bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium Problem in a Rotating Convection Zone
Authors: Vandakurov YU. V. 
Published: July 2016

Taking into account effects produced by the convective motions, the equilibrium problem for a rotating star becomes greatly complicated. We consider this problem for the case of slow rotation in the following approximations.We treat the convection zone as a medium with turbulent viscosity and turbulent thermal conductivity. However, we take into account the nonlinear effects produced by the most rapidly growing perturbations. The corresponding nonlinear terms are calculated by using the solution of linear perturbed equations. Each independent convective mode is supposed to have initially the same amount of kinetic energy.In the limit of small turbulent viscosity, we show that unstable convective perturbations produce a mean azimuthal force due to which rigid rotation appears not to be in the equilibrium. For the case of small-scale perturbations and latitudinal differential rotation, this force is analogous to the viscous force, but the coefficient of viscosity is negative.We suggest that such a force maintains the differential rotation of the solar convection zone. Note that in the case under consideration the latitudinal dependence of the solar heat flux is small. However, difficulties arise due to different conditions at different depths in the convection zone. In this connection, a hypothesis is put forward that magnetic fields are also necessary to get balance in full. A model of the solar cycle is discussed which is similar in some respects to the well-known Babcock model. We propose, however, that the field reversal takes place in the lower layers of that zone where fields are intensified.
On Fast Magnetic Field Reconnection
Authors: Priest E. R. , Soward A. M. 
Published: July 2016

The first model for ‘fast’ magnetic field reconnection at speeds comparable with the Alfvén speed was put forward by Petschek (1964). It involves one shock wave in each quadrant radiating from a central diffusion region and leads to a maximum reconnection rate dependent on the electrical conductivity but typically of order 10-1 or 10-2 of the Alfvén speed. Sonnerup (1970) and Yeh and Axford (1970) then looked for similarity solutions of the magnetohydrodynamic equations, valid at large distances from the diffusion region; by contrast with Petschek's analysis, their models have two waves in each quadrant and produce no sub-Alfvénic limit on the reconnection rate.Our approach has been, like Yeh and Axford, to look for solutions valid far from the diffusion region, but we allow only one wave in each quadrant, since the second is externally generated and so unphysical for astrophysical applications. The result is a model which qualitatively supports Petschek's picture; in fact it can be regarded as putting Petschek's model on a firm mathematical basis. The differences are that the shock waves are curved rather than straight and the maximum reconnection rate is typically a half of what Petschek gave. The paper is a summary of a much larger one (Soward and Priest, 1976).
On the Dipole-Like Progressive Wave in the Photosphere
Authors: Csada I. K. 
Published: July 2016

Statistical analysis of the photospheric magnetic field averaged over 27 day time intervals shows periodical variations. The results of such an analysis are usually considered to be a pure mathematical representation of the observation material and additional analysis is necessary to infer the physical meaning of the results. Some ideas for this analysis are given by the mathematical method of the ‘non-axisymmetric dynamo’ theories which suggest the representation of the field by the series
i.e. the field variation is equivalent to the interference of progressive wave moving parallel to the equator with velocity
If n = 1 the variation is equivalent to a progressive dipole field circulating over the photosphere by a time 2π/Ω and this period can be derived from the 27-day averages. The superimposition of the circulation to the rotation will result in the apparent ‘field rotation’ being observable as recurrence time of the largest magnetic areas. Observational evidences are found for a progressive dipole circulating in a great circle with a period of 4⅙ yr.The higher multipole field components (if n ≥ 2) have no characteristic variations but their mean effect results in statistical spread in the ‘multipole field rotation’.
Flare Colours and Luminosities
Authors: Cristaldi S. , Rodonò M. 
Published: July 2016

Flare colours determined from simultaneous UBV observations made at Catania Observatory and from sequential UBV observations made at McDonald Observatory are presented. They fit fairly well with the theoretical colours computed according to the Gurzadian's (1970) non-thermal model. Only part of the observed flare colours are consistent with the solar type models by Gershberg (1967) and Kunkel (1970).From a B-band patrol of UV Cet-type stars carried out from 1967 to 1972, some quantitative estimates of flare frequencies and luminosities and of their average contribution to the stellar radiation are given.The corresponding parameters for the Sun, which were estimated from ‘white light’ flare activity, are also given for comparison. The Sun and V 1216 Sgr can be regarded as low-activity flare stars of the type found by Kunkel (1973).
Some Statistics of Southern R Coronae Borealis Variables
Authors: Sherwood Vicki E. 
Published: July 2016

UBV observations of RCB stars with δ⩽30° were made at La Silla, Chile in the summer of 1972. Of 26 stars, 5 were below maximum brightness, including R CrB and RY Sgr. On the basis of a comparison of the dispersion in observations of the RCB stars and nearby non-variable comparison stars, 9 RCB stars were found to show significant variation at maximum brightness. They are W Men, UX Ant, UW Cen, DY Cen, AE Cir, S Aps, RT Nor, RZ Nor, and V CrA. The amplitude of these variations ranges from to and tentative periods from 19 to 54 days and > 90 days for S Aps. Similar variations at maximum are already known for R CrB, RY Sgr and XX Cam. Of the 5 stars which showed no significant variation at maximum, DZ And, Z Cir and V 973 Oph (see Orlov and Rodriguez, and Feast, this Symposium) are not RCB stars and SY Hyi is a questionable RCB star; only Y Mus is listed as a definite RCB variable.4 RCB stars in the Large Magellanic Cloud were observed: W Men, SY Hyi, HV 5637, and HV 12842. Absolute magnitudes at maximum of and respectively were derived. When plotted on a colour-colour diagram, most of these stars show an UV-excess for average colours at maximum. In the H-R diagram, they fall in a region where one would expect to find stars which are losing mass.
Spectroscopic Observations of Nova Cephei 1971
Authors: Rosino L. 
Published: July 2016

Spectroscopic observations of Nova Cep 1971 in the visual and infrared regions were carried out at Asiago from July to December 1971. The spectra were characterized at first by the presence of wide emission bands of moderate excitation (H, OI, NI, FeII) accompanied by two absorption systems with mean radial velocity −1300 km s−1 and −2200 km s−1. The velocity was increasing with time. The absorption spectrum disappeared in September and soon the nova entered the nebular stage. The HeI flash was observed in mid-September. In the following months the degree of excitation was steadily increasing. The nebular [OIII] lines became outstanding, even stronger than Hα and the spectrum was characterized by forbidden and permitted lines of relatively high ionization potential (O II, O III, N II, N III, He II).The profiles of the emission bands were complex from the beginning, with a strong central peak. Later, most of the bands split into two separate components, with radial velocities ± 1360 km s−1.The light curve was that of a relatively fast nova. The minimum, B∼ 17.5, was attained in the first half of 1973.
A Survey of Hα in the Brighter Northern Be Stars
Authors: Bidelman William P. , Weitenbeck Anthony J. 
Published: July 2016

Hα observations have been made of the stars brighter than mv = 7.5 and north of δ = −30° contained in the three classical Be-star catalogues of Merrill and Burwell. At least one observation of each star was made at each of the two epochs 1958/9 and 1970/2 at the Lick Observatory and at the Warner and Swasey Observatory respectively. The dispersions used were 88 Å mm−1 at Lick and 66 Å mm−1 and 18 Å mm−1 (with image tube) at Warner and Swasey.Results were as follows: The total number of objects observed was 215. Of these, 32 were supergiants and will be discussed later. Another 16 stars were deemed abnormal in some manner (helium and/or forbidden emission, composite spectrum, markedly violet-displaced Hα emission component: an interesting group of five stars including the nebular variable AB Aurigae). Thirteen of the stars showed no emission at either epoch. Of the 154 presumably normal low-luminosity stars showing emission, 70 displayed shell structure in Hα at one or both epochs, though in over half of these cases the shell absorption was considered ‘weak’. Thirty of the 70 stars varied in their shell characteristics between the two epochs. The total number of stars whose Hα line varied in some respect was 43, or 26 percent of the 167 normal low-luminosity stars observed. Quite a number of the stars observed have been reported to show shell characteristics by others but were not so noted by us.Eight additional Be stars not contained in the Merrill-Burwell catalogues have also been observed. Seven of these are shell stars; the other is the unusually high latitude object HD 127617.It is a pleasure to acknowledge that many of the Lick observations were made by Dr Jack E. Forbes, a graduate student at the time in the Department of Astronomy at the University of California, Berkeley.
Photographic Infrared Spectroscopy and Near Infrared Photometry of Be Stars: (Review Paper)
Authors: Swings J. P. 
Published: July 2016

As the title indicates two topics will be tackled in this presentation: spectroscopy and photometry. Let us therefore define first what ‘infrared’ means for these two subjects. I chose the following definitions:
– photographic infrared spectroscopy: wavelengths Hα ≤ λ < 1.2 μ– near infrared photometry: wavebands: 1.6 μ ≤ λ ≤ 20 μ
Energy Transfer in Contact Binaries
Authors: Moses A. P. , Smith R. C. 
Published: July 2016

The anomalous mass-luminosity relation for the components of a contact binary system is usually explained by postulating strong energy transfer from the primary to the secondary. It has been assumed that the transfer occurs in the common convective envelope surrounding the two stars, but so far the only attempt at a model for the energy transfer has been the sideways convection model of Hazlehurst and Meyer-Hofmeister (1973), which assumes a large-scale circulation of material between the two components.Any detailed discussion of the dynamics in the common envelope must take account of the predominantly vertical motions associated with normal thermal convection, of Coriolis forces and of viscosity. We have constructed an approximate model for the horizontal transfer of energy between the two components, using a mixing-length approach and taking all three factors into account. The major factors are the vertical convection and the Coriolis forces, which together prevent a large-scale circulation of the type proposed by Hazlehurst and Meyer-Hofmeister. Instead, the flow breaks up into smallscale eddies whose horizontal scale is determined by the interaction of convection, Coriolis forces and viscosity. This has the important qualitative consequence that horizontal energy transfer will occur only if the mean horizontal pressure gradient between the two stars exceeds a certain minimum value. This condition can easily be satisfied in the adiabatic zone of the envelope, but may be an important restriction in the super-adiabatic zone.Using our model, we were able to estimate the entropy difference between components which is required to transfer enough energy to explain the observed mass-luminosity relation. We found that equal entropy models are possible only if the contact is deep. Unequal entropy models are possible for any degree of contact, so long as the contact extends down as far as the adiabatic zone. If, as has been suggested, the depth of contact increases during evolution then zero-age models must have shallow contact and hence unequal entropies. Deep contact equal entropy models would then form as a result of evolution.A difficulty is that in our model insufficient energy transfer can occur in the super-adiabatic zone to produce WUMa light curves for the unequal entropy models. This may mean that further work is needed on the exact surface conditions in these stars.
“Three-integral”, collision-free statistical mechanics and stellar systems
Authors: Innanen K. A. 
Published: July 2016

In a recent paper, Innanen and Papp (1977) have introduced and discussed the behaviour of a function they called the “super angular momentum,” ht2. This quantity, although not formally an integral of motion in the classical definition, is nevertheless a straightforward generalization of the classical total angular momentum. The super angular momentum, together with the other two classical invariants, the total energy E, and the Z component of the angular momentum hZ lead to the introduction for each homogeneous stellar system of a new collision-free distribution function

and fo, β and γ are constants. The function f satisfies the fundamental equation of stellar dynamics and shows that the velocity dispersions of stellar systems cannot be isotropic, but rather that
(a)the velocity dispersion in the radial direction is constant (i. e. “isothermal”) and(b)the velocity dispersions in the tangential directions follow the law
That is, the tangential components are “isothermal” at the centre of the system, and decay according to the above equation so as to leave a purely radial distribution in the outer parts.
Correlation Functions for the Gravitational Force
Authors: Cohen L. 
Published: July 2016

Spatial and time correlations of the force acting on a star are derived for finite gravitational systems. It is shown that their behavior is qualitatively different than that for infinite mediums.The dissolution time for a binary system is considered. We explain why Chandrasekhar's dissolution time differs from that given by Ambartsumian and Oort in that it does not depend on the velocities of the field stars. We show that the difference lies in the definition of what constitutes ‘relative change in velocity’ of the two stars in the binary. Indeed, using the general approach of Chandrasekhar and von Neumann (appropriately modified) we derive a velocity dependent dissolution time.
Cosmological Information from New Types of Radio Observations
Authors: Saslaw William C. 
Published: July 2016

To have squeezed the Universe into a ballTo roll it toward some overwhelming question.T. S. EliotSo far, we have mainly discussed what might be called classical methods for investigating cosmological models using radio observations. These mostly involve the number counts as a function of measured flux, angular diameters, and spatial distribution of radio sources at cosmological distances, as well as the measurements of the microwave background. In this review, I have been asked to give a brief description of some new, or non-classical, measurements that might be made. It seems that such measurements fall into one of three categories: Observations which are being made now and which may bear fruit in the next several years, observations which may be possible in the intermediate future several decades from now, and observations which may be possible in the far future - if ever. Naturally I'll try to concentrate on the first two categories since they will be of more interest to most living astronomers during their working lifetimes. Also, since time is short and it is very difficult to predict the future, I'm afraid that this review will be somewhat impressionistic rather than exhaustive. I hope people will describe additional methods during the discussion.
Observational Data on Novae and Supernovae
Authors: Mustel E. R. 
Published: July 2016

The first half of the paper contains a discussion of the chemical composition of the envelopes of supernovae for the period close to light maximum. The principal conclusions are: The abundance of hydrogen in the envelopes of type I supernovae is low, much lower than that of nitrogen; the abundance of oxygen and carbon is also noticeably lower than that of nitrogen; it seems that there is plenty of helium and metals in these envelopes. The information for type II supernovae is more limited. But it is quite certain that the abundance of hydrogen in the envelopes of these stars is much higher than in the envelopes of type I supernovae.In the second half of the paper the problem of supernova remnants is discussed, the circumstellar shells around supernovae (which according to S. van den Bergh and M. Peimbert are ejected from the star before its explosion) are also included. The discussion of this problem permits to confirm again the idea that there is a very close similarity between supernovae and novae. To be more exact there are reasons to suggest that supernovae as well as novae are double star systems, that they are relatively ‘old’, that they are quite peculiar objects and that they are not the final stage of evolution of ‘normal’ stars.
26. The flux of meteors and micrometeoroids in the neighborhood of the earth
Authors: Nilsson C. S. , Southworth R. B. 
Published: July 2016

1. Radio meteor rates for a calculated mass range 10−6 gm to 10−4 gm have been recorded semi-continuously at Havana, Ill., since July 1965. Automatic equipment samples the rate at four different levels of sensitivity each half hour. A flux vs. mass power law has been derived from these data for each of a number of different weeks of observation. Between September 1965 and December 1966 the mean cumulative influx I of meteors/m2/sec/2π ster can best be described by the equation:

where m is the lower mass limit in grams.2. A micrometeoroid detection system, which hopefully was to have measured particle velocities and directions of arrival for masses greater than 10−12 gm, has been flown on the OGO-II satellite. A comprehensive in-flight calibration system has confirmed the correct operation of the experiment for more than one year in space. 700 hours of data have been analyzed and no micrometeoroid events have been observed. This excludes several hundred spurious events from the microphone sensors. The effective detection area of the instrument is 0·8 cm2 ster. Thus, to a probability of 0·86, the average flux of particles of mass greater than 10−12 gm must be less than 6 × 10−2 particles/m2/sec/2π ster.
47. Collisional model of asteroids and their debris
Authors: Dohnanyi J. S. 
Published: July 2016

A collisional model for interplanetary debris, formulated earlier by the writer, is applied presently to the problem of asteroids and their debris. Following observational evidence, a population-index type-number density function is assumed. The integro-differential equation describing the evolution of a system of colliding brittle particles derived earlier is satisfied for this special case. The result is a stable steady state solution subject to certain boundary conditions. It is found that catastrophic collisions dominate over the erosion process in the present steady state model.Using a root mean-squared average collision velocity of 5 km/sec, the population index, α, for asteroids is calculated to be α = 1·837. This value of α is rather insensitive to the physical parameters and is within the margin of error of an empirical least squares fit by the writer α = 1·80 ± ·04 to the distribution of asteroids reported by Kuiper et al. If the largest three asteroids are statistically interpreted, the distribution of asteroids in the asteroidal belt is consistent with the present collisional model. This would imply that most asteroids are fragments from some parent object(s).The theoretical distribution is normalized to the observed number of asteroids in the survey by Kuiper et al., and using the present theory various statistical properties of the population of asteroids and their debris are calculated. The total mass of objects in the asteroidal belt is almost entirely concentrated in the masses of the three largest objects. The total asteroidal mass, crushed yearly, is of the order of 1012 kg and the rate of mass loss to radiation forces is about 7 × 1010 kg/yr.The mean lifetime of large asteroids is found to be of the order of 108–109 years. The lifetime of objects is limited by the probability of catastrophic collisions; erosion and radiation damping only have a minor influence on the particle lifetimes.The erosion rate of the largest objects is of the order of 1m /106 yr, and this rate decreases for smaller objects. Comparison with erosion rates estimated by Whipple indicates that the lifetimes, with respect to erosion, of objects smaller than about 1 kg may be dominated by collisions with cometary particles.
Radio Measurements of Planetary Nebulae
Authors: Thompson A. R. 
Published: July 2016

Sixty-eight planetary nebulae have been investigated in a series of observations at 10-cm wavelength using the two 90-ft diameter antennas of the Owens Valley Radio Observatory. Of these, 52 were found to have flux densities greater than a minimum detectable level of approximately 10–27 Wm–2 Hz–1. To indicate cases of possible confusion in the radio observations, the measured radio position of each nebula was compared with an accurate optical position. For a number of the stronger nebulae angular widths in the East–West direction and flux densities at 21 cm were also measured. The results lead to the conclusion that the radio emission is thermal, and on this basis the expected flux densities in Hβ have been calculated. A comparison with optical data shows values of the Hβ extinction Δ log FHβ, ranging from zero to approximately 2·0 for NGC 6537 and NGC 6369.A small number of nebulae show prominently the effects of self-absorption in their radio spectra. For two of these, IC 418 and NGC 6572, an attempt has been made to derive accurate optical depths and electron temperatures using models based on Balmer-line isophotes. The temperature values have large uncertainties, but appear to be less than the values derived from forbidden-line ratios by a factor of at least 1·5. A possible explanation of this difference in terms of temperature variations within the nebulae is discussed.Preliminary results of observations to detect absorption features at the wavelength of the 21-cm hydrogen line are described for 6 nebulae with high radio-flux densities. Two nebulae, NGC 6369 and NGC 6857 show absorption which is probably attributable to hydrogen clouds within the galaxy. No definite evidence of absorption at frequencies near the radial velocities of the nebulae was found, and an upper limit on the mass of neutral hydrogen in two nebulae is briefly discussed.
The Interpretation of Magnetograph Results: The Formation of Absorption Lines in a Magnetic Field
Authors: Stenflo J. O. 
Published: July 2016

The theory of line formation in a magnetic field is reviewed. It is shown how the formulations by Unno, Beckers, Stepanov and Rachkovsky are related to each other. The general treatment of true absorption, anomalous dispersion, radiative scattering and level-crossing interference is discussed. Special attention is paid to the inhomogeneous nature of the solar atmosphere. The properties of magnetic filaments are reviewed. It is shown how a filamentary structure will drastically influence the interpretation of magnetograph observations. The treatment of line formation in a turbulent magnetic field is also discussed.The fine structure of the solar atmosphere will influence different types of magnetographs in entirely different ways. The relation between the observed magnetic field and the resolution of the instrument is discussed for a Babcock-type, Evans-type and a transversal magnetograph. Finally some suggestions for future work in this field are listed.