Giant elliptical galaxies: The Salpeter initial luminosity function and interstellar matter

It is argued that a Salpeter initial luminosity function is consistent with the observed integral properties of giant elliptical galaxies if the gaseous material lost by evolving stars can be retained in the system for times of the order of 10⁸ yr. One model which emerges is of a highly condensed system consisting mainly of metal-poor population II stars with an admixture (1.5%–15%) of super-metalrich stars born from the gaseous debris, which at the present time constitutes 0.05%–0.5% of the total mass. HighM/L ratios result from obscuration of the starlight, and the missing radiation reappears in the form of a strong I-R flux at wavelengths of the order of 100 . The difference in colour betweengE anddE galaxies is explained in terms of interstellar reddening, and strong interstellar metallic absorption lines are also expected. The model leads to a negligible evolutionary correction to the cosmological deceleration parameterq ₀. An alternative model, in which the stars arenot metal poor, has a more condensed, heavily obscured nucleus, surrounded by the unobscured central bulge of the Galaxy which provides most of the light. In this version a large evolutionary correction would be required.     

Production and propagation of cosmic ray H2 and He3 nuclei

The results of detailed calculations on the production of H² and He³ nuclei by cosmic ray protons and helium nuclei in interstellar medium are presented. The flux and energy spectra of these nuclei as well as those of cosmic ray H¹ and He⁴ nuclei in the vicinity of the Earth are calculated. For this purpose the source spectra are assumed to be in the form of a power law in total energy per nucleon with an additional velocity dependent term. This spectrum denoted as Fermi Spectrum, is about midway between the power law spectrum in rigidity and in total energy per nucleon. The fluxes are calculated taking into account: (1) energy dependent cross-sections of thirteen nuclear reactions of cosmic ray protons and helium nuclei with interstellar H¹ and He⁴ leading to the production of H² and He³ nuclei, (2) angular distributions and kinematics of these reactions, (3) ionization loss of the primary and secondary nuclei in interstellar medium, (4) elastic collisions of cosmic ray protons and helium nuclei, (5) distributions of cosmic ray path-lengths in in terstellar space as in gaussian and exponential forms, and (6) interplanetary modulation of cosmic rays from the numerical solution of the complete Fokker-Planck equation describing the diffusion, convection and adiabatic deceleration of cosmic ray nuclei in the solar system. On comparing the calculated values of H²/He⁴ and He³/(He³+He⁴) as a function of energy with the observed data of several investigators, it is found that agreement between the calculated values and most of the observed data is obtained on the basis of: (a) source spectrum in the form of Fermi Spectrum, (b) distribution of path-lengths as in the gaussian form with a mean value of 4 g cm^–2 of hydrogen or as in exponential form with leakage path length of 4 g cm^–2.     

The formation of condensed carbon particles in the atmospheres of white dwarfs

The existence of condensed carbon in the form of liquid droplets and graphite grains is found in white dwarf atmospheres with parametersg=10⁸ cm s^–2, H/He10^–3, andT _eff6000 K on the basis of model atmospheres techniques. It is shown that the condensation layers are dynamically stable and, consequently, that white dwarfs cannot supply the condensed particles to the interstellar medium. Possible observable effects are considered.     

Solar abundances of light nuclei and mixing of the Sun

Radial profiles of the light nuclei (A 15) are calculated in the non-mixing Sun, taking into account the changes of solar structure with time. The results are discussed in relation to models of solar mixing and compared with abundance determinations at the solar surface or in the solar wind. B cannot be depleted in the outer convective zone without producing a large increase in the He³/He⁴ ratio. A decrease in He³/He⁴ would be accompanied by changes in C¹³/C¹² and N¹⁵/N¹⁴ of a magnitude which is not observed.It is shown that boron could be depleted in the pre-main sequence period of the Sun, if mixing was on a time-scale of 10⁶ yr. The simultaneous small increase in He³/He⁴ does not contradict observation. However, Be would be depleted more strongly than B.A He³/He⁴ decrease is always accompanied by large changes in N¹⁵/N¹⁴ and C¹³/C¹². Since such changes are not observed, it is concluded that the He³/He⁴ ratio in the outer convective zone is a reliable upper limit for (He³ + D)/He⁴ in the solar nebula. Thus the D/H ratio in the protosolar material was much lower than it is in sea water or in carbonaceous chondrites.     

The12C/13C isotope ratio in comets,stars and interstellar matter

The¹²C/¹³C isotope ratio in the interstellar medium and in stellar atmospheres is discussed and compared to the value found in the solar system and especially in comets. The cometary value (100) tends to be slightly above the terrestrial value and is definitively higher than that for interstellar molecular clouds (about 30 to 50).This result implies that comets are not of interstellar origin; that the original isotopic abundances of the primitive solar nebula has been preserved in the cometary material; and that due to an enrichment of the interstellar medium in¹³C, the¹²C/¹³C isotope ratio has decreased by a factor of about 2.5 since the formation of the solar system (i.e., during the past 4.5×10⁹ years) — a result which is roughly in agreement with present theories of the chemical evolution of our Galaxy. The relatively high cometary carbon isotope ratio (as compared to the terrestrial value) indicates that some correction should be applied to the semi-empirical models describing the¹³C enrichment in the Galaxy.Paper dedicated to Professor Hannes Alfvén, on the occasion of his 70th birthday, 30 May, 1978.     

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.     

High-luminosity single carbon stars in stellar and galactic evolution

Summary In the solar neighborhood, approximately half of all intermediate mass main sequence stars with initially between 1 and about 5 Mbecome carbon stars with luminosities near 10⁴ L for typically less than 10⁶ years. These high luminosity carbon stars lose mass at rates nearly always in excess of 10^–7 M yr^–1 and sometimes in excess of 10^–5 M yr^–1. Locally, close to half of the mass returned into the interstellar medium by intermediate mass stars before they become white dwarfs is during the carbon star phase. A much greater fraction of lower metallicity stars become carbon-rich before they evolve into planetary nebulae than do higher metallicity stars; therefore, carbon stars are much more importan t in the outer than in the inner Galaxy.     

Radio source orientation and the cosmological interpretation of the angular size-redshift relation for double-lobed quasars

The angular size-redshift test for quasars was compared with various cosmological models including non standard models. The possible effects of radio source orientation and relativistic beaming were taken into account in the analysis.It was found that orientation effects alone were not sufficient to explain the observed-z relation in terms of Friedmann models. In addition, linear size evolution of the formD ~ (1 +z)^–n , with 0.75 n 1.2 would be required for 0 1.0, or possibly an inverse correlation between luminosity and linear size. The non-standard cosmological models all gave better fits to the deprojected data than the Friedmann models in the absence of evolutionary effects, with the tired light effect providing the best fit.     

Fundamental parameters and intrinsic colors of F,G, and K supergiants and classical cepheids

We used high-resolution echelle spectra with high signal-to-noise ratio to determine with a high degree of accuracy some atmospheric parameters (T _eff, log g and [Fe/H]) for 68 non-variable supergiants of types F, G, and K and 26 classical Cepheids in 302 pulsation phases. Very accurate effective temperatures, with errors of only 10–30 K, were determined by the line-depth ratio method. We found that the observed intrinsic color indices (B ? V)₀ can be related to these parameters: (B ? V)₀ = 57.984? 10.3587(log T _eff)² + 1.67572(log T _eff)³ ? 3.356 log g+ 0.321 V _t + 0.2615[Fe/H] + 0.8833log g(log T _eff). With this empirical relation, the intrinsic colors of individual supergiants and classical Cepheids of spectral types F0-K0 and of luminosity classes I and II can be estimated with an accuracy as high as 0.05 ^m , which is comparable to the accuracy of the most elaborate photometric procedures. In view of large distances to supergiants, the method we propose here allows a large-scale mapping of interstellar extinction with an accuracy of 0.1–0.2 ^m in a quite large region of the Galaxy.     

Numerical simulations of ther 1/4 law

We simulate the evolution of a system of points in a given potential. With a density distribution proportional to r^–n , and a logarithmic potential we obtain a stationary state following ther ^1/4 law of de Vaucouleurs. If we follow this simulation to the Galaxy and to M31, we findn=–4 for the Galaxy andn=–3 for M31.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.     

Quasi-stellar objects as rotating magnetic superstars

In this paper the magnetic superstar model is used to discuss QSO luminosity and density evolution. Our main hypotheses are that (i) mass loss from old stars in massive galaxies cools and then falls into the centre to form a nuclear disc (Bailey, 1980); and (ii) magnetic superstars in galactic nuclei condense out of gaseous material at the centre of a supermassive-magnetised disc (Kundt, 1979). On this generalised model we find that the non-thermal (synchrotron) optical luminosity scales asL _opt L ³ t ^–7/3, whereL is the total blue luminosity of old stars in the galaxy and t is cosmic time. In addition we show that QSO co-moving density follows the lawD(t)exp-(t/t _Evol)^16/15 with an evolution timescalet _Evol = 1.95 × 10⁹ yr. The model as a whole is in good agreement with observations.     

AGNs,X-ray background and the possible candidates for great attractor

In the five last years, different structures (density excess 1) have been proposed as the direct cause of our infall toward the direction of Hydra—Centaurus with a velocity of 500 km s^–1. The direct effect of the mentioned matter accumulations on the X-ray background (XRB) can be estimated as a function of the geometry of the structures and of the cosmological evolution of the sources emitting in the X-ray band (2–10 keV) for different universes (₀1). If the XRB comes mostly from AGNs with low luminosity (L _X <10⁴³ erg s^–1 and, therefore, they will have a weak cosmological evolution) and we consider the difference between the intensities coming from both hemispheres (that oriented toward the direction of our motion and the opposite one) obtained by means of different satellites, we can conclude that some candidates are highly unlikely.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     

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.     

Unbound planets

Current protostellar theory has determined a lower limit to the mass of a pre-stellar gas cloud fragment of ~0.01 M. This suggests that isolated interstellar bodies in the mass range ~10 M_-710_-2 M must have originated within a planetary system. Two possible mechanisms whereby planets are lost from their parental systems to interstellar space are discussed and the abundance and distribution of such unbound planets within the Galaxy is examined. It is found that, except within the central regions of the Galaxy, unbound planets are expected to be scarce. In the solar neighbourhood for instance, the number density ratio of unbound planets to stars is estimated to range between extremes of ~4 × 10^–4–3 × 10^–2 with a most probable value of ~6 x 10^–3. The faint possibility that the hypothetical Planet X might be of extra-solar origin is also discussed.     

Interpretation of XUV spectroheliograms

Some parameters of chromospheric structure are drawn from recently published XUV spectroheliograms. The HeII emission above the limb arises from the small amount of He⁺ still existing at 10⁶°. The larger amounts of He⁺ in the cooler corona at the poles explain the polar cap absorption in 304. The flat distribution of emission in Oiv and Ov, with a sharp spike at the limb, is caused by the rough structure of the chromosphere and the variable excitation in the emitting spicules. The intensity of the Nevii lines shows that the transition zone between chromosphere and corona is very sharp.This research was supported by the National Aeronautics and Space Administration under Grant NASA NGR 05 002 034.     

Programme of the Galactic meridian: Star counts and galactic models. 1. Distributions of stellar magnitudes and colours

A comparison of observed stellar distributions with a three-component model of the Galaxy is presented. The analysis is based on photometric and photoelectric data obtained along the main Galactic meridian and in two fields near the North Galactic pole (programme MEGA). The assumed model considers the Galaxy as composed of the disk (main sequence and disk red giants), the thick disk and spheroid populations. To model the observed colour distribution, we distinguish main sequence stars and disk red giants as the disk subsystem; white dwarfs, subdwarfs and intermediate giants as the thick disk subsystem; extreme subdwarfs, spheroid giants and horizontal branch stars as the spheroid subsystem. A statistical relation between the apparent and absolute magnitudes of stars which make the maximum contribution to the star counts for a given disk subsystem is derived. In order to achieve the best agreement between the model and observations, we fit the values of the ‘dip’ (aw) of the disk luminosity function, the correction to the absolute magnitude of disk red giants (ΔM_V^RG) and the expression for interstellar extinction. As the main result, we obtained aw = 0.6 (logarithmic scale) and ΔM_V^RG = 0.5 mag; the interstellar extinction has to be taken into account by the modified Sandage law.     

A galactic model with a pulsating active nucleus

The chemical evolution of the Galaxy with a pulsating active nucleus is investigated. The surface densities of gas, stellar remnants, stars and chemical species such as helium and heavy elements inZ6 are calculated as functions of the position in the Galaxy and of the evolutional time of the Galaxy. According to this model, the entire luminosity of the galactic disk becomes almost constant at some 2×10⁹ yr after the galactic formation, but the nuclear bulge, whose dimensions gradually diminishes, becomes more and more luminous with time. On the other hand, the abundance depletion of helium and heavy elements appears in the inner region of the disk after some 6×10⁹ yr of the galactic formation. It also becomes clear that the activity for the nucleosynthesis in the nucleus is limited only in the early history of the Galaxy and has been reduced rapidly with time. Using this model, we can account for the observed phenomena such as the smooth dependence of the elemental abundance in the halo population on the distance from the galactic center, the high abundance of heavy elements in quasar spectra and etc.     

The evolution of hydrogen-helium stars

According to the work of Truran and Cameron, and of others, on the chemical evolution of the Galaxy, the first generation of stars in the Galaxy contained principally massive objects. If big-bang nucleosynthesis was responsible for the formation of helium, the first generation of stars would contain about 80% hydrogen and 20% helium, to be consistent with the approximately 22% helium found in recent stellar evolutionary studies of the Sun. The present investigation has followed the pre-main sequence evolution and the main sequence evolution of stars of 5, 10, 20, 30, 100, and 200M . Normal stars in this entire mass range normally convert hydrogen into helium by the CN-cycle on the main sequence. the present hydrogen-helium stars of 5 and 10M must reach higher central temperatures in order to convert hydrogen to helium by the proton-proton chains. Consequently, the mean densities in the stars are greater, and the surface temperatures are higher than in normal stars. In the stars of 20M and larger, the proton-proton chains do not succed in supplying the necessary luminosity of the stars by the time the contraction has produced a central temperature near 10⁸K. At that point triple-alpha reactions generate small amounts of C¹², which then acts as a catalyst in the CN-cycle, the rate of which is then limited by the beta-decays occurring within the cycle. During the evolution of these more massive stars, the central temperature remains in the vicinity of 10⁸ K, and the surface temperature on the main sequence approaches 10⁵ K. The star of 200M becomes unstable against surface mass loss through radiation pressure in the later stages of its main sequence evolution, and these mass loss effects were not followed. Young galaxies containing these massive stars will have a very high luminosity, but if they have formed at one-tenth the present age of the universe or later, then the light from them will mainly reside in the visible or ultraviolet, rather than in the infrared as has been suggested by Partridge and Peebles.     

Structure of the expanding atmosphere of P Cygni

With the aid of the spectra taken in the years 1959–1968, a physical analysis of the atmosphere of P Cygni has been carried out and the motions of the atmosphere have been studied. The variations of radial velocities, the velocity progressions of Balmer and Hei lines, the high rate of mass loss (2×10^–5 M yr^–1), the features of the observed line profiles, especially that of H-K lines of Caii andD ₁-D ₂ lines of Nai confirm the conclusion of Van Blerkom (1978), concerning the assumption of an accelerating atmosphere for P Cygni. The electron density variation with the radius seems to ben _e r ^–5/2, with an average value of 7×10¹¹cm^–3 at the lower boundary of the atmosphere.In order to explain the two absorption components of observed lines, an atmospheric model based on the assumption of three envelopes, two of which accelerate gradually with two different velocity laws (up to 11.2r _c ), and the third of which accelerates rapidly with a standard velocity law (beyond 11.2r _c ) has been developed. From this model and the observed profiles, the geometrical thicknesses of the line-forming regions of H, H, H, and H are derived.The observations were obtained at Haute Provence Observatory (CNRS).     

Origin of low energy cosmic ray positrons at energies ≳2 MeV

It is shown that an appreciable flux of positrons below a few MeV in the cosmic radiation could arise from the decay of cobalt nuclei in the decay chain⁵⁶Ni⁵⁶Co⁵⁶Fe, which occurs in the silicon burning shells of supernovae just after their ejection at relativistic velocities. The equilibrium spectrum of positrons in the interstellar space has been calculated on the assumption that the observed abundance of iron nuclei in the cosmic radiation is the result of the above process. It is found that the observation below about 10 MeV can be well explained with a moderate acceleration of the positrons in the expanding envelope of supernovae prior to their propagation in the interstellar space. The total⁵⁶Ni content in the shells of supernova necessary to account for the observed positrons is in agreement with that required to explain the peak luminosity during the supernova outburst. Since this model deals with positrons created at the time of injection of cosmic rays into the interstellar space, it becomes possible to study the shape of the injection spectrum of cosmic rays.On leave from Tata Institute of Fundamental Research, Bombay, India.