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1.
We review various aspects of the evolutionary history of massive X-ray binaries. It is expected that moderately massive close binaries evolve to Be X-ray binaries, while very massive systems evolve to standard X-ray binaries.The compact objects are formed through supernova explosions. The fairly low galactic latitudes of those systems indicate that the explosion should, in general, not have accelerated the system to a velocity larger than 50kms–1. This implies that the mass of the exploding stars is in general less than 5 to 6M .After the explosion, tidal forces will circularize the orbit of short period systems. Even if the tidal evolution has been completed, the expansion of the optical star during the course of its evolution will continously disturb the stability of the orbit. Short period systems with large mass ratio may eventually become tidally unstable. Cen X-3 may be an example of such a system. The predicted rate of the orbital period decrease of Cen X-3 is in agreement with the observed rate.A way to represent the rotational and magnetic evolution of neutron stars in close binary systems is presented. The observed distribution of the pulsation periods of X-ray pulsars with Be companions is consistent with initial magnetic fields of 1012–1013 G of the neutron stars. We suggest that the fast X-ray pulsars 4U 0115+63 and A 0538-66 are young neutron stars, while Cen X-3 and SMC X-1 are recycled pulsars.The evolutionary relationship between massive X-ray binaries, binary pulsars, and millisecond pulsars is also discussed.Invited paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

2.
We investigate the X-ray and optical properties of a sample of X-ray bright sources from the Small Magellanic Cloud (SMC) Wing Survey. We have detected two new pulsars with pulse periods of 65.8 s (CXOU J010712.6−723533) and 700 s (CXOU J010206.6−714115), and present observations of two previously known pulsars RX J0057.3−7325 (SXP101) and SAX J0103.2−7209 (SXP348). Our analysis has led to three new optical identifications for the detected pulsars. We find long-term optical periods for two of the pulsars, CXOU J010206.6−714115 and SXP101, of 267 and 21.9 d, respectively. Spectral analysis of a subset of the sample shows that the pulsars have harder spectra than the other sources detected. By employing a quantile-based colour–colour analysis we are able to separate the detected pulsars from the rest of the sample. Using archival catalogues we have been able to identify counterparts for the majority of the sources in our sample. Combining this with our results from the temporal analysis of the Chandra data and archival optical data, the X-ray spectral analysis, and by determining the X-ray to optical flux ratios we present preliminary classifications for the sources. In addition to the four detected pulsars, our sample includes two candidate foreground stars, 12 probable active galactic nuclei, and five unclassified sources.  相似文献   

3.
We have investigated the long-term X-ray variability, defined as the root-mean-square (rms) of the All Sky Monitor Rossi X-ray Timing Explorer (ASM RXTE ) light curves, of a set of galactic Be/X-ray binaries and searched for correlations with system parameters, such as the spin period of the neutron star and the orbital period and eccentricity of the binary. We find that systems with larger rms are those harbouring fast-rotating neutron stars, low eccentric and narrow orbits. These relationships can be explained as the result of the truncation of the circumstellar disc. We also present an updated version of the Hα equivalent width–orbital period diagram, including sources in the Small Magellanic Cloud (SMC). This diagram provides strong observational evidence of the interaction of neutron star with the circumstellar envelope of its massive companion.  相似文献   

4.
We report on the long-term variability of the Be/X-ray binary LS I +61° 235/RX J0146.9+6121. New optical spectroscopic and infrared photometric observations confirm the presence of global one-armed oscillations in the circumstellar disc of the Be star, and allow us to derive a V R band quasi-period of 1240±30 d. Pronounced shell events, reminiscent of the spectacular variations in Be stars, are also seen. We have found that the J , H and K infrared photometric bands vary in correlation with the spectroscopic V R variations, implying that the one-armed disc oscillations are prograde. The effect of the oscillations is not only seen in the H α line but is also seen in the He  i λ 6678 and Paschen lines. As these lines are formed at different radii in the equatorial disc of the Be star, such effects confirm the global nature of the perturbation. The Keplerian disc has been found to be denser than the average for a sample of isolated Be stars, which may be indicative of some kind of interaction with the compact companion. Finally, from a Rossi X-ray Timing Explorer observation we derive a spin period of the neutron star of 1404.5±0.5 s.  相似文献   

5.
We investigate the optical counterparts of recently discovered Be/X-ray binaries in the Small Magellanic Cloud (SMC). In total four sources, SXP101, SXP700, SXP348 and SXP65.8 were detected during the Chandra survey of the wing of the SMC. SXP700 and SXP65.8 were previously unknown. Many optical ground-based telescopes have been utilized in the optical follow-up, providing coverage in both the red and blue bands. This has led to the classification of all of the counterparts as Be stars and confirms that three lie within the Galactic spectral distribution of known Be/X-ray binaries. SXP101 lies outside this distribution and is the latest spectral type known. Monitoring of the Hα emission line suggests that all the sources barring SXP700 have highly variable circumstellar discs, possibly a result of their comparatively short orbital periods. Phase-resolved X-ray spectroscopy has also been performed on SXP65.8, revealing that the emission is indeed harder during the passage of the X-ray beam through the line of sight.  相似文献   

6.
We report on two optical candidates for the counterpart to an X-ray source in the Small Magellanic Cloud , 1WGA J0053.8−7226, identified as a serendipitous X-ray source from the ROSAT Position Sensitive Proportional Counter (PSPC) archive, and also observed by the Einstein Imaging Proportional Counter . Its X-ray properties, namely the hard X-ray spectrum, flux variability and column density, indicate a hard, transient source, with a luminosity of ∼     XTE and ASCA observations have confirmed the source to be an X-ray pulsar, with a 46-s spin period. Our optical observations reveal two possible candidates within the error circle. Both exhibit strong H α and weaker H β emission. The optical colours indicate that both objects are Be-type stars. The Be nature of the stars implies that the counterpart is most likely a Be/X-ray binary system. Subsequent infrared (IR) photometry ( JHK ) of one of the objects shows that the source varies by at least 0.5 mag, while the     measured nearly simultaneously with the UBVRI and spectroscopic observations indicate an IR excess of ∼0.3 mag.  相似文献   

7.
We present a catalogue with coordinates and photometric data of 2446 Be star candidates in the Large Magellanic Cloud (LMC), based on a search of the OGLE II data base. The I -band light curves of these stars show outbursts in 24 per cent of the sample (Type-1 stars), high and low states in 10 per cent, periodic variations in 6 per cent (Type-3 stars), and stochastic variations in 60 per cent of the cases. We report on the result of the statistical study of light curves of Type-1 and Type-3 stars in the LMC, and the comparison with the previously reported results of the Small Magellanic Cloud (SMC) sample. We find a statistically significant difference between amplitude, duration and asymmetry distributions of outbursts in both galaxies. Outbursts of SMC Type-1 stars are usually brighter, longer and with a slower decline. We find a bimodal distribution of periods of Type-3 stars in both galaxies, probably related to the recently discovered double periodic blue variables. We find also period and amplitude distributions of Type-3 LMC stars statistically different from those of the SMC stars. Our findings above suggest that the mechanisms causing the observed photometric variability of Type-1 and Type-3 stars could depend on metallicity. Moreover, they suggest that the outbursts are not primarily caused by stellar winds.  相似文献   

8.
X-ray binaries     
Summary The various types and classes of X-ray binary are reviewed high-lighting recent results. The high mass X-ray binaries (HMXRBs) can be used to probe the nature of the mass loss from the OB star in these systems. Absorption measurements through one orbital cycle of the supergiant system X1700-37 are well modelled by a radiation driven wind and also require a gas stream trailing behind the X-ray source. In Cen X-3 the gas stream is accreted by the X-ray source via an accretion disk. Changes in the gas stream can cause the disk to thicken and the disk to obscure the X-ray source. How close the supergiant is to corotation seems to be as much a critical factor in these systems as how close it is to filling its Roche lobe. In the Be star X-ray binaries a strong correlation between the neutron stars rotation period and its orbital period has been explained as due to the neutron star being immersed in a dense, slow moving equatorial wind from the Be star. For the X-ray pulsars in the transient Be X-ray binaries a centrifugal barrier to accretion is important in determining the X-ray lightcurve and the spin evolution. The X-ray orbital modulations from the low mass X-ray binaries, LMXRBs, include eclipses by the companion and/or periodic dipping behaviour from structure at the edge of the disk. The corresponding optical modulations show a smooth sinusoidal like component and in some cases a sharp eclipse by the companion. The orbital period of the LMXRB XB1916-05 is 1% longer in the optical compared to that given by the X-ray dip period. The optical period has been interpreted as the orbital period, but this seems inconsistent with the well established view of the origin of the X-ray modulations in LMXRB. A new model is presented that assumes the X-ray dip period is the true orbital period. The 5.2 h eclipsing LMXRB XB2129+47 recently entered a low state and optical observations unexpectedly reveal an F star which is too big to fit into the binary. This is probably the first direct evidence that an X-ray binary is part of a hierarchical triple. Finally the class of X-ray binaries containing black hole candidates is reviewed focusing on the value of using X-ray signatures to identify new candidates.  相似文献   

9.
Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time-scale that is short compared with the orbital period. We use a combination of hydrodynamic simulations and N -body orbit integrations to study the long-term evolution of a fragmenting disc with an initial mass ratio to the star of   M disc/ M *= 0.1  . For a disc that is initially unstable across a range of radii, a combination of collapse and subsequent accretion yields substellar objects with a spectrum of masses extending (for a Solar-mass star) up to  ≈0.01 M⊙  . Subsequent gravitational evolution ejects most of the lower mass objects within a few million years, leaving a small number of very massive planets or brown dwarfs in eccentric orbits at moderately small radii. Based on these results, systems such as HD 168443 – in which the companions are close to or beyond the deuterium burning limit – appear to be the best candidates to have formed via gravitational instability. If massive substellar companions originate from disc fragmentation, while lower-mass planetary companions originate from core accretion, the metallicity distribution of stars which host massive substellar companions at radii of ∼1 au should differ from that of stars with lower mass planetary companions.  相似文献   

10.
We examine the proposal that the subset of neutron-star and black-hole X-ray binaries that form with Ap or Bp star companions will experience systemic angular-momentum losses due to magnetic braking, not otherwise operative with intermediate-mass companion stars. We suggest that for donor stars possessing the anomalously high magnetic fields associated with Ap and Bp stars, a magnetically coupled, irradiation-driven stellar wind can lead to substantial systemic loss of angular momentum. Hence, these systems, which would otherwise not be expected to experience 'magnetic braking', evolve to shorter orbital periods during mass transfer. In this paper, we detail how such a magnetic braking scenario operates. We apply it to a specific astrophysics problem involving the formation of compact black-hole binaries with low-mass donor stars. At present, it is not understood how these systems form, given that low-mass companion stars are not likely to provide sufficient gravitational potential to unbind the envelope of the massive progenitor of the black hole during a prior 'common-envelope' phase. On the other hand, intermediate-mass companions, such as Ap and Bp stars, could more readily eject the common envelope. However, in the absence of magnetic braking, such systems tend to evolve to long orbital periods. We show that, with the proposed magnetic braking properties afforded by Ap and Bp companions, such a scenario can lead to the formation of compact black-hole binaries with orbital periods, donor masses, lifetimes and production rates that are in accord with the observations. In spite of these successes, our models reveal a significant discrepancy between the calculated effective temperatures and the observed spectral types of the donor stars. Finally, we show that this temperature discrepancy would still exist for other scenarios invoking initially intermediate-mass donor stars, and this presents a substantial unresolved mystery.  相似文献   

11.
Using the numerical code (`Scenario Machine') we study of number and physical properties of binary Be stars. Evolutionary tracks leading to a formation of the observational binary systems are presented. We conclude that synchronization must be taken into account when calculating binary Be star evolution and calculate the minimal orbital period for Be/evolved companion binary. The obtained distributions over orbital parameters are in good agreement with the observational lack of short-period Be/X-ray binaries. According to our calculations 70% of all Be stars must have a white dwarf. The white dwarfs in these systems should be hot enough with the surface temperature distribution peaking at 10000–20000 K. Their detection is possible during the period of the lack of Be star envelope by the detection of white dwarf extremely UV and soft X-ray emission. This method of registration appears to be particularly promising for `single' early-type Be stars because in these systems the white dwarfs must have a very high surface temperature. However, the loss of the Be disc-like envelope does not often occur and it is a rather rare event for many Be stars. The best possibility of white dwarf detection is given by the study of helium spectral lines found in emission from several Be stars. The ultraviolet continuum energy of these Be stars is found to be not enough to produce the observed helium emission. Besides, we also discuss the orbital properties of binary Be star systems with other evolved companions such as helium stars and neutron stars and give a possible explanation for the lack of Be/black hole binaries. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

12.
ULTRACAM: an ultrafast, triple-beam CCD camera for high-speed astrophysics   总被引：1，自引：0，他引：1  
ULTRACAM is a portable, high-speed imaging photometer designed to study faint astronomical objects at high temporal resolutions. ULTRACAM employs two dichroic beamsplitters and three frame-transfer CCD cameras to provide three-colour optical imaging at frame rates of up to 500 Hz. The instrument has been mounted on both the 4.2-m William Herschel Telescope on La Palma and the 8.2-m Very Large Telescope in Chile, and has been used to study white dwarfs, brown dwarfs, pulsars, black hole/neutron star X-ray binaries, gamma-ray bursts, cataclysmic variables, eclipsing binary stars, extrasolar planets, flare stars, ultracompact binaries, active galactic nuclei, asteroseismology and occultations by Solar System objects (Titan, Pluto and Kuiper Belt objects). In this paper we describe the scientific motivation behind ULTRACAM, present an outline of its design and report on its measured performance.  相似文献   

13.
简要地回顾了Ｂｅ／Ｘ射线双星２０多年来在红外、可见光、紫外和Ｘ射线波段所取得的观测结果，着重介绍了多波段联合观测对探讨双星间的相互作用如中子星的吸积方式和Ｘ射线产生的原因等方面的意义，对这些观测结果的分析研究，将是人们了解Ｂｅ／Ｘ射线双星的轨道参数和双星的物理参数、建立理论模型的基础。  相似文献   

14.
Among the dozen known magnetar candidates, there are no binary objects. Given that the fraction of binary neutron stars is estimated to be about 3–10 per cent, it is reasonable to address the question of solitarity of magnetars, to estimate theoretically the fraction of binary objects among them, and to identify the most probable companions. We present population synthesis calculations of massive binary systems. In this study, we adopt the hypothesis that magnetic field of a magnetar is generated at the protoneutron star stage due to a dynamo mechanism, so rapid rotation of the core of a progenitor star is essential. Our goal is to estimate the number of neutron stars originated from progenitors with enhanced rotation. In our calculations, the fraction of neutron stars originating from such progenitors is about 8–9 per cent. This should be considered as an upper limit to the fraction of magnetars, as some of the progenitors can lose momentum. Most of these objects are isolated due to coalescences of components prior to neutron star formation, or due to system disruption after the second supernova explosion. The fraction of such neutron stars in surviving binaries is about 1 per cent or lower. Their most numerous companions are black holes.  相似文献   

15.
Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars. Outside the radio band, the soft X-ray range (～0.1–10 keV) is most suitable for studying radiative mechanisms operating in these fascinating objects. X-ray observations revealed diverse properties of emission from millisecond pulsars. For the most of them, the bulk of radiation is of a thermal origin, emitted from small spots (polar caps) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones. On the other hand, a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated, most probably, in pulsar magnetospheres. There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars, as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions. These and other most important results obtained from X-ray observations of millisecond pulsars are reviewed in this paper, as well as results from the search for millisecond pulsations in X-ray flux of the radio-quite neutron star RX J1856.5-3754.  相似文献   

16.
We present optical spectra of four intermediate-mass candidate young stellar objects that have often been classified as Herbig Ae/Be stars. Typical Herbig Ae/Be emission features are not present in the spectra of these stars. Three of them, HD 36917, HD 36982 and HD 37062, are members of the young Orion nebula cluster (ONC). This association constrains their ages to be ≲1 Myr. The lack of appreciable near-infrared excess in them suggests the absence of hot dust close to the central star. However, they do possess significant amounts of cold and extended dust as revealed by the large excess emission observed at far-infrared wavelengths. The fractional infrared luminosities  ( L ir/ L ★)  and the dust masses computed from IRAS fluxes are systematically lower than those found for Herbig Ae/Be stars but higher than those for Vega-like stars. These stars may thus represent the youngest examples of the Vega phenomenon known so far. In contrast, the other star in our sample, HD 58647, is more likely to be a classical Be star, as is evident from the low   L ir/ L ★  , the scarcity of circumstellar dust, the low polarization, the presence of H α emission and near-infrared excess, and the far-infrared spectral energy distribution consistent with free–free emission similar to other well-known classical Be stars.  相似文献   

17.
Magnetars, neutron stars with ultrastrong magnetic fields  ( B ∼ 1014−1015G)  , manifest their exotic nature in the form of soft gamma-ray repeaters and anomalous X-ray pulsars. This study estimates the birthrate of magnetars to be ∼0.22 per century with a Galactic population comprising ∼17 objects. A population synthesis was carried out based on the five anomalous X-ray pulsars detected in the ROSAT All Sky Survey by comparing their number to that of massive OB stars in a well-defined volume. Additionally, the group of seven X-ray dim isolated neutron stars detected in the same survey were found to have a birthrate of ∼2 per century with a Galactic population of ∼22 000 objects.  相似文献   

18.
Pulsars have been recognized to be normal neutron stars, but sometimes have been argued to be quark stars. Submillisecond pulsars, if detected, would play an essential and important role in distinguishing quark stars from neutron stars. We focus on the formation of such submillisecond pulsars in this paper. A new approach to the formation of a submillisecond pulsar (quark star) by means of the accretion-induced collapse (AIC) of a white dwarf is investigated. Under this AIC process, we found that: (i) almost all newborn quark stars could have an initial spin period of ∼0.1 ms; (ii) nascent quark stars (even with a low mass) have a sufficiently high spin-down luminosity and satisfy the conditions for pair production and sparking process and appear as submillisecond radio pulsars; (iii) in most cases, the times of newborn quark stars in the phase with spin period <1 (or <0.5) ms are long enough for the stars to be detected.
As a comparison, an accretion spin-up process (for both neutron and quark stars) is also investigated. It is found that quark stars formed through the AIC process can have shorter periods (≤0.5 ms), whereas the periods of neutron stars formed in accretion spin-up processes must be longer than 0.5 ms. Thus, if a pulsar with a period shorter than 0.5 ms is identified in the future, it could be a quark star.  相似文献   

19.
We investigate the conditions by which neutron star retention in globular clusters is favoured. We find that neutron stars formed in massive binaries are far more likely to be retained. Such binaries are likely to then evolve into contact before encountering other stars, possibly producing a single neutron star after a common envelope phase. A large fraction of the single neutron stars in globular clusters are then likely to exchange into binaries containing moderate-mass main-sequence stars, replacing the lower-mass components of the original systems. These binaries will become intermediate-mass X-ray binaries (IMXBs), once the moderate-mass star evolves off the main sequence, as mass is transferred on to the neutron star, possibly spinning it up in the process. Such systems may be responsible for the population of millisecond pulsars (MSPs) that has been observed in globular clusters. Additionally, the period of mass-transfer (and thus X-ray visibility) in the vast majority of such systems will have occurred 5–10 Gyr ago, thus explaining the observed relative paucity of X-ray binaries today, given the MSP population.  相似文献   

20.
We present a ∼5-yr optical light curve of the recurrent Be/X-ray transient A0538–66 obtained as a by-product of the MACHO Project. These data reveal both a long-term modulation at P =420.8±0.8 d and a short-term modulation at 16.6510±0.0022 d which, within errors, confirms the previously found orbital period. Furthermore, the orbital activity is only seen at certain phases of the 421-d cycle, suggesting that the long-term modulation is related to variations in the Be star envelope.  相似文献   

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