The strong magnetic fields of the X-ray pulsars Hercules X-1 and 4U 1626–67 and their evolutionary scenarios

We consider the magnetic and spin evolution of the X-ray binary pulsars Her X-1 and 4U 1626–67, assuming that their magnetic fields are of crustal origin. We adopt the standard evolutionary model which implies that the neutron star passes through several phases in a binary system ('isolated pulsar' – propeller – wind accretion – Roche lobe overflow). In the framework of the model under consideration, the strong magnetic fields of relatively old pulsars like Her X-1 and 4U 1626–67 can naturally be understood if, at their birth, they had a sufficiently strong magnetic field, ∼3 × 10¹³ G, comparable to the maximal field observed in radio pulsars.     

Massive X-ray binaries: Their physics and evolution

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.     

Spin-up and spin-down in intermediate polars and X-ray pulsars

The accretion torque theory of Wang (1987) is applied to the spin periods of intermediate polars and X-ray pulsars. It is shown that, if the primaries are spinning near their equilibrium values, the range of positive and negative values ofP/P observed in intermediate polars is readily understood in terms of relatively small variations of mass transfer rateM of the kind generated either by long term (10³ yr) cycling ofM suggested by the nova hibernation model, or by the short term (10 yr) variations caused by magnetic cycling in the secondary stars. The variations in spin rates of the disc-fed X-ray pulsars Her X-1 and Cen X-3 can also be accounted for by the latter process.     

Evolution of massive close binaries and formation of neutron stars and black holes

Main results of computations of evolution for massive close binaries (10M +9.4M , 16M +15M , 32M +30M , 64M +60M ) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars — mass exchange — Wolf-Rayet star or blue supergiant plus main sequence star — explosion of the initially more massive star appearing as a supernova event — collapsed or neutron star plus Main-Sequence star, that may be observed as a runaway star — mass exchange leading to X-rays emission — collapsed or neutron star plus WR-star or blue supergiant — second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars.Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries.     

The bipolar jets associated with the planetary nebulae NGC 2392 and NGC 6543

TheUBV-photometry of a well-known X-ray binary Her X-1/HZ Her over 16 years is presented. The mean light curves of this system were constructed, using our and published data. Based on our observations in primary minimum the colour behaviour of Her X-1/HZ Her was investigated. An additional radiation during total eclipse of accretion disk is found at the ascending branch of the light curve.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

吸积双星脉冲星EXO2030+375中回旋吸收线的迹象

本文作者首次发现了EXO 2030+375的回旋吸收线迹象.这是迄今唯一一个同时有用回旋吸收线直接测量的磁场数据和用吸积演化方法间接测量的中子星磁矩数据的X射线脉冲星.两种测量方法的结果有很大差别,本文提出了可能导致这种差别的物理机制.     

Multicolour photopolarimetry of magnetic cataclysmic variables

Observational evidence of optical cyclotron emission from discrete regions on the highly magnetic white dwarf components of AM Herculis type binaries is presented on the basis of linear and circular polarimetry of EF Eri, AM Her, VV Pup, and V834 Cen. About the geometry of the main emitting region in VV Pup our simultaneousUBVRI photometry during the eclipse by the white dwarf shows that the size of the emitting region (0.1–0.3 in units of the white dwarf radius) increases by a factor of about two from ultraviolet to near-infrared.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Observational evidence for the two types of dwarf nova outbursts

Observed characteristics of outbursts of eight dwarf novae are compared with those predicted for the two types of outbursts by the disk instability theory. OY Car, U Gem, VW Hyi, and WX Hyi are identified as Type A, while RX And, SS Cyg, AH Her, and CN Ori — as Type B.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Secular evolution of the period and inclination of the magnetic to rotation axis and recycled pulsars

Statistical analysis has been carried out of the relations between period and the ageP–t _c, and the inclination of magnetic to rotation axis to the age –t _cof pulsars have been done.Up to characteristic agest _c=3×10⁷ years the period increases as expected for magneto-dipole radiation energy lossesP=P _m (1–exp(–t/ _B ))^1/n–1. Best-fitting parameters of this approximation are the time-scale of the magnetic moment decay _B =4×10⁶ years and breaking indexn=3.6. Fort _c>3×10⁷ years theP–t _cdependence is significantly different.The inclination of magnetic to rotation axis decreases versus age, showing a secular alignment of the axis. But this decrease continues also only up tot _c=3×10⁷ years. Thus bothP–t _cand –t _cdependencies indicate that most of the pulsars of agest _c>3×10⁷ years are not evolutionary continuations of more younger ones, but apparently represent another population of pulsars, which differ by their genetic history or physical processes. This population includes all known millisecond pulsars. We suggest, that this population is a so-called recycled pulsar. The list of candidates of recycled pulsars is presented.A new evaluation of the inclination of the magnetic to the rotation axis for 105 pulsars is presented.     

Free precession of Cyg X-3 and the 34.1-day periodicity

The origin of the 34.1-day periodicity in X-ray and -ray from Cyg X-3 has not been made clear so far. In this paper, we propose a free precession model for an elastic neutron star. This model explains the 34.1-day periodicity and predicts the unobserved spin period for Cyg X-3 to be about 100 ms. Taking into account the possibility that the secular spin angular velocity of the star is different from that observed presently, the analogous long-terms periodicities of Her X-1 and Cen X-3 are also accounted for in this theory.     

Exact cosmological solutions in Brans and Dicke's scalar-tensor theory,II

In addition to our previous paper (Dehnen and Obregón, 1971) the exact cosmological solutions of Brans and Dicke's scalar-tensor theory allowing a power law between the gravitational constant and the radius of curvatureR of the universe are sought in case that — in contrast to our previous paper — the initial conditionR(t=0)=0 is avoided. There exist two different types of solutions especially for the closed space of positive curvature and for positive values of the freely available parameter of the scalar-tensor theory. The radius of curvature and also the gravitational constant increase at first with respect to time and decrease after reaching a maximum value, in contradiction to Dirac's hypothesis whereafter the gravitational constant should decrease with time in an expanding universe. The age of the universe following from these solutions is in accordance with the observations.     

CCD observations of X-ray binaries

During two observation periods in 1984 and 1985 we monitored the faint optical counterparts of seven X-ray binaries with a CCD camera attached to the Cassegrain-focus of the 2.2 m telescope at Calar Alto, Spain. The observation periods were 1984, September 25–27, and 1985, August 8–15.The transient sources 4U0042+32 and 4U0115+63 showed no active state.The search for an optical candidate of 4U0142+62 did not reveal any objectm _v 24 within the EXOSAT error box.Within the EXOSAT error box of EXO2030+37 the reddest object was found to be very faint in blue in contrast to the blue Palomar plate.The analysis of the other three observed sources 4U1837+04, 1H1929+509, and 4U2129+47 is not yet finalized, but no unexpected bright or faint state of the sources has been found, 4U2129+47 is still in its present low state (m _v =18), lasting at least since 1983.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

The steady spin-down rate of 4U 1907+09

Using X-ray data from the Rossi X-ray Timing Explorer , we report the pulse timing results of the accretion-powered, high-mass X-ray binary pulsar 4U 1907+09, covering a time-span of almost two years. We measured three new pulse periods in addition to the previously measured four pulse periods. We are able to connect pulse arrival times in phase for more than a year. The source has been spinning down almost at a constant rate, with a spin-down rate of     for more than 15 yr. Residuals of pulse arrival times yield a very low level of random-walk noise, with a strength of ∼     on a time-scale of 383 d, which is 40 times lower than that of the high-mass X-ray binary pulsar Vela X-1. The noise strength is only a factor of 5 greater than that of the low-mass X-ray binary pulsar 4U 1626−67. The low level of the timing noise and the very stable spin-down rate of 4U 1907+09 make this source unique among the high-mass X-ray binary pulsars, providing another example, in addition to 4U 1626−67, of long-term quiet spin down from an accreting source. These examples show that the extended quiet spin-down episodes observed in the anomalous X-ray pulsars 1RXS J170849.0−400910 and 1E 2259+586 do not necessarily imply that these sources are not accreting pulsars.     

Analysis of spectra of α CMi and α Cen A observed with the orbiting stellar ultraviolet spectrophotometer S59 in ESRO's TD1A satellite

Ultraviolet spectra of CMi and Cen A taken with moderate spectral resolution (approx. 1.8 Å) are used to analyse whether a determination of stellar chemical abundances of Fe and Cr and of the photospheric parameters is possible. For CMi, for which good spectral data are available, we findT _eff=7660±110 K; logg _eff=3.05±0.1. Further, log(Fe)=–0.06±0.09; log (Cr)=–0.01±0.09 with regard to standard (solar) abundances. For Cen A the resulting data — particularly the photospheric ones — are less certain, but it seems that the Fe abundance may be smaller than the standard value.     

Rotating black holes in neutron and quark stars: Phenomenon of pulsars

The phenomenon of pulsars is considered as the evidence for existence of black holes in neutron and quark stars. Within the framework of the degenerated star model with black-hole interior the existence of millisecond pulsars withP<0.5 ms and single pulsars with negative derivative of the period were predicted. The anisotropic accretion of neutron (or quark) star matter on to a rotating black hole leads to the formation of directed radiation (projector), which makes heat spots at surface (volcanos), that explains the nature of pulsating radiation and the complicated structure of impulses. This model gives both the mechanism of self-acceleration of degenerated star rotation (mass accretion on to the internal black hole) producing millisecond pulsars and also the mechanism of significant deceleration of rotation (ejection of neutral mass through a volcanic crater), leading to long-periodic X-ray pulsars. The black hole produces high densities and temperatures of the degenerated star mass that transforms gradually the neutron star into quark star (Cygnus X-3).     

On the Dynamics of Weak Stability Boundary Lunar Transfers

Recent studies demonstrate that lunar and solar gravitational assists can offer a good reduction of total variation of velocity Vneeded in lunar transfer trajectories. In particular the spacecraft, crossing regions of unstable equilibrium in the Earth—Moon—Sun system, can be guided by the Sun towards the lunar orbit with the energy needed to be captured ballistically by the Moon. The dynamics of these transfers, called weak stability boundary (WSB) transfers, will be studied here in some detail. The crucial Earth—Moon—Sun configurations allowing such transfers will be defined. The Sun's gravitational effect and lunar gravitational capture will be analyzed in terms of variations of the Jacobi constants in the Earth—Sun and Earth—Moon systems. Many examples will be presented, supporting the understanding of the dynamical mechanism of WSB transfers and analytical formulas will be obtained in the case of quasi ballistic captures.This revised version was published online in October 2005 with corrections to the Cover Date.     

Three-wave turbulence in pulsar winds

Three-wave interactions can modify the very bright radio waves propagating through dense, magnetized pulsar winds and prevent radiation from escaping, or severely alter the resulting spectrum. Absence of the signatures of such effects in the very bright radio emission from pulsars implies constraints on the structure of their winds, especially for a spherically-symmetric wind which should block the radiation unless that Lorentz factor of the pairs is 8 × 10².Presented at the Cosmic Winds and the Heliosphere conference in Tucson, Arizona, U.S.A., October 18–22, 1993.     

The period and magnetic field distributions of cataclysmic variables: Implications for their evolution

Comparison of the period distributions of various classes of CVs confirms an extreme bias of the synchronous AM Her systems toward short orbital periods, while the DQ Her systems do not differ significantly from the distribution of non-magnetic systems. This suggests either strong selection effects or enhanced evolution of the AM Her systems. There is as yet no obvious bimodality in either the magnetic field distributions of isolated white dwards or of CV primaries. However, clear differences between the two exist: the strongest being that magnetic primaries are overrepresented among short period CVs by more than an order of magnitude in comparison to the field white dwarfs.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Long-term variability of the Be/X-ray binary EXO 2030+375

We present a multi-wavelength study of the Be/X-ray binary system EXO 2030+375. We report that the Be companion is currently in a low-activity phase as indicated by the notable decrease of the infrared and optical emission. If this trend continues the source will lose its circumstellar envelope. Infrared spectroscopy in the IJHK bands is presented for the first time, along with optical and X-ray observations. These infrared spectra agree with the optical companion being an early-type (B0) main-sequence star. When active EXO 2030+375 shows an X-ray outburst at each periastron passage of the neutron star. In addition to the maximum X-ray luminosity displayed at orbital phase ∼0.0, we find a smaller maximum in the light curve at phase ∼0.5. This second intensity peak may be explained if the velocity of the wind is lower than or comparable to the orbital velocity of the neutron star at apastron. We also comment on the relation between the optical/infrared behaviour and the X-ray emission and argue that the X-ray inactive period observed between 1993 August and 1996 April is a result of centrifugal inhibition of accretion of matter rather than a low-activity circumstellar disc.     

Compttonization-softening and the hard X-ray spectrum of CYG X-1

The Comptonization-softening of very hard X-ray photons withEm ₀ c ² in the cold electron gas is discussed. The frequency diffusion equation for Comptonization of hard X-rays has been derived to the zero-temperature approximation. By use of this equation, and under the assumption of pair-annihilation origin of hard X-rays, we calculated the energy spectrum withE>80 keV, for Cyg X-1, which is in good fit with the observation. The high-energy edge 400 keV of the observed spectrum and the small bump in the range 100–200 keV also can be explained by this way.