bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Chromospheres of Pre-Main Sequence Flare Stars
Authors: Carter Bradley D. 
Published: July 2016

AbstractOptical spectra of pre-main sequence flare stars in Orion are presented and analysed by the use of stellar chromospheric models. The stars observed divide into three groups on the basis of their quiescent spectra. The majority of the sample are similar to the dMe stars, with prominent Ca II and Balmer line emission. A second group possesses very strong emission spectra, including He I lines. Stars in third group, however, show little or no emission spectrum. Amongst the emission line stars observed progressively brighter stars exhibit increased Ca II and Balmer line surface fluxes relative to the fainter stars. This trend is also exhibited as a rise in emission line surface fluxes with increasing effective temperature. To analyse this trend a set of non-LTE stellar models were calculated. Using this analysis the trend in line fluxes between stars of different brightness and temperature is interpreted as a spread in the level of chromospheric heating. Furthermore, this trend is interpreted as indicating a spread in the effectiveness of the stellar magnetic dynamos within these stars, perhaps arising from shallowing in their convective layers as they contract to the main sequence.
Continuum Radio Spectrum of the Flare Star AT Mic.
Authors: Large M. I. , Beasley A. J. , Stewart R. T. , Vaughan A. E. 
Published: July 2016

AbstractThe binary flare star AT Mic has been observed with the VLA (5 GHz and 1.5 GHz) and, nearly simultaneously, with the MOST (0.843 GHz). There appears to be a slowly varying component of the radio intensity, with a flux density greater at 0.843 GHz than at higher frequencies. It is suggested that above 1 GHz the emission is possibly produced by incoherent gryosynchrotron radiation, whereas below 1 GHz a coherent mechanism predominates.
Application of the Dipole Model to Selected Magnetic White Dwarfs
Authors: Achilleos N. , Wickramasinghe D. T. 
Published: July 2016

AbstractVarious authors have reported observations of the flux and circular polarization for the three stars PG 1658 + 441, PG 1533 − 057 and K 813 − 14. On the basis of the observational data, the stars were classified as magnetic white dwarfs. To place constraints on the magnetic field strengths and geometries of these stars, the relevant authors qualitatively compared the data with available theory and, in two cases, used a model of optically thin hydrogen threaded by a magnetic field.In this paper we use a more detailed model for magnetic white dwarfs to assess the results previously obtained for these three stars. We find that, in two cases, the observed spectra can be explained by the Zeeman splitting of hydrogen lines in a stellar magnetic field which takes the form of a dipole situated at the centre of the star. The circular polarization data for PG 1658 + 441, however, may indicate a field geometry for this star which is significally different from that of a centred dipole.
Upper limit to the number of galactic sources of ultra-high-energy gamma-rays
Authors: Bird D. J. , Clay R. W. , Edwards P. G. 
Published: July 2016

AbstractThe extreme isotropy of cosmic ray events allows one to put upper limits on any possible non-isotropic contribution to the flux. In particular, one can investigate any excess of events which may be confined to the galactic plane. Such extra events would be expected from galactic ultra-high-energy (UHE) gamma-ray sources. Under the assumption of an isotropic cosmic ray flux, recent Buckland Park data place a 95% confidence level limit on the total southern hemisphere (declination −15° to −55°) flux of UHE gamma-rays at between 0.6 and 6 equivalent Cygnus X-3 sources, depending on assumptions concerning the gamma-ray spectrum.
A Search for Transient Events at 843 MHz
Authors: Amy S. W. , Large M. I. , Vaughan A. E. 
Published: July 2016

AbstractThe Molonglo Observatory Synthesis Telescope is equipped with a transient event monitoring system which operates during normal synthesis observations. The device is designed to respond to impulsive signals which occur within the passband (843.0 ± 1.5 MHz) with time scales between 0.001 ms and 800 ms. The multiple beam facility of the telescope provides some discrimination against local interference. An upper limit of 1.7 × 10−2 events s−1 sr−1 has been placed on celestial events with durations between 1 ms and 25 ms and energy density ≥ 10−28 J m−2 Hz−1. The monitoring system has been recently reconfigured to improve the recognition and rejection of impulsive signals of non-celestial origin.
The Magellanic Stream: New Observations
Authors: Wayte S. R. 
Published: July 2016

AbstractNew HI observations of the Magellanic Stream have been made using the Parkes 64 m telescope. These observations highlight in detail its complicated structure and uncover new features of the Stream. The extreme velocity clouds (EVCs) are morphologically linked to the Stream indicating that these HI clouds are very likely truly part of the Stream. Also it is suggested that many of the high velocity clouds seen around the Stream are indeed part of the Magellanic Stream itself, and that the stream consists of many different velocity components in bulk motion.
Helium in Three H II Galaxies and the Helium Abundance
Authors: Pagel B. E. J. , Simonson E. A. 
Published: July 2016

Extended abstractThe mass-fraction Y of helium in the interstellar medium is between 0.22 and 0.30 wherever it has been measured and it is believed to be the sum of two components: YP from Big Bang nucleosynthesis (BBNS) at about 100 s after the Big Bang (ABB) and a temperature near 0.1 MeV, and ΔY due to processing in stars. Precise measurements of Yp, along with balances of trace elements D, 3He, 7Li also resulting from BBNS, provide important tests of BBNS theory and of parameters of cosmology and particle physics, notably the contribution ΩBO of baryons to the mean density of matter in the universe (in units of the closure density), the number Nv of light neutrino flavours (or families of quarks and leptons) and the half-life т½ of the neutron (Shaver et al. 1983; Yang et al. 1984; Boesgaard and Steigman 1985). Figure 1 shows the predicted abundances from Standard BBNS theory (SBBN) as a function of η = μB/nλ the ratio of baryons to photons (unchanged since e± annihilation a few seconds ABB), which is proportional (through the known temperature of the microwave background) to ΩBOh20 where h0 is the Hubble constant in units of 100 km s−1 Mpc−1. SBBN theory (which assumes a homogeneous Friedmann universe and small lepton numbers), when combined with reasonable ideas on Galactic chemical evolution that predict a primordial (D + 3He)/H ratio below 10−4, imply that η ≥ 3 × 10−10 (shown by the tall vertical line in Fig. 1), which in turn implies YP≥0.210 if Nv = 3 and т½≥10.4 minutes. But this limit can be somewhat relaxed if т½ is smaller (current measurements permit values down to 9.0 minutes, e.g. Last et al. 1988) and/or if the quark-hadron phase transition around 200 MeV is first-order and leads to significant density fluctuations (Kurki-Sunonio et al. 1989; Reeves 1989).
Radio Polarization Observations of Three Southern Galaxies
Authors: Harnett J. I. , Haynes R. F. , Wielebinski R. , Klein U. 
Published: July 2016

AbstractObservations of polarized emission and consequently the investigation of magnetic fields in northern galaxies, have been conducted successfully for some time with, for example, the 100-m Effelsberg telescope of the Max-Planck-Institut-für Radioastronomie and the VLA. However, the opportunity to make corresponding studies in the southern hemisphere has only recently become possible. Therefore, we have begun a long-range project aimed at studying the morphology and dynamics of southern galaxies using the facilities of the Parkes and Molonglo radio telescopes, the Siding Spring optical facilities and the Australia Telescope. Here we present preliminary results from Parkes observations of the three well known galaxies: NGC 253, NGC 4945 and M 83.
Search for Ultra High Energy Gamma Rays from Centaurus A
Authors: Bird D. J. , Clay R. W. 
Published: July 2016

AbstractAn analysis has been made of events recorded in one year from the direction of the active galaxy Centaurus A using the Buckland Park UHE gamma-ray telescope. No statistically significant excess was observed over this period. Data collected between 1984 and 1989 show evidence for an excess of events from this direction at shower sizes in the range of 2 × 105 to 5 × 105 particles.
Solar Cycle Graphics 1700–1988 AD
Authors: Murphy J. O. 
Published: July 2016

AbstractA graphical format has been adopted to depict some characteristic variations associated with the solar activity cycle up to 1988, for both the Zurich annual and monthly mean values over the respective periods from 1700 and 1750. Both low pass and band pass filtering techniques have been employed to smooth the data, the autocorrelation coefficients determined for a high number of lags to illustrate the secular modulation of the maximum values in each cycle and the spectral amplitudes computed to establish periodicities in the chronologies.
The Role of Supercomputers in Astronomical Modelling
Authors: Faulkner D. J. 
Published: July 2016

Abstract
Advances in digital computer technology since the middle decades of the twentieth century have transformed many subject areas in astrophysics. Topics which had previously been dealt with by analytic approximations (usually to a very limited number of special cases) suddenly became amenable to detailed numerical modelling for all cases. Frequently, insights derived from this modelling ran ahead of other techniques in predicting physical phenomena before they were either observed or discerned in purely analytic treatments.
It has sometimes been said that the second half of this century has seen the advent of a totally new modus operandi in scientific research, which ranks alongside the two traditional approaches–experimentation and theory. The most powerful computers now available have greatly accelerated these developments. They employ simultaneous computational techniques (either vector processing or parallel processing, or both), and their throughput is so large that, for most problems, the only way in which the human mind can fully appreciate the scientific content of the numerical results being calculated is by transforming those results into pictorial representations.
This paper draws on my experience as Academic Director of the ANU Supercomputer Facility during the first eighteen months of its operation, to describe the place which I believe super-computers will occupy in the development of astrophysics during the 1990s and into the next century.
Polarization in the Magellanic Clouds
Authors: Haynes R. F. , Wayte S. , Harnett J. I. , Klein U. , Wielebinski R. , Buczilowski U. R. , Bajaja E. , Malin D. , Murray J. D. , Hunt A. J. , Wark R. , Sciacca L. 
Published: July 2016

AbstractWe present preliminary results from a number of deep radio polarization surveys being made of the Magellanic Clouds at 2.3 GHz, 4.75 GHz and 8.55 GHz. Extended and linearly polarized radio emission has been found at 2.3 and 4.75 GHz from both the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). However, as the analysis of these data is not yet complete we present only some of the 4.75 GHz results at this time.
A Linear Acceleration Emission Mechanism
Authors: Rowe E. T. 
Published: July 2016

AbstractA theory of linear acceleration emission, with possible application to pulsars, is developed. The equation of motion for a relativistic charged particle accelerated in the field of a longitudinal wave is solved to first order in the electric potential and used to derive the first order current. The power emitted and the absorption coefficient are calculated and the conditions under which masing can occur are discussed.
Comets: pre- and post-Halley
Authors: Swamy K. S. Krishna 
Published: July 2016

AbstractThe recent intensive study of Comet Halley based onin situmeasurements, observations carried out with rockets and satellites and supplemented with co-ordinated Earth based observations has not only confirmed pre-Halley results, but also has given new insight into the nature of the nucleus, dust, gas and the interaction of cometary plasma with the solar wind. These observations also have raised many new questions and problems. Several of these aspects will be discussed. For a better understanding of these problems, the planned future missions to comets will also be discussed.
Space Astronomy in India
Authors: Agrawal P. C. 
Published: July 2016

AbstractAstronomical observations from space-borne instruments are carried out in India in the areas of infrared, X-ray and gamma-ray astronomy. This paper briefly describes the facilities available in India for conducting experiments in space astronomy using balloons, rockets and satellites. It briefly reviews the important results obtained by Indian astronomers from observations made in India with the balloon, rocket and satellite experiments. The present status of research in different disciplines of space astronomy is discussed.
The Radial Velocity and Metal Abundance of the Sextans Dwarf Spheroidal Galaxy
Authors: Da Costa G. S. , Hatzidimitriou D. , Cannon R. D. , Irwin M. J. , McMahon R. 
Published: July 2016

Extended abstractThe multi-object spectroscopic facility FOCAP at the Anglo-Australian Telescope has been used to obtain spectra centred at the Ca II IR triplet of 14 stars in the field of the Sextans dwarf spheroidal (dSph) galaxy. This satellite of our own Galaxy was recently discovered by Irwin et al. (1990) from APM measures of UK Schmidt Telescope photographic plates.
The Core Jet and Relic Radiation in the Radio Source 1343–601
Authors: McAdam W. B. 
Published: July 2016

AbstractA high-resolution image of the strong extragalactic source 1343–601 has been made with the Molonglo Observatory Synthesis Telescope (MOST) at 843 MHz. The source is identified with a 10 mag galaxy (Mv = −24) which is heavily obscured through our Galaxy. A recent redshift (z = 0.01215) gives a distance of 73 Mpc and a corresponding radio luminosity of log P843 = 24.9.The MOST image shows a core linked by a double jet to asymmetric lobes which are surrounded by a confined balloon (400 × 200 kpc2) of low-brightness plasma. This has a complex network of ridges or flows which lead out into the wider cluster medium. If similar balloons exist around other double sources, they could provide the depolarising medium required by the Laing-Garrington effect.Separate observations show the core is compact with strong X-ray emission.
The Berkeley-AAO Distant Supernova Search
Authors: Couch W. J. , Perlmutter S. , Newburg H. J. M. , Pennypacker C. , Goldhaber G. , Muller R. , Boyle B. J. 
Published: July 2016

AbstractA search for Type Ia supernovae at cosmological distances is being undertaken in an attempt to exploit their standard candle property to constrain the mass density of the universe. We describe the rationale for such a program, the observational approach and strategy taken, and the progress made to date. The science that is being generated by the project in additional to supernova detection is also discussed briefly.
The Possible Progenitors of Planetary Nebulae among OH/IR Stars
Authors: Hekkert P. te Lintel , Zijlstra A. A. 
Published: July 2016

AbstractBased on a new sample of (IRAS based) OH/IR stars, and a catalogue of planetary nebulae compiled by Acker (1983), we study the relation between these two groups of objects, in terms of the kinematics and the Galactic distribution. In contrast with earlier analyses of samples of OH/IR stars, we find a close correlation between the kinematics of the planetary nebulae and the IRAS based sample of OH/IR stars. In particular, we find that the distribution of the planetary nebulae (PN) shows a good correlation with the OH/IR stars which have a low outflow velocity (Vexp < 12.5 km s−1). Whether the high outflow velocity OH/IR stars also have a counterpart among PN is not clear.
Quantum Theory of Stokes Parameters for Thomson Scattering in a Magnetised Plasma
Authors: Chou Chih-Kang , Chen Hui-Hwa 
Published: July 2016

Extended abstractThomson scattering in pulsar magnetospheres has previously been studied by several authors. The most distinguishing feature is the fact that the super-strong magnetic field (B ~ 1012 G) greatly affects the Thomson scattering process, resulting in resonances in the scattering cross-section (Canuto et al. 1971; Herold 1979; Chou 1986; Daugherty and Harding 1986). The important consequences of these cyclotron resonances are the increase in the photon mean free path in the scattering regions, and strongly affecting the angular distribution, and polarisation properties of the scattered photons (Chou 1986; Chou et al. 1989).
Studies on Molecules of Astrophysical Interest
Authors: Singh Markandey , Chaturvedi Jai Prakash 
Published: July 2016

Extended abstractOur recent papers have been devoted to basic studies of diatomic and polyatomic molecules (Singh and Chaturvedi 1989 a,b,c,d; 1990a,b,c). A critical analysis of the 456 available references in literature has been made to select 135 polyatomic molecules, molecular ions and radicals containing from three to thirteen atoms of astrophysical significance. The results have been arranged in a text-cum-tabular form (Singh and Chaturvedi 1989 b,d). The compilation contains various information for each molecule, such as the spectral region, transition levels, and astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar medium. Galaxy, etc.).
Energy Changes of Cosmic Rays
Authors: Gleeson L. J. , Webb G. M. 
Published: July 2016

Recently (Gleeson (1972), Quenby (1973), Gleeson and Webb (1974, 1978)) it has been shown that the mean rate of change of momentum of cosmic rays reckoned for a volume fixed in the solar system iswhere G = (1/Up)(∂Up/∂r)si the cosmic-ray density gradient with Up, the differential number density with respect to momentum p at position r. (cf also the integral form of (1) by Jokipii and Parker 1967).
Planetary Nebulae: Origin and Evolution
Authors: Mallik D. C. V. 
Published: July 2016

AbstractThere has been a great deal of progress in our understanding of planetary nebulae and their central stars during the past decade and a half. Most of this has come about through progress in observational techniques covering almost the entire electromagnetic spectrum. Theories of planetary nebula evolution have been put to better and better tests as more and more discriminating data have become available.This review describes some of the progress made in observations and their interpretation, particularly in the context of the evolution of the nebulae and the central stars. It includes a discussion on the improved determinations of magnitudes and temperatures of the central stars, and of progress in the measurement of distances, and a reassessment of the observed mass-distribution of the central stars. The last topic has been at the centre of a lively debate for almost a decade now and has been responsible for a large number of studies of central star evolution, some this review briefly touchs upon.
Objective Determination of the Large-scale Distribution of Galaxies
Authors: Dodd R. J. , MacGillivray H. T. 
Published: July 2016

AbstractObservations of the large-scale organisation of matter in the Universe are of great importance in present day astronomy. In the visible part of the spectrum such observations are mainly of the distribution of galaxies on the plane of the sky.Direct and objective prism plates obtained using large Schmidt telescopes form the bulk of the material used. The direct plates provide the observations from which the surface distribution of galaxies may be determined and the prism plates and FLAIR, via redshifts, yield extragalactic distances and hence the three dimensional distribution of galaxies.For large-scale surveys the measuring machines used need to be multi-purpose and fast such as COSMOS and SUPER-COSMOS at the Royal Observatory Edinburgh. More specific programs can make use of smaller, slower machines such as iris photometers and microdensitometers.The method of analysing the data produced rely on seeking density enhancements in the general field of galaxies for cluster detection or using correlation techniques for analysis of the galaxy distribution.A description is given of a southern sky catalogue containing 109 objects recently completed and an outline of some of the extragalactic projects underway using this large body of data.
Prospects for an Antarctic Observatory
Authors: Gillingham P. R. 
Published: July 2016

AbstractFollowing a 1989 USA conference on Astrophysics from Antarctica, a number of proposals have been advanced to exploit the great astronomical potential of this region. The most interesting is for an international station at a new site chosen for optimum astronomical performance. Near the highest point of the ice plateau (where the pressure altitude is about 5000 m), the extremely dry cold atmosphere will allow effective observation through many wavelength ranges currently inaccessible from the ground. There is also reason to believe that better seeing than is otherwise obtainable from the Earth’s surface may be achievable. Astronomers interested in future Antarctic observing should co-operate in presenting cases to their governments for support facilities there.
Newly Installed Radio and Optical Telescopes in China
Authors: Wang Jing-Sheng 
Published: July 2016

AbstractNew radio and optical telescopes installed in recent years in China are summarised. These include the 2.16-m optical telescope, the solar magnetic field telescope, the Miyun synthesis radio telescope, the 1.26-m infrared telescope (Beijing Astronomical Observatory), the 25-m radio telescope as the first station of China’s VLBI network, the 1.56-m astrometric telescope (Shanghai Observatory), and the 13.7-m millimetre wave radio telescope.
A CCD Hα Survey of Nearby Southern Spiral Galaxies
Authors: Ryder Stuart D. , Dopita Michael A. 
Published: July 2016

AbstractSome initial results of a flux-calibrated CCD Hα imaging program of bright, nearby southern spiral galaxies are presented. Very few southern hemisphere spiral galaxies have ever been completely imaged in Hα, let alone with a CCD. This survey (which mainly uses the MSSSO 1.0-m reflector with an f/3.5 focal reducer) will, when combined with spectrophotometry of the H II regions thus revealed, allow us to trace the chemical evolution of each galaxy. Furthermore, since the absolute Hα flux is a reliable measure of the high-mass star formation rate in a galaxy, such observational data will permit us to test the predictions of the various star formation theories.
On the Nature of the Redshifts of the Twin Quasars with Discrepant Redshifts
Authors: Sapre A. K. , Mishra V. D. 
Published: July 2016

AbstractWe examine the nature of the redshifts of twin quasars with discrepant redshifts (θ < 100 arcsec, Δz ≥ 0.5) by considering their Hubble diagram. If such twins are physically associated one expects a large scatter in their Hubble diagram. However, we find a statistically significant linear correlation between log (cz) and Vc magnitudes of such quasars, consistent with the hypothesis that their redshifts are cosmological in nature.
Mass Loss in Dwarf Galaxies
Authors: Meurer Gerhardt R. 
Published: July 2016

AbstractFour examples of dwarf galaxies apparently undergoing mass loss are discussed. All have an Hα morphology suggesting a minor axis flow. This is supported by velocity field measurements in three cases. All also have at least one compact central object, probably a young star cluster, apparently powering the flow. Some implications of these results are briefly discussed.