bluuebunny/crossref_metadata_2025 huggingface dataset:
Hot Subluminous Stars
Authors: Greenstein Jesse L.
Published: March 2016

Extensive mass loss is observed for hot subluminous stars, through P Cygni lines in the ultraviolet. This persists in some sub-dwarf 0 stars, but is generally not observed in white dwarfs. The ultraviolet provides determination of effective temperatures. Among nine sdO’s, the maximum temperature reported is definitely below 60, 000 K; an object at 100, 000 K would be distinguishable. The sdO’s show a wide variety of line strengths, notably in N V, C IV and Si TV, as well as He II. One halo sdB is reported as rich in peculiar elements; it shows anomalous N V for its temperature. The comparison of effective temperatures of white dwarfs observed from space and from the ground gives excellent agreement. The hottest white dwarfs are near 60, 000 K, although one (helium-rich) reaches 80, 000 K. Another helium-rich close binary probably has an accretion disk; it is the only white dwarf to show the expanding shell of N V, C IV, Si IV characteristic of some subdwarfs. Two magnetic white dwarfs have been observed; one has strong unidentifiable features and the smallest known radius.
Models of the Interstellar Medium
Authors: de Jong Teije
Published: March 2016

Up-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

The 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.
Overshooting Motions from the Convection Zone and their Role in Atmospheric Heating
Authors: Toomre Juri
Published: March 2016

Chromospheres and coronae in stars appear to require vigorous convection zones just below the surface. If we wish to understand how various dynamical instabilities contribute to the mechanical heating that is required to produce chromospheres, then we must be concerned both with fluid motions in the atmosphere and with the nature of their driving below the surface. One cannot really separate these two subjects. In order to emphasize this link, we will raise some basic questions about convective flows in a stellar envelope and of their penetration into the atmosphere. The significant puzzles between what is observed and what can be theoretically explained should serve to indicate some of the issues that need to be pursued. We will concentrate on the Sun in our discussions: the observations here are sufficiently detailed to provide the explicit challenges to theory unavailable in most other stars. However, we will also turn to A-type stars to illustrate a theoretical procedure for describing convection that may do better than the mixing-length approach in predicting the vertical structure in these flows.
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).
Clustering of Galaxies about Extragalactic Radio Sources-Implications for Observations with the Einstein X-Ray Observatory
Authors: Longair M. S. , Seldner M.
Published: March 2016

The question which we have addressed is “what is the clustering of galaxies about extragalactic radio sources and how does it vary with the properties of the sources such as radio luminosity, optical spectral properties, radio morphology, etc”. Only a small fraction of strong radio sources belong to rich clusters and most of the work on weaker associations is of a somewhat subjective nature. Our approach has been to work with complete, statistically defined samples of bright radio sources and to cross-correlate the positions of the sources with the Lick counts of galaxies. In this approach, we never define exactly what we mean by a cluster as group of galaxies - clustering is simply defined as the amplitude of a correlation function. This approach is only possible because the Lick counts of galaxies have been studied in detail by Seldner et al. (1977) who calibrated the Lick counts over the whole of the sky.
Ages of Galactic and Extragalactic Star Clusters of Various Abundances
Authors: Cannon R.D.
Published: March 2016

In this review I shall concentrate mainly on globular star clusters in our Galaxy since these are the objects for which most work has been done recently, both observationally and theoretically. However, I shall also discuss briefly the oldest open clusters and clusters in the Magellanic Clouds. Little can be said about more distant cluster systems, since the only observations available are of integrated colours or spectra and these seem to be rather unreliable indicators of age. It is perhaps worth pointing out that the title may be slightly misleading; the problem is not so much to determine the ages of clusters of known abundances, as to obtain the best simultaneous solution for both age and composition, since some of the most important abundances (notably helium and oxygen) are virtually unobservable in little-evolved low mass stars.
The Stellar Content of the Nuclei of Spiral Galaxies
Authors: Crampton D. , McClure R.D. , Cowley A.P.
Published: March 2016

Numerous studies have been attempted to determine the stellar content of the nuclei of galaxies. In the case of elliptical galaxies observations show that there is a change in spectral type from later to earlier types correlated with a variation from high to low luminosity (e.g. Faber 1977). This has been interpreted for the most part as being due to differences in metal abundances in an old stellar population, although some recent studies suggest a variation in stellar age may be important as well (e.g. O’Connell 1980, Heckman 1980). The nuclear bulges of spiral galaxies also display a change from late to early spectral type along a sequence from high to low luminosity bulges. In this case, however, the assumption has almost universally been made that these differences are due to differences in age of the stellar population. In particular, most stellar models for the nuclear bulges of spiral galaxies have used solar neighbourhood metal- rich stars, and assumed that the strong hydrogen lines and weak metal lines in late-type spiral nuclei are due to the predominance of a very young main-sequence population rather than old metal-poor stars.
Recently Developed Distance Criteria
Authors: Paturel G.
Published: March 2016

The problem of the determination of distances in astronomy (the so-called problem of the distance scale) is a very old and important problem. About 280 BC Aristarchus of Samos, the famous greek astronomer of the Alexandrian school, already devised a method to find the relative distances to the Sun and Moon in terms of the size of the Earth. Later, Eratosthenes (about 200 BC), another greek astronomer, measured the Earth’s diameter; so the zero-point of this first distance scale was fixed.

Now we are interested by extragalactic distances but the same approach is made : (i) determination of relative distances (ii) determination of the zero-point to obtain absolute distances.

Some distance criteria can be used to determine the zero-point. These criteria cannot generally be used at a great distance. They permit a comparison between galactic objects, like Cepheids, Novae, Supergiants ..., globular clusters..., and the same counterparts recognized in external galaxies. Often application is limited to nearby galaxies. In a first section we will briefly present this kind of distance criteria. For more distant galaxies other criteria must be employed, the zero-point being here fixed with nearby galaxies whose distances are known from the preceding step. We will discuss these criteria in a second section.
Dynamical Interrelations between the Smaller Bodies of the Solar System
Authors: Kresák Ľubor
Published: March 2016

Population of the solar system by different types of interplanetary objects is reviewed. Their sources, evolution and interrelations are discussed, in particular in terms of their degree of stability, potential evolutionary paths and survival times.
Some Features of Evolution of Meteor Streams
Authors: Babadzhanov P.B. , Obrubov Yu.V.
Published: March 2016

It is shown that a number of features of meteor showers such as the correlation of orbital semimajor axes and longitudes of the ascending nodes with meteor magnitudes, the restriction of visibility periods and the displacement of maximum activity dates is explained by the joint influence of planetary perturbations, the Poynting-Robertson effect and its corpuscular analogue, light pressure and ejection velocities of different mass meteoroids from cometary nuclei.
Gamma-Rays from Active Galactic Nuclei
Authors: Kafatos M.
Published: March 2016

Gamma-ray observations from active galactic nuclei (AGN) are important in trying to understand the nature of their central sources. A handful of mechanisms can give rise to γ-rays either from nonthermal or from thermal processes. Hot accretion disks around massive black holes in the centers of AGN could provide the required thermal electrons, pions and relativistic electrons and positrons to explain both the X-ray and γ-ray emission.
Cool Star Winds – Recent Observations and Theoretical Implications
Authors: Hartmann L.
Published: March 2016

Much of our knowledge of winds from late-type stars comes from the detection of ejected material, called circumstellar shells, as observed in absorption lines of low-excitation species such as Mg II, Ca II, Na I, and K I (cf. Reimers 1977). Observations of CS shells are difficult to translate into quantitative mass loss rates, a limitation which has not helped to test various mass loss mechanisms. The data clearly demonstrate one very important fact: shell velocities are very low. In fact, they are so much lower than surface escape velocitiesthat it was not clear that material is actually being lost until Deutsch (1956) detected the existence of the CS absorption shells ejected from α Her and α Sco in the spectra of distant companion stars. Today it is possible to demonstrate the expansion of shells out to several thousand stellar radii in K I scattering (Honeycutt et al. 1980).
Mass Loss from Astronomical Objects; A Summary
Authors: de Jager C.
Published: March 2016

In this summary of the Joint Discussion on mass loss I discuss successively:

(1)

stellar mass loss data and possible mechanisms

(2)

mass loss for special types of stars and suggestions for future research in the stellar case

(3)

interaction with the interstellar medium

(4)

mass loss from quasars
Small-Scale Radio Jets
Authors: Wilkinson P.N.
Published: March 2016

Here I shall interpret ‘small-scale’ to mean a few kpc or less. Such jets occur over a wide range of emitted energies (e.g. 1039erg s–1 in M87, 1046 in 3C273) and we do not know if they are manifestations of the same basic phenomenon or whether Nature is fooling us in some way despite the morpholigicaI similarities. For the moment, it seems sensible to assume an underlying unity and to use the observations to explore the jet phenomenon in different guises.

With the highest resolutions obtainable with VLBI, our goal is to elucidate the nature and properties of the central energy source. To this end, we can ask various questions which our observations are expected to bear upon both now and in the future. How do jets form and propagate from the energy source? Are the jets ccnfined/colIimated or ballistic? Why are some jets much stronger than others - is this intrinsic or an evolutionary or relativistic effect - or all three? Why are only some sources superlumina Is? Why are most jets ore-sided? Does the relativistic velocity implied by super I urninaI motion on the pc-scale continue into the kpc-scale jets?
General Superclustering
Authors: Abell G.O.
Published: March 2016

The distribution of rich clusters of galaxies revealed on the photographs taken for the National Geographic Society-Palomar Observatory Sky Survey shows a strong dumpiness on a scale of 100 Mpc (for H = 50 km s–1 Mpc–1), with vast intraclump regions apparently void of rich clusters (Abell 1958; 1961). Studies of the n-point correlation function by Peebles and his associates (e.g., Peebles 1980 and references therein) show that this large-scale dumpiness applies also to individual galaxies. Peebles’ statistical approach does not, of course, indicate individual superclusters or their structures; that kind of information awaited the breakthrough provided by the development of high-speed detectors, with which radial velocities of large numbers of galaxies can be obtained in reasonable observing times.
NLTE Masking and the Kiev Fe I Oscillator Strengths
Authors: Rutten Robert J.
Published: March 2016

This contribution serves to advertise the empirical solar-spectrum determinations of the oscillator strengths of 860 Fe I lines by Gurtovenko and Kostik (1981), by showing that these Kiev data contain just the lines needed in cool-star abundance analyses, and by explaining why they are so good. For details, see Rutten and Kostik (1982) and Rutten and Zwaan (1983).

Figures 1 and 2 show why the Kiev gf-values are so useful. While the precise Oxford measurements (see Simmons and Blackwell, 1982, for references) cover the low-excitation lines (Fig. la) which are mostly too violet and too strong for abundance studies, the Kiev workers have added the best lines in the solar visual, thus precisely the weaker lines of higher excitation one needs (Fig. 1b). Figure 2 demonstrates this for the solar Fe I curve of growth: the Doppler part, which is the only really useful part, is made up of Kiev lines (dots).
Recent Advances in X-Ray Astronomy
Authors: Tanaka Yasuo
Published: March 2016

X-ray astronomy was born in June 1962 with a totally unexpected discovery of a bright X-ray source (presently known as Sco X-1) in a historic rocket flight conducted by Riccardo Giacconi, Herb Gursky, Frank Paolini and late Bruno Rossi. In the last 30 years, astronomy through the newly opened window has made a dramatic expansion.

The universe contains enormously rich varieties which had been left unexplored until recent times. From 40’s through 60’s, new wavelength windows, radio, infrared and X-rays successively opened. As a result, the presence of objects and regions distributed over an extremely wide temperature range from a few Kelvin through hundreds of millions of Kelvin were discovered. A burst of surprising discoveries made in 60’s marked the opening of a whole new era of multi-wavelength astronomy.
Report of the IAU WGAS Sub-group on Numerical Standards
Authors: Standish E.M.
Published: March 2016

The Report of the Sub-Group on Numerical Standards of the IAU Working Group on Astronomical Standards (WGAS) is presented. The report is intended to incorporate the majority of the responses received from the e-mail recipients of the series of WGAS Circulars. The report proposes to retain the present (1976) IAU System of Astronomical Constants and also proposes to establish a IAU File of Current Best Estimates. Further, the report proposes the establishment of a Maintenance Committee, governed by a set of proposed by-laws, in order to oversee the maintenance of the new file.
Precessional Constant Determined from Optical Astrometry
Authors: Miyamoto M.
Published: March 2016

We have analyzed proper motions of about 30000 K-M giants chosen from the astrometrie catalogue ACRS Part 1 (Corbin and Urban 1991). To avoid localized velocity fields, these K-M giants are chosen from the heliocentric distance interval 0.5 - 1.0 kpc. Starting from the initial trial of the luni-solar precessional correction Δρ ~ —0”.3/cy, we have found that the motion of stars are well expressed in terms of the Oort constants for the K-M giants. After confirming that the K-M giants are in a steady-state, we have applied the velocity-field model of the plane-parallel galactic rotation with non-zero Oort constants. Then, we have found a rational set of the corrections to the FK5 system: Δρ = -0”.27 ± 0”.03/cy and Δe + Δλ = —0”.12 ± 0”.03/cy, as is shown in Table 1 (Miyamoto and Sóma 1993). In consequence, the FK5 system is still rotating.
The Orientation of Future JPL Planetary Ephemerides
Authors: Standish E.M.
Published: March 2016

In the future, the ephemerides produced at JPL will be based upon the reference frame of the radio source catalogues. Recent planetary observations have been made directly with respect to the radio frame, and these observations have shown a satisfying degree of absolute accuracy and internal consistency; they provide an automatic frame-tie.
Current Status of Geophysical Models of Nutation
Authors: Mathews P.M. , Dehant V.
Published: March 2016

Geophysical modeling of nutations involves (a) the formulation of a general theory of the forced nutations of an idealized Earth (spheroidal, oceanless, elastic), supplemented by separate theoretical treatments of the effects of the oceans, anelasticity, and other deviations from the ideal, and (b) fitting of the theoretical expressions to VLBI-estimated amplitudes of the various spectral components of the nutations. The aim is to obtain best-fit estimates of Earth parameters which influence the nutations; and the degree of success of the modeling is judged by the precision of the estimates obtained, as well as the quality of the fit as measured by χ2red, the chisquared per degree of freedom.

We present here our findings from two types of fits using, for the observational input, the nutation amplitude estimates for seven important pairs (retrograde and prograde) of circular nutations, together with their standard errors and mutual correlations, which were kindly furnished by T.A. Herring (private communication, 1993). The theoretical framework employed was that of Mathews et al. (1991), hereinafter referred to as MBHS, together with the Zhu and Groten (1989) rigid Earth nutation series modified to take account of the recently-estimated correction of −0.3mas/cyto the precession constant. Estimates of ocean tide effects, and of anelasticity effects based on Wahr and Bergen’s (1986) results for model QMU with α = 0.15 (hereafter abbreviated to WB), were taken from Herring et al. (1991). Alternative estimates of anelasticity effects (DZ, due to Dehant (1990) based on the Zschau model), were also considered.
Progress in Realization of the Time Unit and Scales
Authors: Kovalevsky J.
Published: March 2016

The establishment of the TAI is done in two steps: the construction of the EAT from clocks in laboratories, then its steering by primary frequency standards. Great progress in the precision and stability of EAL was made by the generalized use of GPS time transfer and by the introduction of hydrogen masers and new very performant clocks. Only two primary frequency standards are sufficiently accurate to steer the frequency of TAI, but new standards are now being assessed. The present stability of TAI is 5.10−15 and the accuracy 2.10−14. Improvements should occur in the years to come.

The establishment of the International Atomic Time (TAI) and the resulting Coordinated Universal Time (UTC) by the time section of BIPM is done in two steps (Guinot and Thomas, 1988). At first, a free atomic scale, EAL (Echelle atomique libre) is built in two month blocks combining data from about 200 atomic clocks kept by 60 laboratories and regularly reported to the BIPM by 45 centres which maintain a local coordinated universal time, UTC(k). Then, the duration of the scale interval of EAL is compared with data from primary caesium standards producing the SI second which, in turn, is converted on the rotating geoid as the unit scale of TAL A linear function of time with the necessary slope is added to EAL to ensure the accuracy of the TAI scale interval.
The Variation of UT from 700 BC to the Present
Authors: Stephenson F.R. , Morrison L.V.
Published: March 2016

Records of solar and lunar eclipses in the period 700 BC to AD 1600 originating from the ancient and medieval civilisations of Babylon, China, Europe and the Arab world are amassed and critically appraised for their usefulness in answering questions about the long-term variability of the Earth’s rate of rotation. Results from previous analyses of lunar occultations in the period AD 1600-1955.5 and from high-precision data in AD 1955.5-1990 are included in the dataset considered in this paper.
Joint Discussion 6: Sun and Heliosphere - Challenges for Solar-Terrestrial Physics, Magneto-and Hydrodynamics
Authors: Huber Martin C.E. , Pedersen Arne , Fröhlich Claus
Published: March 2016

There is one astrophysical system, where the sites of a star’s mass loss can be localised and observed in detail, and where the behaviour of the resulting stellar wind in the star’s environment and around orbiting obstacles can be investigated in situ: it is the Sun, the heliosphere and the surroundings of planets — among the latter most prominently the terrestrial magnetosphere. Indeed, within a year or so a fleet of satellites equipped with sophisticated remote-sensing and in-situ instruments will make this astronomical paradigm, or more precisely, the solar-terrestrial system accessible to intensive, multi-disciplinary study.

Four identical CLUSTER spacecraft, orbiting the Earth within the magnetosphere, the surrounding space and the particularly interesting plasma boundary layers will perform a three-dimensional in-situ study of plasma-heating, particle-acceleration and other small-scale plasma processes (Schmidt and Goldstein,1988). A number of other missions — some of them already in orbit, like GEOTAIL and WIND, some to be launched within one or two years, like INTERBALL and POLAR — will provide information about the Earth’s magnetosphere and the solar wind on larger spatial scales. These missions are described in a Brochure issued jointly by the European Space Agency, NASA, the Japanese Institute of Space and Astronomical Science and the Rssian Space Agency, which can be obtained from A. Pedersen at the above address.
Observable Signals of Coronal Heating Processes
Authors: Venkatakrishnan P.
Published: March 2016

The solar corona is thought to be sustained by waves, currents, turbulence or by velocity filtration. For efficient wave heating of the corona, only the Alfven waves seem to survive the effects of steepening and shock dissipation in the chromosphere (Zirker, 1993, Solar Phys. 148,43) and these can be dissipated in the corona by mode conversion or phase mixing (Priest, 1991 in XIV Consultation on Solar Physics, Karpacz). Enhanced line width of 530.3 nm coronal line seen within closed structures (Singh et al., 1982, J. Astrophys. Astron. 3,248), association of enhanced line width of HeI 1083 nm line with enhanced equivalent width (Venkatakrishnan et al., 1992, Solar Phys. 138,107), and gradients seen in the MgX 60.9 and 62.5 nm coronal line width (Hassler, et al., 1990, Astrophys. J. 348, L77), are possibly some examples of the observed signals of wave heating. Current sheets, produced in a variety of ways (Priest and Forbes, 1989, Solar Phys. 43,177; Parker, 1979, Cosmical Magnetic Fields, Ox. Univ. Press), can dissipate and provide heat. The properties of current sheets can be inferred from fill factors, emission measures (Cargill, 1994, in J.L. Burch and J.H. Waite, Jr. (eds.) Solar System Plasma Physics: Resolution of Processes in Space and Time, AGU Monograph), hard xrays (Lin et al., 1984, Astrophys. J. 283,421), and radio bursts (Benz, 1986, Solar Phys. 104,99). The association of large scale currents with enhanced transition region (deLoach et al., 1984, Solar Phys. 91,235.) and regions of enhanced magnetic shear with brighter corona (Moore et al., 1994, Proc. Kofu Symp) are of some possible interest in this context. Self consistent calculations of the turbulent cascade of energy from the scales of photospheric motions down into dissipative scales (Heyvaerts and Priest, 1992, Astrophys. J. 390,297) predict the width of coronal lines as a function of the properties of the forcing flows. Velocity filtration caused by free streaming effects off a non maxwellian boundary distribution of particles may well result in a plasma having coronal properties (Scudder, 1992a, Astrophys. J. 398,299; 1992b, Astrophys.J.11 398,319). The observable signals are the variation of line shapes with altitude.
Fractionation of the Solar Wind
Authors: Von Steiger R.
Published: March 2016

The composition of the solar wind (SW) is not a true sample of the solar composition, but it is fractionated with respect to the solar photosphere. This fractionation follows the well-known first ionization potential (FIP) pattern: When plotting the SW abundances with respect to the solar abundances as a function of FIP, a step function is obtained (Fig. 1). The step at ∼ 10eV has a height of 3-5 in the slow SW, but this is reduced to 1.5-2 in the fast streams, which originate in the coronal holes. The data given in Fig. 1 are collected and discussed in von Steiger & Geiss (1994), including the “FIP exceptions”, Kr and Xe.

The process leading to the observed overabundance of the low-FIPs has been located to operate by atom-ion separation across magnetic field lines in the chromosphere (Geiss, 1982), because this is the only region of the solar atmosphere where a significant fraction of the gas is neutral. The fractionated abundances observed in the S W are thus important tracers for processes and conditions at this site.
Observations
Authors: Rhodes E.J.
Published: March 2016

The field of observational helioseismology began in 1960 when Leighton, Noyes, and Simon (1962) discovered the so-called solar “5-minute” oscillations at the Mt. Wilson Observatory. However, it was not until roughly two decades ago, when these 5-minute oscillations were demonstrated to be sound, or acoustic waves, which were trapped within the solar interior (Deubner, 1975), that observational helioseismology began to grow in earnest. In the nearly two decades which have elapsed since its infancy, observational helioseismology has been the source of many surprising new results concerning the solar interior - far more results than there is space to list here. These past two decades have also been a time of great intellectual ferment which has led to the development of new instrumental tools and new analysis techniques at an astounding rate, with many of these tools and techniques not even being contemplated two decades ago.
Abundances in Local Group Planetary Nebulae
Authors: Kaler James B.
Published: March 2016

We are able to measure the chemical compositions of hundreds of planetary nebulae in our own Galaxy and in the Magellanic Clouds. Why, therefore, do we need to expend the effort to observe much more difficult targets in other Local Group galaxies? A severe lack of distances does not allow us to place Galactic planetary nuclei on the log L-log T plane with any degree of accuracy, so we cannot properly examine composition differences relative to core mass and state of evolution. We can perform such tasks for Magellanic Cloud objects, but do not know how the Clouds’ low-metallicities affect the results, and thus do not know how this sample of planetaries relates to the nebulae in our own system. We know, for example, that in the Clouds, nitrogen enrichment begins above a core mass of about 0.68 M⊙ (Kaler and Jacoby 1990), but other than a clear link between core mass and chemical enrichment in the Galaxy, do not know at what point it becomes important. To study such relationships, we therefore have to go to other galaxies with a variety of initial conditions for which distances are secure, namely those of the Local Group.
Network of Oriental Robotic Telescopes
Authors: Querci François R.
Published: March 2016

We should like to report on the Network of Oriental Robotic Telescopes, otherwise the ORT network. Our objective is non-stop observations of variable stars by collaboration with other networks of automated photometric telescopes, complementary to the ORT network in longitude and latitude intervals, such as the GNAT in the U.S.A., the Chilean cordillera stations, the South African stations, etc. As a first step we will deal with photometric telescopes, then we will extend them to spectroscopy.

From 12-year archives of meteorological satellites, it appeared that sites located around the north latitude from 15° to 35° and from 10° west to 110° east in longitude have high-quality astronomical conditions with a significant annual number of clear nights. Such sites involve Islamic countries from Morocco to the western deserts of China. In addition to their astronomical history, the Islamic countries are suitable because they have high mountains in semi-desert areas, i.e. a clear sky with low telluric absorption. The final site selection will be based upon local astronomical tests, such as seeing and scintillation measurements.
H2O in Star Forming Regions
Authors: Nisini Brunella , Giannini Teresa
Published: March 2016

This paper will review the importance of the water molecule in the various stages of the star formation process, addressing in particular how the recent observations obtained with the ISO and SWAS satellites have challenged the existing theoretical models.
Astronomy, Physics, and Chemistry of
Authors: Oka Takeshi
Published: March 2016

This is a report of a Discussion Meeting titled “Astronomy, Physics, and Chemistry of ” which was held on February 9 and 10, 2000 at the Royal Society in London.
Analysis of the Residuals between Theoretical Nutations and VLBI Observations
Authors: Dehant V. , Feissel M. , de Viron O. , Yseboodt M. , Bizouard Ch.
Published: March 2016

The recent theoretical developments have provided accurate series of nutations, which are close to the Very Long Baseline Interferometry (VLBI) data. At the milliarcsecond (mas) level, three series are available: MHB2000 (Mathews et al. 2000), FG2000 (Getino and Ferrándiz 2000), and SF2000 (Shirai and Fukushima 2000a,b) (see Dehant 2000, and in this volume, for more information and for a short description of these models).

In the first part of our work we have compared these models with the (VLBI) observations (Ma et al. 2000) by computing rms of the residuals for several time intervals of measurements. We have concluded that these series have comparable precision.
Jets and Outflows from Massive Protostars
Authors: Menten Karl M.
Published: March 2016

Molecular outflows are found in most regions of massive star formation. However, evidence for highly collimated jets from massive protostars is still elusive. This paper briefly summarizes the observational status.
Scattering of Planetesimals from Young Planetary Disks: Application to the β Pictoris System
Authors: Beust Hervé , Thébault Philippe
Published: March 2016

Transient redshifted events monitored in the spectrum of β Pictoris have been interpreted as resulting from the evaporation of numerous comet-like bodies in the vicinity of this star. The dynamical origin for this phenomenon is attributed to mean-motion resonances (4:1 and 3:1) with a Jovian-like planet. Numerical simulations of this phenomenon are able to correctly reproduce the dynamical characteristics of the star-grazers observed. The numerical study allows to estimate the density of the planetesimal disk from which the bodies are supposed to originate, i.e. ∼ a few 108 bodies per AU. A key issue with this model is the refilling of the resonances, as without refilling they should be cleared within a few 105 yr and the observed phenomenon should stop. Collisions among planetesimals are a plausible mechanism. Collisional simulations show that collisions are able to sustain the observed phenomenon over much more than 106 yr, provided the population of the disk is high enough. The mass density of this population is estimated to a few tens of Earth masses per AU, which is only marginally realistic. However, the mass estimate is very poorly constrained.
Comets and Circumstellar Dust
Authors: Waelkens C. , Waters L.B.F.M.
Published: March 2016

Spectra obtained with the Infrared Space Observatory ISO of the dusty disks surrounding young stars display several characteristics which suggest the presence of large amounts of cometary material during these early stages. Of special interest are crystalline silicates and hydrated silicates, which surprisingly appear to be present already in cool material surrounding young objects. Another surprise is the occurrence of cometary features in the disks surrounding some binary post-AGB stars.
Error Growth of the KS Regularized Orbital Motion
Authors: Arakida H. , Fukushima T.
Published: March 2016

Long term integrations of highly eccentric orbits are necessary to study the orbital evolution of comets and some minor planets. We discovered that the KS regularization is effective not only in the sense the magnitude of local error is reduced in the close approach but in the sense it dramatically reduces the positional error growth. In fact, it is in proportion to the fictitious time s while the Cowell method, the usual integration in 3-dimensional space leads to the positional error growing as a quadratic function of time. This good property is independent of the type of the integrators, of the type of the perturbations or of the magnitude of the nominal eccentricity. This phenomenon is based on the fact that the equations of motion in the KS variables are those of perturbed harmonic oscillators. As the best numerical integrator, we recommend the predictor formula of symmetric linear multistep method because (1) it runs fast since only one functional evaluation is required at each step, (2) its error constants are close to the minimum among the class of linear multistep methods, (3) its numerical error of the conserved quantities remains almost constant with time, and (4) it shows no stepsize resonance/instability in integrating the KS regularized equation of motions and the harmonic oscillator potential is the only case where the step size instability does not appear. Therefore the KS regularization is useful to investigate the long term behavior of perturbed two body problems for studying comets, minor planets, Moon, and artificial satellites.
Joint Discussion 5 - Mixing and Diffusion in Stars: Introduction and Brief Overview
Authors: VandenBerg Don A. , Zahn Jean-Paul
Published: March 2016

Our understanding of transport processes in stars is still in its infancy. First consider overshooting. There is now ample evidence from, e.g., the best-observed binary stars and fits of models to observed colour-magnitude (C-M) diagrams that some amount of mixing must occur beyond the classical boundary of the convective core set by the Schwarzschild criterion. Such mixing can be achieved by convective penetration; however, despite impressive progress on the theoretical front, a rigorous prediction of the extent of overshooting has not yet been achieved. As a result, most stellar evolutionary calculations have simply opted to extend convective core sizes by an amount (usually measured as a fraction of a pressure scale height) that produces reasonable consistency with observations. But how realistic are such models? To what extent does the overshooting depend on mass and/or evolutionary state? What is the role of rotation in determining the size of convective cores? How much does rotation-induced meridional circulation contribute to such mixing?
The Importance of Spatial Information in Sunspot Records
Authors: Brooke John M. , Pelt Jaan , Pulkkinen Pentti , Tuominen Ilka
Published: March 2016

We show that the spatial information in historical sunspot records, in particular the latitude of the spots, can be of great importance in determining the long term behaviour of the solar magnetic cycle. We examine a continuous record of sunspots with full spatial data from 1853-1996 compiled from the records of Carrington, Spörer, the GPR and SOON. Analysis of the latitudinally-weighted observations indicates that there is a previously unremarked oscillation of the solar magnetic equator with a period of approximately 90 years.
Driving Layer of Solar Activity
Authors: Wang Jingxiu
Published: March 2016

There should be a driving layer on the Sun, in which the interaction between magnetic field and plasma motion would provide enough magnetic energy and necessary topology for the explosion of solar activity in the corona.

Although the exact location of the driving layer is not known, phenomenologically, the photosphere is acting, in many aspects, as the driving layer. Vector magnetic field measurements on the photosphere are greatly needed in clarifying the nature of the driving. Two elementary processes, flux emergence and cancellation, and one basic structure, magnetic interface between topology-independent magnetic loops, are key elements in the driving.
Oxygen Abundances from Infrared OH Lines
Authors: Balachandran Suchitra C. , Carr John S. , Carney Bruce W.
Published: March 2016

Oxygen abundances are derived from IR-OH lines and compared to published results from UV-OH lines.
X-Ray Substructures of BCS, NORAS, REFLEX, Radio Halos/Relics and Cooling Flow Clusters of Galaxies
Authors: Schuecker Peter , Böhringer Hans , Feretti Luigina
Published: March 2016

The results of a systematic study of substructures in X-ray surface brightness distributions of BCS, NORAS, REFLEX, radio halo, relic, and cooling flow clusters of galaxies based on RASS data are presented. At least 40 percent of the clusters show substructure. Indications for a cluster morphology-density relation are found. The fraction of clusters with substructure seems to be higher for halo and relic clusters and lower for clusters with cooling flow signature.
Radio Sources and Their Environment
Authors: Owen Frazer , Ledlow Mike , Eilek Jean
Published: March 2016

The properties of radio sources in and outside of Abell clusters are reviewed. The properties of sources in and out of Abell clusters are shown to be surprisingly similar. However, sources in dense cluster cores do not fit this pattern and, as in Virgo A (M87), have a significant, sometimes dominant input of energy into the “cooling core” environment.
Geology and Composition of the Icy Galilean Satellites
Authors: Pappalardo Robert T.
Published: March 2016

Analysis of data from the Galileo spacecraft continues to provide significant advances in our understanding of the geology and composition of Jupiter’s icy Galilean satellites Callisto, Ganymede, and Europa.
The Mars Global Surveyor Mission: Description, Status, and Significant Results
Authors: Albee Arden
Published: March 2016

The Mars Global Surveyor (MGS) spacecraft entered an elliptical orbit at Mars on September 11,1997. Until March 1999 it acquired scientific data from decreasing-sized orbits as it alternated between aerobraking and nadir-pointing modes. This time period provided tremendous advances in our knowledge of the shape and topography, the gravity field, the magnetic field, and the atmospheric structure and dynamics of Mars. In April 1999 MGS entered its planned two years in the mapping mode. In this mode the high-gain antenna tracks Earth so that the instruments can take data continuously and so that the camera system can return high-resolution data in real-time. IR spectral and temperature data, as well as high-resolution images are providing new insight into the geologic evolution of Mars. All data is being archived at about six month centers so that it is available in electronic format to the international community.
Black Hole Binary Mergers
Authors: Makino Junichiro
Published: March 2016

I overview the current understanding of the evolution of massive black hole (MBH) binaries in the center of the host stellar system. One of the main questions is whether the stellar dynamical effect can make the MBH binary hard enough that they can merge through gravitational wave radiation. So far, theories and numerical simulations suggested otherwise, since the hardening time scale becomes very long once ”loss cone” is depleted. I’ll present the result of recent simulations on this hardening time scale, and discuss its implication on the formation history of massive black holes.
The Early Chemical Evolution of Dwarf Irregular Galaxies
Authors: Hensler Gerhard , Recchi Simone , Köppen Joachim , Rieschick Andreas
Published: March 2016

Investigations have been performed to understand the age of dwarf irregular galaxies from the point of view of their presently low chemical abundances and the enhanced star-formation rate. While for a few objects, like e.g. I Zw 18, their assumed relative youth can be verified by models taking a double-starburst behavior into account, those dlrrs with old underlying stellar populations have passed the regime of observed N/O-0 values within almost 2 Gyrs after their formation even with gas loss by means of supernova-driven galactic winds. Therefore alternative processes like gas infall must be invoked.