bluuebunny/crossref_metadata_2025_split huggingface dataset:
Report of Special Commission 3 of IAG
Authors: Groten Erwin 
Published: July 2016

AbstractSince the last presentation of SC-3 on numerical values of fundamental geodetic parameters at the IAU General Assembly at Kyoto in 1997 there were some conceptual as well as fundamental numerical changes. The four basic parameters of geodetic (ellipsoidal) reference systems (GRS) can no longer be considered as constant with time:J2,a, ω, and GM have to be replaced by clearly (±10−8or better) specified mean values or have to be associated with a specific epoch or, in case of GM, with specific reference frames (a= semi-major axis of Earth ellipsoid,J2= second degree zonal harmonic of geopotential,ω= spin of Earth rotation). In case of (a, J2....) associated tidal reductions must be specifically defined in view of particular applications and significant differences between different tidal reduction types. Or we may replace “a” by a quantity which is independent of tides like the geopotential at the geoid, W0, where, however, also temporal changes are now discussed. The official geodetic reference systems such as GRS 80 and WGS 84 (revised in 97-form) are also no longer truly representing reality; a new system GRS 2000 is desired. We are, meanwhile, able to define and determine tidal and non-tidal (secular, periodic, aperiodic) variatipns of some fundamental geodetic parameters. Others are under investigation. New precession and/or nutation formulas to be adopted by IAU in 2000 or later would imply, again, changes in geodetic parameters such asH= hydrostatic flattening. Those and related other consequences are considered.
Radio Intra-Day Variability: Answers and Questions
Authors: Jauncey David L. , Kedziora-Chudczer Lucyna , Lovell James E.J. , MacQuart Jean-Pierre , Nicolson George D. , Perley Rick A. , Reynolds John E. , Tzioumis Anastasios K. , Wieringa Mark H. , Bignall Hayley E. 
Published: July 2016

AbstractIntra-day variability (IDV) of active galactic nuclei (AGN) has been detected from gamma-ray energies to radio wavelengths. At high energies, such variability appears to be intrinsic to the sources themselves. However, at radio wavelengths, brightness temperatures as high as 1018 to 1021 K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evidence showing that, at radio wavelengths where the highest brightness temperatures are encountered, interstellar scintillation (ISS) is the principal mechanism causing IDV. While ISS reduces the implied brightness temperatures, they still remain uncomfortably high.
Monitoring the Microarcsecond Quasar J1819+3845
Authors: Dennett-Thorpe J. , de Bruyn A.G. 
Published: July 2016

AbstractWe present the results of a year-long monitoring campaign on J1819+3845. We interpret the results of this WSRT campaign to infer critical source parameters such as source lifetime and structure on tens of microarcseconds. The long lifetime of the source at such high brightness temperatures requires continuous energy injection or exotic emission processes. We have previously interpreted the extreme scintillation of Jl819+3845 as due to a relatively nearby (~ 20 pc) scattering screen. We show this screen has a velocity w.r.t. the LSR of ~ 25 km s−1, as measured by the changing scintillation properties throughout the year: the ‘velocity parallax’.
The Radio Luminosity of Pulsars and the Distribution of Interstellar Electron Density
Authors: Andreasyan R.R. , Arshakian T.G. 
Published: July 2016

AbstractThe radio luminosities of pulsars are given as functions of their period and the time variation of the period. The parameters of that dependence are calculated and independent distances are determined for pulsars. The average electron densities toward the pulsars are determined from the known dispersion measures. The results obtained are used to study the large-scale electron density distribution in the Galaxy. The distribution maximum lies in the vicinity of the Sagittarius spiral arm. The electron density falls off exponentially in the regions between spiral arms.
The Control System of the Active Main Reflector for FAST
Authors: Qiu Yuhai , Zhu Lichun 
Published: July 2016

AbstractThe main reflector of FAST consists of about 1800 elementary units. Each unit has three adjustable supports to fix its position, and its position is adjusted by means of mechanical actuators. According to the radio source position at any given time, all the actuators are continuously adjusted to form a proper paraboloid in real time during the course of the observation. The basic requirements of such a control system are discussed. A fieldbus control system based on LonWorks technology is suggested to control all 1800 actuators. The main advantages of this distributed control system are its reliability, flexibility, efficiency and economics.
GAIA Survey of Galactic Eclipsing Binaries
Authors: Zwitter Tomaž 
Published: July 2016

AbstractThe general importance and capabilities of observations of eclipsing binaries by the forthcoming ESA mission GAIA are discussed. Availability of spectroscopic observations and a large number of photometric bands on board will make it possible to reliably determine physical parameters for ∼ 105 binary stars. It is stressed that current methods of object by object analysis will have to be modified and included in an automatic analysis pipeline.
The Strange Story of BI Lyncis: an Extremely Helium-Rich Subdwarf with a Cool Companion
Authors: Jeffery C. Simon , Cuadrado R. Aznar 
Published: July 2016

AbstractThe star BI Lyn = PG 0900+400 was previously classified as an evolved binary system containing either a hot subdwarf or white dwarf and a thick accretion disk. We have analyzed new intermediate dispersion spectra and demonstrated that both views are wrong. BI Lyn is a highly-evolved system containing a luminous low-mass helium star and a rapidly rotating G-type giant. It may be closely related to the evolved sdO+G binary HD 128220.
The Stellar Wind Geometry of η Carinae
Authors: Smith Nathan , Davidson Kris , Gull Theodore R. , Ishibashi Kazunori 
Published: July 2016

AbstractThe Homunculus reflection nebula around η Carinae provides a rare opportunity to observe a star from more than one direction. For η Car, the nebula’s geometry is known well enough to infer how wind profiles vary with latitude. STIS spectra of the Homunculus show directly that η Car has an aspherical stellar wind. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the polar axis. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, and offer clues to η Car’s circumstellar structure. The bipolar wind geometry may imply that intrinsically asymmetric ejection helped form the Homunculus. It is also critical for understanding this star’s variability and evolution.
Binaries with Invisible Massive Components
Authors: Chochol Drahomír , Mayer Pavel 
Published: July 2016

AbstractV505 Mon is an early type eclipsing binary (usually classified as B5 Ib), in which only spectral lines of the primary component are visible. The radial velocity curve provides f(m) = 4.6 M⊙, suggesting that the secondary, invisible component is more massive. We have found evidence that this star is hidden from view by the disk detected during the primary eclipse. The structure of the disk can be characterized by a central ionization zone surrounded by the neutral outer parts. The profiles of the CII 1335/6 doublet lines were used to derive the rotational velocity of the disk as well as the velocity of the stream from the primary component to the disk. The masses of the components, deduced from the fractional size of the disk, are M1 = 1 M⊙ and M2 = 6.1 M⊙. Due to the low mass of the primary component its supergiant nature can be ruled out. Additional matter of a cloudy nature is present in the system and both components are embedded in an extended atmosphere. V505 Mon seems to be a prototype of the whole group of similar early-type binaries, in which the more massive component is hidden by a circumstellar medium, most likely a disk. Probable members are V742 Cas, V1362 Cyg, V2174 Cyg, V447 Sct and FY Vel with orbital periods between 33 and 225 days. Emission in Ha is always present, but there are no emissions in IUE spectra, so these binaries are distinct from the W Ser type. The evolutionary state of the members of this group is not yet understood.
V471 Tauri and SuWt 2: The Exotic Descendants of Triple Systems?
Authors: Bond Howard E. , O’Brien M. Sean , Sion Edward M. , Mullan Dermott J. , Exter Katrina , Pollacco Don L. , Webbink Ronald F. 
Published: July 2016

AbstractV471 Tauri is a short-period eclipsing binary, and a member of the Hyades. It is composed of a hot DA white dwarf (WD) and a cool main-sequence dK2 companion. HST radial velocities of the WD, in combination with the ground-based spectroscopic orbit of the K star, yield dynamical masses of MWD = 0.84 and MdK = 0.93 M⊙. During the UV observations we serendipitously detected coronal mass ejections from the K star, passing in front of the WD and appearing as sudden, transient metallic absorption. Eclipse timings show that the active dK star is 18% larger than a main-sequence star of the same mass, an apparent consequence of its extensive starspot coverage. The high Teff and high mass of the WD are paradoxical: the WD is the most massive in the Hyades, but also the youngest. A plausible scenario is that the progenitor system was a triple, with a close inner pair that merged after several × 108 yr to produce a single blue straggler. When this star evolved to the AGB phase, it underwent a common-envelope interaction with a distant dK companion, which spiraled down to its present separation and ejected the envelope. The common-envelope efficiency parameter, αCE, was of order 0.3–1.0, in good agreement with recent hydrodynamical simulations.SuWt 2 is a southern-hemisphere planetary nebula (PN) with an unusual ring-shaped morphology. The central star is an eclipsing binary with a period of 4.9 days. Surprisingly, the binary is composed of two main-sequence A-type stars with similar masses of ~ 2.5 M⊙. We discuss scenarios involving a third companion which ejected and ionizes the PN.WeBo 1 is a northern PN with a ring morphology remarkably similar to that of SuWt 2. Although we hoped that its central star would shed light on the nature of SuWt 2, it has proven instead to be a late-type barium star!
The Slow Merger of Massive Stars: Merger Types and Post-Merger Evolution
Authors: Ivanova N. , Podsiadlowski Ph. 
Published: July 2016

AbstractWe study the slow merger of two massive stars inside a common envelope. The initial close binary system consists of a massive red supergiant and a main-sequence companion of a few solar masses. The merger product is a massive supergiant with an interior structure (core mass and composition profile) which is significantly different from that of a single supergiant that has evolved in isolation. Using a parameterized approach for the stream–core interaction, we modelled the merger phase and have identified three qualitatively different merger types: quiet, moderate and explosive mergers, where the differences are caused by the different response of the He burning shell. In the last two scenarios, the post-merger He abundance in the envelope is found to be substantially increased, but significant s-processing is mainly expected in the case of an explosive merger scenario. The subsequent evolution of the merger product up to the supernova stage is also discussed.
CW Leonis, IRC+10216
Authors: Knapp G.R. 
Published: July 2016

AbstractCW Leo is the nearest and brightest example of a highly evolved carbon Mira variable red giant, and is surrounded by an extensive dusty, molecular circumstellar shell produced by mass loss. Since the shell heavily obscures the star, most of the information about CW Leo comes from observations of its shell, whose radial properties encode a history of the star as well as of the interaction between the outflowing gas and the interstellar radiation field. The shell of CW Leo contains a rich variety of molecules, from salts to cyanide, whose isotopic composition shows the effect of nuclear processing in the stellar interior and give information about the formation and composition of the circumstellar dust. This nearby star allows us a detailed look at one of the most eventful and interesting phases in a star’s evolution.
The Formation of Subdwarf B Stars
Authors: Han Zhanwen , Podsiadlowski Philipp , Maxted Pierre F.L. , Marsh Tom R. , Ivanova Natasha 
Published: July 2016

AbstractWe performed full binary evolution calculations and carried out binary population synthesis studies in order to investigate the formation of subdwarf B (sdB) stars via the channels of stable Roche lobe overflow (RLOF), common envelope ejection and helium white dwarf mergers. Our model is successful in the explanation of observational properties of sdB stars, e.g. we explained the orbital period – minimum companion mass (log P – Mcomp) diagram, the effective temperature – surface gravity (Teff – log g) diagram, the orbital period distribution, the log(gθ4) (θ = 5040/Teff) distribution, the mass function distribution, the binary fraction of sdB stars, the fraction of sdB binaries with WD companions, the birth rates, the space number densities, etc. We conclude that (a) the first RLOF needs to be more stabilized than commonly assumed, (b) the first stable RLOF is not conservative, (c) common envelope ejection is very efficient.
The Unusual Evolutionary State of Nova Scorpii 1994
Authors: Tout Christopher A. , Regős Enikő , Wickramasinghe Dayal 
Published: July 2016

AbstractWe have investigated possible models for the evolutionary status of the black-hole soft X-ray transient Nova Scorpii. We propose that it is a main-sequence star in which convective overshooting, or some equivalent mixing, occurs at the core-envelope boundary. Recent detections of chemical pollution on the surface of the secondary suggest that the black hole formed in a supernova whose ejecta left and fell back at a sufficiently low velocity to accrete on to the secondary. We examine the effects of increased opacity, increased metallicity and reduced hydrogen abundance on the evolution of the secondary in the hope that these might lead to an alternative scenario. All these only exacerbate the problem.
Exotic Stars as Challenges to Evolution: an Evaluation
Authors: Jeffery C. Simon 
Published: July 2016

AbstractA star is exotic because, in some way, it extends our knowledge of how stars behave. As we make new observations we discover new phenomena that we do not understand. As we approach an understanding, those phenomena seem less exotic. That is nature. IAU Colloquium 187 set out to discover how far our knowledge of stars now reaches. This is a personal commentary on the proceedings.
Thermal-timescale mass transfer and magnetic CVs
Authors: Schenker Klaus , Wynn Graham A. , Speith Roland 
Published: July 2016

AbstractWe investigate the spin evolution of the unusual magnetic CV AE Aqr. As a prototype for a potentially large population of CVs subject to a thermally unstable phase of mass transfer, understanding its future is crucial. We present a new definition of the magnetospheric radius in terms of the white dwarf’s spin period, and use this along with numerical simulations to follow the spin evolution of AE Aqr. We also present preliminary SPH results suggesting the existence of a stable propeller state. These results highlight the complexity of MCVs and may provide an improved understanding of the evolution of all types of CVs.
Polarized Emission and the Discovery of New Magnetic CVs
Authors: Schmidt Gary D. 
Published: July 2016

AbstractRecent quasar surveys have identified several new magnetic cataclysmic variables accreting at remarkably low rates, ~10−13M⊙ yr−1. The new discoveries raise questions regarding selection effects that may influence the current sample and the traditional evolutionary conclusions that have been drawn. This paper reviews the techniques that have been used to identify polars, including a summary of the optical polarization as a function of accretion rate and magnetic field strength. The new, low-ṁ systems accrete without a shock and cooling is dominated by optical cyclotron emission in very well-defined harmonics. These binaries, which have been found to accrete at far below the rate corresponding to angular momentum loss by gravitational radiation, also appear to contain unusually cool white dwarfs, suggesting that they are either at an advanced age or in unusual evolutionary states.
Hα Doppler Tomography of AM Her: Evidence for Bipolar Accretion
Authors: Papadimitriou Christos , Harlaftis Emilios 
Published: July 2016

AbstractWe present Doppler maps of Halpha emission lines of AM Her from four differents epochs. The tomography shows a strong velocity “spot” emission at (−100,−100) km s−1 and a weaker “spot” emission at (−100,−400) km s−1 which is suggestive of bi-polar accretion onto the white dwarf with stronger emission from the main pole at phase φ=0.0.
AE Aquarii continuum emissions from Radio low frequencies to Infra-Red
Authors: Abada-Simon Meil 
Published: July 2016

AbstractAE Aquarii radio flares are attributed to synchrotron optically thick emission from expanding plasma clouds, and the turnover frequency and the optically thin part of the synchrotron spectrum seem to be between the sub-millimetre and infra-red wavelengths. We present the various processes which may affect the synchrotron radiation at both very low (radio) frequencies and at higher energies, and what they infer on the properties of the radio flare source and its surroundings. We also envisage that both thermal and non-thermal emission processes may explain the puzzling spectrum of AE Aqr.
The Pole Position in October 1980 as Determined from Lageos Laser Data
Authors: Reigber Ch. , Mueller H. , Wende W. 
Published: July 2016

On the basis of 223 passes of Lageos Laser Tracking data taken in October 1980 during the MERIT short arc campaign from 13 tracking sites, the pole position was determined in the orbit correction program MGM along with the initial state vector. This analysis was done for a varying time resolution (5-1 days).Basis of our computation is the GRIM3P gravity model and a station position set derived by UTEX and partly by the DGF1. The formal sigma of the 5 and 2.5 mean values for the pole coordinates is generally about 0.005 arc-seconds.
Atmospheric Angular Momentum and the Length of Day
Authors: Langley R. B. , King R. W. , Shapiro I. I. , Rosen R. D. , Salstein D. A. 
Published: July 2016

AbstractWe have used lunar laser ranging (LLR) observations from the McDonald Observatory in conjunction with pole positions from the Bureau International de l’Heure (BIH) to determine the length of day (l.o.d.) at five-day intervals over the period 1971 through 1979. We compared the changes in these l.o.d. values to those inferred from determinations of the angular momentum of the global atmosphere, for the years 1976-1979, computed from twice-daily analyses of the zonal wind. These latter analyses were carried out by the National Meteorological Center, Camp Springs, MD. In both the observed (LLR) and the inferred (meteorological) values of changes in l.o.d., we have identified the near 50-day oscillation recently noted by Feissel and Gambis at the BIH. For the period of overlapping dates, the two oscillations agree closely in both amplitude and phase. The typical amplitude is about 0.2 milliseconds or approximately half the amplitude of the annual and semiannual variations in l.o.d.
Dissipation in the Moon: A Review of the Experimental Evidence and Physical Implications
Authors: King R. W. 
Published: July 2016

AbstractRecent analyses of lunar ranging observations have revealed strong evidence of dissipation in the moon’s rotation (Ferrari et al. 1980; Cappallo et al. 1981). If interpreted as solid body friction, these results imply a tidal Q of about 25 (±5) at a frequency of one cycle per month. There is little evidence from other studies of the interior structure of the moon to support such a low solid-body Q. Yoder (1981) finds that turbulent fluid friction between the mantle and a core of radius ~300 km is a plausible mechanism to explain the observed dissipation. An iron or iron-sulfide core of this size is consistent with moment-of-inertia (Blackshear and Gapcynski 1977, Ferrari et al. 1980) and seismic (Goins et al. 1979) data, and is not excluded by conductivity data (Goldstein 1979). Stevenson and Yoder (1980) have proposed a model for formation of a solid iron inner core surrounded by a fluid iron sulfide layer of thickness 65 − 180 km.
Relations Between Celestial and Selenocentric Reference Frames
Authors: Kovalevsky J. 
Published: July 2016

AbstractThe very great accuracy with which the motions of the Moon can now be monitored by laser ranging, differential VLBI and occultation observations, implies that the interpretation of the measurements is conditioned by the choice and the accurate knowledge of a selenocentric, a terrestrial and a celestial frames. Two different types of selenocentric reference frames can be envisioned. The present selenographic frames are discussed but the author proposes that one should introduce a system defined by a purely geometric means. Some consequences of such a choice are discussed. One feature of the future conventional terrestrial frame is very important for Earth-Moon dynamics. Its origin should coincide with the center of mass of the Earth as determined by lunar laser ranging. As far as the quasi-inertial reference systems are concerned, the liaisons between a purely lunar dynamical system, subject to some hardly modelable effects, and purely celestial systems are analysed. The reduction of observations made with various techniques implies the use of different systems, and several problems are stated that should be solved before a unique system for Earth-Moon dynamics might be used.
Biases in Pole Position Computed from Data from Different Navy Navigation Satellites
Authors: Anderle R. J. , Colquitt E.S. , Tanenbaum M. , Malyevac C. A. 
Published: July 2016

AbstractBiases have been noted in pole positions computed from Doppler observations of different Navy Navigation Satellites. Studies show that the differences in the orbits of the Navy Navigation Satellites, although small, are large enough so that uncertainties in knowledge of the earth’s gravity field could produce the biases noted.
Astronomical Directories
Authors: Heck A. , Halbwachs J.L. 
Published: July 2016

Astronomical directories are available as CDS Special Publications. They provide practical data that one seeks to have always at one’s disposal on astronomical organizations and related items of interest.Over the years, these directories have proved to be very effective tools not only for improving national and international relationships in amateur and professional astronomy, but also for helping amateur astronomers, laypersons and public bodies to easily contact astronomical organizations as the need arises.IDPAI 1989 (CDS Special Publication 12 - about 500 pages) will be the second edition of the International Directory of Professional Astronomical Institutions. It will gather more than 2600 entries from about 80 countries: professional astronomical observatories and institutions; organizations, universities, departments, groups or companies employing astronomers or researchers in astronomy; related entries of general interest: IAU adhering organizations, professional associations, funding organizations, academies, as well as bibliographical services, software producers, journals, publishers, manufacturers, dealers, etc.