bluuebunny/crossref_metadata_2025 huggingface dataset:
Acceleration of Runaway Electrons and Joule Heating in Solar Flares
Authors: Holman Gordon D.
Published: June 2019

D.C. electric fields provide the simplest and most direct means of accelerating electrons out of a thermal plasma. Most solar flare models result in the production of D.C. electric fields. On the other hand, microwave and hard X–ray observations of flares provide specific requirements for the number and energy of energetic electrons produced during a flare, and the timescales involved in accelerating them. The microwave emission from flares is understood to be gyrosynchrotron radiation from electrons with energies of 100 keV or greater. The hard X–ray emission (≳ 25 keV) can be interpreted as being either thick–target bremsstrahlung from non–thermal electrons (thin–target radiation may also contribute to the X–ray emission, but the process is less efficient), or thermal bremsstrahlung from hot, impulsively heated plasma. Hence, it is of interest to study the electric field acceleration of “runaway” electrons and the simultaneous Joule heating of the thermal plasma in light of these results from flare observations, without recourse to a specific flare model. Some of the results of such a study are summarized here.
Solar Microwave Emission in Active Regions
Authors: Lokanadham B. , Subramanian P. K. , Reddy M. Sateesh , Reddy B. M. , Lakshmi D. R.
Published: June 2019

Multi–frequency Observations of Solar Microwave bursts recorded during solar maximum period 1980–81 are analysed and compared with x–ray data for studying the nature of microwave emissions from active regions. Most of the microwave burst spectra showed that the spectral index below the peak frequency is always less than 2.

The magneto-ionic conditions of the burst sources and the electron energies as obtained from these multi-frequency observations of the bursts showed that the centimetric and x-ray observations are satisfactorily explained, if the emitting regions are dense, hot and compact associated with strong magnetic fields of a few hundred gauss, suggesting that the thermal gyroresonance process is the most likely emission mechanism involved in the emission of microwave and x-ray radiations from the active regions of sun.
Nonlinear Evolution of the Resistive Tearing Mode
Authors: Steinolfson R. S. , van Hoven G.
Published: June 2019

Numerical solutions of the MHD equations are used to investigate the nonlinear behavior of the tearing instability. The mode evolves from a linearly growing excitation, followed by a period of greatly reduced nonlinear growth. Constant-Ψ solutions evolve much more slowly than comparable nonconstant-Ψ modes with orders of magnitude less conversion of the stored magnetic energy. The nonconstant-Ψ computations indicate a reduction by approximately 20% of the energy in the initial shear layer. For long–wavelength solutions, secondary–flow vortices, opposite in direction to the linear vortices, generate a new magnetic island centered at the initial x-point.
Anomalous Transport Induced by Field Aligned Currents and its Relation to Electromagnetic Coupling
Authors: Dum Christian T.
Published: June 2019

The wealth of detailed observations on transport in turbulent plasmas that has become available over the last decade from laboratory experiments, in situ space craft observations and computer simulation demonstrates that in contrast to classical transport, the various steps in the analysis of anomalous transport, involving microscopic processes and the global dynamics, are closely coupled. It also points to many new, exciting, and truly anomalous phenomena. These statements apply especially to the highly dynamic processes connected with field aligned currents. The usually vast difference in time or length scales must allow for considerable simplications in the analysis, depending on the system at hand, but requires careful consideration of the microscopic or macroscopic physics that of necessity is to be treated in a simplified manner. This point is demonstrated by using a marginal stability approach in a numerical model for field aligned currents and electromagnetic coupling in an extended system. Its aim is to see how energy is supplied to a localized dissipation region from a distant generator and how this dissipation in turn affects the global electro-dynamic structure. In addition to the earth's auroral flux tubes, for which this model was primarily designed, these questions are of importance to other extended current systems in astrophysics. Microscopic processes supporting enhanced dissipation and leading to other truly anomalous processes such as acceleration of selected particle groups are then discussed in relation to the global problem.
Plasma Heating by Alfvén Waves - Kinetic Properties of Magnetohydrodynamic Disturbances
Authors: Hasegawa Akira
Published: June 2019

Mechanisms of Alfvén wave heating in space-astrophysical plasmas are presented with particular emphasis on the parallel electric field generated in the magnetohydrodynamic perturbations due to the finite Larmor radius effects.
MHD Equilibrium and Instabilities in Extragalactic Jets
Authors: Ferrari Attilio
Published: June 2019

Morphologies, energetics and nonthermal radiation emission of extragalactic radio sources can be explained in the framework of models based on the physics of supersonic jets interacting with the surrounding intergalactic medium. In this review current physical interpretation of acceleration, collimation, modulation and nonthermal radiation of these jets are discussed. We begin with an analysis of the equilibrium configurations of collimated flows; the propagation outside the galactic nuclei is shown to be modulated by fluid, MHD and resistive instabilities, which, at the same time, support charged particle acceleration by turbulent stochastic processes, and consequently nonthermal radiation emission from the radio to the X-ray range. Large scale morphologies (knots, wiggles and bendings) are considered from the point of view of their interpretation as global perturbations of the flow produced by fluid instabilities.
Is the Jet in M87 Magnetically Confined?
Authors: Hardee Philip E.
Published: June 2019

Calculations of the minimum pressure in the M87 jet show that the jet pressure is an order of magnitude in excess of the thermal pressure in the interstellar medium calculated from the X-ray emission. The continuous energy input required to produce the jet emission is incompatible with a freely expanding jet. On the other hand, the uniform jet expansion, the jet emission and the jet polarization can be explained if the jet is self-confined by j x B forces.
Creation of High-Energy Electron Tails by the Lower-Hybrid Waves and its Relevance to Type II and III Bursts
Authors: Tanaka Motohiko , Papadopoulos K.
Published: June 2019

It is commonly anticipated that high-energy electrons play an important role for the wave emission in flare bursts. For instance, electrons with >100 KeV are considered to create microwave emissions through gyro-synchrotron process and hard x-rays may be due to bremstrahlung with >25 KeV electrons. However, electron acceleration mechanism itself is still in speculations.
Non-Stochastic Acceleration of Protons in the Magnetic Neutral Sheet
Authors: Sakai Jun-ichi , Sugihara Ryo
Published: June 2019

A rapid non-stochastic proton acceleration mechanism by electrostatic waves during the substorm activity in the magnetospheric tail is presented to explain the origin of energetic protons (up to MeV). The protons are accelerated normal to the neutral sheet. Near a reconnection point, however, the protons are also accelerated along the sheet by a second process.
Beam-Return Current Systems in Solar Flares
Authors: Spicer D. S. , Sudan R. N.
Published: June 2019

The importance of electron beams in solar flare dynamics is well known. In order to understand the dynamics produced by beams it is essential to have a clear understanding of the role beam driven return currents play and whether electrostatic or inductive electric fields maintain the return current. We show that inductive electric fields are responsible for driving return currents under solar conditions.
Collisionless Effects on Beam-Return Current Systems in Solar Flares
Authors: Vlahos Loukas , Rowland H. L.
Published: June 2019

A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and nonlinear evolution of plasma waves as a function of time is analyzed with the use of a set of rate equations that follow in time the non-linearly coupled system of plasma waves-ion fluctuations. The nonthermal tail formed during the stabilization of the precipitated electrons can stabilize the Anomalous Doppler Resonance instability and prevent the isotropization of the energetic electrons. The precipitating electrons modify the way the return current is carried by the background plasma. In particular, the return current is not carried by the bulk of the electrons but by a small number of high velocity electrons. For beam/plasma densities ≳ 10−3, this can reduce the effects of collisions and heating by the return current. For higher density beams where the return current could be unstable to current driven instabilities, the effects of strong turbulence anomalous resistivity is shown to prevent the appearance of such instabilities. Our main conclusion is that the beam-return current system is interconnected and how the return current is carried is determined by the beam generated strong turbulence.
Concepts of Reference Systems
Authors: Guinot Bernard
Published: June 2019

With the atomic clocks and VLBI catalogues of extragalactic sources, the theory-independent references for both space and time will be quasi ideal in their underlying principles (non-rotation of very distant objects, constancy of the frequencies associated to atomic transitions). The paper is an attempt to clarify the role of these natural references with respect to those which are implicitly defined by the dynamical theories.

The example of time is discussed, since it already gave rise to serious difficulties, but similar problems may occur about the space references. Such complexities are suprising: one could have expected simplifications from the use of references which are not entangled with theory. Some suggestions are made for the use of these natural references.
Some Effects of Different Sources of Variation of Latitude Data on Meridian Circle Catalogues
Authors: Rafferty T. J.
Published: June 2019

Fundamental meridian circle observations require the variation of latitude to be applied before the observations are combined to form a catalogue. In the past 80 years, different observatories have used various determinations of polar motion to reduce their observations. This study shows that the use of different determinations of the latitude variation significantly affects the individual observations and can introduce large zonal errors of the level of 0.05 seconds of arc into the catalogue's declination system.
The Extragalactic Optical/Radio Reference Frame. A Progress Report, IAU Comm. 24 Working Group
Authors: de Vegt Chr.
Published: June 2019

A catalog of 233 strong compact extragalactic radio sources which display optical counterparts has been prepared by the working group as a basis for the establishment of an almost inertial extragalactic reference frame. Optical properties of the catalog sources are summarized and further requirements for a refinement and extension of the present data are discussed.
Can a System be Defined for the New Edition of the Yale Parallax Catalogue?
Authors: van Altena William
Published: June 2019

A preliminary analysis has been made of data in the forthcoming edition of the Yale Parallax Catalogue to study the possibility of defining a system of observatory zero-points and external accuracies. Based on this analysis and those of several other authors, I conclude that it is not likely that a unique system of zero-points can be established. It may, however, be possible to establish some values for the average external accuracy of the parallaxes, but more work remains to be done on both of these issues. These conclusions are in agreement with those reached by several other authors.
Astrometry of Star Clusters: Problems, Techniques, and Opportunities
Authors: Cudworth Kyle M.
Published: June 2019

The astrophysical problems that can be attacked via proper motions in star clusters are set forth and current techniques and opportunities are described. Cluster membership work continues to progress with recent work mixing plates from various telescopes, including large reflectors. More and better internal motion studies are needed to have a significant impact on the dynamical models. Absolute proper motions of clusters present a very difficult problem, but for globulars, at least, the data are desperately needed.
Design Characteristics of the 1.56 m Astrometric Telescope and its Usage in Astrometry
Authors: Lai Wan , Neng-Hong Zhu , Lan-Juan Wang , Zheng-Hua Yang , Yi-Jin Zheng
Published: June 2019

The 1.56m astrometric telescope (Fig. 1) is designed mainly for determining trigonometric parallaxes of faint stars.

In order to keep the design as simple as possible, the telescope has only a Ritchey-Chretien focus and will accomodate plates 200 × 200 mm. We also plan to design several pieces of auxiliary equipment such as a medium dispersion grating spectrograph, a photometer, a reducing camera, and an electrographic camera, all of which are in the second stage of engineering. The whole project consists of four parts.
The Oscillating Slit Micrometer of the Meridian Circle PMC 190 Tokyo
Authors: Kühne C. , Miyamoto M. , Yoshizawa M.
Published: June 2019

The meridian circle installed at the Tokyo Astronomical Observatory in 1982/83 is equipped with a photoelectric Double Slit Micrometer which is one of the basic prerequisites for fully automatic observation. A slit plate is located in the image field of the telescope. It oscillates parallel to right ascension while being guided at the mean traveling speed of the star.

The paper describes the procedure by which the moment of the star passage through the instrument's meridian and declination is determined. Furthermore, the autocollimation devices are described which are an essential prerequisite for the determination and periodical checking of the instrumental errors.

Also, the measuring devices for the passage of the sun and the moon are dealt with briefly.
A New Astrolabe
Authors: Billaud G.
Published: June 2019

To obtain a quite impersonal astrolabe, a new instrument has been built. The first UTo-UTC results show very good agreement with the BIH scale.
The Design of Modern Meridian Circles for the Observation of Faint Objects
Authors: Yoshizawa M. , Miyamoto M.
Published: June 2019

Definitions of Instantaneous Instrumental Coordinates and Local Horizontal Coordinates of the photoelectric meridian circle of Tokyo Astronomical Observatory are given, and a method to determine the positions of stars by using a scanning double slits micrometer are presented. It is found that stars up to 12.2 mag are observable by making a composite photon intensity. Discussions on the application of observations of faint objects by meridian circles are presented.
Automatic Horizontal Meridian Circle at Pulkovo
Authors: Gumerov R.I. , Kapkov V.B. , Pinigin G.I.
Published: June 2019

The goal of the new design and modernization of transit circles is complete automation (Pinigin and Shornikov, 1983; Hughes,1982; Requieme and Mazurier,1982). For example, all the essential steps of star observations and the determination of the instrument parameters have been automatized at the Tokyo and Brorfelde Observatories (Yoshizawa and Yasuda, 1982; Fogh Olsen and Helmer, 1978). Computer control was introduced for the automation of all the major operations of the Pulkovo horizontal meridian circle (HMC). This involves an automatic setting system (mirror setting), a circle reading system, two photoelectric eyepiece micrometers, meteorological data sensors and a rotating drive of the pendulum horizon (Figure 1). All these are controlled by a microcomputer of the “Electronica C5-12” type.
The Transit Instrument Under Optimum Conditions
Authors: Petrov G.M.
Published: June 2019

On the basis of experience with RA determinations during the polar nights of 1974–1977 on West Spitzbergen and of RA determinations of the Sun, Mercury and Venus at high latitutes one can conclude as follows: At high geographical latitudes the polar night conditions are nearly optimal for absolute determinations of stellar coordinates; high altitude sites near the equator are best for day time observations. It is suggested that observatories be built for absolute position determinations on Spitzbergen, and on McMurdo on the Antarctic Continent. The link between observations in the northern and the southern hemispheres can be established through observations at a high-altitude equatorial observatory, where the Sun and the planets can also be observed.
A New Method of Determining Absolute Azimuth and Latitude and Suggestion for a New Type of Meridian Circle
Authors: Wei Mao , Zhi-Ming Li , Yu Fan , Shiao-Shun Hu , Ming-Huei Du , Hua Li
Published: June 2019

This article describes a new method by which azimuth and the instantaneous latitude of a meridian-prime vertical-transit instrument can be determined absolutely in mid-and low- latitude areas, and discusses some experimental observations obtained on a remodeled ZEISS transit instrument. Requirements for the development of a new type of transit circle along the lines of this new method are also presented.
HIPPARCOS Data Reductions
Authors: Lindegren L.
Published: June 2019

The raw data produced by the European Space Agency's astrometry satellite HIPPARCOS – mainly photon counts from the primary detector (IDT) and star mappers – will be analysed in full by two independent reduction consortia, FAST and NDAC. The aim is however to generate, by 1993, a single catalogue of positions, proper motions, and parallaxes for the 105 programme stars, with additional information on photometry, multiple stars, and minor planets. This review outlines some practical and theoretical features of the data reductions.
The Guide Star Selection System and the Guide Star Catalog for Space Telescope
Authors: Russell Jane L.
Published: June 2019

The Guide Star Selection System (GSSS) will provide relative positions of two guide stars and the target for each observation of the Space Telescope as well as photometry for the guide stars. Being developed at the Space Telescope Science Institute, the GSSS is a production system which is based on PDS measurements of Schmidt survey plates. The specified accuracy for the system is +/−0.33 arcsec for the separation of the guide stars and 0.4 mag in the bandpass of the Space Telescope's Fine Guidance Sensors. The GSSS will produce two catalogs which will be used in the operation of the system. The Guide Star Photometry catalog includes photoelectric measurements (+/−0.05 mag) in B and V for six stars over the guide star range, 9.0 to 14.5 visual magnitude, near the central part of each 6 by 6 deg survey plate. The Guide Star Catalog will include the list of all possible guide stars and brighter, positions (at least +/−1 arcsec) and magnitudes (at least +/−0.4 mag) for essentially the whole sky complete to visual magnitude 15.
Distortions in Compact Steep-Spectrum Radio Sources
Authors: Wilkinson P. N. , Spencer R. E. , Readhead A.C.S. , Pearson T.J. , Simon R.S.
Published: June 2019

The size, and therefore the importance, of the population of compact, steep-spectrum, radio sources has only recently been recognised. While it is now clear that the extended steep-spectrum sources are powered by a pair of, originally anti-parallel, beams which transport energy to the outer lobes some 105–106 parcsec away, our understanding of the compact steep-spectrum sources is almost nil. This is largely because our radio maps have not had high enough resolution to show their structures in any detail. However 1.67 and 5 GHz MERLIN observations (resolutions 0″.25 and 0″.1) of the ~20 steep-spectrum 3CR sources whose LAS is ≲2″ have now allowed us to classify their structures, at least in broad terms. These MERLIN maps, and recent VLBI maps, show that while there is a wide range of structures - from colinear doubles to amorphous “blobs” - the “peculiar” structures are strongly concentrated in the objects whose optical counterparts are called QSO's.
Cores in Extended Quasars
Authors: Barthel P. D. , Miley G. K. , Schilizzi R. T. , Preuss E. , Cornwell T. J.
Published: June 2019

The Nuclear Radio cores of several nearby extended radio galaxies (e.g. M87, 3C236) consist not only of optically thick (< 1 pc) components, but also of emission on somewhat larger scale. As extended radio sources associated with quasars have on average stronger and more luminous radio cores (see e.g. Miley, 1980, Ann. Rev. Astron. Astrophys. 18, 165), we have started a project to study the properties of these quasar cores.
A 10 Station VLBI Map of 3C147 at 1661 MHz
Authors: Simon R. S. , Readhead A. C. S. , Wilkinson P. N.
Published: June 2019

The quasar 3C147 was observed in October 1982 with a ten-station VLBI interferometer in an effort to search for possible superluminal motion (Simon et al. 1983) in the core. Previous observations, in 1976, had revealed that the core consisted of two compact components embedded in a larger halo. The new high quality map reveals that this double structure has disappeared and it is not possible to interpret the structural changes unambiguously in terms of an expansion or contraction.
The Statistics of Bent Jets
Authors: Allan P. M.
Published: June 2019

I present some results of a study of the statistics of bent jets. The general conclusion is that non relativistic jets appear less bent than they really are, while relativistic jets appear more bent.
Stability Properties of VLBI Jets
Authors: Birkinshaw M.
Published: June 2019

The growth lengths of Kelvin-Helmholtz instabilities are calculated for three vortex-sheet bounded beams with v = 0.9c. These beams survive the action of the instability for distances of several hundred beam radii, but no prediction of a single dominant mode of breakup can be made.
A Relativistic Wind-Type Model for the Generation of VLBI Jets
Authors: Ferrari A. , Rosner R. , Trussoni E. , Tsinganos K.
Published: June 2019

We discuss wind-type solutions for flows from accretion funnels, and show under what physical conditions such flows can become supersonic and relativistic already very ciose to the stagnation point within the funnel. The acceleration is due to radiation emitted by the funnel walls, while the location of the transonic points is also affected by the geometrical shape of the funnel's cross-section.
The Structure of the Radio Nucleus of M81
Authors: Crane P. C. , Price R. M.
Published: June 2019

New observations of the radio nucleus of the nearby bright spiral galaxy M81 (NGC 3031) show that the structure of the nucleus is considerably more complex than previously thought. The radio nucleus has a slightly inverted, variable spectrum (de Bruyn et al. 1976; Crane, Guffrida, and Carlson 1976). The variability and VLBI observations (Kellermann et al. 1976; Jones, Sramek, and Terzian 1981) both indicate a linear dimension of ~1500 AU. The recent VLBI observations of Bartel et al. (1982) determined that nearly 100% of the emission originates in an elongated region with linear dimensions of 1000–4000 AU. Peimbert and Torres-Peimbert (1981) have classified the optical nucleus of M81 as Seyfert type 1.5 (the weakest known) with the narrow-emission-line region extending over ~5″ (Münch 1959).
VLBI Observations of Stellar Binary Systems
Authors: Mutel R. L. , Lestrade J. F. , Preston R. A. , Niell A. E. , Phillips R. B. , Webber J.
Published: June 2019

Since 1982 July we have been engaged in a systematic investigation of the milliarcsecond structure of the radio emission from several binary star systems, mainly in the RS CVn class (Hall, 1976). The first few observations utilized the MkII VLBI recording scheme, but no useful data were obtainable because of the relatively low flux levels involved Beginning in 1982 December, we have been using the MkIII system with large telescopes and have successfully detected seven binary systems (UX Arietis, HR 1099, Algol, II Peg, σ Crb, and the distant system LSI 61°303). A summary of the three experiments already completed is given in Table 1.
Set Up and Testing of a Software Package for the Geodetic Analysis of VLBI Data +
Authors: Caporali A. , Labini G. Sylos
Published: June 2019

The need for centimetric accuracies set by the application of the VLBI technique to geodesy implies a considerable computational effort, because of the intrinsic complexity of the model and because there is an increasingly large number of calibrations and corrections which can be accounted for only via software. The program VLBI 3 (Robertson, 1975) has been developed for the geodetic and astrometric analysis of VLBI data. It includes an accurate theoretical model of the observables and is supported by a number of routines for parameter fitting and input/output operations with data and results. The original VAX version of VLBI 3, due to N. Bartel and M.I. Ratner, runs in batch mode and requires routines which are in general unavailable in standard VAX systems. We have prepared (Caporali and Sylos Labini, 1982) a modified VAX version of VLBI 3. This version runs on our standard VAX/VMS computers and contains a number of changes in the FORTRAN source which allow to the user a real time interaction with the program. In addition, having a Tektronix graphic station at our disposal, we decided to replace the existing plot package - which used the line printer - with a “ad hoc” graphic program which permits interactive display of the results of each run of VLBI 3. Our work was mostly concerned with the input/output sections of VLBI 3. The theorical model of the VLBI observables has, for the moment, been left unchanged. We have, however, noticed that the theorical model could be updated and made more precise, e.g. in the computation of the nutation terms and of the aberration. This updating and a more extensive geodetic and astrometric analysis of VLBI data are planned to be done next.
The QUASAT Project
Authors: Schilizzi R. T. , Burke B. F. , Booth R. S. , Preston R. A. , Wilkinson P. N. , Jordan J. F. , Preuss E. , Roberts D.
Published: June 2019

Preston et al (1976) and Burke (1982, these proceedings) have long extolled the virtues of launching a radio telescope into space to increase VLBI baseline lengths and thus angular resolution, and to provide a much enhanced image formation capability. The scientific motivation for this has been covered in a number of memoranda referenced by Burke in these proceedings, and by Anderson et al (1982). Efforts to mobilise western astronomical support for space VLBI met with success in late 1982 at a meeting of US and European radio astronomers in Toulouse, France, at which a decision was taken to propose a joint mission to ESA and NASA. Shortly thereafter, a formal proposal was made to ESA (Anderson et al 1982) for a free flying satellite in an elliptical orbit out to 15000 km from the Earth, designed to observe in concert with the major ground-based VLBI networks and arrays. The mission, dubbed QUASAT, was received favourably in both ESA and NASA, with the result that formal Assessment Studies are scheduled to begin in both agencies in October 1983.
The Determination of Fundamental Proper Motions
Authors: Corbin Thomas E.
Published: June 2019

Fundamental positions and proper motions are derived from absolute catalogs. Taking recent Washington Six-Inch and Seven-Inch Transit observing programs as examples, the observation and compilation of absolute catalogs are discussed. The roles of quasi-absolute and differential catalogs in the formation of fundamental catalogs are also examined. Finally, the current effort to extend the fundamental system to fainter magnitudes than are presently represented in the FK4 is described as well as the expected composition of the forthcoming FK5 catalog.
Fundamental Parameters and Models of Stellar Atmospheres
Authors: Gustafsson Bengt , Graae-Jørgensen Uffe
Published: June 2019

The use of photometric and spectroscopic criteria, calibrated by model-atmosphere calculations, for determining effective temperatures, surface gravities and chemical compositions of stars is illustrated and commented on. The accuracy that can be obtained today in such calibrations is discussed, as well as possible ways of improving this accuracy further for different types of stars.
Un Diagramme Fondamental Luminosite-Type Spectral Pour Les Etoiles Doubles
Authors: Couteau P.
Published: June 2019

In the Hertzsprung-Russell diagram, which is not well known for the binary stars, we can use the unit-mass brightness instead of the brightness itself. For each component this parameter can be obtained using the photometry and the orbital elements of the system. It is only through the orbital constant that the parallax comes in the calculation. This new diagram can be applied to any component of binary stars which orbit and class are known. By using a mass luminosity relationship one can define the zero-age main sequence on the diagram. The evolved stars can thus easily be noticed on the diagram; the mean age of the solar vicinity binary systems should be about 1010 years.
UV Standard Stars by the Variable Procrustean Bed Approach
Authors: Heck A. , Egret D. , Nobelis Ph. , Turlot J. C.
Published: June 2019

Statistical algorithms have been appplied to a set of stellar low-dispersion IUE spectra in order to derive objective spectral classification schemes in the UV. This paper describes how standard stars can be selected, particularly in the context of the VPB approach. Comparisons to existing schemes proved quite satisfactory.
A Note on the Calibration of Effective Temperatures
Authors: Heintze J. R. W.
Published: June 2019

The discrepancy in the derived chemical compositions between B-Al stars and stars of later spectral types can be removed if another Teff-calibration is applied for A and F type stars than the one usually used.
Determination DES Diametres Stellaires Par Occultations. Technique de Reduction
Authors: Froeschlé Michel , Helmer Georges , Meyer Claude
Published: June 2019

Lunar occultations provide measurements of stellar angular diameters, leading thus to a determination of their effective temperatures. Basically, the data reduction process relies on two methods: model fitting and deconvolution. “Integrated deconvolution”, presented here, is a derived method of deconvolution and its results can compare with the two methods. The purpose is to determine the variation of the uncovered surface of the source throughout the occultation instead of extracting the brightness profile of the source. The main advantage provided is that computing the signal derivative is no longer necessary. In addition to saving a lot of computing time, the method affords a good estimate of the apparent speed, precise dating, and the angular separation of double stars down to 0.002 arcsec. After being tested against the usual methods, “integrated deconvolution” is now currently used. Some results are presented here.
Faint Secondary Standards for Spectrophotometry and the Energy Distributions of Horizontal-Branch A-Stars
Authors: Hayes D. S. , Philip A. G. Davis
Published: June 2019

The energy distributions of 16 horizontal-branch A-stars and 11 horizontal-branch stars in globular clusters have been measured using the Harvard Scanners at KPNO and CTIO and the Oke multichannel spectrophotometer on the 5-m telescope at Mt. Palomar (Philip and Hayes 1983, Hayes and Philip 1983). Wavelengths between 3400 and 6800 Å were measured and reduced to absolute energy distributions on the system of Hayes and Latham (1975). The internal measuring errors were ± 0.034 mag. per observation for the 15th mag. globular cluster stars and ±0.025 mag. per observation for the 7th to 11th mag. field stars, averaged over all wavelengths. Eleven of the field stars have been observed over nine times each and have low internal measurement errors; these stars plus four globular cluster stars with low internal measurement errors are recommended as secondary standard stars. (See Table I.)
Analysis of Uvby Photometry and Low-Resolution Spectrophotometry of B Stars
Authors: Tobin William
Published: June 2019

A method of analysis of Strömgren photometry and low-resolution spectrophotometry of B stars is being developed in collaboration with J.P. Kaufmann (Technische Universität, Berlin). A full account will be published elsewhere.
An Effective Temperature Calibration of A UV-Visual Photometric Index for “Normal” Non-Supergiant Stars
Authors: Morossi C. , Malagnini M. L.
Published: June 2019

The determination of the effective temperature of each individual star requires observations of the flux distribution in the largest possible wavelength range. Unfortunately, owing to observational constraints, this requirement severely limits the number of stars for which the direct determination of Teff can be achieved. However, an estimate of Teff for a very large number of stars can be obtained through a calibration of a photometric index versus the stellar effective temperature. The UV-Visual dereddened index, R=log(F 1965/F 5445), has been shown to be suitable for “normal” non-supergiant stars in the spectral type range B5 - F7 (Malagnini et al. 1984). The analysis, with the method described in Malagnini et al. (1983), of stars in the spectral type range B5 - B0, enables us to extend and to refine the already proposed calibration of R versus Teff. By using the complete calibration, the determination of Teff for all the “normal” non-supergiant stars sampled from the 31215 objects in the Catalogue of Stellar Ultraviolet Fluxes (Thompson et al. 1978) is being carried out.
Precise Radial Velocities and Radial Velocity Standards
Authors: Walker G. A. H. , Amor J. , Yang S. , Campbell B.
Published: June 2019

By imposing absorption lines of HF in stellar spectra we can measure changes in r.v. with a precision of ~10m/s from a single spectrum, provided stellar line profiles are not distorted by atmospheric motions. The precision of absolute radial velocities is currently limited to ~100m/s by knowledge of rest wavelengths. Representative results are presented from our three, active PRV programs: velocity variations of δ Scuti stars; a search for unseen companions to late-type stars; and routine observations of certain IAU velocity ‘standards’.
Constraints on Galactic Infall from Studies of Chemical Evolution
Authors: Tosi M.
Published: June 2019

It is shown that, in order to reproduce the observational properties of our Galaxy, models of galactic chemical evolution require a conspicuous amount of gas falling on the disk with very slow time decay. The constraints on the characteristics of this gas derived from the models are presented.
Wave Structure within HI Filaments at High Galactic Latitude and the Nature of “Clouds” in Interstellar Space
Authors: Verschuur Gerrit L.
Published: June 2019

Large amplitude waves have been found in the morphology and velocity patterns of several long filaments of HI at high latitude. HI in the filaments is controlled by magnetic fields and the velocity patterns and morphology bear the hallmarks of Alfvén waves. Enhanced emission features (EEFs), traditionally referred to as “clouds,” are seen wherever a segment of flux tube is viewed end-on. This suggests that HI emission structure teaches us about field geometry and not about cloud physics. Similar effects have been recognized in other regions mapped with high-resolution as well as in completely mapped high-velocity “clouds.”
UV Absorption and Emission Lines from Highly Ionized Gas in the Galactic Halo
Authors: Savage Blair D.
Published: June 2019

Highly ionized gas in the galactic halo has been detected through UV absorption and emission lines. In absorption the species studied include Si IV, C IV and N V. The UV emission studies have recorded C IV and O III]. Absorption measurements toward galactic stars reveal that the |z| distribution of the gas is roughly exponential with a scale height of approximately 3 kpc and has column densities perpendicular to the galactic plane of N ~ 2×1013, 1×1014 and 3×1013 atoms cm−2, for Si IV, C IV and NV, respectively. Similar absorption line profiles for these species suggests a common process for their origin. The presence of N V absorption implies the existence of some gas with a temperature near T ~ 2×105 K. The highly ionized absorbing gas toward distant stars in direction b < −50° has simple and relatively narrow line profiles (FWHM ~ 45 to 70 km−1) and small average LSR velocities while the gas in the direction b > 50° reveals a complex pattern of motions with substantial inflow and outflow velocities. Galactic rotation has an appreciable effect on the absorption line profiles to very distant stars located in the low halo. C IV emission has been seen at greater than a 3σ level of significance in 4 of 8 directions. The emission brightens toward the galactic poles and has a polar intensity I(C IV) ~ 5000 photons cm−2s−1ster−1. If the emitting and absorbing gas coincide in space the measurements imply ne ~ 0.01 cm−3 and P/k ~ 2000 cm−3 K for gas with T ~ 105 K. This phase of the gas fills only a small volume of the space (f ~ 0.03) and accounts for only a small fraction of the total column density of gas perpendicular to the galactic plane [~3×1018 atoms cm −2 vs 3.5×1020 atoms cm −2 for H I and 1×1020 atoms cm −2 for H+]. However, the gas provides a large EUV/UV emission line flux (~1×10−5erg. cm−2 s−1) which corresponds to a H I ionizing flux of ~2×105 ionizations cm−2 s−1. Gas with T near 2×105 K cools very rapidly. Its origin may be associated with the cooling gas of a galactic fountain flow or with thermal condensations in cosmic ray driven fountains. In the nonequilbrium cooling of a Galactic fountain, a flow rate of 4 MO/ year to each side of the Galaxy is required to produce the amount of N V absorption found in the halo while a flow rate 5x larger is required to produce the observed level of C IV emission.
Metals and Molecules in Halo Clouds
Authors: de Boer Klaas S. , Herbstmeier Uwe , Mebold Ulrich
Published: June 2019

The abundance of the elements in clouds of halo gas, as determined from observations, is an important parameter for the test of the validity of models explaining the existence of, e.g., the high latitutude high-velocity clouds (HVCs) of the Milky Way. Individual HVCs have been detected in absorption only on very few lines of sight so that the distance of the HVCs, another important parameter for the models, stays ill determined as well. We will follow here the more or less established convention by calling HVCs those with /v/ >100 km s−1 and IVCs (intermediate-velocity clouds) those with 50 </v/ <100 km s−1. We will define halo as the space with /z/> 1 kpc, although for /b/> 45 also /z/> 0.5 kpc is used.
Magnetic Fields in the Disk-Halo Interface
Authors: Sofue Yoshiaki
Published: June 2019

A review is given of large-scale magnetic fields in disks and halos of spiral galaxies. A particular attention is given to vertical field structures, and we discuss their origin and implication on their interaction with halo gas. We point out that the disk-halo magnetic interface plays an important role in circulation of interstellar gas in galaxies, in particular a large-scale circulartion from the galactic center to outer disk regions.
The Cosmic-ray Halo: Insight from Gamma Rays and Cosmic-ray Observations
Authors: Dogiel V.A.
Published: June 2019

The physical processes that determine the size of the galactic cosmic-ray halo are discussed and observational information on the cosmic-ray halo is summarized. Based on theoretical investigations as well as observations, we conclude that the halo surrounding the galactic disk is extensive and that its extent in the direction perpendicular to the galactic plane is more than 10 kpc.
Ionization in the Interstellar HI Region by Low energy Cosmic ray Electrons
Authors: Chi X. , Wolfendale A.W.
Published: June 2019

Recent observations of the pulsar dispersion measures show a large scale height and relatively high density for the diffuse, ionized gas in HI regions. The maintenance of the ionization requires a pervasive ionizing agent. This agent could hardly be the UV photons from O stars or the extragalactic background UV photons due to their large optical depth; nor could it be the soft X–rays from the hot, ionized gas due to a low flux indicated by observations. Studies of the Galactic diffuse low energy γ-rays provides a clue to this problem. The extraordinarily high intensity of MeV electrons, which is derived from the γ–ray flux, could account for the ionization. In this scenario the electrons do both ionization and heating in HI regions, accordingly the atomic hydrogen gas is warm (~ 104 K). The ionized gas density has a radial gradient with a scale length 4 kpc, there being more ionized gas in the inner Galaxy, due to a gradient in the electron intensity.
Large scale Structure of HI in other Galaxies
Authors: Van Der Hulst Thijs , Kamphuis Jurjen
Published: June 2019

In this paper we discuss the large-scale structures (> 500 pc) of the neutral atomic hydrogen in the disk of nearby galaxies, with an emphasis on finding evidence for neutral gas features in the disk - halo interface. Most nearby galaxies studied in detail appear to have hole and shell type structures in their HI disks and several show evidence for gas at peculiar velocities, probably examples of gas streaming out of the disk into the halo. Not all of the observed phenomena can be explained by stellar winds and supernova explosions and other explanations will briefly be discussed.
Small-scale Properties of HI in Nearby Galaxies
Authors: Braun Robert
Published: June 2019

The instrumental requirements and current observational results are outlined for the study of resolved neutral hydrogen structures in both emission and absorption in external galaxies. Neutral super-shell structures exterior to ionized shells around OB associations seem to be a common phenomenon. Further analysis of existing data should allow quantification of the degree and rate of energy deposition in the ISM by massive stars. HI absorption studies offer great promise in constraining the physical properties of the neutral ISM, including an estimate of the gas pressure. Together these data will provide hard constraints on the existence and prevalence of chimney formation, and hence disk – halo interactions in a variety of galactic environments.
A CO survey of the Halo of NGC 891
Authors: García-Burillo S. , Dahlem M. , Guélin M.
Published: June 2019

We report 12CO J=2-1 line observations of the edge-on galaxy NGC 891, made with the IRAM 30 m telescope. These observations show that the molecular gas probably extends to large distances from the galactic plane.
The Global Mass, Energy and Photoionization Balance of the Disk-Halo Interaction
Authors: Norman C. A.
Published: June 2019

The observational evidence for chimney models of the interstellar medium is reviewed. The variation of the state of the interstellar medium of an external galaxy between the three-phase mode, the chimney mode and the two-phase mode as a function of: galaxy type, galactocentric radius within a given galaxy, and the time varying star formation rate is discussed.

In the context of the chimney models it is shown how the photoionization of the halo can be achieved by utilizing both direct ionizing rays from the central OB association and diffuse reradiation from the chimney walls that will create an extended low ionization halo around chimneys with SII/Hα ~ 0.5.

A number of considerations for future studies that are a direct result of the work discussed at this conference are outlined.
The Structure of the Interstellar Medium
Authors: Bregman Joel N. , Ashe Gregory A.
Published: June 2019

We have compared theoretical HI models to a large area (18°x12°) HI channel map centered at 1 = 205°, b = 0°. One set of models were calculated in which uncorrected clouds of HI populate space. Of the cloud models considered, which include “Spitzer”-type clouds and the McKee-Ostriker formulation, none were able to reproduce the data successfully. In another class of models, holes and holes with shells permeate an otherwise continuous HI medium. Although not entirely successful, these models contain characteristics that are similar to the data. In order to reproduce the amplitude of the HI variations on angular scales of >1°, the volume occupied by ionized gas must be less than 30%, in sharp conflict with the models that suggest that the volume of the ISM is dominated by hot gas.
The Interstellar Disk-Halo Connection in Galaxies: Review of Observational Aspects
Authors: Heiles Carl
Published: June 2019

An impressively large amount of data was presented at this meeting and a review by an ordinary human cannot hope to do full justice to either the authors or the research. Accordingly, I shall concentrate on those aspects that particularly piqued my interest and apologize to those authors whom I overlook. I shall give references in the usual style except for references to papers presented at this meeting, for which I shall simply mention the author(s) with no date.
Looking for Changes in the Saturnian System Between Voyager and Cassini
Authors: Borderies Nicole
Published: June 2019

This paper reviews a number of time-dependent phenomena that are relevant to our understanding of the dynamics of planetary rings and that will be investigated using Voyager and Cassini data. A long time baseline may help us decipher the physics of the spokes, understand better the morphology of the F ring and the rigid precession of non-circular ringlets, measure more precisely than has been done so far the satellites' torques and the viscosity of the A ring, and discover small satellites in the Saturnian ring system. Two exciting possibilities are those of determining the recession rates of the small satellites that border the rings, and of observing changes due to viscous diffusion in the irregular structures of the B ring.
A Catalogue of Periodic Orbits in the Elliptic Restricted 3-Body Problem
Authors: Dvorak R. , Kribbel J.
Published: June 2019

Results of families of periodic orbits in the elliptic restricted problem are shown for some specific resonances. They are calculated for all mass ratios 0 < μ < 1.0 of the primary bodies and for all values of the eccentricity of the orbit of the primaries e < 1.0. The grid size is of 0.01 for both parameters. The classification of the stability is undertaken according to the usual one and the results are compared with the extensive studies by Contopoulos (1986) in different galactical models.
Cross-Tidal Effects and Orbit-Orbit Resonances
Authors: Pauwels Thierry
Published: June 2019

In this paper we discuss the influence of the deformation of a planet caused by a first satellite on the orbit of a second satellite of the same planet, where both satellites are supposed to be involved in an orbit-orbit resonance. Numerical results are given for seven orbit-orbit resonances in the Solar System.
Chaotic Alfvén Waves in Solar and Cometary Plasmas: Summary
Authors: Buti B.
Published: June 2019

The recent observations, of energetic heavy ions in the vicinity of Comet Halley and Comet Giacobini-Zinner, are rather intriguing. Moreover the solar coronal heating is still not well understood and is somewhat puzzling. Since both these observations can not be properly explained by means of classical processes, we have to invoke anomalous heating and acceleration effects due to chaotic and turbulent plasma processes.