The Crab Pulsar(PSR 0531+21) was observed by the four Narrow Field Instruments on board the Italian-Dutch satellite BeppoSAX on August and September 1996, during the Science Verificado Phase. The fine time resolution (15 μs) and the high statistic of the data provided phase histogram of very good quality, well suited for phase resolved spettroscopy over the entire energy band (0.1-300 keV) covered by BeppoSAX payload. In this contribution we present preliminary results of the spectra distribution of the peaks and the inter peak region. Moreover, we also carried out a detailed analysis of the P1 shape and the behaviour of the P2/P1 ratio with the energy.

We have considered a stationary outflowing envelope accelerated by the radiative force in arbitrary optical depth case. Introduced approximations provide satisfactory description of the behavior of the matter flux with partially separated radiation at arbitrary optical depths. The obtained systemof differential equations provides a continuous transition of the solution between optically thin and optically thick regions. We analytically derivedapproximate representation of the solution at the vicinity of the sonic point. Using this representation we numerically integrate the system of equations from the critical point to the infinity. Matching the boundary conditions we obtain solutions describing the problem system of differential equations. The theoretical approach advanced in this work could be useful for self-consistent simulations of massive star evolution with mass loss.

The BVR CCD observations of W UMa-type eclipsing binary SS Arietis were made for ten nights from November 1996 to December 1996 at the Sobaeksan Astronomy Observatory. From the observed light curves, nine new times of minimum lights were derived from the Kwee and van Woerden’s method. Improved light elements for this system were determined from these minimum lights with all the published minima. The analysis of the times of minima of SS Ari confirms that the orbital period of SS Ari has been suffering from a sinusoidal variation as the suggestions of other previous investigators (Kaluzny & Pojmanski 1984, Demircan & Selam 1993). The calculation shows that the cyclic period change has a period of about 56.3yrs with an amplitude of about 0.d052. The period variation has been discussed in terms of two potential mechanisms: 1) the light-time effect due to a hypothetical third body and 2) deformations in the convective envelope of a magnetically active component. The BVR light curves of SS Ari observed for about one month showed the existence of cycle to cycle light variations. Long-term light changes of SS Ari are discussed in terms of the period variation of the binary system.

The post-AGB stars rapidly change their spectral energy distribution on their way from the asymptotic giant branch(AGB) to planetary nebula stage. They are generally surrounded by cool and extended dust shells emitting largely in the infrared wavelengths.

A selected sample of the post-AGB candidates were observed using the CCDand IR camera at Kiso and Nishi-Harima Astronomical Observatory. They were classified based on their broad band spectra from B to K’ band and their evolutionary stages have been discussed using the simple model of the dust shell around a star.

The light variation of some of these objects were monitored and their light curves are also presented.

The radius and temperature excesses are found to be largest for the subgiant stars in DS systems and in low-mass and long-period SD systems, being the smallest for the subgiant stars in AR systems and in low-mass and short-period SD-systems. Subgiant stars in AR and in more massive SD systems exhibit even the temperature deficiency which is the largest for the primariesof the AR systems. Necessity is shown to divide the class of SD systems into several groups according to masses and orbital periods while studying their properties.

By using of a model for the propagation of the emitted X-rays through the infalling material and the reemission of the energy deposited by photoabsorption in the optical (and UV) spectral range (Kim & Beuermann, 1995) we calculated Hϒ line spectrum of intermediate polars. Photoabsorption of X-rays by the infalling material is the dominant process in forming the observed energy-dependent rotational modulation of the X-ray flux. X-ray and optical modulations are sensitive to model parameters in different ways. In principle these dependences allow us to obtain improved insight into the geometry of intermediate polars. Some results of our calculation will be presented in this paper in comparison with the Hβ spectrum calculated by Kim & Beuermann (1996).

Our high-resolution optical spectroscopic survey of the symbiotic star CH Cyg, extending over the quiescent period 1987 - 1989 between two outbursts, shows that the spectrum did not completely lose its symbiotic character. Moreover, signs of radiation of the hot source were present, not only as remnants from the previous outburst, but also as an indication of a new one. Some of the evidences which support this idea are following:

1. • Variation of excitation and vibration temperatures of neutral metals and TiO moleculs respectively

2. • Untypical microturbulent velocity dependance of the excitation potential of the lower state for Fe I

3. • Double-peaked Balmer profiles of Ha and Hb with temporary disappearance of the central absorption

4. • Presence of forbbiden emission lines [FeII] [ SII] [NeIII] together with OIII with complex profile and variable intensity.

A detailed analysis of an extensive collection of primary visual, photographic and photoelectric minima of Beta Lyrae was performed. After removing the effect of the increase in orbital period we applied the Fourier analysis to the 0-C residuals. The most prominent periodicity is 283 days with amplitude about 0.05 days. It confirms the period found in the photometric light curves of Beta Lyrae [Van Hamme, Wilson and Guinan (1995)]. The 283-d quasi-variation of the period may be explained by assymetries of the light curve near the minima caused by some instabilities in disc and/or hot spot(s) brightness.

BC UMa was observed during its rare outburst in 1994. The superhumps with period 0.0619 day are clearly apparent, accompanied by secondary superhumps. This confirms the classification of BC UMa as an SU UMa type dwarf nova. The maximum brightness is 12.5 mag, which is about six magnitude brighterthan quiescence phase, and it makes BC UMa be classified as a TOAD (Tremendous Outburst Amplitude Dwarf-nova). The superoutburst’s magnitude was fainter than the preceeding normal outburst in September 1990. This faint superoutburst is uncommon among SU UMa stars and also among TOADs. The period analysis of the lightcurve taken after the end of the outburst yields the period of 0.0618 day which is shows that late superhumps is in operation.

A Monte Carlo code is used to calculate the profiles and the polarization of Raman scattered O VI lines(λλ6827, 7088) in symbiotic stars. Various wind models around the cool giant are investigated including disk type and bipolar wind models. We obtain a large degree of polarization in the blue part and the red-asymmetric profile, which is generic to the Raman scattered feature in symbiotic stars.

We also investigate the effect of the orbital motion of the hot component around the cool giant, where the orbital velocity is comparable to the wind terminal velocity. In the case of small inclination angle of the orbitalplane, we obtain the polarization flip around the red wing of the scatteredfeature and the triple peak structure in the polarized flux, which is characteristic of many symbiotic systems including RR Tel.

Brief observational consequences are discussed and it is concluded that spectropolarimetry may provide a powerful diagnostic about the physical conditions of symbiotic stars.

A model of internal structure and evolution of the peculiar binary system v Sgr is presented. The model corresponds well to the observed chemical composition of the main component atmosphere (10-4 H, 0.844 He, 0.013 C, 0.042 N by mass). It is supposed that about 5 million years ago the main component passed the stage of hydrogen nuclear burning in the shell over the helium core where the helium-carbon reactions took place. Because of convective mixing, the synthesized carbon diffusing into the hydrogen burning zone was catalyzing the reactions of the CN - cycle. This has resulted in anomalies in the chemical composition, particularly high nitrogen abundance in the layer observed now as the atmosphere of the main component since external layers were thrown off during the evolution. Following the calculated results, the quantitative restrictions of temperature and density in the layers and values of mixing parameters are obtained. It is shown that the best agreement with observations exists if the mass of the matter penetrating from the zone of helium-carbon reactions into the helium layer is 0.25 of the helium-carbon core mass. Moreover, the ratio of mass concentration He/C in this matter should equal 2, and the mass share diffusing into the layer of hydrogen burning should be in the range 0.25 - 0.30 of the layer mass.

On the basis of the analysis of the observed equivalent line widths of FeI, FeII, and TiII in the spectra of Sirius A and Omicron Peg and calculation of abundances of these elements, the oscillator strengths of the lines used are refined. With the improved oscillator strengths, the iron and titanium abundances in the atmosphere of Sirius A are obtained with a higher accuracy than previously:

lgN(FeI) = 7.899 ±0.011,

lgN(FeII) = 7.908±0.010,

lgN(TiII) =5.30±0.02.

The improved accuracy allowed one to conclude that the surface magnetic field is absent in the atmosphere of Sirius A: H =3D 0±100 Gs. The equivalent widths of 7 helium lines of the red region of the spectrum are measured. The calculations of these lines (with allowance for their blending with lines of other elements) show normal helium abundance. Following a comparison of features of Sirius A and Omicron Peg, a suggestion is advanced on possible reasons for the existence of Am stars.

Photometry of AU Ser, a contact binary in poor thermal contact, was made using the 1-meter reflector of the Yunnan Observatory, China, in 1991, 1992and 1995. Our observations, together with Binnendijk’s (1972), show variations in light curves similar to ones of VW Cep:

1. 1) Changes in sign and value of O’Connell effect. According to Binnendijk(1972), the maximum following primary minimum was higher than the other maximum, i.e., the O’Connell effect was positive. In our 1991 and 1992 light curves it became negative. After three years, however, the situation has reversed again.

2. 2) Variations of the difference between minimum depths.The difference in 1991 was smaller than that in 1969 and 1970. It got smallest in 1992 and largest in 1995. The difference increases by about 0.3 mag in three years, which is hard to explained.

3. 3) The phase shift. The observed minimum phase in 1991, 1992 and 1995 have progressively displaced forward with respect to computed minimum phase according to Binnendijk’s ephemeris. The O-C diagram seems to indicate a sudden decrease of orbital period after 1970. Also, short period oscillations have been found at frequencies of 0.0003, 0.005 and 0.0075 Hz. Flickering. with an average amplitude of about 0.05 mag, can be seen in the light curves. The power spectral analysis suggest the existence of oscillations. It is unusual that such oscillations exist in a contact binary.

In the paper we report the discovery of X-ray emission differences in SNR MSH14-63 based on the ROSAT PSPC observation. The structures of MSH14-63 are different in different energy bands. These images along with the radial brightness distributions in these energy bands show the existence of a region which only emit X-ray photons harder than l.OkeV. Though weak, there actually exist large scale X-ray emissions beyond the bright rim in many parts of the northeast remnant component, which is in conflict with the Sedov phase assumption used in previous research. These new soft X-ray features provide astronomers more information to study its physical characteristics.

New CCD observations of the eclipsing binary VW Cephei were made on the 9th and 10th of October 1996 and on the 11th of Nov. 1996. The light curves and short time-scale variations are discussed. Photometric elements were determined from analyses of the light curves. These new solutions are also discussed.

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively.

The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.

We study the short-time evolutionary history of the well-known contact binary VW Cep. Our analysis is based partly on the numerous UBV lightcurves obtained at Tartu Observatory, IUE spectra, and samples from the published data. Special attention is given to the effects of asymmetry of the light curves. A higher degree of asymmetry outside the eclipses along with the significant displacements of the brightness maxima in respect to the elongation phase is interpreted as evidence that a considerable portion of the flaring source is concentrated close to the neck connecting the components. We discuss the nature of asymmetry in terms of possible mass exchange and the flare activity and compare the results of our model computations with the record of orbital period variations over the last 60 years.

Interstellar abundances studies can provide answers to some questions about stellar processes, and they can lead to new questions about others. We will discuss some recent interstellar abundance determinations and their implications for stellar studies.

Although Cd and Sn are chemically similar to elements which are moderately to heavily depleted from the gas-phase interstellar medium (ISM), they appear to have solar-like abundances in inter-stellar clouds. This is likelythe result of these elements being depleted from an ISM which has been enriched with Cd and Sn since the formation of the sun. These two elements are mainly produced by s-process neutron capture in intermediate to low mass AGB stars. The present ISM abundances of Cd and Sn can therefore provide information about s-process yields and the cumulative injection of this material into the ISM over the past 4.5 Gy.

Recent studies of C and O abundances in the ISM have shown that the C/H and O/H are constant out to approximately 1500pc from the sun. Local B star abundance studies, however, find that C/O is not constant, thereby indicating that the ISM is not well mixed or homogeneous. We currently do not have an explanation for this apparent inconsistency between stars and the ISM.

Propagation of the surface waves of the lobe-filing components of close binary systems is investigated theoretically. Such waves are considered to be analogous to the gravity waves of water on the earth. As a result, the equations of the surface wave in the rotating frame of reference are reduced to the so-called Kortewegde Vries (KdV) equation and non-linear Schroedinger (NLS) equation according to its ”depth”. Each of these equations is known to have the solution of soliton. When this soliton is sent to the other component of the binary system through the Lagrangian point, it can give rise to the flare activity observed in some kinds of close binary systems.

From 1994 to 1997, we observed the star HD229221 several times spectroscopically by using the Beijing Astronomical Observatory 2.16 m telescope and the spectrograph Universal.

From the spectra we clearly see that the H-α spectral feature of this star underwent a peculiar variation, from a single emission line to one composed of three components, i.e. emission+absorption+filled emission. In our paper, based on an analysis of its spectral line variation and some physical parameters (e.g. luminosity, age, etc.), we discuss the possible reasons that might cause this peculiar variation.