bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Results and Techniques in Space Radio Astronomy
Authors: Alexander J. K. 
Published: July 2016

The first long wavelength radio astronomical observations from above the ionosphere were performed in the early 1960's using very short antennas on both sounding rockets and satellites. Although these exploratory measurements were sometimes troubled by perturbations arising in the local plasma enivronment and by spacecraft interference, they did develop the fundamental information and techniques on which to build more sophisticated low frequency radio astronomical systems. The first spacecraft designed specifically and exclusively for radio astronomical studies, Radio Astronomy Explorer 1, was launched on July 4, 1968. It carries two gravity-gradient stabilized, 229-m, travelling-wave V-antennas, a 37-m dipole antenna, and a number of radiometer systems to provide measurements over the 0.2 to 9.2 MHz frequency range (λ = 33 to 1500 m) with a time resolution of 0.5 sec and an absolute accuracy of about 25%. Although the observations may seem crude in some cases, when compared with those of ground-based telescopes, the RAE has afforded substantial improvement over the capabilities of the early flight experiments. Through the study of solar radio bursts down to 0.2 MHz, we are getting new information on the density, plasma velocity, and dynamics of coronal streamers out to distances of greater than 50 R⊙. From galactic continuum background maps at frequencies around 4 MHz, we are getting new information on the distribution of the ionized component of the interstellar medium. Cosmic noise background spectra measured down to ~ 0.5 MHz are providing new estimates of the interstellar flux of cosmic rays, of magnetic fields in the galactic halo, and of the nature of radiation from distant extragalactic radio sources.A second RAE spacecraft is now being constructed for launch into a lunar orbit. This satellite will permit radio astronomical measurements at frequencies down to 30 kHz (λ = 10 km), will facilitate the use of the moon as an occulting disk for source position measurements, and will provide new information on the cislunar noise environment required to assess the feasibility of future lunar radio observatories. Studies are in progress on the feasibility and application of orbiting radio interferometers (baselines up to 5 km) and large orbiting filled-aperture telescopes (diameter ~ 1 km).
Les relations entre les mouvements du pole et les fluctuations de la vitesse de rotation de la Terre
Authors: Melchior Paul 
Published: July 2016

On expose comment on peut tenter une ample synthèse des résultats d'observations astronomiques telles que celles du mouvement du pôle et des fluctuations de la vitesse de rotation de la Terre avec des observations de caractère purement géophysique: les marées terrestres, la circulation atmosphérique générale, le retrait progressif des glaciers, etc.On ne peut espéer donner dès à présent une conclusion à chacun des problèmes soulevés par la confrontation de ces données si diverses et l'on relèvera plusieurs contradictions. L'effort accompli dans le cadre de l'Année Géophysique permettra peut-être de lever certaines d'entre-elles et de parfaire la synthèse évoquée ici.
Artificial satellite orbit computations
Authors: Sconzo P. 
Published: July 2016

In this paper an orbit computation program for artificial satellites is presented. This program is operational and it has already been used to compute the orbits of several satellites.After an introductory discussion on the subject of artificial satellite orbit computations, the features of this program are thoroughly explained. In order to achieve the representation of the orbital elements over short intervals of time a drag-free perturbation theory coupled with a differential correction procedure is used, while the long range behavior is obtained empirically. The empirical treatment of the non-gravitational effects upon the satellite motion seems to be very satisfactory. Numerical analysis procedures supporting this treatment and experience gained in using our program are also objects of discussion.
The motion of a lunar orbiter
Authors: Kozai Y. 
Published: July 2016

The motion of an artificial satellite around the Moon is much more complicated than that around the Earth, since the shape of the Moon is a triaxial ellipsoid and the effect of the Earth on the motion is very important even for a very close satellite.The differential equations of motion of the satellite are written in canonical form of three degrees of freedom with time depending Hamiltonian. By eliminating short-periodic terms depending on the mean longitude of the satellite and by assuming that the Earth is moving on the lunar equator, however, the equations are reduced to those of two degrees of freedom with an energy integral.Since the mean motion of the Earth around the Moon is more rapid than the secular motion of the argument of pericentre of the satellite by a factor of one order, the terms depending on the longitude of the Earth can be eliminated, and the degree of freedom is reduced to one.Then the motion can be discussed by drawing equi-energy curves in two-dimensional space. According to these figures satellites with high inclination have large possibilities of falling down to the lunar surface even if the initial eccentricities are very small.The principal properties of the motion are not changed even if plausible values ofJ3andJ4of the Moon are included.This paper has been published in Publ. astr. Soc.Japan15, 301, 1963.
The Micro-Precision Interferometer Testbed Instrument Design
Authors: Hines B. , Neat G. , Colavita M.M. , Calvet R. , Sword L. 
Published: July 2016

The Micro-Precision Interferometer Testbed is essentially a space-based Michelson interferometer suspended in a ground-based laboratory. The purpose of the testbed is to serve as a proving ground for technologies needed for future space-based missions requiring low-vibration environments. A layered control architecture, utilizing isolation, structural control, and active optical control technologies, allows the system to achieve its vibration attenuation goals.This paper focuses primarily on the interferometer instrument design for the testbed and the systems-level tradeoffs between the instrument and other systems due to the fact that the interferometer is on a large, lightly damped, flexible structure rather than on the ground. The testbed is designed to be a fully functioning interferometer spacecraft and makes use of flight-like hardware where possible, including an external star simulator, an attitude control system, fringe detection and tracking systems, delay lines, pointing control, laser metrology systems, and computers and electronic subsystems. The engineering decisions that led to the current instrument configuration are presented and explained.
X-Ray Coronae from Stars
Authors: Pallavicini R. 
Published: July 2016

A number of major advances in stellar coronal physics have occurred since 1990 mainly as a consequence of imaging observations by ROSAT and spectroscopic observations by ASCA. These can be summarised as follows:
1.an all-sky survey has been performed by ROSAT at a sensitivity of ~ 2 × 10−13 erg cm−2 s−1, complemented by pointed observations an order of magnitude deeper;2.complete mapping and deeper pointings have been obtained for virtually all open clusters closer than ~ 500 pc, and covering the age range from ~ 30 Myr to ~ 700 Myr;3.complete mapping and deeper paintings have been obtained for several Star Forming Regions (SFRs) covering the age range ~ 1 to ~ 10 Myr;4.spectroscopic observations of bright coronal sources have been obtained with EUVE and ASCA allowing the derivation of the temperature structure and elemental abundances.
Empirical surface gravities
Authors: Maxted P. F. L. 
Published: July 2016

The surface gravity of a star (log g) is a fundamental parameter in models of stellar atmospheres. Given suitable spectra, log g can be determined from such models with an accuracy of 0.1dex, at best. Detached eclipsing binary stars can provide values of log g an order of magnitude more accurate than this, though for a more limited range of stars. Naturally, less accurate surface gravities can be obtained for a wider range of eclipsing binary stars.These facts are well known, so in this short review I will outline the types of stars to which the two methods have be usefully applied and might be applied in the near future. This naturally leads to the question of where the two ranges overlap and the comparison of results from the two methods. Techniques for allowing this comparison to made directly will be described. Surface gravities derived from winds in hot stars and (indirectly) from gravitational redshifts in white dwarf stars will also be covered briefly.
106-107 K Gas in the Magellanic Clouds
Authors: Snowden S. L. 
Published: July 2016

The Large Magellanic Cloud contains an extensive distribution of hot plasma and is one of the brightest extragalactic regions in the diffuse 0.5–2.0 keV X-ray sky. The plasma is not isothermal but increases in color temperature from west to east from ~106.6 K to ~106.9 K. The total flux from this plasma is ~ 1038 ergs s−1. The average emission measure is ~ 0.014 cm−6 pc, which if the emitting plasma is distributed uniformly throughout the LMC, implies a space density of ne ~ 0.002 cm−3. There is an apparent ¼ keV enhancement in the southwest of the LMC, which if associated with the LMC implies a considerable emission measure of ~ 106 K plasma. (The foreground column density of Galactic neutral hydrogen is ~ 6 × 1020 cm−2, or several optical depths for ¼ keV emission.)The Small Magellanic Cloud exhibits less diffuse X-ray emission in the 0.5–2.0 keV band than the LMC with a total flux of ~ 4 × 1036 ergs s−1. The average emission measure of ~ 0.006 cm−6 pc also implies a space density of ne ~ 0.002 cm−3. The optical depth of Galactic HI for ¼ keV X-rays from the SMC is considerably lower than that for the LMC. However, while there is a significant variation in the ¼ keV band intensity over the SMC field, it is in general not particularly well correlated with anything associated with the SMC, although there is an enhancement which may be related to the leading edge of the SMC. Considerably more work is needed to unravel the origin of the structure, which may be associated instead with either emission or absorption variations in either the disk or halo of the Milky Way.
Modeling the ISM: Molecular Gas, Ionizing Radiation, and Numerical Simulations
Authors: Bregman Joel N. 
Published: July 2016

Three different topics regarding the ISM in the Magellanic Clouds are discussed. First, we examine how the Magellanic Stream can be used as a tracer of the ionizing radiation leaking out of Galaxy and the Magellanic Clouds. We show that the radiation reaching the Magellanic Stream is less than 1% of the ionizing radiation produced by Galactic 0 and B stars. Since about 14% of the ionizing radiation from these stars is required to ionize the Reynolds layer, which is within 1 kpc of the disk, most of this radiation must be absorbed before reaching the Stream.Second, we examine the reliability of using CO as a tracer of H2 in regions of low or modest column densities (not giant molecular cloud complexes). For our Galaxy, the usual CO to H2 conversion factor overlooks a considerable amount of H2 and the evidence suggests that this may be true in the LMC as well. Finally, we present numerical hydrodynamical calculations of the interstellar medium in disk galaxies for a region of size 2 kpc along the plane and 15 kpc out of the plane. The simulations reveal a rich structure of low density hot regions separated by cold dense material, with the resulting position velocity diagrams being qualitatively similar to the recent HI studies of the LMC. A number of other aspects of these simulations are discussed also.
The Magellanic Clouds, Past, Present and Future - A Summary of IAU Symposium No. 190
Authors: van den Bergh Sidney 
Published: July 2016

Important problems to which we would like to find answers are:
•What are the distances to the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC)?•What is the present distribution of stars, gas and dark matter in the Clouds, and how did it evolve?•How, and where, did the Magellanic Clouds form, and how have their orbits evolved?•Finally the recent discovery of numerous microlensing events in the Clouds provides answers to questions that we have only recently started to ask.
An updated GSC as the astrometric reference for minor planet observations
Authors: Röser Siegfried 
Published: July 2016

Minor planet observers generally use the Guide Star Catalog (GSC) as the astrometric reference for the reductions of their CCD frames. Two problems are related with GSC. First, it contains no proper motions, and second, it shows severe systematic errors near the plate edges.I report on the status of a new reduction of GSC and present a first version of STARNET, a catalogue of 4.3 million positions and proper motions using GSC as second, and a new reduction of the Astrographic Catalogue (AC) as first epoch. In STARNET the average rms-accuracy of the proper motions is 5 milliarcsec/year, that of the present-day positions 0.3″.
A Search for Large Voids from Combined Samples of Galaxy Clusters and Galaxies
Authors: Stavrev K.Y. 
Published: July 2016

This paper is part of a more extensive study of the large voids in spatial volumes both wide and deep. Three samples of optical tracers with spectroscopically measured redshifts in a volume with b≥30° and z≤0.14 have been extracted from the catalogue of Lebedev and Lebedeva (1986) and the NASA/IPAC Extragalactic Database (NED):
(1)a homogeneous sample of 277 rich Abell clusters(2)an inhomogeneous sample of 969 objects: rich and poor Abell clusters, Zwicky clusters, other clusters, and groups(3)a sample of 18 623 NED galaxies.
Giant emission features at large distances from PNe: A preliminary investigation
Authors: Zanin C. , Weinberger R. 
Published: July 2016

“Senile” PNe are very old nebulae of extremely low surface brightness and large linear size; they offer e.g. the possibility of probing the conditions of the ISM also non-locally. We give three examples of huge nebulae in a preliminary inquire.NGC 3242: An ESO Schmidt plate obtained in April 1996 shows the ‘wrapped’ morphology of the faint arc discovered by Deeming (1966, Astrophys. J. 146, 287) 11′ south-west of this PN. Probably this arc is part of a giant halo of very low surface brightness around NGC 3242, but up to now the detection of the halo is questionable. A spectrum of the filament obtained at Las Campanas shows [O iii]/Hα ∼ 5 compared with a value of ∼ 3 in the nebula (Perinotto et al. 1994, Astron. Astrophys. Supp., 107, 481). This high ratio is larger than that expected for the excitation class of NGC 3242, even larger than the maximum allowed for a photo-ionized nebula of more or less normal chemical abundance. Thus, due to the spectral characteristic and to the filamentary structure of the arc we suspect that shocks appear to play a role.
Evolutionary Population Synthesis Models of Primeval Galaxies: A Critical Appraisal
Authors: Buzzoni A. 
Published: July 2016

A recognized problem when searching for primeval galaxies at cosmological distances is a definition of a firm selection criterion (alternative to a direct but extremely time-demanding measure of z) to single out high-redshift candidates from the plethora of other more or less peculiar objects (i.e. AGN, starburst galaxies etc.) at lower distances.The case of the HST “Deep Field” (HDF) observations (Williams et al. 1996) is especially relevant in this regard as galaxies up to z = 3.2 have been detected in the field (Steidel et al. 1996).
Investigation of two Planetary Nebulae and their Angular Vicinity in Cygnus
Authors: Saurer W. , Weinberger R. 
Published: July 2016

We present the results of an investigation of M1-79 and K3-82. Physical parameters like expansion velocities, spatial shapes, Zanstrahydrogen-temperatures, etc. were obtained by use of high resolution spectroscopy and CCD-images.The two PN are medium excitation and exhibit usual expansion velocities. To find out the spatial shapes we utilized the simple model of a truncated spherical shell. A comparison between the theoretical intensity ratios from this model and the measurements is leading to the conclusion that both PN have the structure of a ring. K3-82 is seen pole-on, Ml-79 is seen edge-on.
Structure and Morphology of NGC6369
Authors: Chatterjee Tapan K. , Campos J. 
Published: July 2016

NGC 6369 is a remarkable object, especially in the light of structure and morphology. We studied this object by taking many red plates (103aE), coupled with red filters (F29), of varying exposures using the Schmidt Telescope of the INAOE. The structure brought out by the analysis of the plates indicate that the object consists of a prolate disk sphaped ring nebula with a central hole and featuring huge plumes emanating out of the ring which engulf an outer envelope having a diameter about twice that of the ring. The striking feature of the plumes is that they emanate almost symmetrically out of the two prolate ends of the ring and curve out almost symmetrically along opposite directions.A comparison of the structures of this object with the temporal evolution of the gas density in the numerical simulations of a purely gaseous self-gravitating polytropic ring is conducted. Features resembling the plumes of this object are found at a certain stage of the simulations. A careful comparison of the observed and computer generated features indicate a marked similarity in the sense that both, the observed and simulated ring appear to be similar to the cross section of a prolate spheroid at the ends of which emanate the plumes. This seems to confirm that the evolution of this object is consistent with its being a planetary nebula having the appearance of a prolate spheroid with a central hole, which is a basic observational feature of most planetary nebulae.
IRAS Observations of Extended Planetary Nebulae
Authors: Leene A. , Pottasch S. R. 
Published: July 2016

The pointed observations made by the IRAS satellite have been analysed. In total 67 nebulae have been observed of which 10 proved to be resolved. The majority of the observations were carried out with the CPC and with the DSD macro of the survey array (Leene & Pottasch, 1987b). Further special deep maps were made of six nebulae (Leene & Pottasch, 1987a; Leene, 1987). Typical noise levels of the deep images are 0.03–0.1 MJy ster−1.The distribution of emission around the central star confirms that the 12 and 25 μm emission are due to ionic line emission. This is very clear in the nebula NGC 7293 (Leene & Pottasch, 1987a) and in NGC 6853 (Zhang et al., 1987). The other nebulae (A7, A21, A31, A35 and NGC 1360) confirm these findings. The 12 μm emission is most likely due to the NeII (12.81 μm) or due to the SIV (10.52 μm) line. The 25 μm band shows a strong central contribution due to the OIV (25.87 μm) line and a halo of the SIII (18.68 μm) line.
Horizontal-Branch Stars in the Log Teff, Log G Diagram
Authors: Philip A. G. Davis 
Published: July 2016

A review of the available Strömgren four-color data concerning horizontal-branch (HB) stars is presented. Several observers have studied seven globular clusters (with [Fe/H] values from −2.2 to −1.3) and more than 100 HB stars in fields at high galactic latitudes over the last ten years at Kitt Peak, Cerro Tololo, Mt. Wilson and Steward Observatories. The predictions of model atmospheres (Kurucz, 1976) allow one to calculate atmospheric parameters such as θeff, log g, and MV(Philip, Miller and Relyea, 1976). These parameters then can be compared with the predictions of evolutionary models (Sweigart and Gross, 1976).A comparison of the observed data with evolutionary tracks indicates that within the rms error of observation and the computational error of the models the data and the tracks agree quite well. This matches the case for Population I stars, where a similar analysis shows a good match between observational data and evolutionary tracks (Philip,et al. 1977).
A new catalogue of quasi-stellar objects
Authors: Hewitt A. , Burbidge G. 
Published: July 2016

We have prepared a new catalogue of QSOs and BL Lac objects containing approximately 3400 entries. A complete update of the Hewitt-Burbidge (1980) catalogue has been made with approximately another 2000 objects with known redshifts added. The references to discovery, magnitudes, redshifts, color, spectra and polarimetry have been updated for the objects listed in 1980, and complete new references are included for the new objects. In addition to the basic optical information, the new catalogue also contains X-ray, radio and infrared information for all objects. Absorption redshifts are listed when they are available. A supplementary catalogue which is now in preparation will contain similar information for objects described variously as Seyfert galaxies, N systems and AGNs. In doubtful cases we have used the operational dividing line ƶ = 0.1. All objects with ƶ < 0.1 are put in the supplementary catalogue unless their discoverers have unambiguously defined them as QSOs. With approximately twice as many objects included it is interesting to note that:
a)There are still very few genuine BL Lac objects, ∼100.b)The largest number of additions has come from identifications using the objective prism-grism techniques.
Simulations of Large-Scale Structure Compared to Abell Cluster Distribution
Authors: Batuski David J. , Melott Adrian , Burns Jack O. 
Published: July 2016

The amount of structure present among the Abell clusters out to redshift z = 0.085 has been compared with numerical supercomputer simulations (with 643 particles) of the isothermal, neutrino, and cold particle models for large-scale structure, assuming a flat universe and H = 50 km sec−1 Mpc−1. High-density clusters of particles were identified in each simulation. Correlation and percolation tests were then used to compare the spatial distribution of these high-density points with the apparent superclustering among Abell clusters. While all of the models had some small superclusters (the neutrino model has too many), none came very close to possessing the extremely extensive structures found in the Abell clusters (generally, disagreement by 2σ or more).A second set of simulations used the cold particle model with Ω = 0.2 and 0.5. The structures found in these simulations were certainly larger than those of the Ω = 1.0 cold particle case, but still > 2σ too small in comparisons with the Abell clusters.
Diffusion Mechanism of Radiation of a Charged Particle on the Randomly Spaced Dust Grains in the X-Rays
Authors: Gevorkian Zh. S. , Hambaryan V. V. , Akopian A. A. 
Published: July 2016

The theory of diffusion radiation of a charged particle on the fluctuations of the dielectric constant developed by Gevorkian can be explained as follows:A charge moving in a medium creates an electromagnetic field (pseudophoton) which is scattered on the fluctuations of the dielectric constant (here, dust particles) and converted into radiation. In the wavelength region (l « λ « L) (l is the mean free path of the photon in the medium, L is the characteristic size of the system) the main mechanism of the radiation is the diffusion of the pseudophoton (Gevorkian & Atayan 1990, Gevorkian 1992, Gevorkian 1993).