bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metallicity Effects in Massive Star Evolution and Number Frequencies of WR Stars in Galaxies
Authors: Maeder André 
Published: June 2019

The results of new grids of models of massive stars with metallicities Z = 0.002, 0.005, 0.020 and 0.040 and mass loss rates depending on Z are shown. When integrated over the mass spectrum, the models enable us to predict number ratios, such as WR/O, WC/WN, WNE/WR, WNL/WR, WCE/WR, WCL/WR, WO/WR as a function of Z in galaxies.Comparisons between models and observations in galaxies are made and show, as was suggested by Maeder, Lequeux and Azzopardi (1980), that the effects of metallicity on the mass loss rates are the prime agent responsible for the different distributions of massive stars in galaxies.
The Distance to HD 50896 (EZ CMA)
Authors: Schmutz Werner , Howarth Ian D. 
Published: June 2019

The WN5 star HD 50896 lies in the same sightline as the open cluster Cr 121. In order to investigate the possibility of cluster membership, we observed the interstellar Na D lines in the spectra of HD 50896 (=EZ CMa, =WR6) and stars in its neighbourhood (on the plane of the sky) at high spectral resolution (R=80,000 and 105,000). The observations were obtained with the 1.4-m coudé auxiliary telescope and the coudé echelle spectrograph of the European Southern Observatory.From the strengths and velocity structure of the interstellar features it is immediately clear that HD 50896 is not a member of Cr 121; rather, it is a background object. A comparison with spectra of other background stars shows that the line of sight towards HD 50896 is very similar to those of HD 51854 (B1 V) and HD 50562 (B3 III). From intermediate-band and Hβ photometry the distances to these two B stars are 1.75 kpc and 1.95 kpc, respectively. The most red-shifted absorption component in the spectrum of HD 50896 is displaced only slightly more than that of HD 51854, and a little less than that of HD 50562. We conclude that the the most probable distance to HD 50896 is 1.8 kpc.
Design and Fabrication of Large CCDs for the Keck Observatory DEIMOS Spectrograph
Authors: Stover R. J. , Brown W. E. , Gilmore D. K. , Wei M. 
Published: June 2019

The Keck II Deep Imaging Multi-Object Spectrograph (DEIMOS) is a general purpose, faint object, multi-slit, double-beam spectrograph which offers wide spectral coverage, high spectral resolution, high throughput, and long slit length on the sky. This powerful instrument will be the principal optical spectrograph on the Keck II telescope. DEIMOS is optimized for faint-object spectroscopy of individual point sources, low-surface-brightness extended objects, or widely distributed samples of faint objects on the sky. To obtain high resolution (∼ 1 å) and wide spectral coverage (up to 5000 å) the spectrograph uses wide angle cameras and large CCD detectors with many pixels.This paper describes some of the work being carried out to obtain the CCD detectors required for the DEIMOS spectrograph. In addition, results are presented on the fabrication and characterization of a 4k × 2k three-side buttable CCD produced by Orbit Semiconductor, a silicon foundry in San Jose, California. This CCD was fabricated to test the ability of Orbit to produce high quality scientific CCDs with the characteristics required for detectors to be used in DEIMOS and other optical instruments of the Keck Observatory.
3D: The New Near-Infrared Field Imaging Spectrometer
Authors: Tacconi-Garman L. E. , Weitzel L. , Cameron M. , Drapatz S. , Genzel R. , Krabbe A. , Kroker H. , Thatte N. 
Published: June 2019

3D is a next-generation near-IR spectrometer developed at the MPE which offers, in a single integration, the opportunity to image an 8″ × 8″ field across almost the entire K-band at a simultaneous spatial resolution of 0.″5 wide strips which are then aligned optically on top of each other forming a single long slit. This long slit is then used as the input for a grating spectrometer which images it onto a two dimensional detector array. Each detector row then represents the spectrum of one spatial element of the two dimensional field of view. The central part of the optical system is the image slicer which is made of two complex plane mirror systems consisting of 16 segments each. The detector is a NICMOSIII HgCdTe array with 256 × 256 pixels. In the spectral domain the spectrometer provides a resolving power of R = 1000.Here we present not only the design of the instrument but also first data obtained during instrument commissioning at the 3.5-m Calar Alto telescope in December, 1993.
Relativistic Reduction of Astrometric Observations
Authors: Brumberg V. A. 
Published: June 2019

The nonuniqueness of the quasi-Galilean coordinates of general relativity leads to the emergence of unmeasurable coordinate-dependent quantities in astronomical practice. One may offer three possible ways to overcome the related difficulties:
1.developing theoretical conclusions only in terms of measurable quantities2.using arbitrary coordinates and developing an unambiguous procedure for comparing measurable and calculated quantities3.agreement to utilize one and only one coordinate system.In this paper we prefer the second way. After formulating the heliocentric planetary and geocentric satellite equations of motion, the general technique for relativistic reduction in astrometry and geodynamics is developed. Specific algorithms for the reduction of absolute and relative measurements are derived for the one- and the two- body problem. For illustration, the relativistic reduction of stellar parallaxes, Doppler satellite observations, navigation measurements with the aid of satellites and radiointerferometric measurements are presented in detail.
Magnetic Field Structure in Dark Clouds
Authors: Tamura M. , Nagata T. , Sato S. , Tanaka M. , Kaifu N. , Hough J. , McLean I. , Gatley I. , Garden R. , McCaughrean M. 
Published: June 2019

The magnetic field geometry in the central regions of two dark clouds has been mapped by measuring the polarization at 2.2 μm of background stars and of stars embedded in the clouds. The observations were done with the Kyoto polarimeter on the Agematsu 1m IR telescope in December 1984 for Heiles Cloud 2 in the Taurus dark cloud complex, and on the UKIRT 3.8m in May and July 1985 for the ρ Ophiuchus dark cloud core. The main results are:
i)Most of the stars in both regions show polarization and their maxima are 2.7% in Heiles Cloud 2 and 7.6% in ρ Oph, respectively. There are similar positive relations between polarization degree and extinct ion Av's.ii)The distribution of position angles for Heiles Cloud 2 shows a single mode at about 50° and that for ρ Oph shows a bimode, at about 50° and 150°.iii)The magnetic fields, as delineated by the infrared polarization, appear perpendicular to the flattened elongations of the molecular clouds.
Polarization Mapping of Infrared Reflection Nebulae
Authors: Nagata T. , Yamashita T. , Sato S. , Tanaka M. , Suzuki S. , Kaifu N. , McLean I. , Hough J. , Gatley I. , Garden R. 
Published: June 2019

Extensive reflection nebulae have been discovered around GGD27 IRS and around W75N IRS by mapping the infrared polarization in the K band.It was found that the infrared radiation from both objects is extended at λ = 2.2 μm, by using the Agematsu 1-m, the UH 2.2-m, and the UKIR 3.8-m telescopes. We have carried out polarization mapping with the Kyoto polarimeter on the UKIRT in August 1985.
The reference frame of the ephemerides
Authors: Standish E. M. , Newhall X. X. , Williams J. G. , Dickey J. O. 
Published: June 2019

Complete ephemerides of the moon and the four inner planets could be created solely from ranging data alone. Such ephemerides would then be independent from any outside astronomical reference system, and, therefore, would define their own unique reference frame. In fact, this is nearly the case with present-day ephemerides; the accuracy of the ranging data tends to dominate most of the least squares adjustment.This paper outlines the process of creating the lunar and planetary ephemerides along with the orientation of the ephemerides onto the dynamical equinox. The resulting accuracies of these processes are given and a number of uses for the ephemerides are highlighted.
Fundamental radio reference frame from VLA observations of minor planets
Authors: Kaplan G. H. , Johnston K. J. , Seidelmann P. K. , Wade C. M. , Carroll T. S. 
Published: June 2019

The weak thermal emission from the largest minor planets can be detected in the microwave regime by the Very Large Array (VLA). Signal-to-noise ratios are sufficiently high to permit precise measurement of the positions of these objects at all points in their orbits with respect to background extragalactic sources. We are in the process of obtaining observations of astrometric accuracy for minor planets 1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygeia.Minor planets have historically served as “test particles” in the solar system, and optical observations of these objects have been valuable in the determination of fundamental astronomical constants. In particular, optical observations of minor planets have played an important role in the establishment of the fundamental optical reference frame by permitting the determination of the orientation of the Earth's orbit relative to the stars defining the frame.Similarly, radio observations of these bodies can play a corresponding role in the establishment of a fundamental radio reference frame. Our observations will provide a direct link between the dynamical and radio reference frames, and provide important information on the relationship between the radio and optical reference frames.
Capabilities and performance of the upgraded Mark III correlator system
Authors: Whitney Alan R. 
Published: June 2019

The Mark IIIA correlator system is currently operating at the U. S. Naval Observatory in Washington, D.C. in support of VLBI geodetic measurements being made by NASA, NGS, NRL, and USNO. This correlator system, developed at Haystack Observatory, is a second-generation version of the original Mark III correlator, and adds significant new capabilities such as double-speed operation, longer integration periods, and improved internal modelling.The Mark IIIA correlator can simultaneously process up to 10 baselines of data from 5 stations. Experiments including more than 5 stations may be processed with multiple passes through the correlator. The architecture of the correlator allows a future expansion to a maximum of 16 stations. Due to a simple modular design and the low cost of required computer-support equipment, expansion is straightforward and relatively economical.Although current geodetic VLBI observations are made using data from distant natural continuum radio sources, the Mark IIIA correlator was designed to also support processing of data collected from pulsars, artificial earth satellites, and from earth-orbiting antennas receiving signals from natural sources. These capabilities may be important in the future as efforts continue, for example, to tie satellite-related reference frames to current VLBI reference frames.The design approach of the Mark IIIA correlator will be discussed, including its performance with respect to systematic and random errors which may affect geodetic VLBI data.
The Third Reduction Of Giuseppe Piazzi's Star Catalogue
Authors: Proverbio E. 
Published: June 2019

The star observations carried out by Giuseppe Piazzi with Ramsden's large altazimuth circle, which he began in 1792, led to the realization of a 1st and 2nd Catalogue, published by Piazzi in Palermo in 1803 and 1814.During 1845, the original astronomical observations in Piazzi's catalogue, included in “La storia celeste of the Palermo Observatory from 1792 to 1814”, which had been kept at the Brera Observatory in Milan, were published in Vienna.The publication of these observational data revealed a series of errors, real or presumed, which cast doubt on the reliability of the Palermo Catalogue.Towards the end of the last century, upon the suggestion of Giovanni Schiaparelli, work on the reduction of Piazzi's catalogue was once again taken up for the purpose of producing an independent catalogue based on the original observations. This work, carried out by Francesco Porro, led to the production of a corrected catalogue purged of systematic and accidental errors.The third fundamental star catalogue of Palermo may represent the basis for the final reduction of the great Palermo Catalogue of 7646 stars.
The use of wide angle cameras and high speed measuring machines for generating programmes for small telescopes
Authors: Dodd R J , MacGillivray H T 
Published: June 2019

The classical method of discovering objects that vary in position and/or time is to examine well-matched pairs of plates using a blink comparator. This method, being manual, is slow, subjective and, unless several matched plate pairs are used, suffers from incompleteness. The combination of wide angle Schmidt cameras, high speed measuring machines and sophisticated computer software has enabled objective methods for searching for variable objects to be devised. Using such methods it is possible to intercompare stacks of plates digitally. The deepest plate may be used as a master in position and magnitude, eliminating the need for the rest to be well matched. Following measurement and analysis it is a relatively simple matter to prepare lists of variable objects such as RR Lyrae stars, Mira long period variables, cataclysmic variables, active galaxies, comets and asteroids which may then be used as a basis for more intensive study by smaller dedicated instruments.This, however, is only one aspect of the cooperation possible between Schmidt telescopes, measuring machines and small telescopes. In projects involving the study of large numbers of mainly non-variable objects (stars or galaxies) the small telescope has a most important role to play in providing photoelectric magnitude calibrations to convert machine measured magnitudes to a standard system. To date this has been the principal use to which the small telescope has been put, even in the study of the distribution of faint galaxies from Schmidt plates it was a small telescope which provided the necessary measurement of the background sky brightness.A further dimension is provided by the addition of an objective prism to the Schmidt camera. In this case objects readily detected include emission line stars and galaxies. The calibrating power of the smaller instrument is now of value in providing standard galaxy radial velocities to calibrate red shifts measured from the very low dispersion prism.
Circumstellar dust around FU Orionis stars
Authors: Welin Gunnar 
Published: June 2019

It is immediately apparent from IRAS and other far infrared data (figure 1) that all known FU Orionis stars, or fuors, are associated with substantial amounts of cool circumstellar dust.The pre-outburst magnitudes for V1057 Cyg indicate that this star was immersed in circumstellar dust already before its flare-up in 1969–1970, and hence that this dust did not - as has been claimed - appear only after the outburst; regrettably there exist no far infrared data from that time. The colours also exclude the possibility that the star then was of the alleged spectral type KO, but point to it being of a rather early type and obscured by both interstellar, local, and circumstellar matter. For details, see Welin 1985.
The Globular Cluster Population of X-ray Binaries
Authors: Verbunt Frank , Hut Piet 
Published: June 2019

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.
Metal Line Blanketed Non-LTE Model Atmospheres for Central Stars of Planetary Nebulae
Authors: Werner K. , Dreizler S. 
Published: June 2019

Absorption lines of highly ionized iron group elements dominate the UV spectra of many hot stars. They were identified in several central stars as well as in sdO stars, in PG 1159 stars and in the hottest DO and DA white dwarfs. Due to the high effective temperatures atmospheric modelling including metal line blanketing has to be done under NLTE conditions. Adequate models have become available only very recently (Dreizler & Werner 1992). We present new NLTE model atmospheres blanketed by some 120 000 lines from iron group elements (Sc through Ni). We adopted Anderson's (1991) statistical approach along with an opacity sampling technique using our Accelerated Lambda Iteration (ALI) code. We generally found:
— Many strong metal lines cause substantial blocking at the flux maximum.— The temperature in the continuum forming layers is increased by backwarming due to iron group lines; outer layers, cooled by CNO lines, are unaffected.— The line profiles of H and He become deeper and broader, indicating that the neglect of NLTE metal line blanketing could cause the discrepancies encountered when fitting He II and H I lines in hot subdwarfs.
A New Proper Motion Survey of the Pleiades Cluster
Authors: Schilbach E. , Guibert J. , Geffert M. , Hirte S. 
Published: June 2019

A programme for the determination of proper motions and photographic B, V, R magnitudes for stars up to 18m within a 4° by 4° region centered near Alcyone is described. We use MAMA measurements of plates taken with Tautenburg and OCA Schmidt telescopes as well as with the double refractor of Bonn and Carte du Ciel plates. To check the stability of the solution three different methods of reduction are applied.According to the results of the pilot programme a final proper motion accuracy of about 2 mas/a can be achieved for the majority of stars in the survey.
Spherical Galaxies: Methods and Models
Authors: Richstone Douglas O. 
Published: June 2019

Over the last 5 years, considerable progress has been made in our ability to construct self-gravitating stellar equilibria. One of these new methods is essentially a variant of Eddington's (1916) method. Two other key approaches are logical extensions of Schwarzschild's Linear Programming method, and can be applied to nonspherical models as well. These methods are reviewed below.The application of these methods to galaxies has yielded a few very interesting results within the last year or two. The methods described below unambiguously establish M/L's for M87 and M32 within about 30 arc seconds. They strongly support Tonry's contention that the nucleus of M32 contains a large invisible mass, possibly a 107M⊙ black hole. They also suggest that observational recovery of the projected velociy distribution might permit the observer to distinguish between a massive halo and an increasingly tangential velocity distribution function.
Gas and Dust in the Inner Few Degrees of the Galaxy
Authors: Güsten Rolf 
Published: June 2019

This review discusses the complex morphology and perturbed kinematics, as well as the outstanding physical characteristics of the interstellar medium within a few 100 pc of the galactic center. A total of ~107.9 Mo of dense molecular gas, representing ~10% of the Galaxy's neutral mass content, has settled in a thin layer [size: 450 × 40 pc], composed of giant molecular cloud complexes. The spatial distribution is highly asymmetric with respect to the center, and motions differ considerably from equilibrium conditions. The dynamical situation is still obscure (explosive event vs. response to distorted gravitational potential), but any disturbance must have occurred quite recently (τdy ~106 yr). Evidence for large–scale star–forming activity is reviewed, and for a standard IMF, a total star formation rate Φ ~0.5 M0 yr−1 is inferred.The galactic center clouds differ considerably in their physical and chemical characteristics from GMC's in the outer Galaxy. Pervasive high bulk gas temperatures (Tkin ~70 K), mean H2 densities of n ~104 cm−3, and linewidths ≥10–20 kms−1 are probably a consequence of the clouds' location in the steep gravitational potential of the central bulge.
Oxygen Abundances in Bulge-like Dwarf Stars
Authors: Pompéia Luciana , Barbuy Beatriz , Grenon Michel 
Published: June 2019

High resolution échelle spectra were obtained with the FEROS spectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars. From Hipparcos data it appears that the turn-off of this population indicates an age of 10–11 Gyr (Grenon 2000).Oxygen abundances are calculated using the [O I] line at 6300.3 Å. The derived results show an oxygen overabundance for most of our sample stars when compared to their disk counterparts.
Optimization of Gravitational Burst Detectors Using Piezoelectric Transducers
Authors: Maeder D. 
Published: June 2019

A general approach to overall system optimization is developed using the concepts of mechanical and electrical signal-to-noise ratios (MSNR and ESNR). These are proportional to and to respectively, where Qsys=mechanical Q of the complete detector, μ = (transducer mass/metal mass), and n = resolving time in units of one-half of the detector fundamental period. The overall SNR becomes a maximum for n = n∗ = optimum resolving time; this procedure yields whereas Application to ‘strong-coupling’ type antennae (such as divided-cylinder systems) gives a high SNR∗ which depends very little on μ if μ > 0.01. Q-factor and coupling efficiency relations were checked for 22 kg-prototypes using μ = 0.26%, 0.9%, and 1.8%. Two new detector configurations are suggested: the ‘bridged-tube’ allows strong-coupling for very long detectors; the ‘folded-tube’ operates at lower frequencies for a given length.
Amplification of Waves Reflected from Kerr Black Holes
Authors: Starobinsky A. A. 
Published: June 2019

The effect of amplification of electromagnetic and gravitational waves reflected from a rotating black hole (‘superradiance scattering’) is investigated. This effect was proposed by Zel'dovich (1971). It leads, as well as the Penrose process, to the energy extraction from a Kerr black hole at the expense of its rotational energy and momentum decrease. The coefficient of wave reflection R>1 if ω<nω, where ω is the wave frequency, n - its angular momentum and ω is the black hole angular velocity. The value of this effect is not small in the case of gravitational waves, for example, if l=n = 2, ω →nω and a = M, then R≈2.38.There also exists a quantum version of the effect, namely, the one of spontaneous pair creation in the Kerr metric, but this quantum effect is exceedingly small in real astrophysical conditions, because its characteristic time is of the order G2M3/hc4, where M is the black hole mass.
Tidal Tensor and the Emission and Absorption of Gravitational Radiation
Authors: Sejnowski Terrence J. 
Published: June 2019

The absorption and emission of gravitational radiation can be calculated in the long wavelength limit by use of the tidal tensor, defined as the gradient of the gravitational pseudoforce,
thus
where ηb is orthogonal to the 4-velocity ua, and normal coordinates are understood.The exchange of energy and momentum between an extended body and the gravitational field is governed by appropriate integrals of the tidal tensor over space and time.The tidal tensor is the trace Tabdb of the Bel-Robinson tensor Tabcd. In emty space this trace is zero and the tidal tensor vanishes; there is no local exchange of energy.