Coupling equations for a flow-wave field used to faculae heating

In a binary system of a background fluid-wave field, the wave effect may be important in some cases. From general properties of thermodynamics of the medium, we derive the coupling equations for the mean flow-wave field. For six wave modes (Langmuir wave, ion-acoustic oscillations, whistlers, Alfvén waves, magneto-acoustic oscillations, and transverse plasma wave) the corresponding representation of the wave stress tensor is found. Finally, the representation for the Alfvén waves is applied to the faculae heating and a result consistent with observations is obtained.     

Observations of the transient X-ray pulsar KS 1947+300 by the INTEGRAL and RXTE observatories

We analyze the observations of the X-ray pulsar KS 1947+300 performed by the INTEGRAL and RXTE observatories over a wide (3–100 keV) X-ray energy range. The shape of the pulse profile was found to depend on the luminosity of the source. Based on the model of a magnetized neutron star, we study the characteristics of the pulsar using the change in its spin-up rate. We estimated the magnetic field strength of the pulsar and the distance to the binary.     

A study of the new X-ray transient RXTE J2123−058 during its post-outburst state

We carried out I , R , V and B photometric observations of the neutron star X-ray binary RXTE J2123−058 shortly after the end of the X-ray outburst in mid-1998. We adopt the low-mass binary model to interpret our observations. After folding our data on the 0.24 821‐d orbital period, and correcting for the steady brightness decline following the outburst, we observed sinusoidal oscillations with hints of ellipsoidal modulations which became progressively more evident. Our data also show that the decline in brightness was faster in the V band than in the R and I bands. This suggests both the cooling of an irradiation-heated secondary star and the fading of an accretion disc over the nights of our observations.     

Gravitational and electromagnetic emission by magnetized coalescing binary systems

We discuss the possibility to obtain an electromagnetic emission accompanying the gravitational waves emitted in the coalescence of a compact binary system. Motivated by the existence of black hole configurations with open magnetic field lines along the rotation axis, we consider a magnetic dipole in the system, the evolution of which leads to (i) electromagnetic radiation, and (ii) a contribution to the gravitational radiation, the luminosity of both being evaluated. Starting from the observations on magnetars, we impose upper limits for both the electromagnetic emission and the contribution of the magnetic dipole to the gravitational wave emission. Adopting this model for the evolution of neutron star binaries leading to short gamma ray bursts, we compare the correction originated by the electromagnetic field to the gravitational waves emission, finding that they are comparable for particular values of the magnetic field and of the orbital radius of the binary system. Finally we calculate the electromagnetic and gravitational wave energy outputs which result comparable for some values of magnetic field and radius.     

The distortion wave on the light curve of the RS CVn binary UV piscium

The eclipsing binary UV Piscium was observed with the standardUBV filters during 1976-77, 1977-78 and 1978-79 observing seasons with the 1.22-m reflecting telescope of the Japal-Rangapur Observatory. A wave-like distortion on the light curve noticed by Carr (1969), Oliver (1974), Sadik (1979) and Zeiliket al. (1982a) is confirmed by the present observations. Combining our observations with those of Carr, Oliver and Sadik, it is found that the distortion wave is moving towards decreasing orbital phase with a period of about 1200 days. The source of the observed distortion wave is found to be the hotter component.     

Radio occultation measurements and MGCM simulations of Kelvin waves on Mars

We have derived new results concerning thermal tides on Mars from a combination of radio occultation measurements and numerical simulations by a Mars General Circulation Model (MGCM). This investigation exploits a set of concurrent observations by Mars Express (MEX) and Mars Global Surveyor (MGS) in mid-2004, when the season on Mars was midspring in the northern hemisphere. The MEX occultations sampled the atmosphere near the evening terminator at latitudes ranging from 54° N to 15° S. The MGS occultations provided complementary coverage near the morning terminator at latitudes of 35° N and 71° S. The geopotential field derived from these measurements contains distinctive modulation caused by solar-asynchronous thermal tides. Through careful analysis of the combined observations, we characterized two prominent wave modes, obtaining direct solutions for some properties, such as the amplitude and phase, as well as constraints on others, such as the period, zonal wave number, and meridional structure. We supplemented these observations with MGCM simulations. After evaluating the performance of the MGCM against the measurements, we used the validated simulation to deduce the identity of the two tidal modes and to explore their behavior. One mode is a semidiurnal Kelvin wave with a zonal wave number of 2 (SK2), while the other is a diurnal Kelvin wave with a zonal wave number of 1 (DK1). Both modes are known to be close to resonance in the martian atmosphere. Our observations of the SK2 are more complete and less ambiguous than any previous measurement. The well-known DK1 is the dominant solar-asynchronous tide in the martian atmosphere, and our results confirm and extend previous observations by diverse instruments.     

Gravitational wave detection through microlensing?

It is shown that accurate photometric observations of a relatively high-magnification microlensing event  ( A ≫ 1)  , occurring close to the line of sight of a gravitational wave (GW) source, represented by a binary star, can allow the detection of subtle gravitational effects. After reviewing the physical nature of such effects, it is discussed to what extent these phenomena can actually be caused by GWs. Expressions for the amplitude of the phenomena and the detection probability are supplied.     

Rapid periodic light variations of EM Cephei

In 1990 and 1992, using the 60 cm reflector of Beijing Observatory, we carried out photoelectric UBV observations of the Be star EM Cep and obtained 277 data sets. After combining the published minimum times over the years we made the O — C analysis and found an improved period of 0.806184 d or a single wave period of 0.403092d. Our analysis also showed a quickening tendency of the period at a rate dP/dt = −8.8514 × 10⁻¹⁰. The light curve is characterized by sharp minima and broad maxima. We found a detectable variation of the U — B colour index with the phase.     

Spectral analysis of the eclipsing variable V471 Tauri (BD+16°516)

Spectroscopic observations of the white-dwarf eclipsing binary V471 Tauri are reported. The behaviour of the H and K emission lines of Caii are investigated relative to the photoelectric observations, and the existence of a probable correlation between minimum emission line strength and the maximum wave position within the migrating wave is demonstrated.     

Multiwavelength study of the transient X-ray binary IGR J01583+6713

We have investigated multiband optical photometric variability and stability of the Hα line profile of the transient X-ray binary IGR J01583+6713. We set an upper limit of 0.05 mag on photometric variations in the V band over a time-scale of three months. The Hα line is found to consist of non-Gaussian profile and quite stable for a duration of two months. We have identified the spectral type of the companion star to be B2 IVe while the distance to the source is estimated to be ∼4.0 kpc. Along with the optical observations, we have also carried out analysis of X-ray data from three short observations of the source, two with the Swift –XRT and one with the RXTE –PCA. We have detected a variation in the absorption column density, from a value of  22.0 × 10²² cm⁻²  immediately after the outburst down to  2.6 × 10²² cm⁻²  four months afterwards. In the quiescent state, the X-ray absorption is consistent with the optical reddening measurement of   E ( B − V ) = 1.46  mag. From one of the Swift observations, during which the X-ray intensity was higher, we have a possible pulse detection with a period of 469.2 s. For a Be X-ray binary, this indicates an orbital period in the range of 216–561 d for this binary system.     

Short-term pulse frequency fluctuations of OAO 1657−415 from RXTE observations

We present new X-ray observations of the high-mass X-ray binary (HMXRB) pulsar OAO 1657−415, obtained during one orbital period (10.44 d) with the Rossi X-Ray Timing Explorer ( RXTE ). Using the binary orbital parameters, obtained from Burst and Transient Source Experiment (BATSE) observations, we resolve the fluctuations in the pulse frequency at time-scales on the order of 1 d for the first time. Recent BATSE results by Baykal showed that OAO 1657−415 has spin-up/down trends in its pulse frequency time series, without any correlation with the X-ray luminosity at energies >20 keV. In the present RXTE observations the source is found to be in an extended phase of spin-down. We also find a gradual increase in the X-ray luminosity which is correlated with a marginal spin-up episode. The marginal correlation between the gradual spin-up (or decrease in spin-down rate) and increase in X-ray luminosity suggests that OAO 1657−415 is observed during a stable accretion episode where the prograde accretion disc is formed.     

Populating the Galaxy with low-mass X-ray binaries

We perform binary population-synthesis calculations to investigate the incidence of low-mass X-ray binaries (LMXBs) and their birth rate in the Galaxy. We use a binary-evolution algorithm that models all the relevant processes including tidal circularization and synchronization. Parameters in the evolution algorithm that are uncertain and may affect X-ray binary formation are allowed to vary during the investigation. We agree with previous studies that under standard assumptions of binary evolution the formation rate and number of black hole (BH) LMXBs predicted by the model are more than an order of magnitude less than what is indicated by observations. We find that the common-envelope process cannot be manipulated to produce significant numbers of BH LMXBs. However, by simply reducing the mass-loss rate from helium stars adopted in the standard model, to a rate that agrees with the latest data, we produce a good match to the observations. Including LMXBs that evolve from intermediate-mass systems also leads to favourable results. We stress that constraints on the X-ray binary population provided by observations are used here merely as a guide as surveys suffer from incompleteness and much uncertainty is involved in the interpretation of results.     

Relation Between the 3D-Geometry of the Coronal Wave and Associated CME During the 26 April 2008 Event

We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of ∼ 240 km s⁻¹. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of ∼ 750±50 km s⁻¹, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.     

A simultaneous spectroscopic and photometric study of two eclipsing binaries: V566 Oph and V972 Her

In this study, we have performed simultaneous solutions of light and radial velocity curves of two eclipsing binary systems, V566 Oph and V972 Her. We observed both systems spectroscopically with a very recently installed spectrograph on the 40 cm telescope, T40, located in Ankara University Kreiken Observatory (AUKR), for the first time. We made use of the photometric data from the Hipparcos satellite for V972 Her, while we obtained the photometric observations of V566 Oph by using the 35 cm telescope, T35, located also in our observatory campus. We derived the absolute parameters for both systems and discussed their evolutionary states. In addition to the simultaneous analysis, we have also analyzed the change in mid-eclipse times for V566 Oph, and found cyclic variations, for which we have discussed light-time effect and magnetic activity as their potential origin, superimposed on a secular change due to a mass transfer between the components of the binary.     

Cosmic equation of state and advanced LIGO-type gravitational wave experiments

It is hoped that the future generation of interferometric gravitational wave detectors will provide accurate measurements of the final stages of binary in-spirals. The sources probed by such experiments are of extragalactic origin and the observed chirp mass is the intrinsic chirp mass multiplied by (1+ z ) where z is the redshift of the source. Moreover the luminosity distance is a direct observable in such experiments. This creates the possibility to establish a new kind of cosmological test, supplementary to more standard ones.
Recent observations of distant type Ia supernovae light curves suggest that the expansion of the Universe has recently begun to accelerate. A popular explanation of the present accelerating expansion of the Universe is to assume that some part Ω_Q of the matter–energy density is in the form of a dark component called 'the quintessence' with the equation of state p _Q= wρ _Q with w ≥−1 . In this paper we consider the predictions concerning observations of binary in-spirals in future LIGO-type interferometric experiments assuming a 'quintessence cosmology'. In particular we compute the expected redshift distributions of observed events in the a priori admissible range of parameters describing the equation of state for the quintessence. We find that this distribution has a robust dependence on the cosmic equation of state.     

The close binary ZZ aurigae

Between December 23–29, 1981, we made photoelectric observations of ZZ Aur at the Yunnan Observatory and obtained 603 measurements in yellow light and 604 measurements in blue light. We thereby secured the epochs of two principal minima and two secondary minima and discovered that the period of ZZ Aur was just beginning to change. We found the main component to have spectral type A5V and the secondary component, GOV, and we think that this system may be a main sequence binary at the limit of stability.     

The binary system 53 Cam

The orbital elements of the spectroscopic binary 53 Cam were revised using 136 radial velocity measurements. The positions in the vicinity of the periastron predicted for the secondary under the assumption of the spectroscopic orbital elements do not agree with those found by speckle interferometric observations. Nevertheless, we try to estimate the mass of the secondary and the dimensions of the binary system.     

Orbital evolution and orbital phase resolved spectroscopy of the HMXB pulsar 4U 1538-52 with RXTE-PCA and BeppoSAX

We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3–20 keV energy range were fitted ∼6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at ∼6.4 keV in the restricted energy range of 0.3–10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a spherically symmetric stellar wind from the companion star.     

Abundance analyses of three helium-rich sdB stars

We present some preliminary results based on the CoRoT observations of the young distant cluster Dolidze 25. The light curve for the 28 stars observed by the satellite have been analyzed and the relevant periodogram presented. As a result we have found two binary, three Pulsating Be, three SPB, two Spotted and one ellipsoidal variables. Noteworthy, we have also identified one PMS δ Scuti candidate.