bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rr Lyrae Variable Stars
Authors: Romanov Yu. S. , Tsesevich V. P. , Zaikova L. P. , Firmanyuk B. N. , Udovichenko S. N. , Fenina Z. N. , Shakun L. I. 
Published: March 2016

Some twenty years have passed since the decision was taken by the General Assembly of IAU in 1958 to resume a regular control of light variation stability in RR Lyrae stars. With this end in view the revision of elements is carried out at the Odessa Astronomical Observatory yearly, whereas ephemerides of RR Lyrae stars are published at the Krakov Observatory. Now 164 stars brighter than at maximum light visible in the northern hemisphere have entered the list.Considerable photometric observational material analyzed has shown that some RR Lyrae stars have stable periods of light variation (e.g. TV Lib, UY Cyg, SU Dra), while other ones have periods which vary regularly or proportionally to time (e.g. SV Eri, AV Peg, RV CrB) (Tsesevich, 1966; Firmanyuk, 1976; Romanov et al., 1978). In case of DR And at comparatively small amplitude of O-C variation, about 0.15, a synchronous variation in mean light at maximum nearly by has been found (Romanov, 1978). Unfortunately, necessary observational material is frequently unavailable to obtain the unambiguous classification of period stability character. The property of RR Lyrae stars light variation stability is connected with the weakening of KCall absorption line (Tsesevich, 1966, 1971).
Non-Radial Oscillations in Red Giants
Authors: Keeley Douglas 
Published: March 2016

The structure of red giant stars allows non-radial oscillation modes which propagate as p-modes near the surface, to propagate below the convection zone as g-modes with very high radial wave number [Dziembowski (1971, 1977), Shibahashi and Osaki (1976)]. Under some conditions the oscillations in these two propagation regions can be treated as virtually independent normal modes [Shibahashi and Osaki (1976)]. This paper examines the situation in which this approximation is not good, and discusses possible observational consequences of the interaction of the two propagation regions.The linearized differential equations describing non-radial adiabatic oscillations in stars can be written in the form,
1a1b
Mass Loss and Stellar Wind in Massive X-Ray Binaries
Authors: Henrichs H. F. 
Published: March 2016

A number of massive stars of early type is found in X-ray binary systems. The catalog of Bradt et al. (1979) contains 21 sources optically identified with massive stars ranging in spectral type from 06 to B5 out of which 13 are (nearly) unevolved stars and 8 are supergiants. Single stars of this type generally show moderate to strong stellar winds. The X-rays in these binaries originate from accretion onto a compact companion (we restrict the discussion to this type of X-rays).We consider the compact star as a probe traveling through the stellar wind. This probe enables us to derive useful information about the mass outflow of massive stars.After presenting the basic data we derive an upper limit to mass loss rates of unevolved early type stars by studying X-ray pulsars. Next we consider theoretical predictions concerning the influence of X-rays on the stellar wind and compare these with the observations. Finally, using new data from IUE, we draw some conclusions about mass loss rates and velocity laws as derived from X-ray binaries.
X-Ray Studies of Quasars and Active Galaxies with the Einstein Observatory
Authors: Ku William H.-M. 
Published: March 2016

The launch of the Einstein Observatory has added a new and exciting dimension to the study of active galaxies. Not only have a large number of optical and radio active galaxies been detected, but many new examples of high energy activity have been found. The ease with which a large number of quasars may now be studied in the X-ray regime out to a redshift of at least four promises to improve our understanding of the nature of these tremendous powerhouses and the evolution of the universe.The Columbia Astrophysics Laboratory (CAL) is carrying out an extensive program to study active galaxies with the imaging proportional counter (IPC) on board the Einstein Observatory (Giacconi et al. 1979). These observations have already yielded a large number of positive detections including four Seyferts, five N galaxies, seven BL Lacs, and 17 quasars. Upper limits were obtained for eight additional quasars. Six new Seyfert I and/or quasars have been identified from X-ray observations (Chanan 1979). Preliminary results from the first six months of the CAL survey of active galaxies will be presented below. A few representative objects of interest will be discussed briefly. Simple statistical tests will be applied to determine whether X-ray properties can be used to understand the differences and similarities between the various classes of active galaxies. Particular emphasis will be placed on the quasars in our sample. Our results for the quasar survey will be compared with those discussed by Tananbaum et al. (1979). Finally, the implications of the discovery of a large number of quasars will be briefly discussed. (Cosmological parameters of qo = 0 and Ho = 50 km (s Mpc)-1 are used throughout.)
Constraint on Quasar Number Counts from Their Contribution to The X-Ray Background
Authors: Henry J. P. , Soltan A. , Tananbaum H. , Zamorani G. 
Published: March 2016

AbstractObservations with the Einstein X-ray telescope show that quasars, as a class, are luminous X-ray emitters. By coupling our X-ray observations with quasar optical number counts, we can show that the quasars contribute significantly to the diffuse X-ray background. In fact, the X-ray data strongly suggest that somewhat above 20m the slope of the optical counts must flatten.
Red Giants in Globular Clusters and Large-Scale Variations in The Galaxy
Authors: Pagel B. E. J. 
Published: March 2016

SummaryThis review concerns recent work on the determination of overall metallicities [Fe/H] in a number of globular clusters and the systematics of mixing effects displayed (usually) by weak CH and strong CN. Special attention is given to the globular cluster ω Centauri, where both metal abundance variations and mixing effects occur and are closely intertwined. Recent observations carried out at the Anglo-Australian Telescope by E.A. Mallia and D.C. Watts have revealed large variations in the strength of metallic lines across the red giant branch of this cluster.
Mass Transfer between Binary Stars
Authors: Modisette Jerry L. 
Published: March 2016

The transfer of mass from one component of a binary system to its companion can involve ejection of the mass by radiation pressure, by Roche lobe overflow, by centrifugal action through the coupling of the upper atmosphere to the stellar rotation through magnetic fields, and by the dynamics of the atmospheric fluid under the action of an energy source at the photosphere or lower chromosphere. I will primarily address the latter mechanism, which commonly goes under the title of stellar winds. The major determinant of a stellar wind is the energy source. In the case of a binary system, the dynamic effects of the system on the flow pattern, particularly for close binaries, is a second major determinant, once an energy source is available to drive the wind.In addition to ejection, the transfer of mass requires capture of the ejected matter by the companion. The first issue is free particle vs. continuum flow. I will only consider continuum flow, as I doubt the applicability of the free particle concept to any binary system with significant mass transfer, because of the scale height and because of the likely presence of magnetic fields in the interstellar plasma. For more distant binaries, rather simple considerations show that the capture of matter for continuum flow can be enhanced over that for free particle flow.
Astronomy in Ancient Greece
Authors: Hoskin Michael 
Published: March 2016

AbstractScience has spread from western Europe where it developed into recognisably-modern form in the seventeenth century, stimulated by Copernicus’s claim that the Earth is a planet. Copernicus however was an astronomer in the Greek tradition, whose task was to reproduce the planetary paths by geometrical constructions using uniform circular motions. Eudoxus’s attempt to do this with nests of concentric spheres had been superseded by the use of the more flexible techniques necessary to meet the observational standards of the Hellenistic era. Ptolemy’s Almagest synthesised the Greek achievement but its shortcomings led Copernicus to make the Earth a planet.
Modern Cosmology
Authors: Zeldovich Ya. B. 
Published: March 2016

It is a qreat honour to pronounce this lecture before the General Assemhly of United astronomers of all the world.In fact, the astronomers are really more united, than the representatives of manv other sciences. Perhaps this unity is connected with the noble spirit of inquiry into the immense distant worlds, characteristic for astronomers. And of all the problems and all the systems investigated the biagest one is surely the Universe as a whole i.e. the tonic of cosmoloay.This branch of astronomy is the greatest challenge, one is always confronted with the danaer of being captured by prejudices.In the last decades the situation chanaed. At least cosmology has transformed into a respectable science, which it was not say 50 or 60 years ago.There remain deep unsolved questions beginning with the very existence and/or birth of the Universe.But there are also in modern Cosmology definite successes, there are achievements in the understanding of the Universe. The successes are due to the work of many people, they are due to an international collective effort.In a talk in the Odeon, an ancient theatre of Patrai, Greece and also in this high-light paper it seems me unappropriate to give precise citations and to divide priorities. Therefore no names will be called except a handful of great men gone of us - Einstein, Rubble, Friedmann, Jeans, Planck.
Chemical Composition of Halo Field Stars and the Chemical Evolution of the Halo
Authors: Spite Francois 
Published: March 2016

The abundance of the elements in the halo are mostly known from analysis of stellar atmospheres. Data from evolved stars and planetary nebulae have to be used with some caution. I will therefore rely primarily on unevolved cool dwarfs, using other information only as a complement.I will designate these unevolved cool dwarfs indifferently by the words halo dwarfs or Population II dwarfs; such stars were formerly often called subdwarfs for historical reasons. Remaining in the field of vocabulary, I will call underdeficient an element which is deficient, but by a factor smaller than the general deficiency factor for the other elements. Finally, let us recall the classical notation:
The Stellar Content of Elliptical Nuclei
Authors: Faber S. M. 
Published: March 2016

AbstractNew developments in understanding the stellar populations of elliptical nuclei are discussed. Variations in iron-peak spectral features have recently been detected, which are much smaller than changes in CN, Mg, and Na. A study is presently in progress to determine whether this pattern is consistent with lockstep enhancements in all heavy elements. Present evidence on the ultraviolet spectra of ellipticals now suggests that the source of the excess UV light is not young OB stars. A new correlation is also pointed out between UV excess and mean line strength. If real, this trend is further evidence against significant numbers of young OB stars in elliptical galaxies.
Summary
Authors: Freeman Kenneth C. 
Published: March 2016

The old populations of galaxies are particularly vital for understanding the formation and chemical evolution of galaxies. As in any field, ideas come and go, and today’s discussion has given us a valuable assessment of current knowledge and thinking on many topics.The problems of star formation and the IMF are basic to many aspects of work on old populations. The discussion included some interesting ideas on star formation, and a useful warning that there are probably different modes of star formation which may give different IMFs: for example the mode of star formation that is widely studied now (in spiral arms) is probably different to the mode of star formation that was active in forming the stars of the galactic bulge.
The Value of Ho
Authors: Tammann G. A. , Sandage A. 
Published: March 2016

AbstractA brief discussion of the systematic effects of selection bias on the extragalactic distance scale is given. Distance indicators with intrinsic scatter yield only upper limits to Ho, unless the true intrinsic scatter is either small or well determined. Several distance indicators (luminosity index, diameters, globular clusters, 21 cm line widths) are discussed. It is concluded that type I supernovae, calibrated through brightest M supergiants, yield presently the most reliable determination of the large-scale value of the Hubble constant, i.e. Ho(cosmic) = 50 ± 7 km s–1 Mpc–1.
Some Considerations Relating to an Interstellar Origin for Comets
Authors: Clube S.V.M. , Napier W.M. 
Published: March 2016

The idea that the Solar System possesses a primordial isotropic cloud of comets has been with us in quantitative form for about thirty years (Oort 1950). A considerable edifice has been built on this proposition (e.g. Weissmann 1982), which has proved durable despite indications that the cloud may in fact be significantly non-thermal and display Galactic alignments (Tyror 1957, Richter 1963, Oja 1975, Yabushita et al. 1979, Radzievsky 1981). However with the discovery in recent years of a system of massive molecular clouds in the Galactic disc, it has become apparent that the environment in which the Oort cloud has to survive is very different from that envisaged in 1950; a re-appraisal of the standard picture is therefore called for.One corollary of the discovery of the molecular clouds is that the traditional objections to an interstellar comet cosmogony, such as the lack of observed hyperbolic comets and the difficulty of growing and capturing them, may no longer apply (see for example the recent review by Clube & Napier 1982a, hereinafter CN). Another consequence, reviewed here, is that tidal effects due to molecular clouds may be so large that the Oort cloud is frequently disrupted (CN; Napier & Staniucha 1982). In this situation frequent replenishment is implied and it is therefore necessary to discriminate between the primordial and the observed Oort cloud and to consider possible alternative sources for the latter. Such an enquiry would provide constraints on the as yet unsolved problem of comet formation.
Active Nuclei and Redshift Problems
Authors: Burbidge Geoffrey 
Published: March 2016

More than 20 years ago V. A. Ambartsumian proposed that much of the activity in galaxies was dominated and even generated by their nuclei. Subsequent observational work in radio, optical and x-ray frequencies has borne out his prophecy, and major interest has centered about the nature of the machine in the galactic nucleus. The major characteristic of this machine is that it releases energy rapidly and often spasmodically by processes which are not thermonuclear in origin.The original studies which led to the conclusion that nuclei were all important were observations of the powerful radio sources and Seyfert galaxies, and evidence for the ejection of gas from galaxies of many types. The realization that the synchrotron mechanism was the dominant radiation mechanism and the later studies of Compton radiation were fundamental in leading to the conclusion that large fluxes of relativistic particles must be generated in galactic nuclei.
Stellar Winds and the Interstellar Medium
Authors: McCray Richard 
Published: March 2016

AbstractTheoretical models for the interaction of stellar winds and the interstellar medium are described. Stellar wind energy sources are listed, and observations of expanding shells around stars and star clusters are reviewed. Giant expanding shells, or “superbubbles,” with radius > 100 pc, are formed by the combined action of stellar winds and supernovae from clusters of OB stars. Smaller expanding shells around Wolf-Rayet stars are probably formed by the interaction of the WR stellar wind with matter ejected in a previous red supergiant phase of stellar evolution. Stellar wind activity is evident in regions of star formation in dense molecular clouds.
Optical Giant and Supergiant Interstellar Shells
Authors: Meaburn John 
Published: March 2016

AbstractGiant (20 – 260 pc) and supergiant (600 – 1400 pc) filamentary ionized shells are found in several galaxies. Some giant shells are collisionally ionized supernova remnants but many surround ≃ 5 – 50 OB stars and, if approximately spherical, could be formed by the combined effects of successive, 1050 erg, supernova explosions, pressure of the Lyman photons and stellar winds. Other mechanisms are required for their supergiant counterparts for perhaps they are toroidal rings rather than radially expanding spherical shells.
Hydrodynamic Models of the Cometary Atmosphere
Authors: Mendis D. A. 
Published: March 2016

As a cometary nucleus, regarded as an admixture of ices and dust (Whipple, 1950), approaches the sun, the ices sublimate and the resulting gases freely expand dragging along some of the dust.For a typical medium bright comet (e.g., P/Halley) at 1 AU, the cometary atmosphere is collision dominated within a radius Rc, within which the collision mean free path is equal to the radial distance itself. Within this radius, the cometary atmosphere may be considered as a continuum, and described by hydrodynamic equations. Admittedly, this definition of the regime of hydrodynamic flow is rather crude, and what one has is a gradual transition from pure hydrodynamic flow when r << Rc to slip and transitional flow when r ≈ Rc, to free molecular flow when r > Rc. Depending on whether one considers neutral-neutral collisions or neutral-ion collisions Rc ~ 5 × 103 – 104 km for a medium bright comet at a heliocentric distance of 1 AU.
Review of Spectroscopic & Spatial Observations of Cometary Comae
Authors: Barker Edwin S. 
Published: March 2016

During the past few years the field of comet spectroscopy has greatly expanded with observations of comets having nuclear magnitudes in the range of 10-19th magnitude. Although the total integrated magnitudes of several of the comets were brighter than 10th magnitude, the surface brightness of the coma of a comet is low and, with few exceptions, the night sky line at 5577A is brighter than any cometary emission line. The observational programs on which I will concentrate had their start under the P/Tempel 2 and P/Encke observing programs set up by R. Newburn at JPL.Fortunately, the groups listed in Table 1 are regularly scheduled on large telescopes to observe comets. The regularly scheduled telescope time has enabled these groups to study systematically the activity of the available comets brighter than 20th magnitude. Observations have been made with respect to heliocentric distance and distance from the nucleus. The goal of the systematic study of comets is to acquire a uniform data set on comets. The great variety of comet spectra in the past did not provide a useful data base for statistical studies. These older observations ranged from high resolution spectra of brighter comets, to sporadic medium and low resolution spectra and filter photometry of the 10th magnitude comets, to nonexistent spectra of fainter comets.
Needs for Atomic Data for Quantitative Analysis of Stellar Spectra
Authors: Baschek B. 
Published: March 2016

The goal of a quantitative analysis of a stellar spectrum is to derive the physical and chemical state of the stellar atmosphere, i.e. by definition the region emitting the spectrum. Of particular interest are the element abundances, they have to be determined together with the temperatures and densities (pressures) in the atmosphere. A detailed analysis usually is an iterative procedure: a model atmosphere is constructed from reasonable starting values of the parameters (effective temperature, surface gravity, element abundances,...) and used to calculate a theoretical, “synthetic” spectrum. By comparing the observed with the theoretical spectrum, improved stellar parameters are gained for the next iteration step.Ideally, all atomic data entering the analysis should be known with sufficient accuracy, i.e. errors in the analysis should be due to uncertainties in the assumptions of the models, in the treatment of the velocity fields etc., and not due to insufficient atomic data. In the last decade, the ultraviolet portion of the spectrum below λ ≲ 3200 Å has become accessible by satellites such as Copernicus and the International Ultraviolet Explorer (IUE) with high spectral resolution. Studies of stellar spectra in this new range have revealed the needs for a large amount of atomic data required for the analyses.
Cross Sections and Line-Broadening
Authors: Dalgarno A. 
Published: March 2016

Stimulated mostly by the needs of the fusion energy programs, data centres have been established from which information can be obtained on photoionization and recombination processes, electron and ion Impact excitation, ionization and charge transfer cross sections and on electron and proton line-broadening parameters. Regular reports are issued by most of the centres. A partial list follows:(1)Atomic Data for Fusion, Ed. C.F. Barnett, D.H. Crandall and W.L. Wiese: Oak Ridge National Laboratory, P.O. Box X, Bldg, 6003, Oak Ridge, Tenn. 7830, USA.(2)International Bulletin on Atomic and Molecular Data for Fusion, Ed. K. Katsonls: Atomic and Molecular Data Unit, Nuclear Data Section, International Atomic Energy Agency, Wagramerstrasse 5, P.O. Box 100, A-1400 Vienna, Austria.(3)Research Information Center, Institute of Plasma Physics, Nagoya University, Nagoya, Japan, Ed. Y. Itikawa.(4)JAERI Data Center, Division of Plasma Physics, JAERI, 319-11, Tokai-Mura, Japan. K. Ozawa.In addition, Daresbury Laboratory, Science and Engineering Research Council, Daresbury, Warrington WA4 4AD, England, Eds., W. Eissner and C.J. Noble, publishes an Information Quarterly for Atomic Processes and Applications, which reports continuing developments particularly on calculations of electron impact cross sections.
Some Atomic Parameters Pertinent to Studies of Nebular Ionized Plasmas
Authors: Aller Lawrence H. 
Published: March 2016

In order to predict emission line and continuum intensities and assess plasma diagnostics for gaseous nebulae, it is necessary to have accurate atomic parameters. In some Instances the requirements for accuracy are very severe. A variety of data is required:1)Coefficients of continuous absorption;2)Direct and dielectronic recombination coefficients;3)Transition probabilities for permitted lines, so we can accurately predict both recombination line intensities and fluorescent phenomena (e.g., OI λ8446);4)Transition probabilities for forbidden and intercombination lines;5)Collision cross sections for levels which give rise to:
a)resonance transitions,b)intercombination lines,c)forbidden lines;6)Charge-exchange cross sections.
Determination of Precession and Nutation from Lunar Laser Ranging Analysis
Authors: Williams J.G. , Newhall X.X. , Dickey J. O. 
Published: March 2016

AbstractFrom the analysis of 24 yr of lunar laser ranges, the correction to the IAU luni-solar precession constant is found to be −3.2 ± 0.3 mas/yr for a total value of 50.3846˝/yr at J2000. The size of the 18.6 yr nutation of the pole needs to be increased by about 2 mas over the 1980 IAU theory.