Recent surveys at Parkes, in particular the 70 cm survey of the southern sky, have discovered many pulsars, including 17 miilisecond pulsars in the Galactic disk. Timing and polarization observations of some of these pulsars are described. The only two pulsars known to be in orbit around massive non-degenerate stellar compamons were also discovered at Parkes, and some recent observational results for these pulsars are also presented.
We are promoting a supernova(SN) search project with medium size (60cm-105cm) telescopes belonging to public observatories in Japan. The main purpose is to measure the SNe Ia rate, which plays an important role in the chemical and dynamical evolution of galaxies. We expect to measure the SN rate in E/SO galaxies within the 35% error after 2 years run, and the longer run will give the smaller error.
The wind-formed features observed in the early SNe spectra type II and Ia give an evidence of the existence of an ellipsoidal shell formed by the stellar wind prior to the explosion. Such non-spherical shell can occur not only at scales of parsec (the case of SN 1987 A progenitor), but at the scales of 1000 times less. Such shells can be the result of the radial pulsation. The prolate multi-shell structures are interpreted as a result of a pulsation processes with recurrent wind ejections with velocity increasing.
The results of the Crab pulsar observations with the photometrical MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) complex at the 6-m telescope are presented. More than 12 millions photons in UBVR-bands simultaneously with time resolution of 10-7s were detected. Using the original software for search for optical pulsar period, we obtained the light curves of the object with time resolution of about 3.3 μs. Their detailed analysis gives the spectral change during pulse and subpulse, the shape of the pulse peaks, which are plateaus (with the duration of about 50 μs for the main pulse), limits for an amplitude of fine temporal (stochastic and regular) structure of pulse and sub pulse and the interpulse space intensity. The results of CCD-spectroscopy of the Crab pulsar show that its summarized spectrum is flat. There are no lines, neither emission nor absorbtion ones. Upper limit for line intensity or depth is 3.5% with the confidence probability of 95%.
The x-ray pulsar GX 1+4 was observed by us in four balloon- borne experiments carried out from Hyderabad, India during 1991-1995 period with a hard x-ray telescope. The x-ray telescope consists of two collimated large area xenon-filled proportional counters with an effective area of 2400 cm2, a field of view of 5°×5° and sensitive in the energy band of 20 - 100 keV. The pulsar was detected in bright state in two of the four experiments and x-ray pulsations with 120 second period were detected clearly. Pulsation period, rate of change of period with time, pulse fraction, pulse profile and energy spectra of the source were determined from these studies. During March 1995 observation, the x-ray pulse of GX 1+4 was found to be double-peaked compared to a single-peak pulse profile detected in December 1993. Details of these results are presented and their interpretation discussed in terms of the current accretion models of x-ray binaries.
We review current theoretical understanding of the spectral properties (low and high states, transition of states, quasi-periodic oscillations etc.) of the low mass as well as supermassive black hole candidates.
The long-term light curves of the novalikes TT Ari, KR Aur, AM Her and MV Lyr, were compiled and analysed for solar-like cyclical behaviour. The frequency analysis showed long-term cyclical modulations of the brightness of the stars, which can be ascribed to changes of the radii of the late type secondaries in order of ΔR/R ≃ 10 -4-10 -5.
The local instabilities of accretion disks were extensively studied, with the considerations of radial advection, thermal diffusion and different disk geometry, dominated pressure and optical depth. Two inertial-acoustic modes in a geometrically thin, radiative cooling dominated disk depart from each other if very little advection is included. A geometrically slim, advection-dominated disk is found to be always stable if it is optically thin. However, if it is optically thick, the thermal diffusion has no effect on the stable viscous mode but has a significant contribution to enhance the thermal instability.
For obtaining estimates of a total magnetic flux, we propose to use measurements of ∂I/∂⋋. obtained by a modulation method which is formally identical to Stokes V-parameter measurements. In this case the polarization is not analyzed. It is advisable to use in measurements two parts of the spectral line wing.
Using a phenomenological model for the accretion onto the magnetic white dwarf, we calclliated some optical line profiles from the magnetosphere of such systems. Line profiles of these systems seem to be produced in the magnetosphere of the compact star due to the reemission of X-ray produced near the stellar surface. Some results of our new calculation and the analysis of these results will be presented. Our results show that the model used here can reproduce the observed optical line profiles and open the possiblity to determine the parameters of individual systems.
Precise masses, radii, and luminosities from eclipsing binaries and colour-magnitude diagrams for open clusters are classic tools in empirical tests of stellar evolution models. We review the accuracy and completeness required for such data to discriminate between current models and describe some recent. results with implications for convection theory.
The UBV observations of the close binary system CW Cephei were made from August 198:3 to December 1984 during 25 nights using the 61cm Boller and Chivens reflector at the Sobaeksan Astronomy Observatory. The new UBV light curves were analyzed with the recent Wilson-Devinney binary model. Our photometric solution for CW Cep were well consistent with those of Clausen &. Gimenez (1991). Using our photometric solution and Popper & Hill (1991) spectroscopic one, each absolute masses and radii of components for CW Cep were derived as 13.63 M⊙ and 5.83 R⊙ for the primary, and 12.18 M⊙ and 5.14 R⊙ for the secondary, respectively.
UBV observations have been made jointly at three observatories for the recent eclipse of the long period atmospheric eclipsing binary star Zeta Aur in 1995-6. Observations covered successfully the phases before, during, and after the eclipse enable us to determine the accurate time of mid-eclipse and the duration of the totality. The hypothesis of the expansion of the K supergiant has been tested and the positive conclusion may be derived.
The extensive close binary research program earring out at High Altitude Maydanak Observatory (Uzbekistan) by means of the UBVR photoelectric photometry on 1.0 m and 0.6 m Zeiss telescopes is described. It includes more than 240 close binary systems (CBS) in 89 different stellar aggregates. Lightcurves of CBS as well as their orbital elements derived by us are presented.
In order to study the X-ray radiations from solar type strong interacting binary stars, we have collected X-ray data of 44i Bootis (P=0.2678 days, SP=G2+G2) from the EXOSAT data archive. Preliminarly analysis of a part of these data has been already reported by Vilhu & Heise (1986). In this paper, however, we present a more complete light curve in LE region than the previous work, and some unpublished X-ray light curves and spectrums. Using these new materials a new attempt to find the physical explanation about. some observational characteristic figures in the X-ray light curves and spectrums has been made.
To understand the dynamical structures of stellar wind bubble, one and two-dimensional calculations has been performed. Using FCT Code with cooling effects and assuming constant mass loss rate and ambient medium density, we could divide stellar winds into the regime of slow and fast winds. The slow wind driven bubble shows initially radiative and becomes partially radiative bubble in which shocked stellar wind zone is still adiabatic. In contrast., the fast wind driven bubble shows initially fully adiabatic and becomes adiabatic bubbles with radiative outer shell. We also determine analytically the onset of thin-shell formation time in case of fast wind driven bubble with power-law energy injection and ambient density structure. We solve the line transfer problem with numerical results in order to calculate line profile of [OIII] forbidden line.