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1.
Observations of the X-ray pulsar Vela X-1 with the ART-P telescope onboard the Granat Observatory are presented. Variability on a time scale of several thousand seconds was detected; intensity variations are shown to be accompanied by changes in the source’s spectrum. The hardness was also found to be highly variable on a scale of one pulsation period. The source’s spectrum exhibits an absorption feature at energy ～7 keV, which is apparently attributable to cyclotron scattering/absorption in the neutron-star magnetic field. Weak persistent emission was detected during an X-ray eclipse, which probably resulted from the scattering of pulsar emission in the stellar wind from an optical star. 相似文献
2.
G. H. Share 《Astrophysics and Space Science》1976,42(1):29-33
Two bursts of high-energy photons have been discovered during analysis of 2 1/2 years of data from NRL's solar X-ray detector on OSO-6. Both bursts were simultaneously observed by the OGO-5 hard X-ray spectrometer (Kane, 1975). The bursts occurred at about 18 087 s UT on 25 January, 1970, and about 56 532 s UT on 1 October, 1970. The October event was also observed by Vela 5A; however, none of the Vela detectors observed the January event which had an intensity of about 2×10–5 ergs cm–2. Based on these new data, the number of bursts with intensities above about 10–5 ergs cm–2 appears to be about 50% higher than the Vela data alone would indicate.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
3.
We present results of evolutionary computations for massive close binaries with the Brussels simultaneous evolution code for
conservative and non-conservative Roche lobe overflow (RLOF). We discuss mass transfer in massive close binaries during phases
of RLOF, common envelope, spiral-in and merging. We examine the effects of stellar wind during successive stellar evolution
phases and the final fate of primaries. We show how our library can be used to explain well-known binaries such as the WR
+ OB system V444 Cyg, HMXBs Vela X-1 and Wray 977, LMXBs like Her X-1, and binary pulsars. More details on the evolution of
massive close binaries can be found in “The Brightest Binaries” (Vanbeveren et al., 1998). 相似文献
4.
L. Kaper N.R. Trams P. Barr J.Th. Van Loon L.B.F.M. Waters 《Astrophysics and Space Science》1997,255(1-2):199-204
We present the first results of our ISO program on High-Mass X-ray Binaries (HMXBs). Infrared photometry, obtained at different
aspect angles of the systems, is used to investigate the massive star's disrupted stellar wind and the accretion flow towards
the compact X-ray source.
Scenarios for massive binary evolution predict that HMXBs receive a large kick velocity during the supernova explosion of
the compact star's progenitor. One might, therefore, expect to observe wind bow shocks around these systems such as observed
around many OB-runaway stars. Such a wind bow shock has recently been discovered around the system Vela X-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
X-ray binaries such as Cen X-3, Cyg X-1, Vela X-1, 2U1700-37, SMC X-1, Cir X-1, with periods ranging from 2d.087 to 12d.28, are probably evolution products of massive binary systems. The massive primary starts losing mass after core hydrogen burning and undergoes a supernova explosion. The evolution of binary systems consisting of a 20M⊙ primary and secondaries of respectively 14, 10, 8 and 6M⊙ was computed from Main Sequence stage through the X-ray phase, until the second mass transfer phase. Estimates were performed for the evolution of a secondary of 4M⊙. It may be seen that some of these systems during their X-ray phase match the observed mass ratios and periods. 相似文献
6.
The comparative analysis of dense stellar models governed by quadratic and linear equations of state
《New Astronomy》2021
In the present article we construct physically viable models of anisotropic charged compact stellar objects admitting quadratic equation of state and linear equation of state. We analyze the physical behavior of compact star models 4U1538-52, LMCX-4, and Vela X-1 with in the frame work of general relativity. Our stellar models are free from singularities, satisfy all energy conditions and exhibit physically admissible characters. The necessary stability criteria viz. Buchdhal condition, adiabatic index and causality condition all stand true for our charged anisotropic compact stellar models. We also inspect the physical characteristics of compact stars via Linear equation of state by applying slight changes in the parameters of the models pertaining to Quadratic equation of state and analyze the models in the perspective of both equations of state. We study the physical attributes of the model 4U1538-52 extensively by implementing analytical and graphical tools. The models retain their validity for both linear as well as quadratic equations of state, however there is a slight variation in few attributes of the models. 相似文献
7.
We have investigated the long-term flux variation in Cen X-3 using orbital modulation and pulsed fraction in different flux states using observations made with the All-Sky Monitor and the Proportional Counter Array on board the Rossi X-ray Timing Explorer . In the high state, the eclipse ingress and egress are found to be sharp whereas in the intermediate state the transitions are more gradual. In the low state, instead of eclipse ingress and egress, the light curve shows a smooth flux variation with orbital phase. The orbital modulation of the X-ray light curve in the low state shows that the X-ray emission observed in this state is from an extended object. The flux-dependent orbital modulations indicate that the different flux states of Cen X-3 are primarily due to varying degree of obscuration. Measurement of the pulsed fraction in different flux states is consistent with the X-ray emission of Cen X-3 having one highly varying component with a constant pulsed fraction and an unpulsed component and in the low state, the unpulsed component becomes dominant. The observed X-ray emission in the low state is likely to be due to scattering of X-rays from the stellar wind of the companion star. Though we cannot ascertain the origin and nature of the obscuring material that causes the aperiodic long-term flux variation, we point out that a precessing accretion disc driven by radiative forces is a distinct possibility. 相似文献
8.
《Astroparticle Physics》2010,32(6):431-436
We consider Vela Jr. as being the old Supernova Remnant (SNR) at the beginning of the transition from adiabatic to radiative stage of evolution. According to our model, Vela Jr. is situated outside Vela SNR at the distance of ∼600 pc and its age is 17500 yr. We model the high energy fluxes from Vela Jr. and its broadband spectrum. We find our results compatible with experimental data in radio waves, X- and γ-rays. Our hydrodynamical model of Vela Jr. explains the observed TeV γ-ray flux by hadronic mechanism. The proposed model does not contradict to the low density environment of the SNR and does not need extreme fraction of the explosion energy to be transferred to Cosmic Rays. 相似文献
9.
Ulrich Kolb Melvyn B. Davies rew King Hans Ritter 《Monthly notices of the Royal Astronomical Society》2000,317(2):438-446
Cygnus X-2 appears to be the descendant of an intermediate-mass X-ray binary (IMXB). Using Mazzitelli's stellar code we compute detailed evolutionary sequences for the system and find that its prehistory is sensitive to stellar input parameters, in particular the amount of core overshooting during the main-sequence phase. With standard assumptions for convective overshooting a case B mass transfer starting with a 3.5-M⊙ donor star is the most likely evolutionary solution for Cygnus X-2. This makes the currently observed state rather short-lived, of order 3 Myr, and requires a formation rate > 10−7 –10−6 yr−1 of such systems in the Galaxy. Our calculations show that neutron star IMXBs with initially more massive donors (≳4 M⊙ ) encounter a delayed dynamical instability; they are unlikely to survive this rapid mass transfer phase. We determine limits for the age and initial parameters of Cygnus X-2 and calculate possible dynamical orbits of the system in a realistic Galactic potential, given its observed radial velocity. We find trajectories which are consistent with a progenitor binary on a circular orbit in the Galactic plane inside the solar circle that received a kick velocity ≤200 km s−1 at the birth of the neutron star. The simulations suggest that about 7 per cent of IMXBs receiving an arbitrary kick velocity from a standard kick velocity spectrum would end up in an orbit similar to Cygnus X-2, while about 10 per cent of them reach yet larger Galactocentric distances. 相似文献
10.
R. Hanbury Brown 《Journal of Astrophysics and Astronomy》1984,5(1):19-30
The Chatterton Astronomy Department aims to apply interferometers with very high resolving power to optical astronomy. The
programme of the stellar intensity interferometer at Narrabri Observatory was completed in 1972 and since then the work has
been directed towards building a more sensitive instrument with higher resolving power. As a first step a much larger intensity
interferometer was designed but was not built because it was large, expensive and not as sensitive as desired. Efforts are
now being made to design a more sensitive and cheaper instrument. A version of Michelson’s stellar interferometer is being
built using modern techniques. It is hoped that it will reach stars of magnitude +8 and will work reliably in the presence
of atmospheric scintillation. It is expected to cost considerably less than an intensity interferometer of comparable performance.
The pilot model of this new instrument is almost complete and should be ready for test in 1984.
Text of an Academy Lecture delivered at the Raman Research Institute, Bangalore on January 27, 1984. 相似文献
11.
The beaming effect (aka Doppler boosting) induces a variation in the observed flux of a luminous object, following its observed radial velocity variation. We describe a photometric signal induced by the beaming effect during eclipse of binary systems, where the stellar components are late type Sun-like stars. The shape of this signal is sensitive to the angle between the eclipsed star’s spin axis and the orbital angular momentum axis, thereby allowing its measurement. We show that during eclipse there are in fact two effects, superimposed on the known eclipse light curve. One effect is produced by the rotation of the eclipsed star, and is the photometric analog of the spectroscopic Rossiter-McLaughlin effect, thereby it contains information about the sky-projected spin-orbit angle. The other effect is produced by the varying weighted difference, during eclipse, between the beaming signals of the two stars. We give approximated analytic expressions for the amplitudes of the two effects, and present a numerical simulation where we show the light curves for the two effects for various orbital orientations, for a low mass ratio stellar eclipsing binary system. We show that although the overall signal is small, it can be detected in the primary eclipse when using Kepler Long Cadence data of bright systems accumulated over the mission lifetime. 相似文献
12.
We describe the present state of massive star research seen from the viewpoint of stellar evolution, with special emphasis
on close binaries. Statistics of massive close binaries are reasonably complete for the Solar neighbourhood. We defend the
thesis that within our knowledge, many scientific results where the effects of binaries are not included, have an academic
value, but may be far from reality. In chapter I, we summarize general observations of massive stars where we focus on the
HR diagram, stellar wind mass loss rates, the stellar surface chemistry, rotation, circumstellar environments, supernovae.
Close binaries can not be studied separately from single stars and vice versa. First, the evolution of single stars is discussed
(chapter I). We refer to new calculations with updated stellar wind mass loss rate formalisms and conclusions are proposed
resulting from a comparison with representative observations. Massive binaries are considered in chapter II. Basic processes
are briefly described, i.e. the Roche lobe overflow and mass transfer, the common envelope process, the spiral-in process
in binaries with extreme mass ratio, the effects of mass accretion and the merging process, the implications of the (asymmetric)
supernova explosion of one of the components on the orbital parameters of the binary. Evolutionary computations of interacting
close binaries are discussed and general conclusions are drawn. The enormous amount of observational data of massive binaries
is summarized. We separately consider the non-evolved and evolved systems. The latter class includes the semi-detached and
contact binaries, the WR binaries, the X-ray binaries, the runaways, the single and binary pulsars. A general comparison between
theoretical evolution and observations is combined with a discussion of specially interesting binaries: the evolved binaries
HD 163181, HD 12323, HD 14633, HD 193516, HD 25638, HD 209481, Per and Sgr; the WR+OB binary V444 Cyg; the high mass X-ray binaries Vela X-1, Wray 977, Cyg X-1; the low mass X-ray binaries Her
X-1 and those with a black hole candidate; the runaway Pup, the WR+compact companion candidates Cyg X-3, HD 50896 and HD 197406. We finally propose an overall evolutionary model
of massive close binaries as a function of primary mass, mass ratio and orbital period. Chapter III deals with massive star
population synthesis with a realistic population of binaries. We discuss the massive close binary frequency, mass ratio and
period distribution, the observations that allow to constrain possible asymmetries during the supernova explosion of a massive
star. We focuss on the comparison between observed star numbers (as a function of metallicity) and theoretically predicted
numbers of stellar populations in regions of continuous star formation and in starburst regions. Special attention is given
to the O-type star/WR star/red supergiant star population, the pulsar and binary pulsar population, the supernova rates.
Received 17 July 1998 相似文献
13.
During the total solar eclipse at Akademgorodok, Siberia, Russia, on 1 August 2008, we imaged the flash spectrum with a slitless
spectrograph. We have spectroscopically determined the duration of totality, the epoch of the second and third contacts and
the duration of the flash spectrum. Here we compare the 2008 flash spectra with those that we similarly obtained from the
total solar eclipse of 29 March 2006, at Kastellorizo, Greece. Any changes of the intensity of the coronal emission lines,
in particularly those of Fe x and Fe xiv, could give us valuable information about the temperature of the corona. The results show that the ionization state of the
corona, as manifested especially by the Fe xiv emission line, was much weaker during the 2008 eclipse, indicating that following the long, inactive period during the solar
minimum, there was a drop in the overall temperature of the solar corona. 相似文献
14.
K. Kasturirangan U. R. Rao D. P. Sharma R. G. Rastogi S. C. Chakravarty 《Astrophysics and Space Science》1976,42(1):57-62
The paper presents the results on investigations of the ionospheric effects arising out of the transient celestial events at X-ray and gamma-ray energies such as that from X-ray novae and cosmic gamma-ray bursts. The VLF data recorded at Ahmedabad corresponding to the 164 kHz transmission from Tashkent are examined to see whether there are any observable effects time coincident with the transit of the X-ray novae Cen X-4 and Cet X-2 around their intensity maxima. Besides, the VLF data have also been examined in relation to the cosmic gamma-ray bursts detected by Vela, IMP-6 and OSO-7 satellites.Theoretical computations are carried out for estimating electron density enhancements using the available data on intensities and energy spectra for these events. Further, the observational resutls are explained in terms of these theoretical calculations.Presently at Indian Space Research Organization, Bangalore, India.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
15.
The chromospheric phases in the 1971–72 eclipse were observed at wavelength regions containing the K-line of ionized calcium on six nights at ingress and on eight nights at egress at the Okayama Astrophysical Observatory. The linear dispersion of the spectrograms is about 10 Å mm?1. The spectrograms were measured for line intensities of the K-line and for radial velocities of metallic and hydrogen lines. The results are compared with those obtained in the earlier eclipses. The intensities of the chromospheric K-line during this eclipse were relatively ‘weak’ at both ingress and egress and were similar to those in the 1939–40 eclipse. It seems that the chromospheric activity of ζ Aurigae increased after 1939, reached a maximum at 1950–56, and then decreased again until 1971. The radial velocities of the chromospheric lines of hydrogen atoms, ionized calcium, and some other atoms and ions varied with phase showing almost the same characteristic features as in most earlier eclipses. Intensities and velocities were also measured for satellite lines of the K-line. 相似文献
16.
We consider Vela Jr. as being the old Supernova Remnant (SNR) at the beginning of the transition from adiabatic to radiative stage of evolution. According to our model, Vela Jr. is situated outside Vela SNR at the distance of 600 pc and its age is 17500 yr. We model the high energy fluxes from Vela Jr. and its broadband spectrum. We find our results compatible with experimental data in radio waves, X- and γ-rays. Our hydrodynamical model of Vela Jr. explains the observed TeV γ-ray flux by hadronic mechanism. The proposed model does not contradict to the low density environment of the SNR and does not need extreme fraction of the explosion energy to be transferred to Cosmic Rays. 相似文献
17.
Cowsik Ramanath Singh Jagdev Saxena A.K. Srinivasan R. Raveendran A.V. 《Solar physics》1999,188(1):89-98
Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse. 相似文献
18.
The paper presents the variation of 5577 Å line intensity with relative sunspot number, and 10.7 cm solar flux. The study has obtained the following important results.[(i)] The 5577 Å line intensity at Calcutta is plotted against relative sunspot number, and the variable component of 10.7 cm solar flux during 1984–1985, which is the secondary peak of the descending phase of the 21st solar cycle. The intensity curves show periodic variation with different solar parameters.[(ii)] The 5577 Å line intensity at Mt. Abu also shows periodic variation with solar parameters during the period 1965–1968 when there was a peak phase of the 20th solar cycle.[(iii)] A possible explanation for such variation is also presented. 相似文献
19.
At the 1980 total solar eclipse, we searched for high-frequency (0.1–2 Hz) oscillations in the intensity of the 5303-Å coronal green line, as a test of predictions of theories of coronal heating via magnetohydrodynamic waves. Portions of the image 2.5- or 5-arc sec across were fed to cooled photomultipliers using fiber-optic probes. We detected excess power in Fourier transforms of the data for the region between 0.5 and 2 Hz at the level of 1% or 2% of the incident power. Such oscillations could be associated with Alfvén waves that are trapped on loops a few thousand kilometers long or with fast waves that are trapped on loops a few thousand kilometers in diameter. Additional observations at the 1983 eclipse are planned to resolve atmospheric and instrumental contributions. 相似文献
20.
S. S. De Suman Paul S. Barui P. Hazra D. Kala D. K. Haldar A. Ghosh G. Guha 《Earth, Moon, and Planets》2013,111(1-2):79-87
The effect of solar eclipse of July 22, 2009, obscuring up to 91 %, upon the value of point discharge current (PDC) has been reported in this paper. The observation had been taken from Kolkata (Lat. 22.56°N, Long. 88.5°E). During the eclipse period, significant variations in the magnitude of PDC were observed than their average value for the same period in other days. The average value of the PDC for the successive ±10 days adjacent to the solar eclipse day was about 2.253 A.U. (Arbitrary Unit), while the minimum value showed about 2.242 A.U. at the time of greatest phase at 06:26.4 IST (Indian Standard Time). The results are mainly interpreted in terms of changes of the conductivity of the medium during the solar eclipse. 相似文献