bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Cosmic Background Radiation: Some Recent Developments
Authors: Rees M. J. 
Published: March 2016

Diffuse background radiation has been detected over 16 decades of frequency - from a few MHz up to ~3 × 1016 MHz (100 MeV) - and there are upper limits over an even wider range. Generally an important contribution comes from the galactic disc, but in some wavebands it has proved possible to isolate a truly cosmic isotropic component originating beyond our own Galaxy. A simple Olbers-type argument shows that the bulk of any extragalactic radiation field originates at cosmological distances. This is true whether the radiation is emitted by discrete sources, or comes from extragalactic (or pregalactic) space. Thus studies of the isotropie background radiation, or even upper limits to its intensity, yield data that are vital for cosmology, as well as telling us something about the properties of diffuse intergalactic matter, and about intrinsically faint extragalactic objects which cannot be observed individually.In this talk I shall not attempt a systematic review of this extensive subject, but will merely discuss a few recent developments. I shall give special attention to the microwave and X-ray regions of the spectrum, as these are the two bands in which the cosmic background is so strong that it swamps the emission from the Galaxy.
Optical and Radio Information
Authors: Johnson Hugh M. 
Published: March 2016

The six or eight optically identified X-ray sources comprise starlike objects and extended supernova remnants in the Galaxy, well as as a radio galaxy and a quasar. Both X-ray and radiofrequency radiation penetrate the entire galactic plane, but only two or three galactic radio sources have been identified with X-ray sources. This has led Hayakawa et al. to postulate that detectable X-ray sources are not farther than 1 kpc. However, other studies suggest that there is a cluster of a few intrinsically bright sources actually near the galactic nucleus and a scattering of weaker sources near the sun.The distances of X-ray sources can be estimated from extinction by interstellar gas or intergalactic gas on spectra above 10 Å, but the method ultimately depends on the radio and optical data of the gas. Conversely, interstellar densities of certain elements with large photo-ionization cross-sections may be determined from the absorption of X-rays, after calibration of source distances by the methods of optical astronomy.
The Formation of Li, Be, B Isotopes by the Spallation of CNO
Authors: Gradsztajn E. 
Published: March 2016

In 1955 Fowler et al. (1955) suggested that the elements Li, Be and B could be produced at the surface of some stars by the spallation of CNO induced by electromagnetically accelerated particles.Since that time many observational data were gathered, not only on the lithium elemental abundance (Hunger, 1957; Bonsack and Greenstein, 1960), but also concerning the isotopic ratio 7Li/6Li (Herbig, 1964; Wallerstein, 1965). Then, the abundance of beryllium in many stars was measured (Bonsack, 1960; Conti and Danziger, 1966; Merchant, 1966) and the problem was, and still is to explain both 7Li/6Li and Li/Be ratios. In addition to spallation, different possibilities may be invoked, such as the inheritance from galactic gas enriched with matter remaining from a previous generation of stars, or from the big bang; but which can be checked most easily at the present time is the spallation assumption. Indeed, simultaneously with the development of the observations on stars, a program for measuring and calculating the production rates of the light elements has been in progress at Orsay. In 1960 the first experimental result concerning the production of 6Li in 16O by 156 MeV protons was obtained. But it was only in 1965 that the number of experimental and theoretical data on spallation was sufficient to make a valid comparison with abundances observed on the stars as well as in the solar system or in cosmic rays.
Investigation of Possible Abundance Anomalies in Close Binaries of Spectral Types A0-A2 & F5-F6
Authors: Kondo Yoji 
Published: March 2016

This investigation was originally conceived as a follow-up on a work by Abt (1965), in which he finds the close binaries, with periods of about 1–100 days, and with spectral types of about A4-F2 (IV-V), to be all Am stars. The stars to be observed were chosen from the ‘Fifth Catalogue of the Orbital Elements of Spectroscopic Binary Stars’ (Moore and Neubauer, 1948). The criteria in making the selection were that the spectral types are A0-A2 and F5-F6 (IV-V) and that the periods are between about 1–100 days.Spectra of 11 binary systems were obtained at the Coude focus of the 84-inch reflector of the Kitt Peak National Observatory during three nights in May 1967. In addition to the binary stars, 5 standard spectrum stars, i.e. α Lyr (A0V), θ Leo (A2V), σ Boo (F2 V), ι Peg (F5 V) and 110 Her (F6 V), were observed to provide comparisons. The dispersion used was 13·5 Å/mm. Typically 2 or 3 spectra were obtained for each object. A spot densitometer was employed to furnish calibrations for the plates.
The Next Decade in Stellar Atmospheres Theory
Authors: Delache P. 
Published: March 2016

It is a pity for all of us that Dimitri Mihalas was unable to come to Sydney, and I wish, in the first place, to thank him for suggesting this discussion, devoted to a prospective study of our research field. There falls to me the task of trying to sketch what might be the axis of progress in stellar atmosphere theory. This subject is preeminently one which belongs to D. Mihalas; I am afraid that we are going to miss him now more than ever. Furthermore, I feel myself in a bad position for talking on such a large subject, in front of specialists, while I know so little on it. However, I have accepted the task, at the request of the President of Commission 36, with the goal of giving some physical considerations that may initiate reflections and discussions.I am not going, in principle, to give a set of topics whose study should be desirable, or possible, arranged according to the internal logic of a specialist of stellar atmospheres, neither shall I look for bibliographical signs allowing the prediction of active zones or flares in our next cycle of activity!
The Space Density of Faint M-Dwarfs
Authors: Oort J. H. 
Published: March 2016

Donna Weistrop, a student of Maarten Schmidt’s, has found evidence for an unexpectedly high space density of very faint M-dwarfs. This was confirmed by Murray and Sanduleak. The space density inferred from these investigations is comparable to, or possibly higher than, the local gas density. Because there is evidence that the stars concerned are young this appears to present a problem.As the investigation by Murray and Sanduleak is the simpler and more direct of the two I confine my discussion to this. The authors determined proper motions for 21 M dwarfs down to 17m found in an objective-prism survey at the Warner and Swasey Observatory in regions close to the North Galactic Pole. The distance of the stars can be inferred from the reflection of the solar motion. Assuming the ‘basic’ solar motion they found and a space density of 0.23 pc-3 for these stars, corresponding with a mass density of about 0.04 M⊚ pc-3. This is exceedingly high, in view of the fact that the average gas density near z = 0 is only 0.03 M⊚ pc-3. The problem is aggravated by the fact that the stars have low velocities, the dispersion in velocity in one coordinate coming out ± 10kms-1. This is considerably lower than the velocity dispersion of A-type stars, and shows that the stars are young, perhaps about 108 yr. How is it then that the gas has not been completely used up long ago?
Evidence for Lunar-Type Objects in the Early Solar System
Authors: Urey H. C. 
Published: March 2016

Objects of the solar system, in addition to the Sun, can be classified into four groups -the planets, objects of lunar mass, smaller objects of variable mass and the comets.If the solar proportion of gases relative to non-volatile compounds of the variety in the terrestrial planets, namely about 300 times the mass of these elements, were added to the terrestrial planets, they would have masses comparable to those of the major planets. Mercury is low in mass but has a high density, indicating that it has lost several times its mass of silicate materials relative to high density metallic iron. If this were restored and then the component of gases were added, it would also fall into the group rather naturally. Mars appears to be rather small. Uranus and Neptune have rather high densities indicating some loss of gases, probably hydrogen and helium. When we attempt to estimate the mass of primitive solar material from which the planets were evolved, we conclude that they evolved from very similar masses. Later, I shall argue that the process was a very inefficient one.
Soft X-Ray Observations of Supernova Remnants
Authors: Zarnecki J. C. , Culhane J. L. , Fabian A. C. , Rapley C. G. , Boyd R.L.F. , Parkinson J. H. , Silk R. 
Published: March 2016

AbstractObservations of a number of supernova remnants have been carried out with the low energy X-ray telescope on the Copernicus satellite. Data are presented on the X-ray structure of the remnants Cassiopeia A and Puppis-A. Marginal detections or new upper limits are reported for the remnants IC443, DR4, MSH15-52A, Downes 83, Downes 84 and 3C392.
L’astronomie Infrarouge et les Poussieres Galactiques.
Authors: Pecker Jean-Claude 
Published: March 2016

AbstractThe existence, in the Galaxy, of small absorbing dust grains has been known for a long time, as they redden the light of stars located behind them, and obscure by amounts which can often even be several magnitudes… In the infrared, where absorption is smaller, one can see through the dust, while at the same time, one can observe the emission of cold dust clouds. After a brief review of technical developments, the reasons for studying the infrared, and the principles of diagnostics, are given. The analysis of the spectral features leads to identification of ice, graphite, and various silicates, as main constituents of the dust. In the fifth section, examples are given of the various sources that one meets when travelling in the Galaxy: protostars, cold and dilute, dense envelopes of young stars (cold or hot), dilute envelopes of not so young stars, and ejected clouds surrounding evolved objects… The simultaneous observation of dust, molecules and atoms, in the same regions, shows that the knowledge of the circumstellar dense regions might be of a great interest, in the study of the origin of life, and of the evolution of the Universe.
Parallaxes of Selected Stars Near the North Galactic Pole
Authors: Strand K. Aa. , Dahn C. C. , Harrington R. S. 
Published: March 2016

As a contribution toward settling the question of the distances of Murray-Sanduleak (M-S) stars (Murray and Sanduleak, 1972), two of these stars were added to the U. S. Naval Observatory (USNO) program in 1973. After the initial plates had been taken, it appeared that parallax for an additional star could be measured on one series, while parallaxes for two additional stars were possible from the second. As a result provisional parallaxes are now available, Table I.In terms of USNO parallaxes, these are considered provisional because they are based on half the number of plates on which the final parallaxes are ordinarily determined; only small changes are expected when additional material is added beyond the present.
Swedish Programmes Concerning the Z Distribution of Stars
Authors: Oja Tarmo 
Published: March 2016

Swedish investigations on stellar space distribution generally are based on the Uppsala - Stockholm spectral classification system. In this system the properties of the stars are derived from objective prism spectra by means of narrow-band photometry. The main criteria are the hydrogen-line intensities, the intensity of the K line, the intensity of the G band, the break at the G band, and the intensity of the blue cyanogen band (for a description of the system see e.g. Ljunggren and Oja, 1961), when possible supplemented by a measure of the Balmer discontinuity (Rydström, 1976). The method yields absolute magnitudes with a dispersion of about and intrinsic colours (B-V)° with a mean error below for most kinds of stars.Three investigations are relevant to the subject of this Joint Discussion.
The Heterogeneity of Surfaces of Magnetic AP Stars
Authors: Hack M. 
Published: March 2016

AbstractThe observations of spectrum-variability and light-variability of Ap stars are reviewed. It is shown that these variations are interpretable as due to the changing aspect of the spotted surface as the star rotates. It is stressed that we understand fairly well the geometry of the phenomenon but the physics is very far from being understood.Magnetic Ap stars are probably those where the presence of a spotted surface is very evident. Their spectrum-variability (profiles, line-intensity and radial velocity), light-variability and magnetic field variability, all occurring with the same period, are explained in a simple way if we assume that these variations are due to the changing aspect of the spotted surface as the star rotates. The oblique rotator model was proposed by Babcock in 1949 and by Stibbs in 1950 and was worked out in great detail by Deutsch (1954). This model allows us to explain the magnetic field variation from some + 1000 to some - 1000 gauss in a few days; it explains the crossover effect, the line-width versus period relations, the line - intensity and radial velocity variation, and in part also the light curves. The main objection against the oblique rotator hypothesis was the supposed existence of many irregularly variable magnetic stars. However, the large number of observations accumulated in the last twenty years indicates that probably all magnetic Ap spectrum-variables are regular variables with periods which are generally of a few days, but includes a small group of long period variables (100 days up to 23 years for HD 9996). The light variability, which is the quantity measurable with the highest precision, has often remained undetected, because the amplitude is always small, in many cases few hundreths of magnitude.
Optical Spectra of Nuclei of Early Type Galaxies
Authors: Schnur Gerhard F. O. , Sherwood W. A. 
Published: March 2016

Early type galaxies classified as SO by Sandage or lenticulars and SO/a appearing in RCBG have been observed with the IDS on the ESO 3.6 m telescope. The slit was 1” × 4” and the spectral resolution was 9 Å from 3900 Å to 7000 Å. Statistics for the first 50 galaxies observed are given.18% of the sample show the [OIII] doublet stronger than Hß; 32% have spectra dominated by the Balmer series progressing from mainly emission through strong absorption series to weak absorption; 20% have only [NII] or [SII] in emission while 30% show absorption lines and bands. That is, 70% show emission lines toward the nuclear region. Among the 50 galaxies, HI at 21 cm has been detected in 21 galaxies: 16 of these show ionized gas to be present. NGC5273 has Seyfert characteristics with strong [OIII]; Hß has a width of ˜1000 kms-1. The low luminosity end of the Seyfert distribution may be found among normal galaxies.
Models of the Interstellar Medium
Authors: de Jong Teije 
Published: March 2016

AbstractUp-to-date models of the interstellar medium should account for the existence of at least three phases of the interstellar gas, a hot phase at ˜ 106 K (HICM), a warm phase at ˜ 104 K (WICM) and a cold phase at ≤ 102 K (clouds). Recent observations of interstellar absorption lines are used to derive information about the physical properties and the spatial distribution of these phases. Evidence based on observations of C+ absorption lines indicates that the photoelectric threshold of interstellar dust grains is about 6 eV, much lower than previously thought. If the photoelectric threshold is indeed of this magnitude the WICM can easily be heated to temperatures in the range 6000 to 8000 K by photons of the general interstellar radiation field with λ > 912 Å. The analysis of interstellar CH+ and 0 VI absorption lines suggests that these lines are formed in gas associated with clouds in regions of enhanced pressure that occupy about 10 percent of interstellar space (SN cavities). The CH+ lines are formed in compressed WICM shells around clouds and the 0 VI lines in conductive interfaces between the WICM and the HICM. The velocity characteristics of the observed lines make shock waves a less probable source of the absorbing gases.
Observations of Seyfert Galaxies with the International Ultraviolet Explorer
Authors: Ulrich Marie-Hélène 
Published: March 2016

AbstractThe most important observations of Seyfert nuclei to be done in the ultraviolet are 1) the determination of the non-stellar continuum energy distribution and 2) the measurements of the intensities of the permitted lines. The main results obtained so far with IUE on these two points are as follows.The Lyman/Balmer intensity ratio is smaller than predicted by the recombination theory. It cannot be forced into agreement with recombination theory by applying the reddening correction relevant to the narrow line region nor to the continuum. This Lyman/Balmer ratio is therefore caused by the particular physical conditions prevailing in the broad-line region. The smallness of the Lyman/Balmer ratio and the non-detection of the resonance lines of Fell neither in emission nor in absorption show that collisional processes play a dominant role in the excitation of the lines in the broad-line region and that the density in this region is at least 3 × 1010 cm-3.
Plasma Energetics in Solar Flares
Authors: Van Hoven Gerard 
Published: March 2016

I want to begin with the observation, which I will try to make clear in the following, that a solar flare comprises an incredibly complex set of phenomena. This is not only true with respect to what is seen and measured in spectacular examples, but also when one considers the constituent parts of simple, even idealized, cases. A series of different physical effects lead, as one illustration, to radiations from the flare-instability site and its surroundings which span the range from meter waves to gamma rays (Svestka 1976, Sturrock 1979).To fit within the context of this discussion, I will concentrate on the high-temperature and quasi-thermal aspects of a flare, and on the basic physical mechanisms connected with the primary energization and dissipation processes. Thus, I will treat the reconnection of the magnetic field, the bulk acceleration of particles, the thermalization and the ultimate radiation of the energy. I will not treat the optical manifestations or, at the other extreme, the acceleration of very high energy particles.
Hot Plasmas in Supernova Remnants
Authors: Kahn F. D. 
Published: March 2016

Supernovae occur in highly evolved, massive stars and typically release 1051 to 1052 erg. Their light curves show that the stellar radius is about one A.U. at the time of the explosion. The typical energy density in the star is about 1011 or 1012erg cm-3 when the blast reaches the stellar surface. Much of the energy is present in thermal form. Since the density of the material is high, thermal equilibrium is attained rapidiy between the radiation field and the thermal motions. The temperature in the interior of the star becomes about 106K, and most of the energy is present in the form of radiation.At this time the star has a large optical depth, of order 107. Therefore the effective diffusion speed for radiation is very low, about 3000 cm s-1. But the effective sound speed is large, of order 109 cm s-1, and the large input of energy has destroyed the gravitational equilibrium. So the star begins violently to expand, and the pressure of the stored radiation field does work in producing mass motion of the material. Only a small fraction of the radiant energy is released from the exploded star. The photosphere, in this phase, lies in the region where the gas changes from being ionized to non-ionized, so that the photo-spheric temperature remains low, of order 104K. There is little chance of observing any high-temperature phenomena at this stage in the evolution of a supernova.
Recent Work on Beat Cepheids at Mount Stromlo Observatory
Authors: Barrell S. L. , Cogan B. C. , Faulkner D. J. , Shobbrook R. R. 
Published: March 2016

Beat Cepheids continue to pose a number of unanswered questions concerning the behaviour of stars near the short-period end of the Cepheid instability strip; in particular, why is it that such a high proportion of stars with fundamental period ≤ 5 days exhibit simultaneous pulsation in both the fundamental and first-overtone radial modes, and why is it that these stars exhibit such a narrow range of period ratio (P1/P0 ≃ 0.71)? A programme of observation and Fourier analysis of beat Cepheids is presently being undertaken at Mount Stromlo and Siding Spring in an effort to understand these phenomena.There is now evidence that, for the two best observed stars of this class - U TrA and TU Cas, both the period and the relative mode amplitudes are slowly changing with time. U TrA was observed in detail during the years 1953-59 by Oosterhoff (1957) and Jansen (1962), and a new series of 481 five colour observations of this star was obtained by Faulkner and Shobbrook (1979) in 1977. Using E = Σ(Amp × Freq)2 summed over all the Fourier terms for a given mode as a measure of the pulsational energy associated with that mode, we can use this 20 year timebase to calculate the change in relative mode energy. For U TrA the energy of the overtone is increasing (see Table I). Similarly we can compare the fundamental period derived for these 20 years with an earlier period estimate of Oosterhoff (1957) to obtain the rate of frequency change shown.
Observations of Three Radio Galaxies with The Einstein X-Ray Observatory
Authors: Feigelson E. D. , Schreier E. J. 
Published: March 2016

We would like to present early results from the EINSTEIN X-ray Observatory on three radio galaxies: Centaurus A, NGC 315 = DW0055+30, and Cygnus A = 3C405. We hope to demonstrate that imaging X-ray astronomy can provide important insights into the physics and environment of radio galaxies and their extended radio components.NGC 5128, the parent galaxy of the double-double radio source Centaurus A, is the nearest radio galaxy, providing the best testing ground for high resolution X-ray studies. The X-ray morphology has proved to be rich and varied. We detect four distinct components to the X-ray emission: (1) the strong, compact nucleus detected by earlier satellites; (2) extended emission around the nucleus; (3) emission from the inner radio lobes; and (4) a unique X-ray jet between the nucleus and the NE radio lobe. A detailed presentation of these observations can be found in Schreier et al. (1979).