bluuebunny/crossref_metadata_2025 huggingface dataset:
White Dwarfs in Close Binary Systems
Authors: Weigert Alfred
Published: March 2016

While it has not yet been possible to give a detailed step-by-step treatment of the evolution of a single star from the main sequence to the white-dwarf stage, such a treatment is available for close binary systems. It has been shown that by calculating the evolution including mass exchange in a system of main-sequence stars of small mass and relatively large separation, one can follow the system to its final stage of a white dwarf and a more massive main-sequence star. This type of evolution arises when the original primary has exhausted its central hydrogen content when mass exchange starts, and the mass of its helium core is small enough so that electron degeneracy prevents the ignition of helium.
The Need of Ground-Correlated High-Resolution Space Observations in the Visible
Authors: Kiepenheuer K.O.
Published: March 2016

Solar Research during the last decade has definitely shown that almost all primary processes which build up the chromosphere and the inner corona, as well as the observable basic events leading to the optical manifestation of solar activity occur practically all in the subtelescopic range, as far as ground-based observation is concerned. I think here mainly of the great variety of phenomena occurring in the intergranular space (width <0″.3) and intersupergranular space (width <1″). Because of this situation we have only very few reliable information about the structural transition between photosphere and chromosphere, how the granulation goes over into the complex chromospheric structures as bright and dark mottles, spicules, threads, loops, or fibrils. In this region theory can still get along without being disturbed too much by observation. The situation is somewhat like looking into a human face with a resolving power of 1 or 2 cm!
Asymmetry in Solar Spectral Lines
Authors: Magnan C. , Pecker J. C.
Published: March 2016

After reviewing observations of the spectral solar features originated either in the chromospheric layers or in the photospheric layers, from the point of view of the observations, and after having shown the strikingly discrepant set of interpretations that can be found currently in literature, a numerical experiment is performed in a case not too different from the solar case. It is shown that the use of the line bisector to determine, from the asymmetry of a single line, the trend of the velocity field might be considerably misleading, a fact which explains partly the results published in literature.
Optical Observations of X-Ray Binaries
Authors: Hutchings J.B.
Published: March 2016

Recent progress in identifying the optical counterparts of X-ray sources has been slow, mostly because candidates are faint and X-ray data show no periodicities by which the identification can be confirmed. This report therefore deals with the investigation of some candidates to seek confirmation of their identity with the X-ray emitters, as well as details which are new or important concerning the few known binary sources. I shall also make some general remarks on the properties of the sources as they now appear, but leave a critical assessment of the masses to the next speaker.
Lunar Magnetism
Authors: Runcorn S.K.
Published: March 2016

It was not generally anticipated by lunar scientists that the Moon rocks would prove to possess a natural remanent magnetization because the absence of a present field had already been demonstrated and it was almost universally believed that the Moon did not possess an iron core in which such a field could be generated. Consequently the initial investigation of Apollo 11 rocks was directed towards the use of rock magnetic studies as an adjunct to petrological examination. One of the most notable findings of the Apollo programme was the demonstration of the existence of a natural remanent magnetization (NRM) in Apollo 11 lavas and breccias. Experiments on the stability of the NRM enabled it to be concluded that the rocks were already magnetized when they were on the Moon. This conclusion was soon corroborated by the discovery of the existence of a steady magnetic field at the Apollo 12 site of the magnitude expected from the intensity of the NRM of about 36 γ (in addition to the field fluctuating solar wind. It was reasoned from this early work that the natural remanent magnetization had been acquired at the time of origin of the rocks or at least in their early history and a case was made out that this was a thermoremanent magnetization acquired as the lava flows cooled from magma flowing into the mare basin and as the high grade breccias cooled after the impacts. The origin of the natural remanent magnetization of the low grade breccias is more problematic and the role of other kinds of remanent magnetization processes has been investigated, particularly the effect of shock.
Cratering of Terrestrial Planets: Brief Review
Authors: Hartmann William K.
Published: March 2016

Analysis of cratering on all terrestrial planets and satellites has produced tools to study (1) the past meteoroid and planetesimal environment, (2) the erosive environments of planetary surfaces, and (3) the relative and absolute ages of planetary surface units. Important findings include a decline in lunar crater production rate from a value 4 x 109years ago that was thousands of times higher than the present, to present values which have been relatively constant for 2 to 3 x 109years; evidence for an erosive period or periods on Mars that degraded many Martian craters but declined substantially at some time in the past; and the concept of destruction of primeval planetary surfaces by early intense cratering and production of a mega-regolith.
Properties of Radio Sources in Clusters of Galaxies
Authors: Harris Daniel E.
Published: March 2016

“The properties of radio sources in clusters” presupposes that we know something about radio sources out of clusters, or that we even know whether a radio source is “in” or “out” of a cluster. Thus we are faced with the problem of defining what we mean by a cluster. Most of us use Abell’s catalogue of RICH clusters and assume that we are really “in” a cluster. However, most radio sources are identified with faint, distant objects and it is often difficult to know whether the remark “galaxy in a group” or “galaxy in a cluster” indicates a cluster such as the Coma Cluster, a cluster similar to an “open” Zwicky cluster, or a group of galaxies which may be gravitationally bound.

This uncertainty must not be forgotten, and in the following discussion, we will try to limit the effects of this by concentrating on catalogued clusters; ignoring most distant radio galaxies, many of which may be in rich clusters; and also by neglecting quasars, some or all of which may be in clusters.
Hot Gas in Clusters of Galaxies
Authors: Lea Susan M.
Published: March 2016

The idea that gas may be present in clusters of galaxies originated with the missing mass problem—the observation that galaxies in clusters were moving so fast that the inferred galaxy masses (using conventional mass to light ratios for the galaxies) were not enough to hold them together caused astronomers to speculate that the “missing mass” was in the form of gas. Subsequent observations in the 21 cm and La lines as well as radio, optical and x-ray continuum observations have effectively ruled out this possibility in a large number of clusters. However, there is evidence for the presence of gas in smaller quantities in many clusters.
Future Astrometry from Space and from the Ground
Authors: Høg E. , Fogh Olsen H.J.
Published: March 2016

The space astrometry projects being studied by the European Space Agency (ESA) promise an accuracy about ±0″.003 due to photon statistics for about 100 000 stars. Inherent limitations of the space astrometry projects and the future continued importance of ground based astrometry are outlined.
Observational Evidence for Atmospheric Chemical Composition Peculiarities Relevant to Stellar Evolution
Authors: Pagel B. E. J.
Published: March 2016

Abundance peculiarities in successive stages of stellar evolution are reviewed. Main-sequence stars show anomalies in lithium and, on the upper main sequence, the Am, Ap and Bp effects, which may be largely due to separation processes, and helium and CNO anomalies to which nuclear evolution and mixing could have contributed. Red giants of both stellar Populations commonly show more or less extreme variations among the C, N, 0 isotopes, sometimes accompanied by s-process enhancement, due to mixing out in various evolutionary stages. Detailed anomalies expected from galactic evolution are also briefly considered. Novae show strong effects in C, N, 0 and synthesis of heavier elements is displayed by the supernova remnant Cassiopeia A.
Concluding Remarks
Authors: Schmidt H. U.
Published: March 2016

Recent interest in the subject of this discussion gained momentum by an observation which did not concern magnetic fields directly. The filigree which Dr. Richard Dunn on Sacramento Peak found 2 Angstrom off the center of Hαis a bright and crisp structure in the photosphere with a width o: 1/5 arcsec. It was described in proper detail by Dunn and Zirker (1973). Even in the printed pictures in their paper one clearly sees one step beyond the solar granulation. The filigree is certainly related to the small scale structure of the photospheric magnetic field, but it is not yet clear whether the flux elements are exactly cospatial and have the same small dimensions. Simon and Zirker (1974) concluded froi spectra that the field structure is wider than the filigree. On the other hand Harvey (1976) in his excellent review of the observations has also presented the arguments of several authors who conclude that the sizes of the flux elements are as small as those of the filigree. This discrepancy certainly needs further study before such even more delicate questions as the spatial extent of the downdraft inside and around the flux elements can be reliably answered from observations. The theoretical interpretation of the downdraft depends on this answer as different sources of the mass flow are involved: the overlying atmosphere and the convergent mass flow of the surrounding convection. The latter stays partly outside the flux element, partly diffuses into it with an efficiency that might be enhanced by convection of still smaller scale.
Spectral Classification with Objective-Prism Spectra from Skylab
Authors: Henize K. G. , Parsons S. B. , Wray J. D. , Benedict G. F.
Published: March 2016

During the Skylab I, II and III missions, ultraviolet spectra were obtained in 188 fields with a. 15 cm aperture objective-prism spectrograph. The instrument has been described by Henize, Wray, Parsons, Benedict, Bruhweiler, Rybski and O’Callaghan (1975; hereafter referred to as Paper I).

The spectra cover the wavelength region from 1300 to 5000 Å and have a resolution of 2 Å at 1400 Å and 12 Å at 2000 Å. Absorption and/or emission lines of C II λ 1335, Si IV λ 1394, 1403 and C IV λ 1549 are visible in more than one hundred stars. The lines of Si IV and C IV are found to be particularly sensitive to stellar temperature and luminosity. Since these lines are visible in spectra of moderate to low resolution it is clear that they should be of special interest in any UV classification system for faint stars. This paper investigates the correlation of the intensities of the C IV and Si IV lines with MK spectral type, and presents a preliminary classification scheme for 04 to B2 stars based on these lines.
Scientific Need for Space Astronomy
Authors: Goldberg L.
Published: March 2016

Many scientific justifications for space astronomy have been prepared by individuals and committees during the past three decades or more. The first such report that I am aware of, called “Astronomical Advantages of an Extraterrestrial Observatory”, was written by Lyman Spitzer in September 1946, and although its goals were extremely modest by today’s standards, the report did dwell with enthusiasm on the ultimate goal of a large reflecting telescope 4-6 meters in diameter with diffraction-limited optics put into earth-satellite orbit. The latest study, from which I shall quote liberally, has just been published by the Astronomy Committee of the U. S. National Academy of Sciences, and provides the scientific foundation for space astronomy in the 1980’s. Space Astronomy was initiated about one month after the date of publication of Spitzer’s report, when the first high-altitude rocket was launched to observe the sun’s ultraviolet radiation. Since that time, space astronomy has completed two phases and is about to embark on a third. In Phase 1, which lasted until the beginning of Sputnik, observations were made for a few minutes at a time from high-altitude rockets. In the second phase, which is just ending, observations were made with relatively small instruments in earth-orbiting satellites. The observing programs carried out with rockets and small satellites were called experiments because their capabilities and objectives were limited and their lifetimes were short -from a few minutes to about a year.
Atomic and Molecular Gas in the Inner Regions of the Milky Way and Other Galaxies
Authors: Liszt H. S.
Published: March 2016

It seems likely that we inhabit a galactic system which in its gross characteristics exemplifies the present meaning of the word “normal”. The general framework for interpreting the distribution and kinematics of the observed gas consists of a well-defined rotation curve, applicable over the great majority of a thin, nearly flat disk; the stars and gas within this disk are generally quite cold, having little energy in random as opposed to well-ordered motions. In fact, neutral gas in the galactic disk is sufficiently regular in its structure that no grand pattern of spiral arms stands out in sharp relief.

As one moves inward in the Galaxy from the location of the Sun, this regularity persists to within about 4 kpc of the center, at which distance the abundance of gas in either atomic or molecular form drops fairly abruptly. Inside this region, the character of the gas distribution undergoes a marked change and the behaviour observed there, while it may be common to even the best-ordered systems, represents a rather spectacular departure from the organization at larger galacto-centric radii. As the gas abundance increases once more toward the galactic center it is seen to reside in a multitude of individual features having disparate spatial and kinematic properties. Many of these have large and/or obvious components of non-circular motion, usually taken as indicating expulsion of matter from the galactic center region at both large and small angles with respect to the rotation axis of the galaxy at large. Others, while occurring at velocities whose sign is consistent with rotation motion alone, have contradictory changes in velocity with position. Line profiles taken in the inner regions of the Galaxy are generally decomposed according to catalogs of classifiable features but no generally accepted interpretative framework exists as a means of relating the wide variety of observable phenomena.
An Anisotropic Gas Jet from the Nucleus of the Galaxy
Authors: Fukui Yasuo
Published: March 2016

Molecular hydrogen of ≥108M⊚ exists in the galactic center region as has been revealed by recent observations of molecular emission lines. In the inner region of , most of the dominant emission features are located at and 0 km s-1 ≤ v ≤ 100 km s-1 extremely unevenly with respect to the galactic center. As a model of the molecular complex we propose a fan of 360 pc radius whose pivot is at the nucleus. The vertical angle of the fan is about 50° and the central line of the fan makes an angle of about 60° to the line of sight. Molecules in the fan are radially outflowing from the center with the velocity of 110-140 km s-1l. The 1-v pattern of the fan model agrees very well with the observational data. As for Sgr A and Sgr B2 numerical calculation of molecular line profiles has been made by using the large velocity gradient approximation. The calculation shows that the broad and asymmetric line profiles in the complex are well reproduced in the fan model. Further, an isotope effect on line shape is predicted, which will be viable for an observational check of the model.
Kinematics of Nuclei of Sc Galaxies
Authors: Rubin V. C.
Published: March 2016

For a sample of 21 Sc galaxies with a wide range of luminosities, of radii, and of masses, W. K. Ford and I have obtained spectra and determined rotation curves. By their kinematical behavior in their central regions, the Sc’s can be separated into two groups. Some galaxies, generally small and of low luminosity, have shallow central velocity gradients, reflecting their low central masses and densities. Other galaxies, most often large ones of high luminosity, have steep central velocity gradients. One reason this separation by central velocity gradients is of interest is because these galaxies exhibit other significant spectral differences which go hand-in-hand with the kinematical differences.

The small, low luminosity galaxies show emission lines of Hα and [NII], with nuclear Ha sharp and stronger than [NII], and little or no stellar nuclear continuum, just as conventional HII regions. In contrast, the high luminosity galaxies show broad nuclear emission, with [NII] stronger than Ha. These galaxies have a strong red stellar continuum, arising from a red stellar population. The cause of the Hα[NII] intensity reversal in the nuclei of some galaxies remains unknown. However, the strong [NII] emission in generally high luminosity galaxies with massive nuclei, nuclei which show strong red continua, suggests that [Nil] intensity correlates with nuclear luminosity, and in turn with the density and velocity properties of the nuclear populations. We would expect high velocity dispersions and high bulge luminosities for galaxies with strong nuclear [NII] and steep central velocity gradients.
Theoretical Considerations on the Dynamics of Normal Galactic Nuclei
Authors: Sanders Robert H.
Published: March 2016

I want to discuss the origin of non-circular gas motions observed in the nuclei of normal spiral galaxies and the possibility that recurring violent activity in normal nuclei excites such motion. But first, let us review several basic aspects of the nearest normal galactic nucleus — the nucleus of our own Galaxy.

The rotation curve as observed in the 21-cm line of neutral hydrogen gives some indication of the form of the gravitational field in the central region of the Galaxy. Figure 1 is a smooth fit to the rotation curve in the inner few kiloparsecs (solid line) taken essentially from the data of Rougoor and Oort (1960) and Simonson and Mader (1973). This rotation curve, within 1 kpc of the centre, is completely accounted for by the mass distribution implied by the extended 2.2-μ emission (Becklin and Neugebauer 1968, Oort 1971). Moreover, there is little doubt that this centrally condensed mass distribution should be identified with the bulge or spheroidal component of the Galaxy, because the spatial distribution of the 2.2-μ intensity is practically identical to the distribution of visible starlight in the bulge of M31 (Sandage, Becklin, and Neugebauer 1969). The conclusion is that the bulge overwhelmingly dominates the gravitational field inside of 1 kpc.
Ultraviolet Spectra of Planetary Nebulae and their Central Stars
Authors: Seaton M. J.
Published: March 2016

Antediluvian UV observations of planetary nebulae were made using rockets and the ANS, TD-1 and Soyuz-13 satellites: this work is reviewed by Gurzadyan (1978) and Pottasch (1978); see also Bohlin et al. (1978), Pottasch et al. (1978) and Lutz and Carnochan (1979).

With IUE came the deluge. To my knowledge, IUE observations have been made of 54 planetaries, and work continues by many groups, on making observations and reducing and interpreting the data. The present report describes some preliminary results.
Secular Instabilities
Authors: Paczyński B.
Published: March 2016

The relation between a linear series and thermal (i.e. secular) stability of stellar models is discussed. Models of accreting degenerate dwarfs are considered as an example of transition from instability to stability. This transition occurs while the accretion rate increases. Such models are relevant for novae and symbiotic stars.

I shall limit this presentation to the secular i.e. thermal instabilities of stellar models in the hydrostatic and thermal equilibria. The time dependence of a small perturbation of an equilibrium model is assumed to be exponential, but the eigenvalues do not have to be real. In general they are complex. That means that thermal instability, if present, may either lead to an exponential growth of a perturbation, or may lead to oscillations with a growing amplitude. The complex nature of the eigenvalues makes a search for them difficult and no general prescription is available for a search to be complete and successful. However, a search for real eigenvalues is much easier. Some information about the presence of purely exponential modes may be achieved even without searching for them by means of calculating a linear series of stellar models. I shall describe this concept in this communication.
Optical Spectrum Variability of Seyfert Galaxy Nuclei
Authors: de Bruyn A. G.
Published: March 2016

In this contribution I will present some results of a program aimed at determining the optical variability characteristics of Seyfert galaxy nuclei. It has been known for more than a decade that the continuous, non-stellar light of Seyfert nuclei can vary significantly on a time scale of months to years (see, e.g., Lyutyi, 1973, 1977; Penston et al., 1974; Penfold, 1979). In recent years there also have been various reports of variations in the intensity of the broad optical emission lines (Boksenberg and Netzer, 1977; Tohline and Osterbrock, 1976) following the pioneering work by Souffrin et al. (1973) and Cherepashchuk and Lyutyi (1973). However, very little is known on the details of the continuum variations and how they relate to the line variability. Such information could provide valuable constraints on the fashionable photo-ionization models for the broad line region (BLR) and the structure of the latter.
X-Ray Imaging Studies of NGC 1275 and The Core of The Perseus Cluster
Authors: Grindlay J. , Branduardi G. , Fabian A.
Published: March 2016

The EINSTEIN X-ray Observatory has been used to study the X-ray emission from the center of the Perseus cluster, including the active galaxy NGC 1275. Both a point source and extended (˜ 6’) source are observed from NGC 1275. The central 40’ × 40’ region of the Perseus cluster around NGC 1275 displays an interesting temperature and surface brightness distribution. Simple hydrostatic isothermal sphere models do not well describe the cluster emission. The surface brightness of the high resolution image of NGC 1275 can be fit with a constant-pressure but centrally-cooling (i.e., temperature increases with radius) gas which suggests a radiative cooling accretion flow onto NGC 1275.
On the Differences at Chromospheric Levels between RS Cvn-Type Binaries, Active and Quiet Chromosphere Single Stars, and Active and Quiet Regions in The Sun
Authors: Linsky Jeffrey L.
Published: March 2016

RS CVn-type systems exhibit many similarities to active regions on the Sun. In the last few years considerable progress has been made in quantifying the differences between the atmospheric properties of solar plages and quiet regions. These differences, as summarized in Linsky’s (1979) review, can be simply explained by additional nonradiative heating and include the following: (1) temperature enhancements in the photosphere, (2) heating of the temperature minimum and its displacement downward in mass column density, (3) enhanced radiative losses in the chromosphere and transition region (typically by a factor of 10), (4) steeper chromospheric temperature gradients, and (5) enhanced pressures and densities at the top of the chromosphere, throughout the transition region, and at the base of the corona (again typically by a factor of 10).
Origin and Development of Solar Flares
Authors: de Jager C.
Published: March 2016

A review is given of knowledge on solar flares with particular emphasis on progress made during the international Solar Maximum Year (1979-1981).

The pre-flare structure is described by a flux tube model or a circuit model. The instability leading to a flare may occur by a disturbance of the field topology (mostly: field emergence) followed by field-line reconnection (circuit coupling). In the first, impulsive, phase of a flare this causes jets of energetic electrons, originating near the top of the flux tube, to bombard lower chromospheric regions: footpoint heating. In the second (‘gradual’ or ‘diffuse’) phase heated gas from the footpoints ascends convectively upward producing a large cloud of hot gas. Consequent shock wave phenomena cause moving fronts and associated waves in the high parts of the corona; these show up in coronagraphic or radio-observations. In some cases it happens that several hours after a large flare extended loop-like structures appear of fairly high temperature (> 6 MK), emitting a very faint X-ray flux. They are the basic structures of a more extended configuration, visible on metric radio waves, and pointing out from the area where the flare occurred. They may extend to distances of ≈ 106 km or more from the solar surface.
Nuclear Constraints on the Age of the Universe
Authors: Schramm David N.
Published: March 2016

In this paper a review will be made of how one can use nuclear physics to put rather stringent limits on the age of the universe and thus the cosmic distance scale. As the other papers in this session have demonstrated there is some disagreement on the distance scale and thus the limits on the age of the universe (if the cosmological constant Λ = 0.) However, the disagreement is only over the last factor of 2, the basic timescale seems to really be remarkably well agreed upon. The universe is billions of years old - not thousands, not quintillions but billions of years. That our universe has a finite age is philosophically intriguing. That we can estimate that age to a fair degree of accuracy is truly impressive.

No single measurement of the time since the Big Bang gives a specific, unambiguous age. Fortunately, we have at our disposal several methods that together fix the age with surprising precision.
A New Method for Evaluating the Hubble Constant
Authors: Rubin Vera C. , Thonnard Norbert
Published: March 2016

We have devised a procedure for evaluating the absolute magnitudes of galaxies from their optical rotation curves, as an extention of the conventional Fisher-Tully method. We describe here how this method can be employed to evaluate the Hubble constant. From observations of 23 Sb field galaxies with luminosities ranging from –19.5 to –23.0 (adopting H=50 km s–1 Mpc–1), we have produced synthetic rotation curves showing the systematic progression toward increasing velocity with increasing luminosity within a given Hubble type. (See Thonnard and Rubin, Carnegie Yrbk 80, p. 551 for details of producing such a set of curves). By matching even a small portion of a rotation curve with these curves, the absolute magnitude of an Sb galaxy can be estimated to about ±0.5 mag. This magnitude, of course, is based on an assumed value for H.
X-Ray Variability of Active Galactic Nuclei
Authors: Schwartz Daniel A. , Madejski Greg , Ku William H.-M.
Published: March 2016

X-ray variability of active galactic nuclei is commonplace on scales from days to years. It also occurs, although rarely, on time scales as short as 200 seconds. Both these statements must be strongly qualified by the irregularity and insensitivity of the available observations. In the X-rays we expect that we are seeing deep within the active nucleus, near what is usually taken to be a massive black hole. The X-ray variability time scales may then give us the fundamental structural length scales. We would like to review data on active galaxies, present our new data on Einstein observations of BL Lac objects, and discuss all these in terms of a statistical quantification of the observations.
Star Formation Activity in Giant HII Complexes
Authors: Heidmann J.
Published: March 2016

With the advent of powerful instruments in various spectral domains many scientists became involved in the study of giant HII regions - i.e. regions as important as 30 Doradus in the Large Magellanic Cloud or NGC 604 in Messier 33 - and of HII complexes still more active such as isolated extragalactic HII regions, some galactic central regions, chains in large spirals and clumpy irregular galaxies.

In view of the importance of these investigations for the problems of formation and evolution of stars and of galaxies, we organized a Meeting at thelAU XVIIIth General Assembly on”Giant HII complexes outside our Galaxy”with the following program:

a-

Observational results and their primary interpretations in the X-ray, UV, visible, IR and radio domains.

b-

Confrontation with related investigations in our Galaxy and general interpretations.
UV Observations of Close Binary Stars
Authors: Polidan R. S.
Published: March 2016

Ultraviolet spectroscopic observations made with the Copernicus and IUE spacecraft have been analyzed. The observations represent a collaborative effort with G. J. Peters.

Observational evidence supporting the existence of a turbulent accretion layer has been discussed earlier by Peters. Ionization equilibrium calculations suggest the following physical conditions in the layer: T ~ 125000 K°, Ne ~ 109 cm-3; composition: Nitrogen rich, carbon poor. Observations also show the region to be turbulent and not co-rotating with the accreting star. We conclude that the region is formed by new material arriving from the secondary and that the accretion process is turbulent.
X-Ray Superbubbles
Authors: Cash Webster
Published: March 2016

Four regions of the galaxy, the Cygnus Superbubble, the ƞ Carina complex, the Orion/Eridanus complex, and the Gum Nebula, are discussed as examples of collective effects in the interstellar medium. All four regions share certain features, indicating a common structure. We discuss the selection effects which determine the observable x-ray properties of the superbubbles and demonstrate that only a very few more in our galaxy can be detected in x-rays. X-ray observation of extragalactic superbubbles is shown to be possible but requires the capabilities of a large, high quality, AXAF class observatory.
The Soft X-Ray Background
Authors: Kraushaar W. , Burrows D. , McCammon D. , Sanders W.
Published: March 2016

Maps in three energy bands from the recently-completed Wisconsin survey of the soft X-ray sky are presented. The lowest energy data require emission, almost certainly from hot interstellar gas, from regions within 100 pc of the sun. The data do not require diffuse emission from beyond the neutral galactic gas but are compatible with such emission under certain assumptions.
Local Cells of the Universe: Two Voids of Diameter 200 MPC
Authors: Einasto J. , Corwin H.G. , Huchra J. , Miller R.H. , Tarenghi M.
Published: March 2016

Recent studies of the spatial distribution of galaxies and of clusters indicate that practically all clusters and a vast majority of galaxies are concentrated into supercusters. The space between superclusters has no rich clusters and very few galaxies. The whole structure is cellular, with cell walls formed from sheetlike superclusters and the empty cell interiors being huge voids.

In this presentation we show how the observed distribution of clusters, and the Local Supercluster in particular, are part of a cellular structure and suggest that the entire pattern of superclustering is cellular. Our study is based on the recently completed CFA redshift survey. All other available redshifts are also used, including cluster redshifts where available.
Atomic Energy Levels and Spectra: Astronomical Needs
Authors: Cowley Charles R.
Published: March 2016

The astronomer’s requirements for atomic data are so massive that it is not easy to approach this subject in a way that will sound responsible to someone who is not thoroughly familiar with the situation. The simple truth is that there is hardly an atomic species, neutral or ionized, for which additional data is not urgently needed in some domain of astronomy. This comes about partly because of the high temperatures and very long path lengths in astronomical objects which can make them extremely powerful light sources. More generally, we can say that conditions in the astronomer’s violent universe manage to render large volumes of phase space available to the atoms which occupy it.

While the truth is that we need to know “everything,” one task of the present paper is to cast this need in a pragmatic form. This will be done by reviewing certain problems in the very recent history of astronomical spectroscopy, where real progress has come about as a result of new work on atomic spectra. Many of the illustrative problems are taken from the spectroscopy of upper main sequence, chemically peculiar or CP stars.
The High Energy Frontier
Authors: Rubbia Carlo
Published: March 2016

This is a review of the present status of particle physics and the main scientific goals in our work at the “High Energy Frontier” with specific emphasis on connections to Cosmology. Based on an extraordinarily successful Standard Model, our field is exploring the fundamental questions such as the nature of mass and the unification scheme which only a few decades ago seemed to belong mostly to the realm of dreams. Neutrino masses and oscillations, the key to CP-violation and proton decay are actively searched for at accelerators and underground experiments.
Report of the IAU WGAS Sub-group on Issues on Time
Authors: Seidelmann P.K.
Published: March 2016

Included in the nine adopted recommendations of the IAU Working Group on Reference Systems (Hughes, et. al., in 1991), were recommendations for the introduction of Geocentric Coordinate Time (TCG) and Barycentric CoordinateTime (TCB), the renaming of the Terrestrial Dynamical Time (TDT) as Terrestrial Time (TT), and the approval to continue the use of Barycentric Dynamical Time (TDB) when that is desirable. The relationships between these different time scales and the reason for their introduction was given by Seidelmann and Fukushima (1992). Since it was recognized that there were some unresolved issues as a result of these recommendations, a subcommittee of the Working Group on Astronomical Standards was established for Issues on Time.
An a priori model for the reduction of nutation observations: KSV1994.3 nutation series
Authors: Herring T.A.
Published: March 2016

We discuss the formulation of a new nutation series to be used in the reduction of modern space geodetic data. The motivation for developing such a series is to develop a nutation series that has smaller short period errors than the IAU 1980 nutation series and to provide a series that can be used with techniques such as the Global Positioning System (GPS) that have sensitivity to nutations but can directly separate the effects of nutations from errors in the dynamical force models that effect the satellite orbits. A modern nutation series should allow the errors in the force models for GPS to be better understood. The series is constructed by convolving the Kinoshita and Souchay rigid Earth nutation series with an Earth response function whose parameters are partly based on geophysical models of the Earth and partly estimated from a long series (1979-1993) of very long baseline interferometry (VLBI) estimates of nutation angles. Secular rates of change of the nutation angles to represent corrections to the precession constant and a secular change of the obliquity of the ecliptic are included in the theory. Time dependent amplitudes of the Free Core Nutation (FCN) that is most likely excited by variations in atmospheric pressure are included when the geophysical parameters are estimated. The complex components of the prograde annual nutation are estimated simultaneously with the geophysical parameters because of the large contribution to the nutation from the S1 atmospheric tide. The weighted root mean square (WRMS) scatter of the nutation angle estimates about this new model are 0.32 mas and the largest correction to the series when the amplitudes of the ten largest nutations are estimated is 0.17 ± 0.03 mas for the in phase component of the prograde 18.6 year nutation.
Recent Results of the Nutation Theory for a Rigid Earth
Authors: Souchay J. , Kinoshita H.
Published: March 2016

Although the main questions remaining in the frame of the study of the nutation-precession phenomena concern principally the effects due to physical interactions, recent works have shown that even in the simplified case of a rigid Earth model of nutation, important changes have to be taken into account. Here we present the various steps having led to a more complete and more accurate rigid Earth nutation theory, since the pionnier work of Woolard (1953), insisting on the most recent improvements.
Internal dynamics and magnetism of the Sun
Authors: Paternò L.
Published: March 2016

The present internal dynamics and magnetism of the Sun have been determined by the initial conditions in the pre-main sequence age, by the angular momentum loss and its redistribution in the interior, and the interaction of motion with magnetic field.

The history of the Sun rotation is traced back by observing the present rotation of stars with the same mass as the Sun at earlier evolutionary stages. The present angular momentum of the Sun, as deduced from its internal rotational behavior derived from helioseismological data, appears to be a small percentage of the original one contained in similar mass stars (T Tauri and α Persei). It is not easy to reconcile the sharp decrease in the surface angular velocity, which follows the α Persei phase, with the subsequent soft decrease, taking place after Pleiades phase, unless some very effective mechanism transfers angular momentum from inner to outer regions, where is lost in the solar wind. Such a mechanism is probably magnetic in origin, since purely hydrodynamic instabilities fail to transfer angular momentum at a rate sufficient to determine the presently observed flat radial gradient of the internal angular velocity.
Dust Around Young Stars: How Related to Solar System Dust?
Authors: Hanner Martha S.
Published: March 2016

Study of the dust in circumstellar disks around young stars is currently an extremely active area in astronomy. There is little doubt that accretion disks are a natural part of protostellar evolution. Much recent observational and theoretical work is giving us a clearer picture of the physical conditions in dust disks and their evolutionary progression. IRAS observations revealed that many main-sequence stars, such as p Pictoris, have circumstellar disks. But whether these disks are related to planetary formation is not yet understood.

A portion of the dust in disks around young stars ultimately may be incorporated into planetary systems. Thus, study of the dust in our own solar system complements the remote sensing of protostellar regions and aids in reconstructing the evolutionary history of the dust. Since comets formed in the cold outer regions of the solar nebula, they may contain intact interstellar grains. As the comets lose material during passage through the warm inner solar system, some of these grains will be released into interplanetary space. Technical advances now allow analysis of individual micrometer or smaller grains in interplanetary dust particles and primitive meteorite samples. Isotopic anomalies and patterns of crystal growth in these particles are yielding tantalizing clues about the interstellar material incorporated into these solar system samples.
Synthetic Template Spectra
Authors: Kurucz Robert L.
Published: March 2016

I will compute representative spectra for all spectral types for which my model calculations (Kurucz 1992; 1993a; 1994a) are valid. High-resolution zero-rotation fluxes and intensities will be distributed on CD-ROMS together with programs (Kurucz 1993B) for broadening the spectra to arbitrary rotation velocities, macroturbulent velocities, and instrumental profiles, and for transmitting the spectrum through an atmosphere.

Since the line data are still not well determined, I actually have to make two calculations, one with only the lines with good wavelengths to preserve wavelength detail, and one with all lines, including predicted, to preserve the energy distribution for photometric calibration. In the first case the spectrum is usable as a radial velocity, abundance, or classification template. Even though the line list is incomplete, its signal-to-noise can be higher than that of observed spectra for cross-correlating.

The models are plane parallel, LTE, in hydrostatic equilibrium, and have no triatomic opacities. Therefore, M stars and supergiants cannot be computed realisticly. The abundances available now are scaled-solar and alpha-enhanced scaled-solar. Individual abundances can be changed for the spectrum calculation. My new model atmosphere program, ATLAS 12 (Kurucz 1993c), which does not yet work, will allow arbitrary abundances.

I have made test calculations for Arcturus, the sun, Vega, Sirius, and a17000K B. star. Figure 1 shows the effect of resolution on the appearance of the spectrum. Figure 2 shows the effect of rotation. The spectrum for Arcturus is displayed in Kurucz (1994b) with the molecular bands labelled.
Planetary Nebula Luminosity Functions and Prospects for the Future
Authors: Ciardullo Robin
Published: March 2016

Until now, [O III] λ5007 surveys of extragalactic planetary nebulae (PN) have been aimed at determining distances and identifying test particles for future (cinematica] studies. However, PN observations are useful in another area of astrophysics - the investigation of stellar populations. Because the production rate of [O III] bright PN in a galaxy can vary by an order of magnitude, this number is potentially a powerful discriminant between age and metallicity in an evolved stellar population. A strong inverse correlation exists between galaxy absolute magnitude and bolometric luminosity-specific PN density (α2.5), with the small metal-poor ellipticals having values of α2.5 in exact accordance with the predictions of stellar evolution theory. This correlation, along with the direct dependence of α2.5 on galactocentric radius, and the scatter in α2.5 seen in “young” galaxies, argues strongly that elliptical galaxies are old systems which follow a metallicity sequence. It also suggests that the combination of absorption line spectroscopy, UV photometry, and PN measurements can be a powerful probe of elliptical galaxy stellar populations.
Cepheid Variables: Period and Mass Determination
Authors: Moskalik Pawel
Published: March 2016

Determination of masses has been a long standing problem in the Cepheid research. Since the early days of Cepheid modeling different methods of mass calibration have lead to conflicting results, implying serious discrepancies between the evolution and pulsation theories (see Cox 1980 for a review). In recent years this situtation has been mostly remedied, and the Baade-Wesselink masses, pulsation masses and evolutionary masses are now in good agreement with each other (e.g., Gieren 1989). However, both the bump masses inferred from the position of the secondary bump on the light curve and the beat masses obtained from the period ratios of the double mode Cepheids turned out to be very resilient to a reconciliation.

There are 13 Cepheids in the Galaxy in which two vibrational modes are simultaneously excited (e.g., Szabados 1988). The period ratios measured in these variables can be used in conjunction with the linear pulsation theory to infer the masses of these stars. The method was first applied by Petersen (1973) who obtained masses ranging from 1Mʘ to 3Mʘ for Cepheids with fundamental mode periods between 2.1 d and 6.3 d. Such ‘beat” masses are 2—4 times smaller than the evolutionary or Baade-Wesselink masses for these objects.
Theoretical Simulations of Fundamental Processes of the H2 Formation Reaction on Dust Surfaces
Authors: Takahashi Junko
Published: March 2016

Classical molecular dynamics (MD) computer simulations were performed to investigate the whole fundamental processes of the H2 formation reaction on the amorphous water ice as a model surface of icy mantles of dust grains. The product energy distribution and formation pumping mechanism of H2 for med on dust grains were also examined.
Environs and Formation of Massive Stars
Authors: Lizano Susana , Garay Guido
Published: March 2016

Massive stars in our Galaxy are born predominantly within the dense cores of giant molecular clouds. They affect their environment very soon after a stellar core has formed through their large rate of ionizing photons and their strong stellar winds. Massive stars are formed in clusters with stellar densities n* ~ 104 stars/pc3 and sizes 0.2 — 0.4 pc, and seem to preferentially form near the central region of the cores. Disks have been found in several sources (see Cesaroni, this volume). Associated with massive stars also are bipolar molecular outflows, which have masses, mass loss rates, and energies that are factors of ~ 100 larger than those of low mass stars (see review of Churchwell 1999).

An understanding of the physical processes that dominate during the early stages of formation of massive stars and their influence back on the molecular gas from which they formed requires a detailed knowledge of the physical conditions of the environment prior to and after the formation of the star. Here we present an abstract of an extensive review on this subject by Garay & Lizano (1999). For compactness, most of the references have been omitted.
The Spacewatch Outer Solar System Survey
Authors: Larsen Jeffrey A.
Published: March 2016

We present our results from a wide area search for the brightest and rarest members of the Transneptunian and Centaur/Scattered-Disk asteroid populations. Our data encompasses 1483.8 square degrees of sky taken with the Spacewatch 0.9 meter telescope on Kitt Peak between September of 1995 and September of 1999. We found five new Transneptunian asteroids, three new Centaurs, and two new Scattered Disk Objects. These objects are among the larger members of the population and their relative brightness will make them ideal candidates for physical observations.
Pluto: A Planet or a Trans-Neptunian Object?
Authors: A’Hearn Michael F.
Published: March 2016

The purposes of classification and taxonomy are reviewed. Using examples from fields ranging from paleontology to planetology, I argue that non-exclusive classifications, which allow Pluto to be considered both a planet and a TNO, provide the most desirable approach to progress in our science.
Composition of Comets and Interstellar Dust
Authors: Ehrenfreund Pascale
Published: March 2016

Recent observational results from ground and space-based observatories in combination with laboratory simulations allow us to monitor the evolution, survival, transport and transformation of cosmic dust from molecular clouds and the diffuse interstellar medium, until their incorporation into Solar System material. The composition of comets encodes information on their origin and can be used as a tracer for processes which were predominant in the protosolar nebula. A comparison of the composition and abundances of interstellar molecules and cometary volatiles reveals a general correspondence, but discrepancies are also apparent. Detailed studies indicate that cometary ices are a mixture of original interstellar material with material that has been moderately to heavily processed in the pre-solar nebula. The inventory and distribution of ice and organic molecules in interstellar clouds and in comets and their common link are briefly described.