bluuebunny/crossref_metadata_2025_split huggingface dataset:
The motion of a geosynchronous satellite
Authors: Bhatnagar K. B. 
Published: June 2019

The motion of a geosynchronous satellite has been studied under the combined gravitational effects of the oblate Earth (including its equatorial ellipticity), the Sun, the Moon and the solar-radiation pressure. It is observed that the orbital plane rotates with an angular velocity the maximum value of which is 0.058°/yr. and regresses with a period which increases both as the orbital inclination and the altitude increase. The effect of earth's equatorial ellipticity on the regression period is oscillatory whereas that of Solar-radiation pressure is to decrease it.The synchronism is achieved when the angular velocity of the satellite is equal to the difference between the spin-rate of the Earth and the regression rate of the orbital plane. With this angular velocity of the satellite, the ground trace is in the shape of figure eight, though its size and position relative to the Earth change as the time elapses. The major effect of earth's equatorial ellipticity is to produce a change in the relative angular position of the satellite as seen from the Earth. If the satellite is allowed to execute large angle oscillations the mid-point of oscillation would be at the position of the minor axis of the earth's equatorial section. The oscillatory period T has been determined in terms of the amplitude Γ and the tesseral harmonic J2(2). From this result we can determine the value of J2(2) as T and Γ can be observed accurately.
The Mass Loss Rate of SK 80 (07Iaf) in the Small Magellanic Cloud
Authors: Willis A J , Howarth I D , Nandy K , Morgan D H 
Published: June 2019

The star SK 80 in the SMC is classified as 07Iaf by Walborn (1976) who notes that it is the only confirmed Of star in that Galaxy known to date. A knowledge of the mass loss properties of OB stars in the Magellanic Clouds is of interest because of the recent evidence that such stars show reduced mass loss properties than their galactic counterparts (Hutchings 1980) and for Of stars because of the possible link between such stars and Pop I transition WNL stars (Conti 1976).We have secured HIRES IUE and optical spectra of SK 80 and have attempted to derive the mass loss rate from these data.
Radio and Millimetre Observations of Larger Molecules
Authors: Avery L. W. 
Published: June 2019

The number of known interstellar molecules has increased steadily since 1970 and stands presently at 68. of the molecules discovered in recent years more than half contain three or more heavy elements.The number of sources where HC5N or HC3N has been detected now includes 21 dark clouds, four circumstellar shells, two bipolar nebulae, the line of sight to the Cas A supernova remnant, and possibly a comet. the more abundant large molecules are useful diagnostic probes, and preliminary statistical equilibrium calculations of the widespread new ring, C3H2, are presented which indicate its usefulness as an indicator of H2 density.
Hβ Profile Variations in the Spectrum of Seyfert Galaxy NGC 5548 Nucleus
Authors: Chuvaev K. K. 
Published: June 2019

The spectra of NGC 5548 galaxy nucleus obtained at the Crimean Aetrophysical observatory on 2.6-m Shain telescope from April till August 1985 showed strong variations of Hβ line profile. The profile being almost symmetrical in April became more and more asymmetrical in June-August, the flux in blue wing increased twofold in respect to the red one. Such variations of line profile were accompanied by continuum decrease.We suppose, that the observed variations might be explained by the appearance of the absorbing matter located on the line of sight between the nucleus and the gas responsible for the intensity increase in the blue wing of Hβ line. This gas might have been ejected close to the line of sight direction.
Superassociations in the Arms of Normal and Active Galaxies
Authors: Melnick Jorge 
Published: June 2019

The properties of violent star formation regions in the arms of spiral galaxies are reviewed with the aim of providing the foundations on which models of nuclear starbursts can be built. It is argued that the classical examples of extranuclear starbursts, giant HII regions and Superassociations, are closely related but fundamentally different classes of objects; their properties are reviewed and discussed in detail.It is shown that giant HII regions are a homogeneous class of gravitationally bound objects ionized by starburst clusters and that the initial mass functions of these clusters change according to their chemical composition being flatter for metal poor systems. Superassociations are loose associations of associations which generally contain one or more giant HII regions. Star formation in superassociations is self-sustaining and therefore these structures may last much longer than individual giant HII regions.Isolated superassociations or HII galaxies are shown to have the same global properties as giant HII regions in late type galaxies. In particular, the correlations between Hβ luminosity and emission line velocity width are similar for both classes. Since HII galaxies can be observed out to large distances this correlation provides a potentially powerful method to calibrate the extragalactic distance scale. A preliminary calibration gives HO = 95 ± 9 km/sec/Mpc.The relations between the properties of giant HII regions and Superassociations with those of their parent galaxies are briefly discussed.
Seismological investigations of compact stars
Authors: Winget† D. E. 
Published: June 2019

Since Landolt's discovery of the first ZZ Ceti star, the ranks of the compact pulsators have swollen to include planetary nebula nuclei, hot pre-white dwarf stars, hot and cool white dwarf stars, and possibly even neutron stars. The discovery of multi-periodic variations in these objects has helped to usher in a new era of rapid progress in the field of stellar seismology. For the compact stars this rapid progress is the result of a combination of four fortunate circumstances: their physical structure is relatively simple; typical amplitudes are small enough to be both readily observable and amenable to linear analysis; the wealth of observed periods in each object provides many independent clues to the underlying structure of the compact stars; and the periods are short enough that we can observe many cycles in a night, thereby completely resolving the period structure in many of these stars.In this review I will discuss the current state of our understanding of these objects, with special emphasis on their distribution in the H-R diagram, range of pulsation properties, possible mode selection mechanisms, excitation of the pulsations, problems of convection, and particularly the measurement and interpretation of period changes. In addition to the results of recent research, I will review the techniques used to obtain them, pointing out both their strengths and weaknesses. I will close with a discussion of some of the important problems facing us in the study of these objects, and attempt to identify potentially fruitful directions for future research.
A Spectroscopic Study of Binary Star Planetary Nebulae
Authors: Walsh J.R. , Walton N.A. , Pottasch S.R. 
Published: June 2019

A comprehensive spectrophotometric survey of the central stars of planetary nebulae with known or suspected binary star nuclei (BSPN) is underway. The aims of this programme are: to determine the nature of the companion to the ionising star of the nebula; to estimate the spectroscopic distance from the spectral type and magnitude of the companion and thence to determine the luminosity of the hot star; to compare the morphologies and excitation/abundance characteristics of BSPN with those of PN produced by single star evolution. The advantage of the distance determined from this simple method is that it is independent of any assumptions about the planetary nebula, in contrast to most other PN distance estimators.To date 75 percent of known or suspected BSPN have been observed with the 2.5m Isaac Newton Telescope and the 1.5m ESO spectroscopic telescope at low and intermediate dispersions. A selection of preliminary results from the programme is presented, highlighting the binary central stars of NGC 246 and Abell 65.
Caractéres spectrophotomètriques de l'age
Authors: Chalonge D. 
Published: June 2019

RésuméSur les trois paramètres utilisés dans la classification tridimensionnelle deux sont indépendants de l'absorption interstellaire : ce sont D et λ1 qui mesurent la grandeur et la position dans le spectre de la discontinuité de Balmer. Si l'on classe les étoiles de la population I en se bornant à l'emploi de ces deux paramètres, on obtient directement et sans qu'aucune correction soit nécessaire un graphique analogue au diagramme HR : les points représent ant les étoiles de divers amas connus permettent de « graduer en âge » le diagramme composite ainsi établi directement et l'on peut en déduire des informations sur l'âge des étoiles individuelles n'appartenant pas aux amas précédents.On a de même commencé à construire le diagramme relatif aux étoiles de la population II voisines du soleil.
The Cold Interstellar Medium in Elliptical Galaxies – Observations of HI and Radio Continuum Emission
Authors: Knapp G. R. 
Published: June 2019

About 10% of nearby elliptical galaxies contain HI, with typical values of M(HI) ~ 5 × 108 M⊙ and M(HI)/LB ~ 0.03 M⊙/L⊙. The HI content is unrelated to the stellar content, (unlike the situation in spiral galaxies) suggesting that the HI in early-type galaxies has an external origin and is not produced by mass loss. This conclusion is strengthened by the distribution and kinematics of the HI structures, which lie outside the main optical body of the galaxies, have much larger specific angular momentum than do the stars, and are often highly inclined to the kinematic and distribution axes of the optical bodies.The HI and stellar kinematics show that the rotation curves of E and SO galaxies are approximately flat from small (a few hundred pc) to large (10-20 kpc) radii, as is the case for spirals. Likewise, large mass-to-light ratios are found for some systems. Comparison with mass models derived from X-ray emission suggests that these may in some cases overestimate the mass.The presence of HI is shown to enhance the likelihood that an E/SO galaxy has a nuclear radio continuum source, in agreement with models which suggest that the central engine is fuelled by cold gas. Current data suggest that the gas-to-dust ratio for the cold interstellar medium in ellipticals has a value similar to that found in the solar neighborhood.
Galactic Centers – Ours and Other Galaxies'
Authors: Rieke G. H. 
Published: June 2019

Viewed from outside the Local Group, the Galactic Center would be a paragon of ordinariness, both with regard to its stellar population and its nonstellar emission in the radio, infrared, and X-ray.Nonetheless, at a very modest level it shows evidence for many of the processes that we believe dominate the properties of exotic galactic nuclei.
Extrasolar Planets and Prospects for Terrestrial Planets
Authors: Marcy Geoffrey W. , Butler R. Paul , Vogt Steven S. , Fischer Debra A. 
Published: June 2019

Examination of ∼2000 sun–like stars has revealed 97 planets (as of 2002 Nov), all residing within our Milky Way Galaxy and within ∼200 light years of our Solar System. They have masses between 0.1 and 10 times that of Jupiter, and orbital sizes of 0.05–5 AU. Thus planets occupy the entire detectable domain of mass and orbits. News & summaries about extrasolar planets are provided at: http://exoplanets.org. These planets were all discovered by the wobble of the host stars, induced gravitationally by the planets, causing a periodicity in the measured Doppler effect of the starlight. Earth–mass planets remain undetectable, but space–based missions such as Kepler, COROT and SIM may provide detections of terrestrial planets within the next decade.The number of planets increases with decreasing planet mass, indicating that nature makes more small planets than jupiter–mass planets. Extrapolation, though speculative, bodes well for an even larger number of earth–mass planets. These observations and the theory of planet formation suggests that single sun–like stars commonly harbor earth–sized rocky planets, as yet undetectable. The number of planets increases with increasing orbital distance from the host star, and most known planets reside in non–circular orbits. Many known planets reside in the habitable zone (albeit being gas giants) and most newly discovered planets orbit beyond 1 AU from their star. A population of Jupiter–like planets may reside at 5–10 AU from stars, not easily detectable at present. The sunlike star 55 Cancri harbors a planet of 4–10 Jupiter masses orbiting at 5.5 AU in a low eccentricity orbit, the first analog of our Jupiter, albeit with two large planets orbiting inward.To date, 10 multiple–planet systems have been discovered, with four revealing gravitational interactions between the planets in the form of resonances. GJ 876 has two planets with periods of 1 and 2 months. Other planetary systems are “hierarchical”, consisting of widely separated orbits. These two system architectures probably result from gravitational interactions among the planets and between the planets and the proto-planetary disk out of which they formed.
Aperture synthesis observations of Orion-KL in CS lines and 3mm continuum
Authors: Murata Y. , Kawabe R. , Ishiguro M. , Hasegawa T. , Hayashi M. 
Published: June 2019

We have made aperture synthesis maps toward the Orion-KL nebula in CS(1-0), CS(2-1) and 3mm continuum with the Nobeyama Millimeter Array (NMA). The CS(1-0) maps were obtained across the central 2′ region of the Orion-KL nebula. Our maps show the rotating disk around the KL nebula with the diameter of 0.3 pc and the mass of 25 M⊙. The disk clearly shows the Keplerian rotation, which indicates that the mass of the KL nebula is 100 — 150 M⊙. The shell structure around the molecular outflow is also found in CS(1-0) map. This structure also appears in CS(2-1) map.From 3mm continuum map, we have found at least six continuum sources. One of them is f-f emission from the ultra-compact HII region around BN. Other sources are the dust clumps whose masses are estimated to be 1 — 4 M⊙. The distribution of the dust clumps shows clear anti-correlation with the 20 μm emissions. This indicates that the 20 μm emissions are obscured by these dust clumps.
A very straight and collimated outflow in the core of OMC-1
Authors: Schmid-Burgk J. , Güsten R. , Mauersberger R. , Schulz A. , Wilson T. L. 
Published: June 2019

We have recently discovered a large-scale (200″) outflow system in the core of OMC-1 (fig. 1), centered about 100″ South of IRc2 and extending over some 120″ (red lobe) resp. 60″ (blue) along a position angle of —31° (Schmid-Burgk et al. 1990). The blue lobe which might actually protrude into the HII region M42 is poorly defined in CO 2-1, but the red lobe reveals a number of remarkable properties which we summarize here:The outflow is very straight and smooth. Over the full length of 120″, the center of any cross scan deviates by not more than about 1″ from a straight line. This line passes to within 2″ the peak of the submm source FIR4 of OMC-1 (Mezger, Wink and Zylka 1990) and the mm continuum peak CS3 (Mundy et al. 1986); it also cuts across the red and blue SiO-outflow lobes recently discovered some 5-10″ to either side of FIR4 (Ziurys, Wilson and Mauersberger 1990). It thus seems that the “base” of our large-scale CO jet can be seen as well.
On the Nature of the Emission of the Crab Nebula
Authors: Shklovsky I. S. 
Published: June 2019

The emission of the Crab Nebula is perhaps connected with the internal motions of the gas. As shown by the observations, the power of the emission sources differs by some hundred times in different points of the amorphous mass (“wisps” and other details). Oort and Walraven believe the “wisps” to be condensations of relativistic electrons ejected from the central star. However, there are some other variable details elsewhere in the nebula (as described by Lampland, and Oort and Walraven).Oort and Walraven's hypothesis met some important difficulties: (a) the direction of the magnetic lines in this region of the nebula is perpendicular to the wisp's velocity; (b) the dimension of the wisp is about three light months, while it appears during a month and faster, so that the relativistic electrons moving along the lines of force have no time to spread along the wisp; and (c) if the strength is not changing, the energy of the relativistic electrons in the wisp must be some hundred times greater than the density of the magnetic energy, consequently the field strength must grow in the wisp to keep the electrons in the volume.
Secular Motions of Extragalactic Radio-Sources and the Stability of the Radio Reference Frame
Authors: Eubanks T.M. , Matsakis D.N. , Josties F.J. , Archinal B.A. , Kingham K.A. , Martin J.O. , McCarthy D.D. , Klioner S.A. , Herring T.A. 
Published: June 2019

The best current approximation to an inertial reference frame is provided by Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources with red shifts (z) up to 3.8. The stability of the resulting reference frame directly depends on the amount of any secular changes in the observed source positions.Two types of potentially observable secular motions should be present in extragalactic source positions. Gravitational accelerations of the solar system will cause secular motions through aberration, amounting to, e.g., about 4 microarcsec (μas) year–1 due to the mass of the galaxy. Extragalactic mass concentrations will cause gravitational deflections in the apparent positions of more distant radio sources, and these will change with time as the mass concentrations evolve. This effect could easily cause secular motions of order 1 μas year–1 in some, or even most, radio sources with z ≥ 1.The present astrometric VLBI data set contains about one million observations over a 15 year period, with current source proper motion formal errors being as small as 2.5 μas year–1. Proper motion estimates from these data reveal many sources with statistically significant proper motion estimates of order 30 μas year–1, about an order of magnitude larger than expected. Work continues to determine if the observed motions are due to systematic errors or reflect true secular changes in source positions. The results from a continued proper motion analysis of the complete astrometric VLBI data set will be presented.
Some Physical Parameters and UVBY β Photometry of Trapezium Type Multiple Systems
Authors: Salukvadze G.N. , Javakhishvili G. Sh. 
Published: June 2019

The presented paper deals with the results of electrophotometric observations of 59 components of 19 trapezia in Strömgren and Crawford six-colour photometric system. The multiple systems, selected from the Abastumani Catalogue of Trapezia (Salukvadze, 1978), are: ABAO 2, 8, 34, 48, 51, 62, 75, 94, 245, 312, 313, 316, 324, 348, 356, 363, 387, 396.Observations were made on the 125-cm mirror telescope with the use of a one-channel photometer, based on photon counting, with diaphragms 10″ and 20″. Reduction was done on the Observatory computer with a procedure described by Salukvadze and Javakhishvili (1989).We calculated the indices [m1],[c1] and [u-b] as in (Strömgren 1967, Philip and Egret 1980). The unreddened indices (b-y), m1 and c1 were calculated by the formulae of Crawford (1975).Semi-empirical calibrations for effective temperature, bolometric correction and mass for early-type stars, using Strömgren photometric indices c0 and beta, are given by Balona (1984). In order to determine absolute magnitudes we used the calibration from Balona and Shobbrook (1984).
The Hubble Constant and the Deceleration Parameter
Authors: Tammann G. A. 
Published: June 2019

A preliminary report is given of recent work with A. Sandage on the Hubble constant. Through a chain of distance indicators in Sc and Ir galaxies (cepheids, brightest stars, H iiregions, and luminosity classes) the distance scale is carried beyond any possible local anisotropy of the velocity field. Special care is taken to allow for the dependence of the intrinsic properties of the distance indicators on the size of the parent galaxy, and for the effect of the Malmquist correction.H0is found to be 55 ± 7 km s-1Mpc-1; within the errors no systematic changes with distance were found.Aformalvalue of the deceleration constantq0= 1 ± 1 was recently derived by Sandage (1972a) and Sandage and Hardy (1973). The most important correction to this value is probably the luminosity evolution of galaxies, which tends to pushq0below 0.5. The ensuing evidence for anopen universeis also favored by independent arguments.
A κ-ϵ Model of the Lower Overshoot Layer
Authors: Petrovay K. 
Published: June 2019

One region where discrepancies between the seismic and standard solar models continue to exist is the overshoot layer below the convective zone (Gough et al. 1996). A main reason for this discrepancy is clearly the lack of a realistic physical model for astrophysical overshoot. Beside numerical experiments, the most promising approach to the construction of such a model is based on the Reynolds-stress formalism of turbulence theory (Speziale 1991). As a first step toward the development of a more complete Reynolds stress model of the overshoot, here we present a simple κ-ϵ model, valid under the following conditions:
(a).Incompressibility: ∂iVi = 0. Owing to the short length scale (cf. Fig. 1), this assumption is somewhat better founded here than in other models.(b).Closure: Let and . (w = vz vertical velocity; κ ≡ V2/2: kinetic energy; ϵ: dissipation rate). Now assume Cwk = const., Cwt =const. This is warranted if l/Hv ≃constant (Hv: scale height of V2), which will be seen indeed to be the case in our model, cf. eqs. (3)–(4).(c).No correlation with thermodynamic fluctuations: . The assumption implies that these correlations vanish in a very thin (≪ Hp) transition layer below △▽ = 0. No change in the geometrical flow properties is expected in such a thin layer, so lo, Cwk, and Cwϵ should be the same as in the lower part of the unstable layer. On the basis of numerical experiments here we use lo = HP, Cwk = 0.6, Cwϵ = 3, q = 2.4. (The index ‘0’ refers to values at z = 0 i.e. at △▽ = 0.) Note however that V may be significantly reduced in the transition layer, so Vo (and thus ) is undetermined in the present model.
Stellar velocity distribution in the presence of scattering massive clouds
Authors: Renz W. 
Published: June 2019

The purpose of this contribution is to show1. a systematic perturbation-theoretical method of solving multivariate Fokker-Planck equations (FP eq.) as they appear in galactic dynamics.2. that it is not only important to consider the cooling of the stellar disk by birth of new stars but also to include stellar death processes in the equation. This leads to different stellar velocity distributions.3. that the input of new stars into circular orbits as it is done in recent numerical work (Sellwood and Carlberg, 1983) leads not only to the cooling effect wanted but also to an additional damping effect on spiral waves.