of EUV Lines at the Solar Limb Observed with SUMER/SoHO. Relation to Spicules

We study the broadening of EUV line widths as we move from the disk through and off the solar limb. This broadening maximizes at approximately 10 Mm above the limb. We use one raster scan and two time series obtained by SUMER/SoHO to examine a possible correlation between this phenomenon and spicule activity. It appears that spicule presence leads to even wider profiles whereas the appearance of macrospicules extends the broadening to even greater distances above the limb. We suggest that this correlation might imply that spicules are responsible for this disk‐to‐limb behavior even in regions where they cannot be observed.

First Photometric Observations of Recently Discovered Binaries

We present preliminary results of BVRI photometry of binary stars out of an observing list of short period binaries without any previous multifilter observations. The purpose of this project is to obtain photometric elements and the absolute parameters for further understanding of the evolutionary processes for these systems. The observations took place at the Kryonerion Astronomical Station (NOA). New times of minima are presented and a more accurate ephemeris is suggested.