Surface composition of magnetic neutron stars

The relative abundances of seven constitutent nuclei, He⁴, C¹², O¹⁶, Ne²⁰, Mg²⁴, Si²⁸ and Fe⁵⁶, are calculated as a function of time for neutron star atmospheres within which exist magnetic fields of the order of 10¹³G. The opacity, equation of state of the electrons, and cooling rate of the magnetic star are discussed, and it is shown to be a reasonable approximation to assume an atmosphere to be isothermal. The effects of particle diffusion are included in the nuclear reaction network. Computations are performed both for a constant mass atmosphere and for an atmosphere in which mass is being ejected. It is found that the final abundances are model independent as long as the initial model contains predominantly He⁴. The relative abundances are compared to the cosmic ray spectrum. For both the constant mass and mass loss atmospheres, nucleosynthesis proceeds virtually completely to Fe⁵⁶. However the outermost layers of the envelope, in which no mass is being ejected, are composed almost entirely of He⁴ with trace amounts of Fe⁵⁶. After the loss of about 10²¹ g, only Fe⁵⁶ is ejected from atmospheres expelling mass.A portion of the research on which this paper was based was performed while L. C. Rosen was present at the Lawrence Radiation Laboratory, Livermore, California.     

A Population II main sequence

Results of calculations of main sequence stellar models for metal poor star are presented. A fictitious pre-main sequence evolution was computed in order to give the distribution of the primary elements H, He³, He⁴, C¹², N¹⁴ and O¹⁶ in the stellar interior. The selected initial chemical composition wasX=.9,Z=.001.Comparison with previous results indicates a life-time of the main sequence phase shorter than it was believed before.     

Expansion of neutron star matter and its final nuclear composition

The final nuclear composition of the matter expanding from the density of a neutron star is investigated. It is assumed that starquakes cause the cracks which penetrate the neutron star crust and that the neutron star fluid can flow out through the cracks into space. The change with time of the nuclear composition of this matter is calculated by use of the compressible nuclear mass formula, and the hydrodynamics of the system is followed by the effect of nuclear transformation with time of the second fission of heavy neutron-rich nuclei, which is followed by a rapid rise to above 10⁹ K. If the value of the -strength function exceeds about 10^–5.5 MeV^–1 s^–1, the system proceeds to a state of nuclear equilibrium in the later expansion stage and the nuclear composition is reshuffled, finally to be transformed into neutron-excess, stable nuclei within the atomic mass region 80A120. It also becomes clear that if the strength function has a value smaller than the above critical value, then the neutron-rich nuclides withA[200, 400] are copiously produced. These results will also be applied in the cases of a neutron-star-black-hole collision and the explosion of a neutron star associated with the catastrophic phase transition within the neutron star core. The astrophysical implications are briefly discussed.     

Brans-Dicke cosmology,II

We discuss the implications of the Brans-Dicke scalar-tensor theory for cosmology with particular emphasis on the primordial element abundances that would obtain. Two general classes of models are found. Models of one class expand through the nuclear burning stage slightly more rapidly than the general relativistic case: models of the other class may expand at any rate whatsoever. The first class of models yeilds primordial abundances of D, He³ and He⁴ in agreement with their general relativistic values if the present mass density is low. High-density cosmologies, however, would produce too much He⁴. The second class of models yields element abundances which are far too high unless the expansion rate was quite large: in this case no He⁴ at all is produced. Finally, we determine the rate of change of the constant of gravitationG at the present epoch. For all but a very small class of models is negative at the present epoch. Models with positive values of at the present epoch produce no primordial He⁴ whatsoever, and have ages significantly lower than the corresponding general relativistic ages.     

Explosive nucleosynthesis and the composition of metal-poor stars

The character of the nuclear abundances synthesized under explosive carbon, oxygen and silicon burning conditions is demonstrated to be dependent upon the initial metal content of the star. Specifically, for metal-poor stars, the calculated abundances both of odd-Z nuclei and of the neutron rich isotopes of even-Z nuclei are found to be substantially reduced. This odd-even effect inZ is consistent with spectral studies of metal deficient stars.     

Nucleosynthesis in supernova outbursts and the chemical composition of the envelopes of neutron stars

The formation of chemical elements in the envelopes of neutron stars is considered at the densities ?=10⁷ to 10¹³ g cm^?3. It is shown, that the compression of cold and hot matter leads to different chemical compositions. The compression of cold matter is accompanied by a decrease of atomic weightA, up to ?≈3×10¹² g cm^?3. One may distinguish the following stages during the compression of hot matter: quasi-equilibrium, when there exists both nuclear equilibrium and kinetic equilibrium in β-processes; and limited equilibrium, when the total number of nuclei is constant. It is shown that a nonequilibrium chemical composition may be formed in the envelopes of neutron stars where there is an excess of neutrons in the presence of superheavy nuclei. The nuclear energy, stored in the neutron star envelope may be sufficient to support neutron star luminosity at a level of ～ 10³⁶ erg s^?1 over a period of ～ 10⁵ yr. Possible applications to the problem of X-ray sources and pulsars are discussed. The formation of the heavy nuclei in Supernovae explosions is considered briefly. Rough estimates are made for the differences in chemical composition of ejected matter during the explosions of stars of different masses and Supernovae of different types.     

Photometric and spectroscopic study of silicon Ap-star HD193722

The period of light variationP=1 _. ^d 13316 has been found for the silicon B9 IVp star HD 193722. Spectroscopic study of this star was based on 35 spectrograms with dispersion 4 Å mm^–1 well distributed in phase. The measurements of radial velocities of spectral line components for SiII, HeI, EuII, FeII and SrII allowed us to localize several regions on the surface of the star with enhanced abundance of these elements. The phase of maximum light inU, B andV was found to be the same as the phase of maximum Eu abundance. The coincidence of the regions with larger abundance of Si and He in HD 193 722 disagree with the hypothesis of diffusion in the presence of a magnetic field developed by Michaud (1971), to explain the peculiar chemical composition of Ap-stars.HD 193722 is a silicon B9 IVp star for which the magnetic field has not been measured. In the list by Palmeret al. (1962) its rotational velocityV sini is given as 250 kms^–1. As will be seen below, this value is too high. Megessier (1971) determined from hydrogen line profiles and continuous spectrumT _eff=13 000° and lgg=3.5.The results of photometric and spectroscopic study of HD193722 are given below.     

Constraints the properties of neutron star matter from the mass of neutron star PSR J1614-2230

The constraints on the properties of neutron star matter from the mass of neutron star PSR J1614-2230 are examined in the framework of the relativistic mean field theory. We find that there are little differences between the σ potentials of large mass neutron star and those of canonnical mass neutron star. For potentials of ω, ρ, neutrons and electrons, the values corresponding to the large mass neutron star are larger than those to the canonnical mass neutron star as the baryon number density is more than a certain value. We also find that for the relative particle number density of electrons, muons, neutrons and protons and the pressure of the neutron star, the values corresponding to the large mass neutron star are far larger than those to the canonnical mass neutron star. For the relative particle number density of hyperons Λ, Σ^?, Σ⁰, Σ⁺ and Ξ^?, the values corresponding to the large mass neutron star are far smaller than those to the canonnical mass neutron star. These mean that the larger mass of neutron star is more advantageous to the production of protons but is not advantageous to the production of hyperons.     

On the problem of big bang nucleosynthesis

Supporters of the standard Big Bang theory point to the abundances of light elements, predicted by Big Bang Nucleosynthesis (BBN) as one of the main observational supports of the theory. However, current data no longer confirm BBN. Instead, measurements of the abundances of He³, He⁴, and D clearly contradict BBN at more than a 3 level, eliminating a key support of the Big Bang.     

The role of massive AGB stars in the early solar system composition

Abstract— We demonstrate that a massive asymptotic giant branch (AGB) star is a good candidate as the main source of short‐lived radionuclides in the early solar system. Recent identification of massive (4–8 M⊙) AGB stars in the galaxy, which are both lithium‐ and rubidium‐rich, demonstrates that these stars experience proton captures at the base of the convective envelope (hot bottom burning), together with high‐neutron density nucleosynthesis with ²²Ne as a neutron source in the He shell and efficient dredge‐up of the processed material. A model of a 6.5 M⊙ star of solar metallicity can simultaneously match the abundances of ²⁶Al, ⁴¹Ca, ⁶⁰Fe, and ¹⁰⁷Pd inferred to have been present in the solar nebula by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material, and taking into account a time interval between injection of the short‐lived nuclides and consolidation of the first meteorites equal to 0.53 Myr. Such a polluting source does not overproduce ⁵³Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements. It is usually argued that it is unlikely that the short‐lived radionuclides in the early solar system came from an AGB star because these stars are rarely found in star forming regions, however, we think that further interdisciplinary studies are needed to address the fundamental problem of the birth of our solar system.     

A New Ionization Correction scheme for He+/H+ and the determination of the helium abundance inHii regions

We have developed a New Ionization Correction Factor (ICF) scheme for He⁺ based on the definition of the radiation softness parameter (Vilchez and Pagel, 1988) which is very sensitive to the effective temperature of the ionizing star(s) and, therefore, a good indicator of the He⁺–He⁰ ionization structure whilst remaining insensitive to other nebular parameters. The ICF() relationship is obtained making use of the Stasinska (1980, 1982) photoionization models. After comparison with previous semiempirical approaches in the literature and its application to a selected sample of abundances it is found that this ICF scheme seems a powerful tool for the determination of He abundances, particularly for objects of intermediate to low excitation.     

Spectroscopic evidence for mass loss from CH Cygni

Some high-dispersion spectrograms of CH Cygni taken in epochs at which only the M6 spectrum is visible and after the explosions of June 1967 and July 1968 have been studied. The strong negative radial velocities of the Caii chromospheric absorptions and the turbulent motions broadening the emission, lines ofHi, Hei, Feii, [Feii] prove that mass is lost from the star at a rate of the order of 10^–8 solar masses per year. Arguments are given in favour of the hypothesis that CH Cygni is a close binary composed of an M giant and a blue unstable subdwarf.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.     

Models for the formation of binary and millisecond radio pulsars

The peculiar combination of a relatively short pulse period and a relatively weak surface dipole magnetic field strength of binary radio pulsars finds a consistent explanation in terms of (i) decay of the surface dipole component of neutron-star magnetic fields on a timescale of (2–5) × 10⁶ yr, in combination with (ii) spin-up of the rotation of the neutron star during a subsequent mass-transfer phase. The four known binary radio pulsars appear to fall into two different categories. Two of them, PSR 0655 + 64 and PSR 1913 + 16, have short orbital periods (<25 h) and high mass functions, indicating companion masses 0.7M⊙ (∼1 (± 0.3) M⊙ and 1.4 M⊙, respectively). The other two, PSR 0820 + 02 and PSR 1953 + 29, have long orbital periods (117d), nearly circular orbits, and low, almost identical mass functions of about 3×10^-3 M⊙, suggesting companion masses of about 0.3M⊙. It is pointed out that these two classes of systems are expected to be formed by the later evolution of binaries consisting of a neutron star and a normal companion star, in which the companion was (considerably) more massive than the neutron star, or less massive than the neutron star, respectively. In the first case the companion of the neutron star in the final system will be a massive white dwarf, in a circular orbit, or a neutron star in an eccentric orbit. In the second case the final companion to the neutron star will be a low-mass (∼ 0.3 M⊙) helium white dwarf in a wide and nearly circular orbit. In systems of the second type the neutron star was most probably formed by the accretion-induced collapse of a white dwarf. This explains in a natural way why PSR 1953 + 29 has a millisecond rotation period and PSR 0820 + 02 has not. Among the binary models proposed for the formation of the 1.5-millisecond pulsar, the only ones that appear to be viable are those in which the companion disappeared by coalescence with the neutron star. In such models the companion may have been a red dwarf of mass 0.03M⊙, a neutron star, or a massive (>0.7M⊙) white dwarf. Only in the last-mentioned case is a position of the pulsar close to the galactic plane a natural consequence. In the first-mentioned case the progenitor system most probably was a cataclysmic-variable binary in which the white dwarf collapsed by accretion.     

Pick-up Ion Measurements in the Heliosphere – A Review

Measurements of the composition and spatial distribution of pick-up ions inside the heliosphere are reviewed. The first interstellar ⁴He⁺pick-up ions were detected with the SULEICA instrument on the AMPTE spacecraft near Earth's orbit. Most data on pick-up ions were taken in the solar-wind and suprathermal energy range of SWICS on Ulysses while the spacecraft cruised from 1.4 to 5.4 AU and explored the high-latitude heliosphere and solar wind from the ecliptic to ± 80^° heliolatitude. This includes the discovery of H⁺, ⁴He⁺⁺, ³He⁺, N⁺,O⁺, and Ne⁺ pick-up ions that originate from the interstellar neutralgas penetrating the heliosphere. From their fluxes properties of the interaction region between the heliosphere and the Local Interstellar Cloud such as the limits on filtration and the strength of the interstellar magnetic field have been revealed. Detailed analysis of the velocity distributions of pick-up ions led to 1) the discovery of a new distinct source, the so-called Inner Source, consisting of atoms released from interstellar and interplanetary dust inside the heliosphere, 2) the determination of pick-up ion transport parameters such as the long mean free path for pitch-angle scattering of order1 AU, and 3) detailed knowledge on the very preferential injection and acceleration of pick-up ions during interplanetary energetic particle events such as Co-rotating Interaction Regions and Coronal Mass Ejections. SWICS measurements have fully confirmed the theory of Fisk, Koslovsky, and Ramaty that pick-up ions derived from the interstellar gas are the dominant source of the Anomalous Cosmic Rays; they are pre-accelerated inside the heliosphere and re-accelerated at the solar-wind Termination Shock according to Pesses, Eichler, and Jokipii. The data indicate that the Inner Source of pick-up ionsis largely responsible for the occurence of C⁺ in the Anomalous Cosmic Rays. The abundances of recently discovered Inner-Source Mg⁺ and Si⁺ are solar-wind like and consistent with their abundances in the energetic particles associated with Co-rotating Interaction Regions. Knowledge on the injection and acceleration processes in Co-rotating Interaction Regions is applied to discuss the current observational evidence for the Interplanetary Focusing Cone of the interstellar neutral gas due to the Sun's gravitational force. The 25–150 keV/amu suprathermal ⁴He⁺ pick-up ion fluxes measured by CELIAS/STOF on board SOHO over 360^° of ecliptic longitude represent a `local' ionization and acceleration of interstellar atoms at 1 AU or smaller heliocentric distances. Completing the first limited data set of SULEICA/AMPTE on ⁴He⁺ pick-up ions they indicate a density enhancement in the Interplanetary Focusing Cone which is confirmed by recent SWICS/ACE data. Clear evidence for signatures in ecliptic longitude are found in the data on energetic neutral H fluxes observed with the CELIAS/HSTOF sensor on board SOHO. These fluxes are enhanced in the upstream and downstream directions of the interstellar wind. Detection of energetic H atoms, which propagate unaffected by the Heliospheric Magnetic Field, provided for the first time a diagnostic tool for observations near Earth to analyze the structure in ecliptic longitude of the interface region between the heliosphere and the Local Interstellar Cloud. This revised version was published online in July 2006 with corrections to the Cover Date.     

Symbolic analytical solutions for the abundances differential equations of the Helium burning phase

In this paper, a literal analytical solution is developed for the abundances differential equations of the helium burning phase in hot massive stars. The abundance for each of the basic elements ⁴He,¹²C,¹⁶O and ²⁰Ne is obtained as a recurrent power series in time, which facilitates its symbolic and numerical evaluations. Numerical comparison between the present solution and the numerical integration of the differential equations for the abundances show good agreement.     

Nuclear reactions on accreting neutron star surface

The production of X-rays and gamma-rays in bursts is believed to be due to the rapid burning of matter accreted onto a neutron star surface from its companion, most probably a giant star. The accreted matter consists mainly of hydrogen and helium and a very small amount of heavy elements. Due to the infall of matter, the temperature at the bottom layers is raised to a value of the order of 10⁸ K. The neutron star surface density is>10⁷ g cm^–3. As hydrogen burning is a slow process under any temperature and density conditions, we consider the helium-burning reactions as the source of gamma-rays in the neutron star surface. Under high-density conditions the ordinary laboratory reaction rates should become modified. At high-density conditions, the strong screening effect due to the polarising cloud of electrons around the ions become important and enhances the reaction rates considerably. The helium-burning reactions are calculated under such conditions. The abundances of helium-burning products such as¹²C, 1¹⁶O, and²⁰Ne, etc., are computed. Under high-density and temperature conditions carbon is found to be more abundant than oxygen. Neon is completely absent in almost all the relevant physical conditions in which a strong screening effect is operative. It is suggested that explosive burning of accreted helium of 10^–13 M will account for the observed energy of gamm-ray burst.     

Cosmic-ray production of deuterium,He3, lithium,beryllium, and boron in the Galaxy

The production of deuterium, He³, lithium, beryllium, and boron by galactic cosmic rays in the interstellar medium, over the life of the Galaxy, is calculated. It is found that high-energy - reactions contribute in an essential way to the observed lithium. When allowance is made for the interchange of material between stars and the interstellar gas and for the change of cosmic-ray intensity with time, the Li⁶, Be⁹, and boron produced turn out to be ample to explain the observed abundances, and with remarkable internal consistency. Deuterium and He³ arenot produced in significant amounts, nor Li⁷ in sufficient amount, however. To explain the Li⁷/Li⁶ ratio measured terrestrially and in chondritic meteorites, we invoke cosmological production of Li⁷. This implies the production of deuterium, He³, and He⁴ as well, in amounts consistent with observation. The theory in its present form cannot explain a solar-system Li⁷/Li⁶ ratio of 12and stellar ratios as low as 3, but additional processes can be adduced to reconcile them. The consistency of the numbers when cosmological production is included lends additional support to the big-bang hypothesis. An incidental result is that the mean luminosity of the Galaxy over its lifetime has been about 3 times its present luminosity.     

On steady-state nuclear burning in accreting neutron stars

The properties of the hydrogen burning shell in the envelope of an accreting neutron star have been studied for a range of mass accretion rates, neutron star radii, and metal abundances of the accreted matter. It is found that the hydrogen burning shells lie at densities ranging from 10⁵–6×10⁶ gm cm^–3. For mass accretion rates in excess ofM _c2 hydrogen and helium burn together. ForM _c1MM _c2, the hydrogen burning shell is stabilized by the limited CNO cycle. Implications of these results to the X-ray burst phenomena are briefly discussed.     

Tunnel effect in molecules in strong magnetic fields of neutron stars

It is shown that, in the strong magnetic field of the neutron starB=10¹²–10¹³ G, the probability of the tunnel effect in the molecules increases significantly. It is quite probable that this effect can catalyze nuclear reactions at the neutron star surface.     

A hydrodynamic model for asymmetric explosions of rapidly rotating collapsing supernovae with a toroidal atmosphere

We numerically solved the two-dimensional axisymmetric hydrodynamic problem of the explosion of a low-mass neutron star in a circular orbit. In the initial conditions, we assumed a nonuniform density distribution in the space surrounding the collapsed iron core in the form of a stationary toroidal atmosphere that was previously predicted analytically and computed numerically. The configuration of the exploded neutron star itself was modeled by a torus with a circular cross section whose central line almost coincided with its circular orbit. Using an equation of state for the stellar matter and the toroidal atmosphere in which the nuclear statistical equilibrium conditions were satisfied, we performed a series of numerical calculations that showed the propagation of a strong divergent shock wave with a total energy of ～0.2×10⁵¹ erg at initial explosion energy release of ～1.0×10⁵¹ erg. In our calculations, we rigorously took into account the gravitational interaction, including the attraction from a higher-mass (1.9M_⊙) neutron star located at the coordinate origin, in accordance with the rotational explosion mechanism for collapsing supernovae. We compared in detail our results with previous similar results of asymmetric supernova explosion simulations and concluded that we found a lower limit for the total explosion energy.