bluuebunny/crossref_metadata_2025_split huggingface dataset:
HIPPARCOS Satellite and the Organization of the Project
Authors: Kovalevsky J. 
Published: June 2019

The HIPPARCOS satellite is an approved project of the European Space Agency since 1980. A sketch of the past and future development of the project is given. The resulting astrometric parameters and magnitudes of 100 000 stars should be available circa 1993. Many astronomical groups are involved in the preparation of the mission together with ESA bodies and industry. Their functions and mutual interfaces are described.The main features of the satellite are presented. While observing out of the atmosphere removes most of the effects that limit the accuracy of ground based astrometry, new causes of systematic or random errors appear in an instrument designed for a millisecond of arc level of precision. The main limitations that have been identified are discussed: basic angle unstability, mechanical jitter, grid irregularity, diffraction chromatism, shape of the image dissector sensitivity profile. The consequence is that the presently expected basic measurement precision is limited not only by the photon count errors. However, all these effects are taken into account when assessing a final accuracy of 0″.002 for the astrometric parameters of a 9-th magnitude star.
3C205 - A Source with Extraordinary Alignment and a VLBI Hotspot
Authors: Lonsdale C. J. 
Published: June 2019

High resolution maps of 3C205 using MERLIN and the European VLBI network (EVN), some of which are shown in Fig.1, reveal unusual characteristics in this high redshift (z = 1.534) source. The most striking of these are as follows:
1)The hotspots A and B, and the core C are aligned to within 0″.05 (at the hotspot), as measured on the MERLIN 6 cm map.2)The compact feature in the southern hotspot (A1) has projected dimensions of ~0″.03 x ~0″.015 (see Fig.1d). The corresponding minimum internal energy density of this feature is ≳2.3 × 10−6 erg cm−3.3)There is a continuous zig-zag ridge in the southern component, which starts with a definite spur of emission extending in a south-east direction from the compact feature A1 (see Fig.1b). The magnetic field in A1 is in approximately the same position angle as this spur and the VLBI elongation, which both point towards a bright secondary peak in the southern lobe (1a and 1b).
Merlin Observations of the OH Maser Emission from IRC+10420
Authors: Diamond P. J. 
Published: June 2019

MERLIN observations of the 1612 and 1665 Mhz OH masers from the supergiant IRC+10420 reveal several major departures from the usual morphology of OH/IR stars.IRC+10420 is one of the most unusual OH maser sources yet found. It is an F8 supergiant with strong OH maser emission at 1612, 1665 and 1667 Mhz. A north-south optical nebulosity with an angular size of 2 arcsec has been detected (Thompson and Boroson,1977) and its peculiar IR properties are reminiscent of Eta Carina. These characteristics make IRC+10420 unique among Type II OH/IR stars.
The Diffuse Ionized Gas Perpendicular to the Plane of NGC 891
Authors: Dettmar R.-J. , Keppel J.W. , Roberts M.S. , Gallagher J.S. 
Published: June 2019

Hα images and long-slit spectra of NGC 891 show the presence of a thick layer of diffuse ionized gas (DIG) in this edge-on galaxy. Hα emission originating in the DIG of NGC 891 is detected out to several kpc above the midplane with a typical scale height for the electron density ne(z) of he~ 600 pc. The distribution of the gas is very inhomogeneous with a large scale asymmetry and filamentary structure. Individual Hα emitting structures can be traced out to 4-5 kpc above the midplane. The emission line ratios of [NII] and [SII] to Hα vary with height above the disk. We compare these properties with the analogous gas phase in our Galaxy.The distribution of the DIG is related to star formation in the underlying galactic disk and we conclude that in NGC 891 the interstellar medium is heavily effected by processes related to star formation.
Planetary Nebulae in the Magellanic Clouds
Authors: Jacoby George H. 
Published: June 2019

The identification and masses of Magellanic Cloud planetary nebulae are discussed. The masses are shown to be uncertain and should not be directly compared to values for galactic planetaries.The kinematics suggest that the planetary nebulae belong to a younger rather than an older population. Abundance analyses show the Magellanic Cloud planetaries to be deficient in most elements, but the abundances of helium and carbon are comparable to values found for galactic planetaries.
How Many Star-Forming Regions are there in the Milky Way?
Authors: Lodén L.O. 
Published: June 2019

There are very good reasons to believe that every stellar clustering in the Milky Way is a star-forming region or at least that every association is such a region and the minor clusterings adjacent sub-regions.Some star-forming clusterings are still active but it seems as if a majority should be burned-out. The problem is to estimate the total number of clusterings in the present Milky Way, de-activated and disintegrated as well as active.
Chemical Evolution of the Galactic Disk and Bulge
Authors: Wyse Rosemary F.G. 
Published: June 2019

The Milky Way Galaxy offers a unique opportunity for testing theories of galaxy formation and evolution. The study of the spatial distribution, kinematics and chemical abundances of stars in the Milky Way Galaxy allows one to address specific questions pertinent to this meeting such as
(i)When was the Galaxy assembled? Is this an ongoing process? What was the merging history of the Milky Way?(ii)When did star formation occur in what is now “The Milky Way Galaxy”? Where did the star formation occur then? What was the stellar Initial Mass Function?(iii)How much dissipation of energy was there before and during the formation of the different stellar components of the Galaxy?(iv)What are the relationships among the different stellar components of the Galaxy?(v)Was angular momentum conserved during formation of the disk(s) of the Galaxy?(vi)What is the shape of the dark halo?(vii)Is there dissipative (disk) dark matter?
A re-interpretation of the definition of UT1
Authors: Sinclair A. T. 
Published: June 2019

SummaryUniversal time is a commonplace quantity, and yet it has no generally accepted definition. The expression for sidereal time is often quoted as a definition, but this does not convey much meaning to the average person. Also sidereal time is measured from the equinox of date, and so involves the precession formulae of the stellar reference frame, and hence may not be ideal for other modern techniques of observation. Guinot (1979) has proposed a broad definition of UT1:“UT1 is an angle which is proportional to the sidereal rotation of the Earth, the coefficient of proportionality being chosen so that UT1, in the long term, remains in phase with the alternation of day and night. In some applications, UT1 can be considered as a non-uniform time scale”.
Cataclysmic Binaries: Optical and Geometrical Thickness of Disks and the Visibility of the Primary Components
Authors: Smak Józef. I. 
Published: June 2019

Accretion disks in cataclysmic binaries are optically thick (in the vertical direction), except for the case of inner parts of cool disks in dwarf novae at quiescence, which are optically thin. In long period Algols disks are cool and optically thick; their atmospheres can be quite extensive.Except for inclinations close to i = 0°, disks obscure either one or both hemispheres of the central star, the obscuration being either partial or total. In particular:
(a)In stationary accretion cataclysmic binaries (old novae and nova-like systems), at inclinations close to 90° the white dwarf is fully obscured; at i < 85° only its top hemisphere becomes visible.(b)In dwarf novae at quiescence, at inclinations close to 90°, the obscuration of the white dwarf is either complete (for disk radii Rd ≥ 4 × 1010 cm), or limited to its equatorial parts (for Rd ≤ 2 × 1010 cm); at i ≈ 85 – 88° the top hemisphere becomes fully visible, while the bottom hemisphere is fully obscured; at i < 85°, due to the low optical thickness of the inner disk, parts of the bottom hemisphere near the equator also become visible.(c)In long period Algols the situations is similar as under (a); in addition, depending on inclination, part of the obscuration can be due to the atmosphere of the disk.
Theoretical Models of Magnetic Flux Tubes: Structure and Dynamics
Authors: Steiner O 
Published: June 2019

Two types of model calculations for small scale magnetic flux tubes in the solar atmosphere are reviewed. In the first kind, one follows the temporal evolution governed by the complete set of the MHD and radiative transfer equations to a (quasi) stationary solution. From such a solution the continuum contrasts of a photospheric flux tube in the visible and in the infrared continuum at 1.6 μm have been computed and are briefly discussed. The second, more empirical type of method assumes the flux tubes to be in magnetohydrostatic equilibrium. It is computationally faster and more flexible and allows us to explore a wide range of parameters. Models and insights obtained from such parameter studies are discussed in some detail. These include an explanation for the peculiar variation of the area asymmetry of Stokes V profiles across the solar disk in terms of mass motions in the surroundings of magnetic flux tubes.Furthermore, a two-dimensional model of the lower chromosphere that has been developed is presented. Emphasis is laid on the effect of thermal bifurcation of the lower chromosphere on the structure of the chromospheric magnetic field. If the cool carbon monoxide clouds, observed in the infrared, occupy the non-magnetic regions, the flux tubes expand very strongly and form a magnetic canopy with an almost horizontal base. This has consequences for the spatial distribution of the Ca II K spectral line emission.Finally, some consideration is given to the formation and destruction of intense magnetic flux tubes in the solar photosphere. The formation is described as a consequence of the flux expulsion process that leads to a convective instability. A possible observational signature of this mechanism is proposed.
The Near-Infrared Capabilities of LEST
Authors: Engvold Oddbjørn 
Published: June 2019

The Large Earth-based Solar Telescope (LEST) will be a powerful, next-generation telescope with unprecedented angular resolution, capable of highly accurate polarimetry of the Sun, covering the optical spectral range from about 300 nm into the near infrared to about 2.5 μm.The telescope is a 2.4-m aperture, “polarization-free” concept based on a modified Gregorian optical system. A fast polarization modulator will be located close to the secondary focus of the system. An actively controlled NTT-type main mirror, a high precision pointing and tracking system, a helium-filled light path and a thin entrance window, together with an integrated adaptive optics system, will give the telescope near diffraction-limited performance in the visible. LEST will be sited on La Palma, in the Canary Islands, near the caldera rim on the Roque de los Muchachos Observatory, which often offers excellent seeing. A frequently occurring seeing parameter of ro = 15–20 cm in the visible will correspond to ro ≥ 1 m in the near IR.The construction of LEST will begin in 1993, and the telescope is to be ready for “first light” in 1997. The telescope facility will accommodate a large number of focal plane instruments on a spacious instrument table. LEST will be made available for near-IR instrumentation from the start of its regular operation.
Angular Momentum Growth around Local Density Maxima
Authors: Heavens A. F. , Peacock J. A. 
Published: June 2019

We have calculated the growth of angular momentum about local density maxima at early epochs. We find that high peaks experience higher torques than low peaks, counteracting the short collapse time during which the high peaks can acquire angular momentum. Which effect is dominant depends on the perturbation power spectrum: for power spectra characteristic of both cold dark matter and hot dark matter, the effects nearly cancel, and the total angular momentum acquired by a collapsing object is almost independent of the height of the peak. Furthermore, the distributions of angular momenta acquired by collapsing protosystems are extremely broad, for all power spectra, far exceeding any modest differences between peaks of different height.These results indicate that it is not possible to account for the systematic differences in angular momentum properties of disk and elliptical galaxies simply by postulating that the latter arise from fluctuations of greater overdensity, contrary to some recent suggestions. The figure shows the probability distributions for the final angular momentum acquired by peaks of dimensionless height 1–4, for a power spectrum similar to cold dark matter. A fuller account of this work has been submitted to MNRAS.
A New Approach To Traditional Chinese Astronomy
Authors: Kistemaker J. , Zhengzong Yang 
Published: June 2019

We have made a systematic investigation of the traditional Chinese stellar sky, using Yi-Shitong's precise stellar maps at the Amsterdam Zeiss Planetarium, reproducing the positions of pole, hour circles and equator for any epoch between 1000 and 3000 BC at the latitude of Xian.The right ascensions of the 28 boundary hour circles of the traditional lunar lodges, as well as the declinations of the various determinative stars, give insight into the possible original meaning of star names and ages. The four cardinal directions along the celestial equator (α Hya, η Tau, β Aqr and Sco) fit best with 2250±50 years BC.
The Compared Efficiency Of Centering Algorithms
Authors: Bienaymé O. , Motch C. , Crézé M. , Considère S. 
Published: June 2019

SummaryThe purpose of this study is to compare the quality of three digital image centering algorithms; 1) the fit of marginal distributions by Gaussian, 2) the maximum of the Autocorrelation of a stellar image by its symmetrical, 3) the 2–dimensional fit of stellar images by a mean stellar Profile.The two main conclusions are: 1) the 3 centering methods give the same accuracy if the star is isolated, bright and unsaturated. But as soon as one of these conditions fails, fast algorithms lack robustness and the only reliable method is the 2-d profile fit, 2) preliminary tests on Schmidt plates digitized with the MAMA (Machine Automatique à Mesurer pour l'Astronomie) show that under the above restrictions, the centering algorithms do not alter the final astrometric accuracy, neither do the digitizing machine.
Theory of Evolution of Central Stars of Planetary Nebulae
Authors: Paczyński B. 
Published: June 2019

Young central stars of planetary nebulae burn hydrogen and helium in the shell sources. Within less than 104 years nuclear fuel is exhausted and old central stars cool off at almost constant radius to the white dwarf stage.Young, i.e., luminous central stars should follow complicated loops on the H-R diagram as a result of helium shell flashes. FG Sagittae is the example. This should be a typical behaviour and a systematic search for light variations on a time scale of years or decades among other luminous entral stars should be undertaken. Because of rapid evolution of their nuclei many planetary nebulae may be far from the ionization equilibrium. This should be taken into account when the effective temperature and bolometric luminosity of the central stars are estimated.
The optical system of the Mt John one metre telescope
Authors: Nankivell G. R. , Rumsey N. J. 
Published: June 2019

The telescope will be used at the Cassegrain focal plane only. Two interchangeable systems of secondary optics are required to give relative apertures of:
(a)f/13.5 for spectroscopy and photometry over a small field.(b)f/8 for photography over as wide a field as practicable.
An off-the-shelf Reticon system
Authors: Honeycutt R. K. , Peery B. F. 
Published: June 2019

EG&G Princeton Applied Research produces a Reticon detector system intended for laboratory applications. However, current versions of the system are well-suited to astronomical observations at observatories with modest financial and technical resources.The detector inputs are intensified by microchannel plates, fiber-optically coupled to a 1024-pixel Reticon. Controller and readout electronics, and software for data pre-processing and graphical display are also available off-the-shelf, enabling the observer to put the system to use without a major development effort.
The Second Byurakan Spectral Sky Survey
Authors: Markarian B.E. , Stepanian J.A. , Erastova L. K. 
Published: June 2019

The method of the Second Spectral Survey carried out with the Byurakan 1-m Schmidt telescope is discussed. The limiting magnitude is fainter in comparison with the First Byurakan Survey at about 2–3m.The results of low dispersion (500 objects) and slit spectroscopy (300 objects) based on observations with the 6-m telescope of Special Astrophysical Observatory for four fields of the Second Survey are presented.The luminosity function of faint UV galaxies is discussed. The completeness of AGN of the Second Survey and their surface and space densities are also estimated. The surface density of QSO and ELG is estimated and these data are compared with the results of other surveys.New observational data obtained with the 6-m telescope are compared with the new data of different deep surveys carried out during last years.
1–3-Day Variations of the Broad Emission Lines of Seyfert Nuclei
Authors: Bochkarev Nikolay G. 
Published: June 2019

One of the principal problems of investigation of AGNs is to understand the nature of the central objects and the physical processes which yield their gigantic luminosities. This requires us to consider the innermost parts of AGNs (3–30 gravitational radii, i.e. ≲ 1016 cm: angular size less than 1 milliarcsecond).1–3d variations of the relative shape of broad emission line profiles of active galactic nuclei (AGN) are perhaps the most informative probe of the innermost parts of AGNs (r = 1015–16 cm from the centre). Optimal objects for these observations are Sy 1.5 with strong variations of the non-thermal continuum (e.g. NGC 4151). The expected amplitude of the variations ranges from a few percent to 10–20%. The optimal spectral resolution is 0.5–5 Å. It is very desirable to complement spectral observations with photometric data. The results of the first set of such observations with the 6-meter telescope are reported.
The Primeval Hadron: Origin of Rotation and Magnetic Fields in the Universe
Authors: Muradian R.M. 
Published: June 2019

The problem of the origin of celestial bodies - stars, galaxies and their clusters - is discussed proceeding from the concept of superheavy strongly interacting elementary particles termed superhadrons.Starting from generalized Regge law the universal relationship between mass and intrinsic angular momentum of cosmic objects has been established. Expressions are obtained for parameters of stars and Universe via fundamental constants. The prediction of the global rotation of the Universe is discussed and the problems of cosmic magnetic fields and energy problem in active galaxies are considered.
Molecular outflows and mass loss in pre-main-sequence stars
Authors: Levreault Russell M. 
Published: June 2019

We have conducted a survey for molecular outflows toward 71 pre-main-sequence stars using the J = 2 → 1 transition of CO. Outflows were detected and mapped toward 20 of these objects and in an additional six background sources not included in the original survey. The outflow sources range in mass from 0.5 to 30 M⊙, in luminosity from 4 to 1.1 × 105 L⊙, and in age from < 104 to ~ 106 years. In the H-R diagram, the outflow sources form a distinct band running across the top of the diagram.Roughly half of the observed outflows are bipolar at some level; the rest show a rich variety of morphologies. In addition to the CO (J = 2 → 1) data, we have obtained CO (J = 1 → 0) and 13CO (J = 1 → 0) observations that enable us to estimate the excitation temperature and optical depth in each outflow, leading to the derivation of outflow masses. The observed outflows range in mass from 0.01 to 56 M⊙, in size from < 0.07 to ~ 5 pc, and in age from ~ 103 to 5 × 105 years old.Simple momentum conservation arguments are then used to derive the mass loss rates necessary to produce the observed outflows. The results range from ~ 10−8 to ~ 10−3 M⊙ yr−1. Correlation of these mass loss rates with other parameters shows that pre-main-sequence mass loss goes as the square root of the bolometric luminosity and as the 1.7 power of the stellar mass. Implications for these findings on the nature of the pre-main-sequence mass loss mechanism, for self-regulated low-mass star formation, and for formation of the terrestrial planets are discussed.
Star formation in the southern complex region NGC 3576
Authors: Persi P. , Perrari-Toniolo M. , Spinoglio L. 
Published: June 2019

NGC 3576 (RCW 57) is a very bright optically visible nebula (~10' in size) located near the galactic plane at a distance of 3.6kpc. The region is associated with the HII region G291.28–0.71 (Retallack & Goss), and with a giant molecular cloud of M≃9×104 M⊙ (Cheung et al.1980) The source is reported in the IRAS Small Scale Structure Catalog. From the observed far-IR fluxes we derive a total luminosity of L(FIR)≃7×105 L⊙, suggesting that at least seven possible 07–09 stars could ionize the entire observed region. A cluster of five IR sources and extended 10μm emission were found by Frogel & Persson (1974). IRS 1 is a very compact object (<3'), while IRS 2–5 show diffuse infrared emission. In addition IRS 2, very close to IRS 1, is coincident with the radio emission peak. An H2O maser source and NH3 emission are present in the complex region.We present multidiaphragm photometry from 1 to 20μm of 1RS 1, IRS 3 and IRS 4 and CVF observations between 2-μm and 8–13μm of IRS 1, collected at the 1m and 3.6m ESO telescopes.
The Effects of Inverse Compton Scattering on the Pulsars' Radiation
Authors: Xia X.-Y. , Deng Z.-G. , Qiao G.-J. , Wu X.-J. , Chen H. 
Published: June 2019

Our calculations show that the cross section of the inverse Compton scattering in strong magnetic fields may be larger than that of Thompson scattering by sevaral orders of magnitude in the case of polar cap surface of pulsars. We can also see that when the energy of e± exceeds a certain value, their energy loss caused by the inverse Compton scattering may be larger than the energy gain from electric field in the inner gap, which implies that the e± could not be accelerated to γ = 106. Meanwhile, the electrostatic forces acting on the electrons will be balanced by the radiative pressure if temperature T > 108 K.It is beleived that the surface temperarure for most of pulsars is less than 106 K, in that case the ions of iron can not be emitted from the surface of pulsars. However, the temperarure at the polar cap can be increased to 3×106 through the bombardment of electrons to the polar cap according to R-S model. This quasi-equilibrium state by self-regulating must make the coherent radio emission unstable on the contrary.