摘要:

We present the results of evolutionary computational for the low‐mass binary (LMB) with 1.4M⊙neutron star (NS) as a compact companion and 1M⊙red dwarf as a donor star. At the moment of filling of the Roche lobe by the red dwarf an orbital system of a system is 9.h4. We take into account the illumination of the donor star by energetic quanta and particles from the NS. We focus on a regime of ‘‘non‐catastrophic’’ heating when at the beginning of mass‐transfer phase the pulsar’s illumination activates the mass loss by a donor star rather than vaporizes its outer layers. We also incorporate the effect of sweeping of overflowing plasma out of the system by the pulsar’s magneto‐dipole radiation. One issue is that the evolution of such a system may result in the formation of the LMB with rapidly rotating NS and 0.2M⊙red‐dwarf companion, and having orbital period ∼(6–7)h. Another issue we investigate is the regime of episodic mass loss (with approximately Eddington rate) by the donor star commencing at the late stage of evolution before the donor star reached the minimum mass ∼0.2M⊙and shrinked within its Roche lobe. The relevance of this regime to the question of whether the LMXBs may be descendants of weakly magnetized millisecond pulsars is briefly discussed. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46034

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We discuss the origin and evolution of short‐period, low‐mass binary pulsars with evaporating companions. We suggest that these systems descend from low mass x‐ray binaries and that angular momentum loss mainly due to evaporative wind drives their evolution tending towardd log Pb/d log m2=−1 at late stages. We derive constraints on the energy and angular momentum carried away by the wind based on the observed orbital parameters. In our model the companion remains near contact and its quasi‐adiabatic expansion causes the binary to expand. Short term oscillations of the orbital period may occur if the Roche‐lobe overflow forms an evaporating disk. Possible links to related systems such as 4U16126‐67 and 1E2259‐586 are briefly discussed. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45976

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In recent years, the discovery of orbital period changes and eclipses in binaries with neutron stars has led to a new wave of excitement over these systems. They have also led to speculation that the traditional views of x‐ray binary evolution may be incomplete. Here I briefly discuss the observed orbital period derivatives and possible analogies between these binaries and other types of compact binary. I conclude that stellar activity in a late‐type companion is the most likely cause for the anomalous orbital period changes, and that it is also a strong candidate for explaining the eclipse phenomenon in at least some observed systems. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45977

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We briefly review the processes by which Thorne‐Z˙ytkow objects (TZ˙Os), i.e., red supergiants with neutron cores, are believed to form. The energy source in massive TZ˙Os is nuclear burning, provided by a modified rapidpprocess. After ≲106yr, this process is expected to break down, leading to a neutrino runaway and the collapse of the TZ˙O envelope. Part of the envelope will be accreted by the neutron‐star core, which will be spun up and may be transformed into a black hole. The rest of the envelope is likely to form a centrifugally supported disk. This disk will ultimately become gravitationally unstable, possibly forming one or more self‐gravitating objects (planets or low‐mass stars) in the process. The final system may be a spun‐up pulsar surrounded by planets, a low‐mass x‐ray binary, or a low‐mass black‐hole binary like V404 Cygni. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45980

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

X‐ray irradiation in binaries with accreting neutron stars can drive large mass outflows from the surface of companion stars. The resulting mass and angular momentum loss influence binary evolution. We summarize here recent results of detailed calculations of irradiation‐driven mass loss rates and binary evolution of low‐mass x‐ray binaries. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45981

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The properties of accreting x‐ray pulsars are reviewed paying particular attention to their pulse and orbital periods and high‐energy x‐ray spectra. The importance of making broad‐band x‐ray measurements of these systems is demonstrated. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45982

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The processes that are important in x‐ray pulsar emission are dominated by the strong magnetic fields of the accreting neutron star. These processes include the channeling of accretion flow from the companion via either a disk or a wind onto the neutron star polar caps, the deceleration of the accreting particles and the radiation mechanisms that form the spectrum. I will review x‐ray pulsar emission models in both the high‐luminosity sources, where the accreting plasma is stopped by radiation pressure, and the low‐luminosity sources, where the accretion flow is stopped by either a collisionless shock or Coulomb collisions. The formation of cyclotron lines in pulsar spectra will also be discussed. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45983

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This is a review of our understanding of the evolution of the spin periods of neutron stars in accretion‐powered binary x‐ray pulsars during the course of evolution of these binary systems. I discuss how neutron stars born in binaries as rotation‐powered pulsars are initially spun down by electromagnetic and plasma torques, until accretion of matter from the companion star begins. I describe how accretion torques spin up and spin down the star during the main x‐ray emission phase of neutron stars accreting from disks, winds, or equatorial rings produced by mass loss from their companions. I outline the final phase of spinup of the neutron stars into recycled rotation‐powered pulsars. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45984

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

BATSE detection of a new hard x‐ray pulsar is reported. The source was first observed on 14 Jul 1993, reached a maximum intensity on 25 Jul 1993, then declined smoothly until it became undetectable on 16 Aug 1993. The BATSE location was adequate to permit OSSE, ASCA, and ROSAT observations, leading to an improved source location. The observed period at the solar system barycenter was 93.548±0.002s, 93.5665±0.0005s, and 93.541±0.004 on 15 Jul 1993, 23 Jul 1993, and 10 Aug 1993, respectively. The source is detected between ∼20 keV and 160 keV, with a spectrum fit by an optically thin thermal bremsstrahlung form, having a kT of 25.4±2.1 keV during the rise to maximum intensity, decreasing monotonically during the remainder of the outburst to 17.1±2.5 keV on 5 Aug 1993. The pulse profile in this energy range has a single broad peak, with the maximum occurring later at higher energies. The pulse profile, intensity history, and spectral behavior observed by BATSE are reported. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45985

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The BATSE experiment on CGRO, a nearly continuous all sky monitor, is capable of detecting and monitoring pulsars in the hard x‐ray/gamma‐ray energy range. Using data processed with a global background subtraction method, we are able to construct pulsed intensity and pulse period histories for the accreting binary x‐ray pulsar 4U1538‐52 in the 20–50 keV energy band. This pulsar, which has a pulse period of approximately 530 seconds, is believed to be a wind accretor with a high mass companion. It was observed by previous experiments to be in secular spin down during the 1976–1988 period. Here we report observing, for the first time, a secular spin up trend. We are able to use this data to improve the upper limit on orbital period changes. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45986

出版商:AIP    

年代:1994

数据来源: AIP