bluuebunny/crossref_metadata_2025 huggingface dataset:
New Results from Complete Samples of Faint Radio Galaxies and Quasars
Authors: Blundell K.M. , Rawlings S. , Eales S.A. , Lacy M.
Published: July 2016

In any flux-limited sample a tight correlation of luminosity (P) and redshift (z) is inevitable. It is therefore necessary to obtain complete samples at lower and lower flux-limits in order to have adequate coverage of the P–z plane, essential if we are to decouple the trends in epoch from trends in luminosity. This we have done for a number of flux-limits — giving coverage of the P–z plane seen in Fig. 1. Our redshift information is spectroscopic; the results of Eales et al (in prep.), namely the increased scatter in the

K-z plot for samples lower in luminosity than 3C, strongly warn us against using redshifts estimated from K-magnitudes.
High Redshift Radio Galaxies
Authors: Meisenheimer K. , Hippelein H. , Neeser M.
Published: July 2016

One hundred years after G. Marconi recorded radio waves over a distance of more than 1000 m, the most sensitive radio telescopes are able to detect the radio emission from light travel distances at least 1.4 × 1023 times greater. The electromagnetic waves from these distant objects are red shifted by Δλ/λ = z > 4. It is not the mere distance of high redshift objects which is fascinating, but rather the fact that one looks back into the early history of the universe by observing them: Objects at a redshift of 4 shined at a time when the universe had reached only about 1/5 of its present age.
Reliability tests for Doppler imaging
Authors: Unruh Y.C.
Published: July 2016

In recent years, Doppler imaging codes have been developed by a number of different groups and successfully applied to map the spot distribution on stellar surfaces. As more and more images are obtained we tend to see a pattern of high-latitude spots, particularly on RS CVn systems. These high-latitude spots were and still are greeted with scepticism as they are inferred from non-varying profile deformations. Here, I describe some of the problems of Doppler imaging and their likely impact on the resulting images.
Eclipse mapping and related techniques
Authors: Rutten René G. M.
Published: July 2016

Eclipse mapping is a technique to deduce spatial structure on very small angular scales in eclipsing cataclysmic variable stars (CVs). By analysing the eclipse light curve, information is obtained on the brightness structure of the accretion disk and of the compact mass-accreting object in these systems. This information would otherwise be well beyond the resolving power of any optical telescope. Since the development of the eclipse mapping technique by K. Horne, about one decade ago, it has now become an important tool in the study of CVs. Originally eclipse mapping was employed to construct brightness maps of accretion disks in broad spectral bands. Recently, maps of much higher spectral resolution have become available from which optical and UV spectra have been reconstructed in spatial detail across accretion disks. Such information is very important for our understanding of the physics of the accretion process.

In this paper I will describe the eclipse mapping technique and review recent results. In conjunction, I will briefly highlight other techniques related to the mapping of surface structure in CVs.
Phase-coherent interferometric imaging
Authors: Baldwin J.E.
Published: July 2016

The essence of high resolution interferometric imaging is Michelson interferometry and it has a long history. Yet the symposium programme describes it as the Last Frontier! Why was it not crossed decades ago? This paradox needs some explanation. I suspect that many participants here are tourists in interferometry, as I am in their fields, so it is interesting to look at the key developments since Michelson invented the field. It is, of course, a personal view.
Observing stellar surface structure with the ESO-VLT interferometer
Authors: Von Der Lühe O. , Solanki S. , Reinheimer Th.
Published: July 2016

The ESO Very Large Telescope (VLT) has the capability to coherently combine the light from four 8m telescopes and from smaller Auxiliary telescopes with baselines 4m and 200m (VLT Interferometer or VLTI). The resulting resolution approaches 0.5 milli-arcsec at visible wavelengths and 1 milli-arcsec in the near infra-red. We estimate that about 2000 nearby bright stars can be resolved with these baselines. The surface of about 400 stars, mainly K and M giants, can be mapped with a resolution of a dozen pixels or better across the stellar surface. This resolution permits detailed studies of the structure of stellar atmospheres, their hydrodynamics and magneto-hydrodynamics. VLTI can easily resolve starspots and very likely also convection cells on an active K-type giant at 10pc distance. A marginal detection of the largest starspots on a very active solar-type star at the same distance may be possible, but it appears very unlikely that the surface structure on an inactive solar-type star can be imaged.

We present computer simulations of stellar surfaces to study in detail the response of the interferometer to an extended, complex source. First results which simulate the end-to-end process in a simplified manner indicate that useful maps can be produced provided that a sufficient number of baselines are combined in Earth-rotation synthesis mode. We also give arguments that high spectral resolution will prove essential to constrain reconstructed maps.
Surface lithium and cool spots
Authors: Fekel F. C.
Published: July 2016

Observations of lithium in sunspots resulted in the prediction of significant lithium equivalent-width variability in chromospherically active stars. Lithium observations of several types of active stars, such as pre-main-sequence stars and late-type dwarfs in very young clusters, whose members are assumed to be nearly coeval, as well as post-main-sequence objects, show a significant range of abundances. Thus, a number of researchers over the past decade have investigated star spots as the possible cause of the various observed lithium-abundance spreads. Observationally, some evidence has been found for lithium equivalent-width variations. Computed synthetic spectra indicate that under certain conditions significant variations should be detected, but such conditions are not often met except perhaps in the most active stars. While variations have been claimed for some T Tauri stars, simultaneous photometry and spectroscopy will be needed to explore the complex relation of spots and lithium-abundance variations. The fact that some post-main-sequence stars have lithium abundances similar to those of pre-main-sequence stars complicates the identification of isolated pre-main-sequence systems.
NLTE model atmospheres for M dwarfs and giants
Authors: Hauschildt Peter H. , Allard France , Alexander David R. , Schweitzer Andreas , Baron E.
Published: July 2016

The atmospheres of M stars are dominated by a small number of very strong molecular compounds (H2O, TiO, H2, CO, VO). Most of the hydrogen is locked in molecular H2, most of the carbon in CO; and H2O, TiO and VO opacities define a pseudo-continuum covering the entire flux distribution of these stars. The optical “continuum” is due to TiO vibrational bands which are often used as temperature indicators for these stars. These may be the depth of the bands relative to the troughs in between them; or the depth of the VO bands; or of the atomic lines relative to the local “continuum”; or even the strength of the infrared water bands; all of these depend on the strength of the TiO bands and the amount of flux-redistribution to longer wavelengths exerted by them. Departures from LTE of the Ti I atom, and thus the concentration of the important TiO molecule, could, therefore, have severe and measurable consequences on the atmospheric structure and spectra of these stars.
Pulkovo Observatory and the National Observatory Movement: An Historical Overview
Authors: Dick Steven J.
Published: July 2016

The patronage of national governments has played an important role in the history of astronomy, classically in the form of National Observatories. In this paper we 1) argue that the last three centuries have seen what we may call a “national observatory movement,” in that national governments during this period increasingly supported astronomical observatories, and in that such institutions share certain common properties of origin, purpose and evolution; 2) demonstrate the important role that Pulkovo Observatory has played in this movement; and 3) compare certain aspects of the Pulkovo Observatory and the United States Naval Observatory as exemplars of this species founded within a decade of each other under very different political conditions.
The Pulkovo Programme for the Study of Visual Double Stars
Authors: Kisselev A. A. , Bykov O. P. , Kalinichenko O. A. , Kiyaeva O. V. , Romanenko L. G. , Shakht N. A.
Published: July 2016

The observation of visual double stars at Pulkovo is a traditional work of Pulkovo astronomers started by W. Struve in 1830 at Dorpat (now Tartu). After the Second World War and restoration of the observatory in 1960, the observations of double stars have been carried out with help of 26-inch Zeiss refractor using the photographic technique. We observe the visual binaries which satisfy the conditions of highest accuracy of astrometric reduction: d > 3′, m < 12.0, dm < 1.0, δ>20°.
On the Programme of Ground-Based Observations of Bright Selected Minor Planets for 1991–2000
Authors: Batrakov Yu.V. , Shor V.A.
Published: July 2016

The programme of observations of 10 bright minor planets for 1991-2000 is proposed. One of the main aims of the programme is the determination of the orientation parameters and the systematic errors of star catalogues.
Oceanic Influences on the Angular Velocity of the Earth
Authors: Brosche P.
Published: July 2016

Hydrodynamical computations of the major partial tides in the oceans have been evaluated for the changes both in moment of inertia and relative angular momentum due to ocean currents. If the system solid Earth plus oceans is seen as an isolated system for these time scales, the oceanic variations lead to mirror-like changes in the rotation of the solid Earth. Amplitudes are of the order of 0.1 ms in Universal time. In contrast to the effects of solid Earth tide, phases are away from equilibrium phases.
Difference Between Dynamic and Stellar Reference Frames: Results Based on Astrometric Observations of Martian Satellites
Authors: Emelyanov N.V. , Kolyuka Yu.F. , Kudryavtsev S.M. , Kuimov K.V. , Tikhonov V.F. , Chazov V.V.
Published: July 2016

The possibility of using precise astrometric observations of Martian satellites in 1988 for improving the mutual orientation of the dynamic and stellar reference frames is discussed. The results obtained lead to the conclusion that the stellar reference frame is rotated about the X axis of the dynamic one. However, the value of this rotation (∼2.″5) proves to be unrealistically large and repetitions of precise observations of Martian satellites are needed in the future for verifying this result.
Sidereal Years — Catalogue Uses in Archaeoastronomy
Authors: Barlai K. , Ecsedy I.
Published: July 2016

In ancient societies the Sun was the natural time marker in daytime and base for the calendar. At night, however, the stars, their movements, risings and settings, disappearence and reappearence served quite obviously as time-keepers, and people were not always conscious that they measured time using two slightly but fundamentally different clockworks.
Relativistic Reduction of Astrometric Observations at Points Level of Accuracy
Authors: Brumberg V. A. , Klioner S. A. , Kopejkin S. M.
Published: July 2016

The framework of general relativity theory (GRT) is applied to the problem of reduction of high precision astrometric observations of the order of one microarcsecond. The equations of geometric optics for the non-stationary gravitational field of the Solar system have been deduced. Integration of the equations of geometric optics results in the isotropic geodesic line connecting the source of emission (a star, a quasar) and an observer. This permits to calculate the effects of relativistic aberration of light due to monopole and quadrupole components of the gravitational field of the Sun and the planets taking into account their motions and rotation. Transformations between the reference systems are used to calculate the light aberration occurring when passing from the satellite system to the geocentric system and from the geocentric system to the baryecntric system. The baryecntric components of the observed position vector reduced to the flat space-time are corrected, if necessary, for parallax and proper motion of a celestial object using the classical techniques of Euclidean geometry.
Astrometric Interferometry — Can It Establish a Fundamental System?
Authors: Kaplan G. H.
Published: July 2016

The astrometric optical interferometer on Mt. Wilson is providing a new source of astrophysical and astrometric data on bright stars. The instrument, with 12-meter baselines, has been in operation since late 1986. The interferometer is capable of wide-angle astrometry, that is, the determination of very precise stellar positions within a reference frame defined by bright stars spread across a large area (of order one steradian) of the sky. This paper addresses the question of whether such an instrument can be used to establish a fundamental system — that is, one tied to the Earth in some well-defined way. Some astrometric data from this instrument are presented to illustrate the difficulties involved. Proposed means of addressing these problems in future instruments are discussed.
The USNO (Flagstaff Station) CCD Transit Telescope and Star Positions Measured From Extragalactic Sources
Authors: Stone Ronald C. , Monet David G.
Published: July 2016

The USNO (Flagstaff Station) is in the process of modernizing its 8-inch transit telescope. The upgraded instrument will use a CCD detector to measure the positions of both bright and faint stars directly with respect to extragalactic sources. Moreover, it will be able to observe large numbers of stars very rapidly, and improvements in accuracy are expected with further upgrades (e.g. CCD circle scanners, an interferometric telescope monitoring system, networks of environmental sensors). Many research opportunities related to coordinate systems exist for this telescope.
Optical Astrometry of Extragalactic Radio Sources With the Tautenburg Schmidt Telescope
Authors: Dick W.R. , Kumkova I.I.
Published: July 2016

Optical positions of objects from the IAU Commission 24 Working Group list of benchmark radio sources have been derived which will contribute to the link of the radio and optical reference frames. Results for 11 objects with an r.m.s. position error of 0.″2 are presented and discussed.
A Comparison of the Accuracy of the Determination of right Ascension by Means of Transit Instruments of Different Types
Authors: Izmailov S. P. , Litkevich N. G. , Sadzakov S. N. , Simonenko V. D. , Suchkova T. I. , Tolchelnikova-Murri S.A. , Turenko V. I.
Published: July 2016

A special series of observations of the groups of stars performed in Pulkovo, Chile, Kharkov and Belgrade were used to compare the mean errors of the right ascension by means of the method eliminating the influence of the errors of the source catalogue. The results show the advantage of the small transit instruments over transit circles of the classical type.
A Comprehensive Astrometric Data Base: An Instrument for Combining Earth-Bound Observations With Hipparcos Data
Authors: Wielen Roland
Published: July 2016

The astrometric data bank ARIGFH will contain all relevant astrometric data on stellar positions and proper motions of stars from ground-based observations and space missions. For each star in the ARIGFH, the best available position and proper motion shall be derived. We rediscuss the accuracy of proper motions and positions of fundamental stars, resulting from a combination of data in the FK5 with the expected results from a revised HIPPARCOS mission. The FK5 data could be significantly improved even by rather degraded positions from a revised HIPPARCOS mission.
Current Status of the Project of Photographic Fourfold Coverage of the Northern Hemisphere of Sky
Authors: Kislyuk V.S.
Published: July 2016

The project of fourfold coverage of the northern hemisphere of the sky by means of wide-angle astrographs was proposed in 1977 (Kolchinsky and Onegina, 1977). This project is known as FON (fotograficheskij obzor neba) — photographic survey of sky.
Research on the Errors in Determination of Precise Optical Positions of Radio Sources
Authors: Chun-Lin Lu , Dong-Ming Li
Published: July 2016

To link the optical reference frame to extragalactic radio frame, an observation program is in progress in Purple Mountain Observatory (PMO) and Shanghai Observatory. In this program, 70 extragalactic sources will be observed with the 1.56 m astrometric reflector in Shanghai. The secondary reference stars are determined with the twin astrograph (D = 40 cm, f = 300 cm) in PMO, and about 50 radio stars and some bright extragalactic sources will be observed with the twin astrograph.
Comparison of Optical and Radio Positions of Stars
Authors: Morrison LV , Argyle RW , Requième Y , Mazurier JM
Published: July 2016

The positions of radio stars measured with respect to the VLBI network of extragalactic sources provides an important link between the optical and extragalactic reference frames. The establishment of this link was brought a stage nearer realization with the publication by Florkowski et al.(1985) of the radio positions of 20 stars measured with the Very Large Array (VLA) of the National Radio Astronomy Observatory, and the publication by Lestrade et al.(1985, 1988) of 10 stars measured with the VLBI network.
An Advanced Astrometric Sensor Array
Authors: Monet David G. , Ables Harold D.
Published: July 2016

The U.S. Naval Observatory has commissioned the fabrication of an array of six charge-coupled devices (CCDs) bonded to a single silicon substrate for precision astrometry of sources spanning a large range in apparent brightness. The array includes one CCD with rapid readout capability for imaging bright stars. We present the design parameters and the anticipated performance characteristics of this sensor.
Sunspot Seismology Theory
Authors: Davila Joseph M.
Published: July 2016

Recent observations have demonstrated that sunspots can absorb significant p-mode wave power, and that this absorption has a well defined wavelength dependence. These observations open, for the first time, the potential to deduce semi-empirically the subsurface structure of sunspots and active regions. Several physical mechanisms have been proposed to explain the absorption. In this paper, the proposed mechanisms are reviewed and their viability in view of the current knowledge of the scattering process is discussed.
Wave Propagation in Sunspots
Authors: Hasan S.S.
Published: July 2016

In this paper, wave propagation in sunspot umbrae is analysed. The stratification in a typical umbra is approximated by a model atmosphere, extending vertically from a depth of a few thousand kilometres below the photosphere, to the transition region. No boundaries are imposed in the horizontal direction. It is assumed that this atmosphere is embedded in a uniform vertical field. Using a Rayleigh-Ritz variational technique, the normal mode frequencies of the umbra are calculated for different values of the horizontal wave number k. A theoretical diagnostic diagram is generated. An interesting feature of the solutions is the existence of ‘avoided crossings’, similar to those found in the study of global oscillations. The nature of the wave modes is examined by decomposing the eigenvectors into longitudinal and transverse components. In general, it is found that the character of a mode changes with height. For large k, modes with periods in the 2-3 min range, correspond to low order modes in the present calculation. Above the photosphere, they resemble slow waves.
Coronal Heating by D.C. Currents
Authors: Heyvaerts J.
Published: July 2016

Present views on DC current coronal heating are presented. The relation to AC mechanisms, the importance of MHD turbulence in both processes, and the convergence of presently proposed ideas is outlined.
Wave Energy Dissipation in the Solar Atmosphere
Authors: Aihua Zhou
Published: July 2016

There are two regions of rapid dissipation when Alfvén waves propagate from the transition region to the corona. They occur respectively in a range of several hundred kilometers above the base of the transition region and in the corona at about 1-3Ro. The heating of the atmosphere by wave dissipation could be one order of magnitude larger than heat conduction in the coronal part with a lower temperature and density and stronger magnetic field. Wave heating could also become more important when the magnetic field divergence becomes stronger.
Storage and Release of Magnetic Energy in a Force-Free Field
Authors: Aly J.J.
Published: July 2016

For a 3D force-free field occupying a half-space D = {z > 0}, we discuss: i) the storage of free magnetic energy when the field evolves quasi-statically as a consequence of motions imposed to its footpoints on the plane {z = 0}; ii) the release of this energy during a reconnection process implying a rearrangement of the lines which is either local, occuring in the neighbourhood of spontaneously formed current sheets, or global, occuring in an explosive flare-like way.
Super–Alfvénic Beam–Plasma Instabilities in Solar Flares
Authors: Verheest Frank
Published: July 2016

Special type III radio bursts with significantly lower drifts have been attributed to proton beams at the flare site. These low energy beams (some MeV) are nevertheless super-Alfvénic. Recent reports deal with the stability of such beams against resonant scattering by waves below the proton gyrofrequency. Here a different mechanism is proposed, namely nonresonant Alfvén instabilities, which may have higher growth rates and can thus dominate. A selfconsistent multispecies plasma description of such instabilities, developed for solar wind and cometary plasmas, is applied to slowly drifting type III radio bursts. The instability growth rate is fairly insensitive to the beam velocity but decreases with the ratio of beam to ambient plasma densities. Even low beam densities can trigger these nonresonant and hence generic instabilities. Moreover, growth rates are sizeable fractions of the wave frequency, whereas resonant instabilities would give much lower values at low beam densities.
Ion Cyclotron Instability and Electron Acceleration in Coronal Magnetic Flux Tubes
Authors: Min-jian Xu , Ding-yi Li , De-yu Wang , Shih-tung Tsai
Published: July 2016

Part of the energy of low solar corona may be released and converted to plasma energy that may be the dominant source of solar flares. Recently, many physical mechanisms have been proposed to accelerate ions and electrons. In the magnetic mirror device of fusion research, ion cyclotron instability and the energetic ion losses have been discovered and the plasma becomes electron rich.
Electron Beams and Langmuir Turbulence in Solar Type III Radio Bursts Observed in the Interplanetary Medium
Authors: Lin R. P.
Published: July 2016

The ISEE-3 spacecraft has provided in situ observations of electron beams, plasma waves, and associated solar type III radio emission in the interplanetary medium near 1 AU. These observations show that electron beams are formed by the faster electrons arriving before the slower ones, following an impulsive injection at the Sun. The resulting bump-on-tail in the reduced one-dimensional distribution function, f(v||), is unstable to the growth of electrostatic electron plasma (Langmuir) waves. The Langmuir waves are observed to be highly impulsive in nature. The onset and temporal variations of the observed plasma waves are in good qualitative agreement with the wave growth expected from the evolution of measured f(v||). However, far higher Langmuir wave intensities are predicted than are detected. In addition, the lack of obvious plateauing of the bump-on-tail suggests that the waves have been removed from resonance with the beam electrons by some wave-wave interaction. Bursts of low frequency, 30–300 Hz (in the spacecraft frame) waves are often found coincident in time with the most intense spikes of the Langmuir waves. These low-frequency waves appear to be long-wavelength ion acoustic waves, with wave number approximately equal to the beam-resonant Langmuir wave number. The observations suggest several possible interpretations: modulational instability, electrostatic decay instability, and electromagnetic decay instability; but none of these are fully consistent with the observations. Microstructures, too short in duration to be resolved by present experiments, have been invoked as an explanation of the phenomenon. Experiments are currently being developed to study these processes using fast wave-particle correlation techniques.
VLA Observations of the Coronal Plasma
Authors: Lang Kenneth R.
Published: July 2016

VLA observations at 20-cm wavelength specify the brightness temperature and magnetic structure of plasma constrained within coronal loops in solar active regions. Comparisons with simultaneous SMM observations at soft X-ray wavelengths lead to measurements of physical parameters like electron density, electron temperature and magnetic field strength. Such comparisons also indicate coronal loops can be detected at either radio or X-ray wavelengths while remaining invisible in the other spectral domain, and that the dominant radiation mechanisms can be thermal bremsstrahlung or thermal gyroresonance radiation. VLA observations at the longer 90-cm wavelength reveal the thermal emission of a hot transition sheath enveloping a cooler, underlying Hα filament seen in absorption. The 20-cm VLA observations indicate that the precursor, impulsive and post-flare components of solar flares originate in spatially separated and resolved sources.
Observations of Solar Continuum Emission at Decameter Wavelengths
Authors: V. Sastry Ch.
Published: July 2016

We observed the continuum emission from the radio sun when there is no burst activity at λ = 8.7 m with the large decameter wave radio telescope at Gauribidanur (Latitude 13° 36‘ 12“ N and 77° 27‘ 07“ E) with a resolution of 26'/40'. A compound grating interferometer with one dimensional resolution of 3' is also used. These observations are made during August 1983 and June 1986. The brightness temperature at the center of the sun varied from 0.2 106 K to 0.8 106 K during these periods on time scales of several hours to a day. Since the sun is absolutely quiet during these periods we believe that the radiation is purely thermal in nature. In this case the observed brightness temperature variations imply large scale density variations by more than a factor of three if the corona is optically thin at these wavelengths. Alternatively if the corona is optically thick the observations imply real electron temperature variations with or without accompanying density variations.
Behaviour of Whistlers in Coronal Magnetic Traps and Its Relevance to a New Fine Structure in Solar Type IV Radio Bursts
Authors: Chernov G.P.
Published: July 2016

A possible contribution of whistlers to fine structure production due to the coalescence process with plasma waves 1 + w → t at frequencies ω1 ± ωw = ωt is estimated. A whistler ray tracing in the solar corona with the twice Newkirk density model and with a dipole magnetic field using a standard numerical integration of the Haselgrove two-dimensional equations is performed.
Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa G. , Gopalswamy N. , Kundu M. R.
Published: July 2016

A statistical analysis of Clark Lake microbursts was performed using a data base consisting of ~ 100 bursts. The results are: (1) Microburst sources are well correlated with coronal streamers and active regions. (2) The peak brightness temperature (T^) of the microbursts is in the range 6 × 105 K to 6 × 107 K (see Fig. 1; see also Kundu et al, 1986; White et al, 1986; Gopalswamy et al. 1987) whereas it is quite high for normal type III bursts (107 < Tb < 1012 K - Dulk and Suzuki, 1980). (3) The source size varies over a wide range of 5.5 − 10.5 arc min at 73.8 MHz, 8.5 − 13.5 arc min at 57.5 MHz, 10.5 − 16.5 arc mins at 50 MHz and 12.5 − 22.5 arc min at 38.5 MHz. (4) The drift rate lies mainly in the range 4.5 to 6.5 MHz s−1, with an average value of ~ 5.5 MHz s−1.
Some Results Concerning the OB Aggregate Around Eta Carinae
Authors: Feinstein A.
Published: July 2016

UBV observations of stars in the small and compact cluster Tr 15 located 20 arcmin north of Eta Carinae confirms its physical connection to the OB aggregate comprising TR 14, Tr 16 and Cr 228. Its corrected distance modulus is Vo–Mv = 12.1, with a mean interstellar absorption of Av = 1.4 ± 0.2 mag. Two very red variable stars, RT Car, close to the cluster (2 arcmin), and BO Car, about 8 arcmin southeast, appear to be related to the cluster itself. These two are the only bright red supergiants in the whole region, and from the RICK measures the probable membership of both is verified. The extinction law from the B-V, V-I diagram indicates a higher value of R in comparison with the normal one, but lower than the amount derived earlier for the Tr 14/16 (Feinstein, Marraco, and Muzzio 1973), and which is also confirmed with new measures in this photometric system. The extinction law for the young cluster NGC 6611 (Feinstein, in preparation) appears to be the same, in spite of being probably younger.
Supernovae and the Ap Phenomenon
Authors: Rajamohan R. , Pati Ashok K.
Published: July 2016

We present evidence that relates the phenomenon of the chemically peculiar stars of the upper main sequence to supernovae explosions in young galactic clusters and associations. In the Upper Scorpius region of the Scorpio-Centaurus association we find that the radio shell discovered by Sancisi and Van Woerden (1970) from 21 cm observations and interpreted by them as an old supernova remnant has interacted with dense clouds. This remnant is seen clearly in the deep sky, narrow-band, H-alpha pictures of Sivan (1974). We find that the peculiar stars lie close to, or along the edges of, the interaction.
The Cluster NGC 330 in the SMC: Radial Velocities of Individual Stars
Authors: Feast M. W. , Black C.
Published: July 2016

Radial velocities based on 81 image tube spectra at 30 Å mm−1 are given for 25 stars (17 early type supergiants or upper main sequence stars and 8 late type stars) in the young SMC cluster NGC 330. An upper (one standard deviation) limit to the velocity dispersion is found to be 2 km s−1. The mass-to-light ratio is likely to be less than 0.1 in solar units. Results for other young Magellanic Cloud clusters derived on the assumption that they are tidally limited are consistent with this result. Spectroscopic binaries with semi-amplitudes, K, greater than about 10 km s−1 appear to be rare or absent amongst the stars studied.
Some Color-Magnitude Diagrams and Abundances in the Magellanic Clouds
Authors: Hardy Eduardo , Melnick Jorge , Reheault Claude
Published: July 2016

Some C-M diagrams and photometric abundances are presented of clusters and their adjoining fields in areas of the Clouds, in an attempt to derive properties which would allow a comparison with regions in the Galaxy.
A New Scenario for the Formation of Globular Clusters and Their Peculiarities
Authors: Di Fazio Alberto , Renzini Alvio
Published: July 2016

Globular clusters in galaxies still challenge astronomers to find a satisfactory explanation for a number of their properties, namely: (i) their very formation; (ii) the origin of their heavy elements; (iii) the trend of their metallicity with distance from the centre of the parent galaxy; (iv) the apparent correlation of their average metallicity with the mass of the galaxy with which they are associated; and, (v) the need of a “second parameter” (age? helium? [CNO/Fe]?) to explain the variety of morphologies of their colour-magnitude diagrams. Dwarf spheroidal galaxies pose similar problems, to an even more puzzling degree. It is clear that an understanding of the above topics is practically the same as the understanding of the very early evolution of galaxies. Any model for the formation and early evolution of galaxies should necessarily be tested whether or not the predicted properties of the associated globular cluster family are in agreement with the observational constraints. Conversely, any attempt to account for the characteristics of globular clusters would be blind without the support of detailed protogalactic models.
Variables in NGC 4590
Authors: Andrews Peter J.
Published: July 2016

A photoelectric sequence has been set up in the Oosterhoff Type II cluster NGC 4590 (M68) and UBV photographic photometry has been secured for all the uncrowded stars using the Radcliffe 1.9 m telescope. A series of 40 plates in each of UBV have enabled light and colour curves to be obtained for all the uncrowded RR Lyrae variables. For most of these, periods were found very similar to those found by Osterhoff. One star, however, showed variable amplitude from night to night and great difficulty was encountered in fitting a single period. Subsequent p.e. photometry with the 1.0 m SAAO reflector has indicated that this RR Lyrae variable is pulsating in at least two modes. The mean colour is that of the transition from fundamental to first overtone pulsators, as shown by the other ab and c type variables in the cluster. The two periods found are 0.526 and 0.392 days with amplitudes 0.39 and 0.47 mag indicating a ratio P1/Po ~ 0.745. Further observations are planned to give an accurate value for this ratio and to obtain simultaneous radial velocities to give mass and radius information.
Evidence for Spectral Differences Among 47 Tucanae Turnoff-Region Stars
Authors: Hesser James E.
Published: July 2016

Evidence that spectral differences observed among globular cluster giant stars with similar V and B-V values persist to fainter absolute magnitudes has been slowly accumulating in the past few years. In the case of 47 Tucanae, photometric evidence for CN strength variations extending to MV=1.5 mag was found from DDO photometry (Hesser, Hartwick and McClure 1976, 1977). Subsequently, CN strength variations at MV=+3.5, i.e., stars at the base of the vertical rise on the subgiant branch, were found by low dispersion spectroscopy (Hesser 1978). Kraft (1979) and collaborators have found evidence for star-to-star variations in NH and CH strengths among subgiant stars below the horizontal-branch level in the metal-poor cluster, M92; and Hesser and Harris (1979) have found CN and CH features to exhibit wide ranges among similar stars in M22, a metal-poor cluster with some apparent similarities to the otherwise uniquely anomalous cluster, Omega Centauri.
Variable Stars in the Globular Cluster NGC 6934
Authors: Sawyer Hogg Helen , Wehlau Amelia
Published: July 2016

In the first program of direct photography with the 72-inch telescope of the Dominion Astrophysical Observatory, 1931–1934, the compact and distant globular cluster NGC 6934 in Delphinus was searched for variables for the first time by HSH. The 51 discovered were published in 1938 (Sawyer-Hogg 1938). From 1935 to 1964 the observational program was continued with the 74-inch telescope of the David Dunlap Observatory and a total of 161 plates was accumulated. In addition, six Mount Wilson plates from 1911 to 1917 were available to us.
Surface Brightness Profiles of 68 Globular Clusters Derived From Electronic Camera Recordings
Authors: Kron Gerald E. , Gordon Katherine C. , Hewitt Anthony V.
Published: July 2016

Images of 68 globular clusters have been recorded in 125 exposures made with the electronic camera of the U.S. Naval Observatory on the 24-inch, 40-inch and 61-inch reflecting telescopes at the Flagstaff Station. The images were electronically malfocussed to allow the integration of light from the fainter cluster stars without saturation of the central portions of the brighter star images. Spacial information thus lost was partly regained by subsequent linear deconvolution of the cluster profiles by means of a star profile used as the point spread function.
The Axially Symmetric Wind Magnetosphere
Authors: Schmalz R. , Herold C. , Herold H. , Ruder H.
Published: July 2016

A central question in magnetospheric theory of pulsars is: how does a rapidly rotating magnetized neutron star manage to short-circuit its huge unipolar induction voltage? This problem is best studied in an idealized geometry like the parallel rotator. The theory must at least include basic plasma physics with relativistic particle inertia. Even the simplest model will require a global self-consistent solution of both Maxwell's equations and relativistic MHD-equations of motion. Assuming time independence, axial symmetry and charge separation, we reduce this problem to three coupled, quasilinear second order partial differential equations for three dimensionless scalar quantities Φ, f and Γ (see Schmalz et al., 1980):

Here x and z are cylindrical coordinates measured in units of the light cylinder radius. Φ is the stream function which is constant on stream lines, f = x · vφ/C is connected with the angular momentum (vφ = toroidal velocity), and Γ = 2∊γ = 2∊/(1 - v2/c2)1/2 where ∊ = mc2/(eBoa2ω) is a dimensionless parameter. Taking electrons (mass m, charge e) and typical neutron star parameters (radius a = 10 km, angular velocity ω = 30/s, polar field strength Bo = 108 T), we have ∊ ≈ −10−12.
A New Formulation of the Equations Governing the Pulsar Magnetosphere
Authors: Schrüfer E.
Published: July 2016

The relatively slow progress in both analytical and numerical work on the structure of the pulsar magnetosphere calls for a reformulation of the equations governing the magnetosphere. Since the set of equations for the pulsar magnetosphere are nonlinear anyway, one should not hesitate to use nonlinear representations for the field intensities and the current from the very beginning. Those nonlinear representations can be chosen to fulfill certain equations automatically and are therefore more adapted to the problem. The aligned rotator was formulated to some extent in this way by Schmalz et al. (1979). We formulate here the general problem and use for this the calculus of differential forms and some theorems concerning the normal form of forms (= representation of a form with a minimal number of scalar functions and their gradients). In the language of forms Maxwell's equations read

where F is the field intensity 2-form and j the current 3-form. The first equation states that F can be derived from a 1-form A: F = dA, the usual vector potential. A consequence of the second equation is dj = 0, the continuity equation for the current. Now since j is a simple closed 3-form, it can be represented by three scalar functions ⊘,χ,Ψ in the following way

which obviously satisfies dj = 0. This is the normal form of the 3-form with the properties mentioned above.
The Slot Gap Model of Pulsars
Authors: Arons Jonathan
Published: July 2016

A general picture of pulsar magnetospheres is outlined which suggests polar current flow should proceed within a magnetic flux tube with conducting boundaries. The dynamics of this current flow is considered, including the effect of formation of pair plasma on the potential. A slot gap surrounding the stream of pair plasma is described, and the electric fields and J·E work done in the gap are calculated. The inapplicability of curvature emission to the formation of γ-ray pulses is discussed. The dynamics of pair plasma flow is described, including electrostatic trapping of low energy positrons, polar cap bombardment and heating, and the emission of soft X-rays from the cap. The relation of this current flow and polar cap heating to the formation of fluctuations on the radio subpulse time scale is also described. The importance of the boundary layer between the pair plasma and the slot gap is illustrated by calculations of the boundary layer structure and microscopic instability, which show that this region may be the source of pulsar emission.

I will describe a number of quantitative results and qualitative aspects of work in progress on the “slot gap” model for the emission regions of a pulsar, proposed by Arons and Scharlemann (1979, hereafter AS) and by Arons (1979b, hereafter I). The results and ideas concern the dynamics and emission physics of relativistic plasma and current flow along the polar field lines of an isolated, rotating magnetized neutron star with the axis of its dipole moment oblique to the rotation axis - a pulsar. The quantitative modelling is confined to the physics within a polar flux tube and is therefore “local”. Full detail will be given in papers now being written. However, development of this type of model requires the use of boundary conditions which follow from a qualitative view of the whole magnetosphere. Because this view involves some qualitative ideas not widely discussed in the literature, I describe it briefly.
Observational Consequences of Polar Cap Theories
Authors: Cheng Andrew F.
Published: July 2016

Possible observational consequences are outlined for pulsar models with positive ion outflow at the polar caps together with e+-e− pair production discharge there. A characteristic thermal x-ray luminosity is maintained by discharge heating in regions of positive current outflow. A decrease in polar cap thermal x-ray emission may occur during radio nulls. Two mechanisms are identified which can yield temporal modulation of the outflowing ion and e+-e− plasmas, and which may lead to modulation of coherent radio emission on observed microstructure timescales. These are: (1) polar cap temperature oscillations which occur preferentially in pulsars of low surface magnetic field, and (2) the tendency of sparks to migrate toward the convex side of the magnetic field lines.
The Pulsar Magnetic Window
Authors: Shukre C. S. , Radhakrishnan V.
Published: July 2016

Triggering of the spark discharges in the Ruderman and Sutherland model by background gamma rays is shown to be effective only within a narrow range of neutron star magnetic fields centred on 2.5 × 1012 gauss. This calculated range of field strengths is in good agreement with ‘observed’ values, suggesting that (a) such triggering is operative, and (b) that neutron stars with much stronger fields do not function as pulsars.
Maser Pulse Emission Mechanisms
Authors: Melrose D. B.
Published: July 2016

The difficulties with “coherent” curvature emission by bunches of electrons formed through a streaming instability suggest that it cannot account for the observed radio emission for existing polar-cap models of pulsars. Amongst alternative maser mechanisms, that involving acceleration emission due to the electric fields in the waves generated by the bunching instability can account for the gross properties of the observed emission, provided that the relativistic electrons have γ ≤ 10 in the wave frame.
Pulsar Polarization
Authors: Backer D. C.
Published: July 2016

Over ten years ago Radhakrishnan and his coworkers in Australia detected a smooth variation of the electric vector through 90° during the brief pulses from the Vela pulsar. This observation led to the hypothesis that pulsar radiation is beamed along a magnetic pole. While subsequent observations gave ample support to this model, we find that less than half of the pulsars have average profiles which are consistent with the magnetic pole hypothesis. Statistical analyses of individual pulse polarization data now reveal that the average profiles obscure the basic nature of linear polarization in pulsars: two orthogonal modes are typically present, and individually these modes agree with the magnetic pole model. We explain the occurrence of orthogonal modes by a simple geometry for the polarized subpulse beam in relation to the magnetic axis. Theoretical models for subpulse polarization invoke both a combination of emission mechanism effects and propagation effects. We conclude with directions for further research.
Microstructure Crosscorrelation in Pulses Simultaneously Observed at Frequencies Separated by up to 1 GHz
Authors: Boriakoff Valentin , Ferguson Dale C.
Published: July 2016

Microstructure crosscorrelation of pulses observed simultaneously at various separations in frequency in the range of 196 to 1420 MHz was done for PSR 0950+08 and PSR 1133+16 at the Arecibo Observatory. Microstructure and subpulse components were identified in the crosscorrelations, and their behaviour vs. pulse longitude was studied. Drastic differences in the subpulse and micropulse behaviour are noted, related in particular to component separation in the double peak average pulse profile of PSR 1133+16. Here the subpulses follow the average pulse profile component separation but the microstructure does not. Interpretation and constraints in terms of some current theories are also presented.
X-ray and Gamma-ray Observations of Pulsars
Authors: Buccheri R.
Published: July 2016

Measurements of pulsars in the energy domain above ~ 1 keV have provided in the last few years new and interesting results. This paper presents a review of the observational features of PSR 0531+21 and PSR 0833–45 (the Crab and Vela pulsars). Searches for pulsed emission from old radio pulsars in the same energy domain are also reviewed and results assessed. The comparison of the observed features with each other and with the corresponding features observed at lower energies reveals similarities and differences capable to constrain theoretical models with special regard to the geometry of the emission mechanisms.
Glitches, Timing Noise, and Pulsar Thermometry
Authors: Greenstein George
Published: July 2016

It is shown that under certain assumptions the response of a neutron star to a perturbation in its temperature will be an increase in pulse repetition rate. Detailed models are presented which show behavior indistinguishable from the Vela pulsar period jumps. There appears to be no theoretical difficulty in arranging these events to recur every few years.
Interpretation of Binary Pulsar Observations
Authors: Blandford R. D. , DeCampli W. M.
Published: July 2016

The nature, dynamics and evolution of the three known radio pulsar binaries are discussed. The system containing 1913+16 appears to comprise two ~1.4 M⊙ components, and to undergo orbital decay as predicted by general relativity. It is proposed that 1913+16 has a neutron star companion and that 0655+64 and 0820+02 have white dwarf companions which should be observable optically.
CONCLUDING REVIEW
Authors: Radhakrishnan V.
Published: July 2016

I am afraid the best I can do on the next few pages is to convey the personal impressions that I have been left with after listening to sixty odd talks on almost every topic connected with pulsars. It is obviously impossible even to mention, leave alone comment on, each one of the papers that have been presented in these four packed days. Those few I touch upon will naturally reflect my personal biases for which I ask that you please bear with me.
10. Objective Prism Surveys for New White Dwarfs
Authors: Stephenson C. B.
Published: July 2016

The spectroscopic criteria for identifying strong-lined DA-type stars on low-dispersion objective prism plates are reviewed, as are the objective prism surveys made to date with discovery of white dwarfs a partial or major objective (Table I). It is claimed that there may be upwards of 100 undiscovered white dwarfs brighter than B magnitude 14.0. Some data for all the white dwarfs so far discovered by objective prism are collected in Table II; new identification charts are given for two of these.