bluuebunny/crossref_metadata_2025 huggingface dataset:
CCD Development Activities at ESO
Authors: Iwert O.
Published: June 2019

Advanced CCD detectors are the backbone of modern astronomical instrumentation working in the 300–1000 nm spectral range. The status and results of the different projects to design, manufacture and implement new CCD detectors for the ESO VLT instrumentation are presented. Emphasis is put into ESO's development activities together with industry's, and into first measurement results of thinned arrays in large formats obtained in 1994. In addition some recent cryostat developments are shown to illustrate the different requirements of VLT instruments in this area.
The Lick Observatory Two Micron Camera
Authors: Gilmore K. , Rank D. , Temi P.
Published: June 2019

Lick Observatory has recently developed a near infrared camera for astronomical imaging. The new camera has been built around a Rockwell NICMOSII 256 × 256 HgCdTe focal plane array. The dewar and optics were manufactured by Infrared Laboratories in Tucson, Arizona while the electronics and data system were designed and fabricated at Lick Observatory.

The new instrument was designed to image faint galaxies and other astronomical objects as well as embedded infrared sources in star formation regions. The camera has cold focal plane scales of 0.2, 0.4 and 0.6 arcseconds per pixel when used at the telescope. Standard H, J and K as well as narrow band special purpose filters are contained in two independent motorized filter wheels.

The camera performance with different plate scales and filters as well as the mechanical, optical and electrical lay-out will be shown. M 42 will be used for characterization of the camera's performance.
The Impact of Infrared Array Technology on Astronomy
Authors: Fazio Giovanni G.
Published: June 2019

Over the past ten years a technological revolution has occurred in the development of two-dimensional infrared array detectors for astronomical observations. The wide application of these arrays for both ground-based and space observations has resulted in a profound change in the capabilities and perspective for infrared astronomy, resulting in new views of the infrared sky. A review will be presented describing these detectors, the numerous advantages they provide for astronomical observations, the present state of array technology, and the potential for future growth.
Cosmic Ray Events and Natural Radioactivity in CCD Cryostats
Authors: Florentin-Nielsen Ralph , Andersen Michael I. , Nielsen Sven P.
Published: June 2019

We have found that many materials that are most commonly used in CCD cryostats are weakly radioactive and therefore contribute to what is rather liberally labelled as Cosmic Ray Events. Some standard optical glasses that are extensively used for lenses and optically flat windows such as UBK-7 contain large amounts of potassium 40, which renders them useless as windows in CCD dewars. Cobalt 60 is sometimes found in excessive amounts in some steel alloys, even in Covar used as a thermal match to silicon. The choice of materials that emit a minimum of ionizing radiation is discussed.
The CCDs at ESO: A Systematic Testing Program
Authors: Abbott T. M. C.
Published: June 2019

It is incumbent upon ESO to ensure that its CCDs perform according to advertised specifications (Abbott 1994). We describe a systematic, regular testing program for CCDs which is now being applied at La Silla. These tests are designed to expose failures which may not have catastrophic effects but which may compromise observations.
Estimation of the Errors Involved in the Intensity Measurement of Low S/N Ratio Emission Lines
Authors: Rola Claudia , Pelat Didier
Published: June 2019

We present a detailed analysis on the extent of the errors in the intensity measurements of low signal-to-noise narrow emission lines. Our first goal is to determine a model for the probability distribution function (p.d.f.) associated with the measured intensities of a line characterized by its signal-to-noise ratio. Our final purpose is to provide an error domain: — for the measured signal-to-noise ratio of an observed line; — for the ratio of two lines in terms of their signal-to-noise ratios, and eventually (with the knowledge of the noise energy) to get errors on the corresponding intensities and intensity ratios.
Resistive Instabilities in Astrophysical Conditions: A Critical Discussion
Authors: Batistoni P. , Einaudi G. , Rubini F. , Chiuderi C. , Torricelli G.
Published: June 2019

Resistive instabilities have often been indicated as the possible cause of rapid release of energy in astrophysical situations. A correct assessment of the validity of this idea requires a detailed analysis of the theory of resistive instabilities in the regimes of astrophysical interest. In particular, effects as the presence of asymmetries due to current gradients, the influence of geometry and of shear flows must be explicitly evaluated. We have started a program of investigation on this subject, whose preliminary results are reported here.
Kinetic Theory of Alfvén Wave Heating
Authors: Mahajan S. M.
Published: June 2019

In a magnetohydrodynamic description of a plasma, the shear Alfvén wave is characterized by a continuous spectrum (the MHD continuum) which results from a singularity at ω ≃ k||(r)VA(r), where ω is the frequency, k||is the wave number along the direction of the magnetic field and VA= B0/(4ρπ)1/2is the Alfvén speed, and r is the direction of inhomo-geniety. The associated electromagnetic fields become large at this resonance layer [in fact, in ideal MHD they become singular], and if some dissipation is allowed, the transfer of energy from the waves to the electrons can take place. These continuum modes are localized in space, and can be effective in heating plasmas in narrow regions around the resonanct surface. Recently,1-3a new class of nonsingular global eigenmodes of the plasma have been discovered which are wide spread in the plasma, and could effectively transfer energy to the bulk of the plasma. These modes arise because of a strong coupling between the shear and the evanascent compressional mode. The coupling is provided by gradients of density, equilibrium current and nonideal effects like finite ω/ωci, where ωciis the ion cyclotron frequency. In order to understand the effectiveness of these modes to heat plasmas, i.e., to determine the effective impedance, the energy deposition profiles, parametric dependence of the heating efficiency, etc., a kinetic theory with the electron parallel dynamics is needed. We have developed a detailed kinetic theory to study the structure of the continuum as well as global eigenmodes in an inhomogenous current carrying plasma. The global modes are comparatively much less damped than the continuum modes (which become discrete in the kinetic theory) and hence are easier to excite. The implication, of course, is that the large part of energy transfer in a Alfvén Wave experiment would be mediated through these global modes. This theoretical conjecture is already confirmed in laboratory experiments on PRETEXT Tokamak.

I will present the basic theoretical analysis as well as discuss the implications of these findings.
A Proposal for Scanning Meridian Circle
Authors: Kharin A.S.
Published: June 2019

The space based determination of astronomical data will have significant advantages over the ground based ones. However, in the mean time the requirements for traditional astrometry technique do not decrease, but, on the contrary, increase, especially in view of the existing plans for large programs of ground based determinations of absolute and differential positions of stars and solar system bodies.
The Use of Photographic Positions in Determining

Azimuth

of a

Meridian Circle
Authors: Fabricius C.
Published: June 2019

The azimuth of a meridian circle may be determined using stars within 1°–2° of the pole combining observations in upper and lower culmination of stars which have well known right ascensions. The right ascensions are determined photographically using only declinations in the reduction, thus making the azimuth determination independent of the right ascension system. The declinations of the pole near stars are determined with the meridian circle.
On the Implementation of Absolute Meridian Observations in Low Latitude Stations
Authors: Dong-Ming Li
Published: June 2019

Mao et al. (1983) have originally stated that in order to record the transit times of a star at meridian transit as well as at prime verticale transit the chassis of the instrument would have to have two pairs of supports. In my opinion, it may be difficult to develop such an instrument with the required aperture of 20 cm and a focal length of over two meters, especially when the declination system must be very stable.
The IAU Numbering System of Radio Sources
Authors: Elsmore B.
Published: June 2019

The convention for numbering radio sources adopted by the IAU uses the 1950 coordinates of right ascension in hours and minutes, followed by the declination truncated to tenths of a degree. It was designed for a growing population of sources so that new sources may be added and given an IAU number, unlike, for example, the listing in the BD catalogue which is a closed assembly.
The Reconciliation of Optical and Radio Positions
Authors: Argue A. N.
Published: June 2019

The optical and radio positional reference systems are reviewed. A preliminary comparison indicates that the two do not at present agree to better than 0″.2 or 0″.3.
Results of VLBI Observations of Radio Stars and Their Potential for Linking the HIPPARCOS and Extragalactic Reference Frames
Authors: Lestrade Jean-Francois , Preston Robert A. , Niell Arthur E. , Mutel Robert L. , Phillips Robert B.
Published: June 2019

VLBI observations of bright radio stars have been initiated in an attempt to measure the positions and proper motions of their radio components in order to tie the future HIPPARCOS stellar frame to a VLBI extragalactic reference frame. Through VLBI observations of a sample of 20 known radio stars we have identified 11 stars that should be appropriate for both astrometric VLBI and HIPPARCOS observations. Our measurements indicate that the angular extent of their radio emitting regions is small, i.e. < 3 milliarcseconds for 7 of them. Most of these radio stars belong to the RS Canum Venaticorum class of binary systems.
Extragalactic VLBI at 89 GHz
Authors: Backer D. C.
Published: June 2019

Radio interferometry at 89 GHz with transcontinental baselines can probe the region of active galaxies and quasars where collimation of relativistic outflows occur on length scales of 1017–18cm. Three experiments have been conducted recently to demonstrate the feasability and importance of this investigation. Highlights of the three pioneering experiments are discussed below. Results obtained for the luminous sources 3C84, 3C273 and 3C345 are then summarized.
Compact Doubles: A Genuine or Illusory Class?
Authors: Phillips R. B. , Hodges M. W. , Mutel R. L.
Published: June 2019

Symmetric, two-sided morphology seems to argue against relativistic effects dominating compact radio emission. This kind of structure has been reported for a number of sources (Phillips and Mutel 1982; Pearson 1983) based on maps made at one frequency. Various arguments, all indirect, can be made for these sources being (1) Twin regions formed at the ends of jets which emerge from an invisible core, or (2) misidentified core-jet sources wherein the core and an unusually bright knot are wrongly taken to be a “double.” A telling test of both hypotheses is to map the sources in question over an octave or so of frequency. Proponents of view (1) would predict that the two double components will show nearly identical spectral indices and that weak central cores with flat or rising spectra might even be revealed. Champions of view (2) would predict that one end or the other will dominate at high frequencies (the core!) or that complex bridges of emission (the jet!) will be revealed between the components at low frequencies. We have followed our initial discovery of 5 symmetric compact doubles by (A) attempting to enlarge the sample of symmetric sources available to study, and (B) by investigating at 5 GHz those doubles for which the best maps exist at 1.7 GHz.
The Southern Hemisphere VLBI Experiment (Sheve)
Authors: Preston R.A. , Jauncey D.L. , Tsioumis A. , Meier D.L. , Skjerve L.J. , Ables J. , Batchelor R. , Faulkner J. , Hamilton P.M. , Haynes R. , Johnson B. , Louie A. , McCulloch P. , Moorey G. , Morabito D.D. , Nicolson G. , Niell A.E. , Robertson J.G. , Royle G.W.R. , Slade M.A. , Slee O.B. , Watkinson A. , Wehrle A.E. , Wright A.
Published: June 2019

The Southern Hemisphere VLBI Experiment (or SHEVE) was a joint US-Australian-South African venture with both astronomy and geodesy goals. The principle astronomy goal was to make models or maps of the following sources: at 2.3 GHz (with six antennas and 9 usable baselines) – Centaurus A (the nearest active galaxy), Circinus X-1 (a flaring binary), the VELA pulsar, and 26 other active galactic nuclei and quasars; at 8.4 GHz (only one baseline) – Centaurus A and the galactic center.
Statistical Properties of Compact Sources
Authors: Machalski J.
Published: June 2019

The analysis is based on VLA 1465-MHz observations of GB and GB2 sources (Machalski et al. 1982; Machalski and Condon 1983a, 1983b). From those flux-density limited samples compact sources were selected. The following definition of source “compactness” has been used

Subjects of analysis were: (a) fraction of compact sources among radio galaxies, quasars, and “empty field” sources, (b) identification rate vs. high-frequency spectral index for compact sources, (c) spectral-index distributions for compact identified and/or EF sources, (d) flux-density ratio for double compact sources, and (e) correlation between radio and optical luminosities for compact sources.
X-Ray Properties of Extragalactic Compact Objects
Authors: Zamorani G.
Published: June 2019

The compact objects which are the subject of this talk are essentially quasars and Seyfert galaxies; I will only briefly mention a couple of results about BL Lac objects. Before describing the X-ray properties of these objects, it is useful to introduce a “working” definition of radio-quiet and radio-loud quasars: I will call radio-loud quasars all the objects which have been detected at radio frequencies and have a spectral index between radio (5 GHz) and optical frequencies (2500 A) greater than 0.35 (Zamorani et al. 1981); all the other objects will be considered radio-quiet. Note that this definition is independent of distance and is a function only of the relative importance of radio and optical emission.
The Nucleus of NGC1275
Authors: Romney J. D. , Alef W. , Pauliny-Toth I.I.K. , Preuss E. , Kellermann K. I.
Published: June 2019

The bright radio nucleus 3C84 of the peculiar galaxy NGC1275 was among the first sources studied by VLBI techniques sixteen years ago (Clark et al., 1968). Early observations at short centimeter wavelengths using arrays of up to four telescopes (Schilizzi et al., 1975, and references therein) demonstrated the presence of structure significantly more complex than that seen in other strong compact objects, but were insufficient to determine the brightness distribution with the relatively primitive methods then in use. By the time of the most recent international VLBI symposium (Aug. 1978, in Heidelberg, FRG), Pauliny-Toth et al. (1976) had succeeded in modelling the structure seen by a 4-station transatlantic array, revealing three distinct bright emission regions aligned in position angle −9°, and connected by non-colinear, more diffuse features. Further observations and a reanalysis of earlier data by Preuss et al. (1979) confirmed previous inferences that the three major condensations remained stationary but varied in brightness.
Sub-Luminal Motions in the Nucleus of M 87
Authors: Reid M. J. , Schmitt J. H. M. M. , Wilkinson P. N. , Johnston K. J.
Published: June 2019

We have observed the nucleus of the elliptical galaxy M87 with VLBI arrays at 18 cm wavelength at two epochs separated by about two years. The results of the first epoch observations taken at 1980.12 are described in detail by Reid et al (1982, Ap. J. 263, pp 615-623). They indicated that the nucleus of M87 exhibited a highly asymmetric emission pattern with a bright “core” and long, thin “jet” extending for more than 0.05 arcsec towards the 20 arcsec jet seen in radio, optical, and X-ray radiation. This morphology is remarkably similar to that seen in the quasar 3C273. Asymmetric core-jet structures, possibly coupled with super-luminal motions as in 3C273, have been interpreted in the framework of relativistic beaming models (cf. Blandford, McKee, and Rees: 1977, Nature 267, pp 211–216). Therefore, we conducted second epoch observations of M87 at 1982.27 to look for such motions.
Extended Structure Around Superluminal and Other Core-Dominated Radio Sources
Authors: de Bruyn A.G. , Schilizzi R. T.
Published: June 2019

The maps that we will show you today probably have the lowest resolution of any that you will see this week. They were made from data taken by the Westerbork Synthesis Radio Telescope (WSRT), which has a maximum baseline of 2.8 km, yielding a resolution of 3″.5 (λ 6 cm), 12″.5 (λ 21 cm) or 29″ (λ 49 cm). Because the WSRT is an EW-array the resolution in declination is worse by a factor 1/sin δ. This is unfortunate since three interesting superluminal sources are close to the equator. For two of these, namely 3C120 and 3C273 we nevertheless have obtained some interesting results.
Physics of Relativistic Jets on Sub-Milliarcsecond Scales
Authors: Rees Martin J.
Published: June 2019

The observed superluminal components have (deprojected) lengths of ~ 1020 cm, and imply relativistic bulk motions on these scales. There are, however, persuasive reasons for attributing the primary energy production to scales 1014–1015 cm. Moreover, the initial bifurcation and collimation must also be imposed on these small scales if the long-term stability of the jet axis in extended sources is due to the gyroscopic effect of a spinning black hole (Rees 1978). The issues I shall address in this talk are: how the jet gets from ~ 1015cm to ~ 1019 cm; and what VLBI data can tell us about the properties of galactic nuclei on scales below ~ 1019 cm — scales where optical and X-ray studies provide some evidence, but where there is no short-term hope of achieving spatial resolution.
Turbulent Cascade in VLBI Jets
Authors: Zaninetti L. , Pelletier G.
Published: June 2019

In the framework of continuous beam from small (VLBI region) to large scales (VLA region), we deduce some typical quantities of VLBI-jets like maximum luminosity and time-scales of formation of turbulence in the hypothesis of turbulent cascade triggered by relativistic Kelvin-Helmholtz instabilities.
Interrelation of Present Optical and Radio Reference Frames
Authors: de Vegt Chr.
Published: June 2019

Comparison of optical and radio positions in the northern hemisphere yields local systematic differences up to 0″.2, mainly due to combined systematic errors of current optical reference frame and contributing main catalogues. Interrelations of radio/optical frame and future developments are discussed.
Accurate Positions of 120 Radio Sources with Declinations Above −45°
Authors: Niell A. E. , Fanselow J. L. , Sovers O. J. , Thomas J. B. , Liewer K. M. , Treuhaft R. N. , Wallace K. S.
Published: June 2019

Development of a catalogue of approximately 100 radio sources having positional accuracy of ~0.005 arcseconds is one goal of the DSN radio reference frame program. This objective is set by the navigation requirements of the Galileo Project for reconstruction of the probe entry angle into the atmosphere of Jupiter. These radio positions are determined by VLBI observations using the antennas of the NASA Deep Space Network on two intercontinental baselines – California-Spain and California-Australia. Since 1978, measurements have been made simultaneously at 2.3 and 8.4 Ghz. Sixteen to twenty-four hours of data on each of the two baselines are usually obtained within a few days of each other, and since mid-1982 these pairs of observations have been made at approximately six week intervals.
Stellar Absolute Fluxes and Energy Distributions from 0.32 to 4.0 μM
Authors: Hayes D. S.
Published: June 2019

The absolute fluxes and energy distributions of stars are the foundation of the calibration of fundamental effective temperatures and bolometric corrections. In this paper I will review recent progress in the calibration of absolute fluxes and energy distributions in the visual and IR parts of the spectrum. In the visual, the calibration of the absolute flux and energy distribution of Vega has settled down well, and the remaining difficulties include the lack of a worldwide common list of brighter secondary standard stars, the lack of enough satisfactory fainter secondary standard stars and the possibility of variability in Vega. In the IR, the process of arriving at a dependable and accurate calibration, and of linking it to commonly used photometric systems, is in its infancy. A final, and rather special problem, is the question of the calibration of the Sun. The Sun is a special case both because it is so well studied astrophysically and because its extreme brightness makes it very difficult to calibrate photometrically. Some progress has recently been made on the calibration of the absolute flux and energy distribution of the Sun, and I will discuss this work.
Calibration of Fundamental Stellar Quantities: Summary and Conclusions
Authors: Lyngå Gösta
Published: June 2019

At a time when so much of the prestigious astronomical research is devoted to new and highly speculative phenomena, it has been rewarding to see and hear the cautions and accurate approach to the measuring and interpreting of stellar quantities. It has been shown by many speakers, perhaps clearest of all by our participant of honor Professor Popper, how insufficient attention to calibration problems can lead to erroneous results.
Visual Binaries and the Calibration of the Main Sequence
Authors: Rakos Karl D.
Published: June 2019

147 of the best known visual binary stars have been used for an independent calibration of the main sequence in the interval −0m.15 ≤B-V≤0m.80. The (Mv, B-V) diagram is found to be equal to the composite open cluster diagram for the age group between 8.35 and 8.43 × 108 years - very hot stars excepted. The cosmic scatter of the main sequence is discussed. It appears that only a small number of visual binaries in our sample are simple binary systems.
Standard Stars for the Comparison of Methods of Diameter Determination
Authors: Pastori L. , Pasinetti L. E. , Antonello E. , Malaspina G.
Published: June 2019

Fracassini, et al. (1983) suggested a preliminary list of stars suitable for use as standards for methods of determination of stellar apparent diameters and absolute radii. According to their criteria, only stars with at least three methods of determination were considered; moreover, only if the percentage error of the data was <10% were they considered as “standards”. This simple statement is not completely satisfactory, because of some ambiguous cases. For instance, the interferometric method (code 1), Wesselink's method (6H) and Barnes and Evans' (6G) method are not independent.
Steps Toward a Physical Calibration of UBV Photometry
Authors: Buser Roland , Kurucz Robert L.
Published: June 2019

The large data base of photoelectric measurements on the Johnson UBV system has been a primary source of information in many fields of astrophysical interest. The availability of UBV data for virtually all types of stars known to make up the stellar populations in galaxies requires a continued effort toward establishing a fully physical calibration of these data in order to propagate effectively our improving knowledge on stellar evolution and stellar atmospheres (i.e., the HR diagram) through the observations relevant to the structure and evolution of the galaxies. One of the major links in this long chain of scientific progress is provided by the synthesis of stellar photometric properties from theoretical model atmospheres. This paper will briefly address some of the basic problems involved in the synthetic color calculations and discuss the theoretical calibration of UBV photometry as obtained from various grids of model atmospheres covering a large range of stellar types.
On the Accuracy of Infrared Photometry
Authors: Papoular R. , Pégourié B.
Published: June 2019

Photometric errors due to scintillation are considered in detail. Given noise characteristics, the standard deviations, as deduced from observations, are computed for the quantities measured at successive steps of the photometric procedure. This allows us to understand better the errors computed on-line in observatories, and to understand better the overall error. The latter can be minimized by suitable changes in the time sequence of the measurement.
The Estimation of the Electron Density ne with a Narrow-Band Photometric System Calibrated by Model Atmospheres
Authors: Gerbaldi M. , Morguleff N.
Published: June 2019

A spectrophotometer was originally designed by Barbier (1960) for the study of early-type stars. The band passes were chosen to measure the features of the hydrogen spectrum. To the first definition of the system (Barbier and Morguleff 1964), two more bands were added, specifically devoted to the peculiar stars of type Ap and Am (Gerbaldi 1972). The interpretation of these observations has already been given separately. We will concentrate here on the calibration of this spectrophotometric system in terms of Teff, log g and electron density ne.
On the Homogenization of Photometric Data
Authors: Manfroid J. , Heck A.
Published: June 2019

Catalogs of averaged photometric data have been published for several photometric systems. The homogenizing procedures used to produce them are not without pitfalls. We question the accuracy of these methods with the available data.
Introduction to Fountains, Wind, Infall (and Magnetic Fields and Dynamo Mechanisms)
Authors: Kahn F. D.
Published: June 2019

The galactic fountain is formed by hot gas rising from the galactic disk. The lines of force of the interstellar magnetic field are dragged along in the flow. This lecture deals with the geometry and topology of the configuration of the field that is set up. The fountain flow acts as a dynamo, and the presence of the magnetic field plays an important part in the ionization balance of the gas as it returns towards the disk.
The Stellar Disk–Halo Connection
Authors: Wyse Rosemary F. G. , Gilmore Gerard
Published: June 2019

The thick disk is the stellar disk-halo connection. At least near the solar circle, this component is on average as old as the system of disk globular clusters, or ~ 12 Gyr. This implies that it most probably formed early in the process of Galaxy formation, so that its properties – chemical abundances, stellar kinematics and spatial distribution – contain clues to the physics of these stages of Galaxy evolution. Its present-day importance for the interstellar disk-halo connection lies in the evolution of its constituent stars – gas loss through winds on the red giant and asymptotic giant branches, through planetary nebulae prior to white dwarf formation, and through supernovae. This gas loss results in mass injection, momentum injection and energy injection into the interstellar medium from a stellar population with a scale height of ~ 1kpc.
Is there Evidence for Disk-Halo Connections in M31?
Authors: Berkhuijsen Elly M. , Golla Götz , Beck Rainer
Published: June 2019

There is some evidence for disk-halo connections in M31, i.e.: (1) The central area seems inclined w.r.t. the main disk. (2) In several regions in the southern half the magnetic field has a significant component perpendicular to the disk. However, (3) any general emission from a thick disk at λ75 cm is ~100x weaker than that from our Galaxy. The uniform disk field seems to inhibit cosmic-ray diffusion perpendicular to the plane, and/or the field at high z is exceptionally weak.
Cool Ionized Gas in Galaxy Thick Disks
Authors: Israel F. P.
Published: June 2019

Spiral galaxies whose radio continuum emission is dominated by their disks show a flattening of the radio continuum spectrum at frequencies well below 1 GHz. The effect appears to be stronger for edge-on than for face-on galaxies The most feasible explanation appears to be that the flattening reflects free-free absorption of nonthermal emission by a very low temperature ionized gas. This gas is probably highly clumped, and must be well-mixed with the nonthermally emitting plasma.
Numerical Simulations of Galactic Outflow and Inflow Phenomena
Authors: Tomisaka Kohji
Published: June 2019

The recent progress of numerical studies on outflow phenomena from the galactic disk to the halo is summarized. Firstly, a galactic-scale outflow is considered. If the high-velocity cloud is formed from the radiatively cooled gas, which was originally ejected from the disk as a hot gas, the temperature and density at the base of the halo should be ~ 106 K and 10–3 cm–3. Next, recent results of numerical simulations of the evolution of superbubbles, through which hot gas flows out to the halo, are reviewed. In the case of a thin disk whose density scale height is H ≃ 100 pc, the shell begins to be accelerated upwardly after several dynamical time scales. After that, the polar cap of the shell is broken and the hot gas flows away into the halo. In the case of a thick disk (H ≃ 500 pc) or a magnetized disk with a magnetic field parallel to the disk (B ≃ 5μG), the shell is not accelerated and never shows blow-out.
A Planetary Theory with Elliptic Functions and Elliptic Integrals Exhibiting no Small Divisors
Authors: Williams Carol A.
Published: June 2019

This paper develops a planetary theory in three dimensions with elliptic functions and elliptic integrals. In an earlier treatment, (Williams, Van Flandern, and Wright, 1987) presented a two dimensional planetary theory to the first order of a Picard iteration. The theory did avoid expansions in powers of the ratio of the semi-major axes and it contained only two explicit small divisors, n – n′ and 2n – n′. These advantages are retained in the new theory and in fact no small divisors appear explicitly. Secular terms are removed by adopting an averaging technique rather than continuing the Picard iteration. The Lie series method of (Deprit, 1969) is chosen for the averaging. In order to simplify the Lie operator, the framework for the problem is chosen to be the circular restricted three body problem written in the polar-nodal coordinates of Whittaker. The algorithm is described and a few representative terms are discussed.
The Dynamics of Meteoroid Streams
Authors: Wiliams I. P.
Published: June 2019

Meteor showers are seen at regular and frequent intervals on Earth. They are caused by meteoroids (that is small dust grains) in a coherent stream, all moving on similar heliocentric orbits, burning up on encountering the atmosphere of the Earth. Such streams contain 1012 or more meteoroids, with the mass of the visible meteoroids ranging up to about 1 g. The main evolutionary effect on such streams is gravitational perturbations by the planets. Though grain-grain collision may be catastrophic for the two grains involved, it has no effect on the remainder of the stream, other than the fact that there are now two less grains in it. Solar radiation has some effect, but this can be included in the equations of motion. Because of the large numbers of particles involved, meteoroid streams represent a laboratory where many of our dynamical concepts can be tested.

At a basic level, meteoroid streams represent a collective dynamical phenomenon in which all members display roughly the same behavior. One of the fundamental questions which can be investigated is whether the behavior of the mean orbit of the whole stream represents the mean behavior of the stream members. Within the boundaries of some meteor streams lie regions where the orbits are in high order resonance with Jupiter. This also represents a phenomenon of interest. Finally, the possibility exists that some streams are in chaotic regions and it is interesting to investigate whether or not meteoroids in such regions do display chaotic behavior.
Molecules in Planetary Nebulae
Authors: Black John H.
Published: June 2019

The study of molecules in planetary nebulae is still in its infancy; therefore, it is appropriate both to review existing knowledge and to anticipate developments that will arise as the subject matures. Briefly stated, this subject consists of observations of hydrogen, H2, and carbon monoxide, CO, molecules in a very few nebulae; the tentative identification of the hydrogen molecular ion, H2+; unsuccessful searches for various other species; some theoretical work on molecular processes relevant to planetary nebulae; and the study of molecules in possible precursors of planetary nebulae. Such a facile summary might suggest that molecules are mere curiosities of peripheral interest; on the contrary, it can be asserted that molecular studies of planetary nebulae will yield important new information about their origins, structures, and evolution.
On the O III/O II Problem in Medium and High Excitation Planetary Nebulae
Authors: Che Anne , Köppen J.
Published: June 2019

Numerical models have been constructed for twelve ionization bounded, medium to high excitation planetary nebulae. In most objects the excitation sensitive line ratio (O III) λ 500.9 nm / (O II) λ 372.7 nm is predicted to be too low as compared to observations. A similar systematic discrepancy is observed for [S III] λ 953.2 nm / (S II) λ 672.0 nm. We investigated the following effects on the ionization structure of the nebulae: 0++ + HO → 0+ + H+ charge exchange reaction, energy distribution of ionizing radiation and density distribution of gas in the nebular shell. The results show that density distribution is the most important factor determining the 0 III/O II and S III/S II line intensity ratios. While a factor of ten decrease in the charge exchange coefficient is required to explain the systematic discrepancy, a reduction of nebular radius by a few percent - truncated nebula (quasi density bounded model, but nebula still optically thick to Lyman photons) - suffices to produce the correct 0 III/O II ratio. Also, a density gradient of n ∼ r−1 to r−2 yields much better agreement with observations. Realistic variations in stellar spectrum hardly affects the 0 III/O II line intensity ratio.
Numerical Gas-Dynamic Investigation of the Whimper Model for the Formation of Planetary Nebulae
Authors: Purton C. R.
Published: June 2019

The suggestion that the shells of planetary nebulae may be formed at the interface between two stellar winds of different velocity (“Not with a bang, but a whimper”) (Kwok, Purton and FitzGerald, 1978, Astrophys. J. 219, L 125) is investigated using the ‘beam scheme’ (Sanders and Prendergast, 1974, Astrophys. J. 188, 489) adapted to a system with spherical symmetry. Initial conditions include the remnant wind from the red giant phase and a highspeed wind from the hot nucleus ( (two tests), v = 103km s−1). The collision began at a radial distance of 200 AU. A third test at 50 AU indicated that the end result was insensitive to the details of the transition from one mass-loss mechanism to the other.
Evolution and Mass Distribution of Central Stars of Planetary Nebulae
Authors: Schoenberner D. , Weidemann V.
Published: June 2019

Considerable progress has been made in our understanding of the evolution of the central stars of planetary nebulae (NPN) compared to the situation five years ago at the Ithaca Symposium where Shaviv (1978) and Paczynski (1978) reviewed the subject. Shaviv stressed the necessity to start theoretical calculations with realistic initial models but doubted - in view of the loops in the HR diagram made by flashing stars - if the Harman-Seaton sequence could be taken as a single evolutionary sequence. Paczynski pointed out how strongly the theoretical rate of evolution depends on the stellar mass - a result which had appeared in his earlier calculations (1971) - and expected the existence of more flashing NPN's of the FG Sagittae type among the luminous (L > 104 L⊙) central stars, for which the core mass luminosity relation (Mc > 0.7 M⊙) combined with the core mass interpulse time relation predicts fairly short (2.10 yrs) intervals between flashing events. Weidemann, however, at the Symposium and shortly thereafter (1977a) concluded in view of the lower effective temperature derived by Pottasch et al. (1978) and the observed narrow mass distribution of white dwarfs around a 0.6 Mo. combined with the theoretical predicted horizontal tracks from the red giant branch towards the NPN region at a luminosity given by the core mass luminosity relation that the high luminosity part (and also the “upturn”) of the Harman-Seaton sequence does not exist. He also proposed an increase in the distances by an average factor of 1.3 compared to the Seaton/Webster (Seaton, 1968) or Cahn/Kaler (1971) scale in order to bring the observed NPN on the 0.6 M⊙ track in the HR diagram and to lower the NPN birth rates to a value compatible with white dwarf birth rates.
The Distances of PN and the Galactic Rotation Curve
Authors: Schneider S.E. , Terzian Y. , Purgathofer A. , Perinotto M.
Published: June 2019

The problem of determining the distance scale for planetary nebulae (PN) is approached through the kinematics of this subpopulation in the galaxy. To this end, we have compiled a catalogue of all known radial velocities for 457 galactic PN with standardized error statistics. External (calibration?) errors of the same magnitude as internal spectral line deviations are noted.
VLA Observations of Planetary Nebulae at the Galactic Centre
Authors: Gathier R. , Pottasch S.R. , Goss W.M. , van Gorkom J.H.
Published: June 2019

The Very Large Array (VLA) in Socorro, New Mexico, has been used to measure the 6 cm continuum flux densities and the angular sizes of 42 planetary nebulae (PN) in the direction of the galactic centre (GC). These were all optically confirmed PN for which the radial velocities (and positions on the sky) make it very likely that they are close to the GC. With a detection limit of about 1 mJy, 34 PN were detected. Their flux densities range from 2 to 100 mJy. Initially we used a configuration of the VLA with an instrumental resolution of 1″. About 80% of the detected PN could be clearly resolved with this resolution. The unresolved PN were observed again with a configuration of the VLA that has a resolution of 0″.4. For all but one of the 34 detected PN we could determine reliable angular sizes. The inferred total ionized masses range from < 0.01 to ~ 0.5 M⊙, assuming a distance to the GC of 9 kpc. The results argue strongly against the use of the Shklovsky method for distance determinations. Previous measurements of PN at the GC showed that their luminosities were substantially higher than those for nearby PN (Pottasch, 1980). The luminosity distribution of the PN in our sample is broader towards lower luminosities (up to the detection limit of the observations), but the luminosities are still high compared with nearby PN. We interpret this as a selection effect: by studying only optically confirmed PN, the intrinsically brightest PN are selected.
Birthrate of PN
Authors: Mallik D.C.V.
Published: June 2019

Recent observations of planetary nebulae have called into question the Shklovsky method of measuring distances. For those planetaries for which independent distance and electron density determinations are available, it is found that the ionized mass and the radius are linearly correlated (Maciel and Pottasch, 1980) and also that the ionized masses increase with decreasing electron density (Pottasch, 1981). These relations imply that the nebulae are optically thick in Ly continuum radiation and the distances based on the Shklovsky method are overestimates. Using an empirically determined mass-radius relationship Maciel and Pottasch have obtained new distances for the nebulae in the catalogue of Milne and Aller (1975). We have used the more complete catalogue of Cahn and Kaler (1971) to obtain distances corrected for possible variations in the ionized mass and have compiled a new list of local planetaries. We obtain a surface density of 15 ± 3 kpc−2 and a planar number density of 44 ± 4 kpc−3.
Detection and Study of Secondary Structures in Some Planetary Nebulae
Authors: Louise R.
Published: June 2019

In order to detect faint nebulosities associated with planetary nebulae, long exposure plates are made on nine selected nebulae, using a large bandwidth (Δλ = 50 Å) interference filter coupled with an ITT image tube. Some peculiar features are observed, but they do not all account for “secondary structures” following Louise's terminology. We discuss the difficulties encountered by the photographic method.
A Dynamical and Chemical Study of NGC 6302
Authors: Danziger I.J. , Baade D. , Atherton P. D. , Taylor K. , Boksenberg A.
Published: June 2019

From five spectrograms obtained at five different positions in the nebula, relative ionic concentrations have been derived with respect to the nucleus. They show that the degree of excitation generally decreases with distance from the nucleus. But there are also areas with locally enhanced or attenuated excitation. Taurus data, a series of two-dimensional monochromatic images centered on (OIII) λ 5007, have been used to construct a two-dimensional velocity map. It shows a large-scale structure similar to the one of direct images with the biconical pattern being at least partly present. Areas of locally lower radial velocity which seem to be inversion symmetrically distributed with respect to the centre, are also distinguished. They do not have pronounced counterparts on direct images. The cavity model suggested by Barral et al. (1982, MNRAS 199, 95) for NGC 6302 and Icke's biconical flow model (1981, Ap. J. 247, 152) are discussed.
Recombination Spectra of Planetary Nebulae
Authors: Bogdanovich P.O. , Rudzikas Z.B. , Feklistova T. H. , Kholtygin A.F. , Nikitin A.A. , Sapar A.A.
Published: June 2019

The lines of the transitions between the subordinate levels of the CIII, NIII etc. ions are observed in the spectra of planetary nebulae (PN) (1). Their theoretical intensities may be found by solving the stationarity equations and accounting for both the recombination and cascade radiative transitions. It is possible to calculate the recombination spectra in various approaches: the single- or multi-configuration approximations (SCA and MCA) making use of both the superposition of configurations (SC) or the multiconfigurational Hartree-Fock-Jucys equations (2), taking into consideration the contribution of the dielectronic recombination to the intensities of the recombination lines. The energy spectra, the transition probabilities etc., as a rule ought to be calculated in the intermediate coupling scheme (2). Both analytical or numerical (e.g. Hartree-Fock) wave functions may be adopted.
High Dispersion IUE Observations of NGC 3918
Authors: Pẽna M. , Torres-Peimbert S.
Published: June 2019

Our results are based on SWP 3215, a 120 min large aperture exposure. The electron density derived from N IV), Si III) and C III) ratios are log Ne < 4.3, 5.0 and 3.5. The measured resonance line ratio 1239/1243 of N V is 1.2 ± 0.1 and 1549/1551 of C IV is 1.9 ± 0.2. Both ratios are expected to be 2.0. Furthermore, it had already been reported that the C IV and N V resonance lines are fainter than predicted from models by factors from ~ 4 to ~ 6 (Torres-Peimbert et al., 1980, The First Two Years of IUE, NASA CP-2171, 641). Internal dust cannot account for any significant deviation from 2 for the resonance doublet ratio of N V (Hummer and Kunasz, 1980, Ap. J., 236, 609). However, the anomalous ratio of N V could be explained by a generally distributed hot ionized medium compatible with the C IV absorption found in approximately the same direction by Cowie et al. (1981, Ap. J., 248, 528).
Observations of the 30 μm feature in IRC + 10216
Authors: Herter T. , Briotta D.A. , Gull G.E. , Houck J.R.
Published: June 2019

New observations of the unidentified 30 μm spectral feature found in two planetary nebulae and four carbon stars are reported. The carbon star IRC + 10216 was observed from the Kuiper Airborne Observatory over the range 30 to 37 μm. These new data confirm the existence of the feature and determine its shape beyond 30 μm. The determination of the long wavelength end of the spectral excess depends critically on the assumed underlying continuum. A combined spectrum of the excess is presented and shows the feature to extend at least to 37 μm.
OH/IR Stars: Dark Planetary Nebulae?
Authors: Herman J.
Published: June 2019

The OH maser emission from OH/IR stars (type IIb) originates from the thick circumstellar dust shell. As the envelope is expanding and the strongest maser emission comes from the front- and the backside, where the gain pathlength is longest, we can measure a definite phaselag (and hence a diameter) between front- and backside of the shell for all sources that are variable.
Concerning the Temperatures of Central Stars of Planetary Nebulae
Authors: Kohoutek L. , Martin W.
Published: June 2019

Recently Pottasch (1981, Astron. Astrophys. 94, L13) published extremely high effective temperatures of some central stars of planetary nebulae (> 200 000 K). Our study of planetary nebulae based on photoelectric photometry does not confirm his results. A histogram of Tz(HI) and Tz(HeII) shows smooth distribution of Tz with the maximum of about 48 000°K (HI) and 90 000°K (HeII), respectively; the effective temperature of none of the 62 planetary nuclei exceeds 120 000°K.
UV Radiation from Central Stars of Planetary Nebulae
Authors: Cerruti-Sola M. , Perinotto M. , Cacciari C. , Patriarchi P.
Published: June 2019

The flux originating from the central stars of 27 planetary nebulae in the spectral range 1200-2000 Å has been deduced from the analysis of a large number of released IUE low resolution spectra.
Fabry-Pérot Radial Velocities of S274: a Planetary Nebula
Authors: Recillas-Cruz E. , Pismis P.
Published: June 2019

The bright nebula S274 (YM29), 8′ across has been classified as a planetary by Abell (1966) although it has been considered a SNR by other authors. We have determined radial velocities at 173 points on this nebula from four Fabry-Pérot interferograms. The velocity field exhibits a great deal of structure. The average expansion velocity is + 31.5 ± 8 km s−1. The mean radial velocity of S274 is not well determined due to the nature of the velocity field, while the overall velocity (173 points) is + 33 ± 21 km s−1. Points at the outer boundary yield an average of 22 ± 14 km s−1 while the average of the double points is 25 km s−1. The age of expansion of the nebula is estimated at 6.8 × 103yr. The physical parameters of this object are consistent with those of a planetary nebula.
A Historical Review of Star Formation: Observation and Theory
Authors: Lang Kenneth R.
Published: June 2019

We present a historical review of evidence for ongoing star formation in our Galaxy beginning with the discovery that interstellar space is not empty. The discoveries of interstellar dust, interstellar hydrogen and molecular clouds are reviewed. Observational investigations of dark clouds are then traced from the photographs of Edward Emerson Barnard to contemporary studies of their molecular constituents. A historical overview of observational evidence for new-born stars includes T-Tauri stars, young stellar clusters, sequential star birth and infrared stars beginning with Alfred Joy, Merle Walker, Becklin, and Neugebauer, and Adrian Blaauw and continuing to giant molecular clouds and IRAS. Theoretical studies of gravitational collapse and the early stages of stellar evolution are also placed within a historical context.
A Study of Interstellar Ultraviolet Extinction in OB Associations and Star - Forming Regions
Authors: Aiello S. , Barsella B. , Chlewicki G. , Greenberg J. M. , Patriarchi P. , Perinotto M.
Published: June 2019

We studied the interstellar UV extinction towards 115 stars, selected from IUE data bank, belonging to a variety of different galactic areas, including well-known dense clouds.