On the lifetime of bright X-ray sources

The lifetime of massive X-ray binaries is (2–5)×10⁵ yr, this time close to the nuclear one. The lifetime of nonmassive X-ray binaries close to thermal one, (0.5–1)×10⁷ yr. Massive systems may be conserved at supernova explosion, the probability of the conservation of nonmassive system is (1–3)×10^–3.     

The formation and evolution of low-mass close binaries with compact components

We discuss the formation and evolution of interacting low-mass close binaries with a He-1CO- or ONe-dwarf neutron star or a black hole as a compact component. Mass exchange leads to cataclysmic events in such systems. The rate of semidetached low-mass close binary formation is 5×10^–3 yr^–1 if the accreting component is a He degenerate dwarf, 5×10^–3 yr^–1 if it is a CO-dwarf and 3×10^–8 yr^–1 if it is a neutron star. Systems with compact accretors arise as the result of the common envelope phase of close binary evolution or due to collisions of single neutron stars or dwarfs with low-mass single stars in dense stellar clusters. Evolution of LMCB to the contact phase in semi-detached stages is determined mainly by the angular momentum losses by a magnetic stellar wind and radiation of gravitational waves. Numerical computations of evolution with momentum loss explain observed mass exchange rates in such systems, the absence of cataclysmic variables with orbital periods 2^h–3^h, the low number and the evolutionary status of systems with orbital periods shorter than 80^m. In conclusion we list unsolved problems related to magnetic stellar wind, the distribution of young close binaries over main initial parameters, stability of mass exchange.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.     

On evolution of contact eclipsing binaries

It is shown that during contact eclipsing binaries evolution under the influence of stellar wind, magnetic stellar wind and with matter transfer by gas flow, in binary stellar systems there may take place a process of star merger (low mass stars) within 10⁵–10⁷ yr and a fast increase of distance between stars of massive binaries. W UMa-type stars are a finite evolutionary stage of very close and low mass binary pairs. As for contact systems of early spectral types (CE-systems), they are more varied in evolution.     

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.     

On the accelerations of the Moon and Sun,the constant of gravitation,and the origin of mountains

In a previous paper Lyttleton (1976) has shown that the apparent secular accelerations of the Sun and Moon, as given by de Sitter, can be largely explained if the Earth is contracting at the rate required by the phase-change hypothesis for the nature of the core. More reliable values for these accelerations have since become available which warrant a redetermination of the various effects concerned on the basis of constantG, and this is first carried out in the present paper. The lunar tidal couple, which is the same whetherG is changing or not, is found to be (4.74±0.38)×10²³ cgs, about three-quarters that yielded by the de Sitter values, while within the theory the Moon would take correspondingly longer to reach close proximity to the Earth at about 1.5×10⁹ years ago.The more accurate values of the accelerations enable examination to be made of the effects that a decreasingG would have, and it is shown that a valueG/G=–3×10^–11 yr^–1 can be weakly satisfied compared with the close agreement found on the basis of constantG, while a value as large numerically asG/G=–6×10^–11 yr^–1 seems to be definitely ruled out. On the iron-core model, an intrinsic positive component of acceleration of the angular velocity cannot be reconciled at all with the secular accelerations even for constantG, and far less so ifG is decreasing at a rate suggested by any recent cosmological theory.ItG=0, the amount of contraction available for mountain-building would correspond to a reduction of surface area of about 49×10⁶ km² and a volume to be redistributed of 160×10⁹ km³ if the time of collapse were 2.5×10⁹ years ago. For earlier times, the values are only slightly reduced. IfG/G=–3×10^–11 yr^–1, the corresponding values are 44×10⁶ km² and 138×10⁹ km³ for collapse at –2.5×10⁹ yr, and not importantly smaller at 38×10⁶ km² and 122×10⁹ km³ for collapse at –4.5×10⁹ yr. Any of these values would suffice to account in order of magnitude for all the eras of mountain-building. An intense brief period of mountain-building on an immense scale would result from the Ramsey-collapse at whatever time past it may have occurred.     

Rate of stellar collapses in the Galaxy

From an analysis of pulsar spatial and luminosity distributions, the number density of observed pulsars in the local region is determined to be 1.1±0.4×10^–7 pulsar pc^–3. Multiplication by the detection factor and by the ratio of Galaxy mass to local matter density and division by a mean lifetime of pulsars of 3×10⁶ yr suggests a pulsar birth every 4 yr. A stellar collapse might occur even more often.Supported in part by the U.S. Energy Research and Development Administration and by the National Science Foundation.     

X-ray observation of the Jovian impacts of comet Shoemaker - Levy 9

An ASCA observation of the Jovian impact of the comet Shoemaker-Levy 9 is reported. Four impacts of H, L, Q1 and R were observed and four impacts of B, C, G, and Q2 were observed within 60 minutes after their impacts. No significant flaring of X-ray emission was observed. Upper limit X-ray fluxes of 90 % confidence level, averaged 5 minutes just after the impacts, were 2.4 × 10^–13 erg sec^–1 cm^–2, 3.5 × 10^–13 erg sec^–1 cm^–2, 1.6 × 10^–13 erg sec^–1 cm^–2 and 2.9 × 10^–13 erg sec^–1 cm^–2 for the impacts of H, L, Q1 and R, respectively, in the 0.5(0.7 for H and Q1)–10 keV energy range. However, a hint of X-ray enhancement around Jupiter from July 17 to July 19 was detected with about 2 6 × 10^–14 erg sec^–1 cm^–2 in the 0.5–10 keV energy range.     

A possible observational constraint on the production of lithium by galactic novae

Recent computations (D'Antona and Mazzitelli, 1982), together with the general scheme of evolution of cataclysmic binaries (CBs), lead to conclude that the secondaries in those CBs having periods shorter than 4.5 hr have a large³He content in the envelope, ranging from 10^–4 (P=4.5 hr) to >2×10^–3 (P=3 hr) in mass fraction, if the nova systems have an age of some billion years. The consequence on the frequency of novae outbursts is shortly examined. If lithium is produced by galactic novae, the⁷Li content of old disk stars should be very close to the Population II content.Presented at the 5th European Workshop on White Dwarfs, Kiel, 1984.     

Formation of Thorne–Żytkow objects in close binaries

Thorne–?ytkow objects (T?Os), originally proposed by Thorne and ?ytkow, may form as a result of unstable mass transfer in a massive X-ray binary after a neutron star (NS) is engulfed in the envelope of its companion star. Using a rapid binary evolution program and the Monte Carlo method, we simulated the formation of T?Os in close binary stars. The Galactic birth rate of T?Os is about \(1.5\times 10^{-4}~\hbox {yr}^{-1}\). Their progenitors may be composed of a NS and a main-sequence star, a star in the Hertzsprung gap or a core-helium burning, or a naked helium star. The birth rates of T?Os via the above different progenitors are \(1.7\times 10^{-5}\), \(1.2\times 10^{-4}\), \(0.7\times 10^{-5}\), \(0.6\times 10^{-5}~\hbox {yr}^{-1}\), respectively. These progenitors may be massive X-ray binaries. We found that the observational properties of three massive X-ray binaries (SMC X-1, Cen X-3 and LMC X-4) in which the companions of NSs may fill their Roche robes were consistent with those of their progenitors.     

Soft X-ray enhancement during flares

The estimates of quiescent and flare time temperatures of soft X-ray emitting regions on the Sun are obtained for flares observed during March–August 1967 from X-ray observations in two soft X-ray bands, 2–12 Å (Explorer-33 data) and 8–12 Å (OSO-3 data). It is concluded that hot coronal condensation, originally at 2–3 × 10⁶ K, is raised to the temperature of about 4–5 × 10⁶ K and is responsible for soft X-ray enhancement.On leave from Physics Department, College of Engineering, Aurangabad, India.     

The secular behavior of X-ray and radio emission from supernova remnants

General models for the secular behavior of the radio and X-ray emission from supernova remnants are examined and compared with the observations. Hot plasma and synchrotron models for the X-ray emission are considered. Among other things, it is concluded that (1) the total kinetic energy released in most supernova outbursts is probably less than about 10⁵¹ ergs; (2) continuous injection probably occurs for at least 10 yr in every case and about 1000 yr in most supernova remnants, in which case the supernova remnants 3C392, W28, Pup A and IC443 should produce 1–10 keV X-ray fluxes 10^–10 ergs/cm² sec; and (3) the X-ray sources in the Crab Nebula, Cas A and Tycho can be explained in terms of a model wherein continuous injection occurs for 300 yr for the Crab Nebula, much less than 250 yr for Cas A and much longer than 400 yr for Tycho. Finally, it is shown that if Tycho and Cas A contain an X-ray star such as NP0532, it is quite possible that the X-ray emission from those sources is predominantly due to the X-ray star.Supported by the Air Force Office of Scientific Research under Contract No. F44620-67-C-0065.     

The relative abundance of the isotopes of Li,Be and B and the age of cosmic rays

Using a balloon borne double dE/dx x total energy telescope we have determined the isotopic composition of cosmic ray Li, Be and B nuclei in the energy range 100–250 MeV nuc.^–1. The measured mass resolution, for these nuclei is 0.3 AMU. The observed isotopic composition is in agreement with that predicted on the basis of interstellar fragmentation with the exception of a deficiency of Be¹⁰. If the low abundance of Be¹⁰ is attributed to the decay of this radioactive isotope we obtain a mean cosmic ray lifetime of (3.4 _–1.3 ^+3.4 )×10⁶ yr.A recent measurement which we have used in this paper gives this lifetime to be (1.5±0.3)×10⁶ yr (Yiou and Raisbeck, 1972).     

The angular momentum loss of low-mass close binary systems

The detailed evolution of low-mass main-sequence stars (M < 1M ) with a compact companion is studied. For angular momentum loss associated with magnetic braking it is found that about 10^–11–10^–12 M yr^–1 in stellar wind loss would be required. This wind is 10²–10³ times stronger than the solar wind, so we believe here magnetic stellar wind is insufficient. It is well known that there is mass outflow in low-mass close binary systems. We believe here that these outflows are centrifugal driven winds from the outer parts of the accretion disks. The winds extract angular momentum from these systems and therefore drive secular evolution. Disk winds are preferred to winds from the secondary, because of the lower disk surface gravity.     

Dynamical tides in close binary systems

The aim of the present paper will be to investigate the circumstances under which an irreversible dissipation of the kinetic energy into heat is generated by the dynamical tides in close binary systems if (a) their orbit is eccentric; (b) the axial rotation of the components is not synchronized with the revolution; or (c) the equatorial planes are inclined to that of the orbit.In Section 2 the explicit form of the viscous dissipation function will be set up in terms of the velocity-components of spheroidal deformation arising from the tides; in Section 3, the principal partial tides contributing to the dissipation will be detailed; Section 4 will be devoted to a determination of the extent of stellar viscosity — both gas and radiative; while in the concluding Section 5 quantitative estimates will be given of the actual rate at which the kinetic energy of dynamical tides gets dissipated into heat by viscous friction in stellar plasma.The results disclose that the amount of heat produced per unit time by tidal interaction between components of actual close binaries equals only about 10^–10th part of their nuclear energy production; and cannot, therefore, affect the internal structure of evolution of the constituent stars to any appreciable extent. Moreover, it is shown that the kinetic energy of their axial rotation can be influenced by tidal friction only on a nuclear, rather than gravitational (Kelvin) time-scale — as long as plasma or radiative viscosity constitute the sole sources of dissipation. However, the emergence of turbulent viscosity in secondary components of late spectral types, which have evolved away from the Main Sequence, can accelerate the dissipation 10⁵–10⁶ times, and thus give rise to appreciable changes in the elements of the system (particularly, in the orbital periods) over time intervals of the order of 10⁵–10⁶ years. Lastly, it is pointed out that, in close binary systems consisting of a pair of white dwarfs, a dissipation of the kinetic energy through viscous tides in degenerate fermion-gas could produce enough heat to account, by itself, for the observed luminosity of such objects.     

Solar and cosmic X-rays above 7.7 keV

Since its launch on March 8, 1967, the OSO-III has continuously observed solar and cosmic X-rays over the 7.7–210 keV range. The sun emits many impulsive X-ray bursts having fluxes several orders of magnitude above the background level of 8 × 10^–9 ergs(cm²-sec)^–1 at 7.7 keV and characteristic times on the order of 5 min. Ninety-five such events having fluxes >3 × 10^–5 ergs(cm²-sec)^–1 were detected in the period from March 8 to June 15, 1967. The cosmic X-ray source Lupus XR-1 has been observed to have a power law spectral form and no significant time variations over a 40-day period. Upper limits have been obtained on the hard X-ray flux of the peculiar galaxy M 87.     

Discovery of two cosmic X-ray bursts in 1970

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.     

Chromospherically active binaries,kinematics and age connections

Space velocities of 146 chromospherically active binary stars have been calculated. Containing F to M spectral types on the Main Sequence together with G and K giants, this very heterogeneous sample has been divided into subsamples in order to segregate stars so that they have similar kinematics and ages. Dispersions of space velocity components and other kinematical quantities (velocity averages and |Z| distributions) of these groups imply their ages as: Both old and young Main-Sequence systems (<10×10⁹ yr and 1×10⁹ yr, respectively) exist in the sample. Systems containing subgiants (single- and double-lined) or double-lined giants as their companions have ages about 2–3×10⁹ yr. Single-lined giants appear to be older than intermediate disk population stars (>5×10⁹ yr). The possible existence of white dwarfs as invisible companions of some of the single lined giants is suggested in order to explain why these systems are older than double-lined giants.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.     

Vacuum energy in cosmic dynamics

The analysis of the Th/U ratio in meteorites and the evolutionary ages of globular clusters favour values of the cosmic age of (19±5)×10⁹ yr. This evidence together with a Hubble parameterH ₀>70 km s^–1 Mpc^–1=(14×10⁹ yr)^–1 cannot be reconciled in a Friedmann model with =0. It requires a cosmological constant in the order of 10^–56 cm^–2, equivalent to a vacuum density _v =10^–29 g cm^–3 The Friedmann-Lemaître models (>0) with a hot big-bang have been calculated. They are based on a present value of the baryonic matter density of ₀=0.5×10^–30 g cm^–3 as derived from the primordial⁴He and²H abundances.For a Hubble parameter ofH ₀=75 km s^–1 Mpc^–1, our analysis favours a set of models which can be represented by a model with Euclidean metric (density parameter ₀=1.0, deceleration parameterq ₀=–0.93, aget ₀=19.7×10⁹ yr) and by a closed model with perpetual expansion (₀=1.072,q ₀=–1.0, aget ₀=21.4×10⁹ yr). A present density parameter close to one can indeed be expected if the conjecture of an exponential inflation of the very early universe is correct.The possible behaviour of the vacuum density is demonstrated with the help of Streeruwitz' formula in the context of the closed model with an inflationary phase at very early times.     

Soft X-ray and microwave observations of hot regions in solar flares

Hot regions in solar flares produce X-radiation and microwaves by thermal processes. Recent X-ray data make it possible to specify the temperature and emission measure of the soft X-ray source, by using, for instance, a combination of the 1–8 Å (peak response at about 2 keV) and the 0.5–3 Å (peak response at about 5 keV) broad-band photometers. The temperatures and emission measures thus derived satisfactorily explain the radio fluxes, within systematic errors of about a factor of 3. Comparison of 15 events with differing parameters shows that a hot solar flare region has an approximately isothermal temperature distribution. The time evolution of the correlation in a single event shows that the hot material originates in the chromosphere, rather than the corona. The density must lie between 10¹⁰ and 2 × 10¹¹ cm^–3. For an Importance 1 flare, this implies a stored energy of roughly 2 x 10³⁰-10²⁹ ergs. A refinement of the data will enable us to choose between conductive and radiative cooling models.