bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Coronal Rotation by the Spectroscopic Method
Authors: Stepanov V. E. , Tjagun N. F. 
Published: July 2016

Coronal rotation is different in the northern and southern hemispheres of the Sun and varies with the cycle of solar activity. A sharp decrease in linear velocity by 0.4 km s−1on the latitude and its relative constancy in the latitude interval 35° < φ < 50° are the most typical.In the southern polar region an intensive stream of coronal gas directed oppositely to the solar rotation was detected during the time interval 1969–1972. In the greater part of the latitude range, on average, the corona rotates more slowly in comparison with the solar atmosphere at the photospheric level.
Theory of Convection in a Deep Rotating Spherical Shell, and Its Application to the Sun
Authors: Gilman Peter A. 
Published: July 2016

The theory of convection in a rotating spherical shell, when applied to the Sun, should ultimately satisfy at least three broad constraints. The radial heat flux by the convection must not vary significantly with latitude; an equatorial acceleration must be produced; and the convection must give the right dynamo action to produce the gross features of a solar cycle.Important quantities to look for in the observations with which a convection theory can be compared include evidence of global velocities of giant convection cells, differences in motion features between low latitudes and high, persistence of motion features over successive rotations, evidence of excess brightness and variations in total solar luminosity, correlations of velocities between northern and southern hemispheres, and between north-south and east-west motions, and time periodic changes in motion fields.The general theory of convective motions in a rotating spherical shell such as the convection zone of the Sun has developed rapidly over the last several years, but is still a long way from providing quantitative models which agree in a satisfactory way with the main solar observations. Most work has (for mathematical reasons) employed the Boussinesq approximation, and most has been either linear or nearly so. Early work demonstrated the basic ability of global convection to transport momentum toward the equator, but whether an equatorial acceleration results depends on the effects of competing angular momentum transport processes, namely transport in the radial direction by convection, and transport by axisymmetric meridional circulations. The end result can be assessed only by nonlinear calculations.Some recent calculations directed at this question by the author indicate that, at least at Prandtl number of unity, convection growing from an initial state of solid rotation produces equatorial acceleration only when equatorial modes dominate and the rotational constraint is sufficiently strong, which results in a convective heat flux which is strongly dependent on latitude. When the rotational constraint is broken enough to give convection at all latitudes and therefore more nearly uniform heat flux, equatorial deceleration and angular momentum mixing in latitude results. A few calculations for Prandtl number substantially smaller than one give results which suggest it is possible to produce equatorial acceleration and nearly uniform heat flux, but these solutions appear not to be unique. In particular, the amount of differential rotation present in the initial conditions appears to be important in determining the final state.
Abundance Effects in Spectral Classification
Authors: Jaschek C. 
Published: July 2016

The paper attempts to put together the spectroscopic definitions used in the literature for different groups of peculiar objects linked with abundance anomalies.The groups discussed are:
O-type subdwarfsCNO starsHe-strong starsHe-weak starsB-type subdwarfsAp starsAm starsλ Boo starsδ Del starsFm starsA-F-G stars with weak metal linesStars with CN anomaliesStars with CH anomaliesBa starsIn each case the useful range in dispersion is quoted and bibliographic references are provided.
Effects of Heavy-Element Abundance on Classification of G-Type Giants
Authors: Keenan P. C. 
Published: July 2016

Five stars, including ζ Cyg, which had been classified as G6 II to G8 II bright giants, were found by O. C. Wilson to have K-line luminosities close to those of class III giants. These stars show enhancement of the lines of Ba II and other heavy-metal ions also. To eliminate the serious effect of this abundance anomaly on the spectroscopic luminosities new luminosity criteria involving only intercomparisons of lines of elements of the fourth period (Ti, Fe, etc.) were applied on 9 Å mm−1 Coudé spectrograms taken by O. C. Wilson. This Coudé classification gave luminosity classes near IIIa for these stars, implying absolute magnitudes considerably below those of bright giants but somewhat above Wilson's MK values.Another advantage of Coudé classification is the possibility of estimating luminosities for individual barium stars. From Wilson's plate of HD 205011 a luminosity class of III-IIIa is derived. This is consistent with the mean value of Mv = −0.4 derived from statistical parallaxes by MacConnell, Frye and Upgren (Astron. J. 77, (1972), 384) for the barium stars.The detailed account of this investigation will be published elsewhere.
Spectral Classification of B and A Stars from Data of S2/S68 Experiment
Authors: Cucchiaro A. , Jaschek M. , Jaschek C. , Macau-Hercot D. 
Published: July 2016

The S2/S68 experiment on the satellite TD1A has supplied, in the wavelength region of 1350 Å to 2550 Å, a very large number of spectra of early stars.A statistical study, as well as a general analysis of these spectra, has been carried out in order to establish criteria relative to the spectral region envisaged and independent of any previous study in the visible. On the basis of these criteria a system of classification has been outlined.In a first stage, the spectra of stars visually classed from B0 to A5 have been considered. From four sets of spectrophotometric criteria a two-dimensional ultraviolet classification has been derived.
On the Origin of Nova-Like Binary Systems
Authors: Gorbatsky V. G. 
Published: July 2016

Basic physical characteristics of nova-like binary systems are similar to W UMa systems. Externally, however, these systems are different – nova-like systems contain a white dwarf as a component, whereas both components of W UMa systems are near the main sequence. The hypothesis is suggested of the origin of contact W UMa systems by means of the fission of the rapidly rotating isothermal helium core of an evolved giant star. The contraction of the more massive component leads to the formation of a white dwarf and consequently to the transformation of a W UMa type system to a nova-like system.Submitted to Astrophysics and Space Science.
A Study of Be Stars in Clusters
Authors: Schild R. , Romanishin W. 
Published: July 2016

Calibrated spectrograms at Hα of 566 stars in 29 young galactic clusters led to the detection of 41 Be stars in clusters. Using cluster membership we have inferred ages and intrinsic (B – V) colors of Be stars to permit a discussion of their evolutionary states.Rotating stars can become Be stars in their early hydrogen burning evolution away from the main sequence. Both the fraction of stars showing hydrogen emission and the strength of emission appear to vary little during the first 80% of post main sequence evolution. However, at the onset of gravitational core contraction, both the fraction of stars showing emission and their mean emission strength undergo a fourfold increase. Many stars in the core contraction phase develop an intrinsic (B – V) excess of 0.15 mag. due to the H− free-bound continuum radiation. Because of the great strength of Hα emission and the short time duration of the effect, the extreme Be stars would be excellent probes for studies of spiral structure and would also serve as probes for studies of ages and distances of extragalactic systems.Analysis of the corrected colors of the Be stars in clusters suggests that the Lucy and Solomon (1970) mechanism for reduction of effective surface gravity by ultraviolet resonance line scattering is probably important for the hotter Be stars. However, a discrepancy exists for the cooler stars between the predicted and observed colors.
Late Stages of Close Binary Systems
Authors: Van Den Heuvel E. P. J. 
Published: July 2016

The expected final evolution of massive close binaries (CB) in case B is reviewed. Primary stars with masses ≳ 12–15 M⊙ are, after loosing most of their envelope by mass exchange, expected to explode as supernovae, leaving behind a neutron star or a black hole.Conservative close binary evolution (i.e. without a major loss of mass and angular momentum from the system during the first stage of mass transfer) is expected to occur if the initial mass ratio q0 = M20/M10 is ≳ 0.3. In this case the primary star will be the less massive component when it explodes, and the system is almost never disrupted by the explosion. The explosion is followed by a long-lasting quiet stage (106–107 yr) when the system consists of a massive main-sequence star and an inactive compact companion. After the secondary has left the main-sequence and becomes a blue supergiant with a strong stellar wind, the system becomes a massive X-ray binary for a short while (2–5 × 104 yr).The numbers of Wolf-Rayet binaries and massive X-ray binaries observed within 3 kpc of the Sun are in reasonable agreement with the numbers expected on the basis of conservative CB evolution, which implies that several thousands of massive main-sequence stars with a quiet compact companion should exist in the Galaxy. About a dozen of these systems must be present among the stars visible to the naked eye. During the second stage of mass exchange, large loss of mass and angular momentum from the system is expected, leading to a rapid shrinking of the orbit. The supernova explosion of the secondary will in most cases disrupt the system. If it remains bound, the final system will consist of two compact stars and may resemble the binary pulsar PSR 1913 + 16.In systems with q0 ≲ 0.2–0.3 large mass loss from the system is expected during the first stage of mass exchange. The exploding primary will then be more massive than its unevolved companion and the first supernova explosion disrupts the system in most cases. In the rare cases that it remains bound, the system will have a large runaway velocity and, after a very long (108–109 yr) inactive stage evolves into a low-mass X-ray binary, possibly resembling Her X-1.
Long Propagation Periods of Residuals in the Motion of a Comet
Authors: Kiang T. 
Published: July 2016

P/Halley In a previous paper (Kiang 1973), I derived a differential equation which governs the behaviour of the residual O - C in the time of perihelion passage of a comet. The work was stimulated by the discovery (Brady 1972) that a long periodicity of about 600 years seemed to be present in the residual for P/Halley. The derivation was based on the following assumptions:
1.The system consists of only the Sun, Jupiter and P/Halley, and Jupiter is assumed to move in a circular orbit with a period P′ = 11.8614 yr.2.P/Halley is assumed to move in a fixed Keplerian orbit with a period P = (13/2) P′ exactly, so that the whole system is strictly recurrent with a period Po = 13 P′ = 154.198 yr.
Warping and thickness of galactic gas layers
Authors: van Woerden Hugo 
Published: July 2016

SummaryThe evidence for warps in the gas layers of galaxies is reviewed. Both the 21-cm line intensity distribution on the sky in edge-on systems and the hydrogen velocity fields in other systems indicate that warped gas layers are common, more common than close companions. Hence, warps probably persist for several times 109 years.The thickness of the gas layer in NGC 891 appears to increase outward, similarly to that in our Galaxy.
The Dynamical Evolution of Binaries in Clusters
Authors: Heggie D. C. 
Published: July 2016

Using information on the rates at which binaries suffer encounters in a stellar system (Heggie, 1974a), we here study the effects of such processes on the evolution of the system itself. First considering systems with no binaries initially, we show that low-energy pairs attain a quasi-equilibrium distribution comparatively quickly. Their effect on the evolution of the cluster is negligible compared with that of two-body relaxation. In small systems energetic pairs may form sufficiently quickly to exercise a substantial effect on its development and on the escape rate, but in large systems their appearance is delayed until the evolution of the core is well advanced. In that case they appear to be responsible for arresting the collapse of the core at some stage.Binaries of low energy, even if present initially in large numbers, are likely to have at most only a temporary effect on the evolution of the system. High-energy pairs are not easily destroyed, and so, if present initially, their effect is persistent. It competes with two-body relaxation especially when the fraction of such pairs and the total number-density are high, as in the core, where, in addition, binaries tend to congregate by mass segregation. When encounters with binaries become important, being mostly ‘super-elastic’ they enhance escape and lead to ejection of mass from the core into the halo, thus accelerating the rate at which mass is lost by tidal forces. It is difficult to decide observationally whether globular clusters possess sufficiently large numbers of binaries for these effects to be important.
34. Meteor mass distribution from underdense-trail echoes
Authors: Šimek M. , McIntosh B.A. 
Published: July 2016

The amplitude of meteor echoes is recorded on a logarithmic scale by a high-power radar equipment (λ = 9·2 m, PT=3 MW, G = 5·6) at Springhill Meteor Observatory near Ottawa. The smallest amplitude measured corresponds to a pulse power of 10−12 W, which represents a minimum electron line density of about 7 × 1011 el/m or a radio magnitude of + 10.Distribution curves of number of echoes as a function of echo power have been obtained from some 50 samples of 500 meteors each, at various times of day on about 1 day per month. The slopes showed little variation throughout the year. The statistical error in the slope value for any one sample was small, ~ 2–3%. However, determination of the mass index s from these slopes involves several problems. On the basis of simplest theory we have obtained for the sporadic background,

with no definite seasonal or diurnal variation.During shower periods, lower values of s were obtained. For the 1966 Leonids, s for the shower was determined by estimating the percentage of shower meteors in the total sample. A value s = 1·7 ± 0·1 was obtained as the mean of 6 samples. It is not known to what extent the height-ceiling effect influences the observation of this shower.
38. Discrimination of stream and sporadic meteors
Authors: Southworth R. B. 
Published: July 2016

Southworth and Hawkins (1963) described a criterion for distinguishing stream meteors from sporadics. A function D of the orbital elements was proposed as a measure of the difference between two orbits. A sporadic meteor was then defined as one whose difference D from all other observed meteors exceeded an empirically determined minimum. Any two meteors that differed by less than the minimum were defined to be members of the same stream.D may be taken to be a distance in a five-dimensional space, whose coordinates are orbital elements. It is now proposed that a stream would be better defined as a statistically significant concentration of meteors in this orbit-space. The procedure has been programmed for a computer, and applied to the Harvard-Smithsonian radar observations.
Review of Atomic Collision Processes
Authors: Seaton M.J. 
Published: July 2016

The following processes have to be considered.
(a)Radiative capture,
The number of captures on the level i of the atom X, per unit volume per unit time, is NeN(X+)αi(Te), where the recombination coefficient αi (cm3 sec−1) may be expressed in terms of the cross-section for photo-ionization from level i.(b)Cascade,
The coefficients α(c)i and αi′i are defined to be such that NeN(X+) α(c)i is the number of atoms entering i due to capture and cascade, and that NeN(X+) αi′i is the number of photons emitted in the i′→ i line.(c)Collisional transitions between excited states, including: collisional redistribution of angular momentum; collisional redistribution of energy between highly excited states; and collision processes which depopulate metastable states.(d)Effects of radiative transfer. The following limiting cases have been considered:
Case A: Nebulae optically thin in all spectrum lines.Case B: Nebulae optically thick for transitions to the ground state.Case C: As Case B, but with absorption of stellar quanta in transitions from the ground state, assuming the central star to radiate as a black body.
Ly-α Radiation Densities in Planetary Nebulae
Authors: Capriotti Eugene R. 
Published: July 2016

The average Ly-α radiation densities are calculated for 9 planetary nebulae from the observed λ 10830/λ5876 line-intensity ratios under the assumption that the 23S state of He I is depopulated via photo-ionization by Ly-α radiation. Three of the nebulae are probably optically thick in their respective hydrogen Lyman continua. For these objects, the Ly-α radiation densities as determined from the λ10830/λ5876 line-intensity ratios may represent the actual Ly-α radiation densities. If they do, then the Ly-α radiation pressures exceed the respective gas pressures in these objects. For the remaining nebulae, it seems that the observationally determined Ly-α radiation densities are representative only if either one or both of the following conditions is fulfilled in each case:
(1)The object is essentially optically thick in the hydrogen Lyman continuum when other properties show it to be optically thin in the hydrogen Lyman continuum.(2)We are viewing the object during a specific 100-year time span during the course of its evolution.
Prominences in active regions
Authors: Kleczek J. 
Published: July 2016

As an interplay of plasma and magnetic field the solar prominences represent a nice example of cosmical hydromagnetics. Due to stronger magnetic fields in active regions the prominence processes are more violent there than in non-active regions. Observing with a coronagraph or watching prominence movies one recognizes some characteristic processes in prominences of active regions:
(a)Condensation of Hα material in coronal space without any direct observational evidence of the material supply. It seems that the material had been ejected in the form of corpuscular radiation, captured, thermalized and cooled down to 104 °K, when it becomes observable in the Hα line.(b)Dissolution of the Hα material. Knots, streamers of sprays, surges and puffs often undergo a reverse process: they dissolve and disappear when observed in Hα. Similar dissolution is typical for a great part of the material in eruptive prominences.(c)Spiraling motion and detwisting of streamers are observed in surges, sprays, funnels and also in eruptive prominences. In the prominence movies of HAO Boulder, Sacramento Peak Observatory and Pic-du-Midi we have found many nice examples. In most cases (if not in all) the detwisting resulted in a marked simplification of the prominence structure.(d)Emerging magnetic fields may be seen in form of small rising and expanding Hα loops (velocities about 50 km/sec). In this type of loops the material is dragged out of the chromosphere. A similar process with low velocities has been observed in 5303 Å movies of coronal condensations.(e)Capture of a surge by transversal magnetic fields has been observed and photographed on October 7, 1956. Surge material has been captured in a complex loopy structure and then streamed sunwards along the loops. This event shows that capturing of plasma streamers by transversal magnetic fields does occur on the Sun and that the material supply for AS prominences (see item (a)) would thus be possible.(f)Collisional processes occur in different forms. One has been just described in item (e). However, the well-known prominence of Lyot from 1937 shows that a surge hits a prominence without being (completely) captured. The prominence which has been hit decays and the surge material seems to be reflected (at least partly) downwards. Two colliding knots may bypass each other in complicated trajectories. Cases have been recorded of falling prominence knots being stopped and accelerated upwards, with measured acceleration more than 10 solar g.(g)Oscillating prominences at the limb have been photographed. The oscillations followed shortly after a nearby flare-spray event. This may be the counterpart of the disk phenomenon discovered by astronomers of Lockheed Observatory.
Solar active regions in Mg II light
Authors: Fredga Kerstin 
Published: July 2016

During 1965 two rockets were launched in order to obtain monochromatic pictures of the Sun in the Mg II line at 2802·7 Å. The Mg II filterheliograms have been compared with simultaneous Hα and Ca II K spectroheliograms. An important observation from both flights concerns the relative intensities of different active regions. In the Hα pictures there are old fairly faint active regions and newly formed more intense regions. In the Mg II pictures, however, the older regions appear more intense than the younger regions.Different explanations for this intensity-reversal effect have been considered. The effect has also been looked for in broadband Ca II H filterheliograms, with negative results, however.
New aspects of the role of development and structure of solar active regions in the arrangements of the corona based on its geomagnetic displays
Authors: Bednářová-Nováková B. , Halenka J. 
Published: July 2016

The coronal plasma, which is the cause of geomagnetic storms, can impinge on the Earth only when some coronal formation is pointing towards the Earth. If no such formation is directed towards the Earth, a period of geomagnetic calm follows.It was found that certain coronal formations, governed clearly by the appropriate local magnetic fields, correspond to the individual stages of development of active centres. Above the sunspot groups, there occur either conical rarifications or cylindrical, condensed fluxes dependent on a relatively non-variable, or unstable magnetic field. The filaments which outlive the sunspot period, provided they are located in floccular fields, are appropriate to streamers of helmet shape. The final stage of the active region, characterized by the presence of filaments only (called ‘free filaments’ by the authors), does not change the arrangement of the corona appreciably, i.e. the normal shape, or so-called minimum type. On the basis of the mentioned relations, it is possible to determine the shape and direction of so far currently unobservable coronal structures from chromospheric situations.The mentioned facts enable a unified interpretation of the geomagnetic activity during the whole of the solar cycle to be made. The differences given for some types of storms (sporadic and recurrent, sudden and gradual commencement), may be explained by the various arrangements, occurrences or absences of local magnetic fields. The paper presents examples of chromospheric situations which were used, in some cases, at the Geophysical Institute in Prague for forecasting geomagnetic activity.