Showing papers in "The Astrophysical Journal in 1978"
TL;DR: The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars as discussed by the authors, and the value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag).
Abstract: The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars. The distance to 10 stars exceeds 2 kpc and 34 stars lie beyond 1 kpc. Stars with color excess E(B-V) up to 0.5 mag are observed. The value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag). For stars with accurate E(B-V), the deviations from this mean are generally less than a factor of 1.5. A notable exception is the dark cloud star, rho Oph. A reduction in visual reddening efficiency for the grains that are larger than normal in the rho Oph dark cloud probably explains this result. The conversion of atomic hydrogen into molecular form in dense clouds was observed in the gas to E(B-V) correlation plots. The best estimate for the mean total gas density for clouds and the intercloud medium, as a whole, in the solar neighborhood and in the plane of the galaxy is 1.15 atoms per cu. cm; those for the atomic gas and molecular gas alone are 0.86 atoms per cu cm and 0.143 molecules per cu cm respectively. For the intercloud medium, where molecular hydrogen is a negligible fraction of the total gas, atomic gas density was found to equal 0.16 atoms per cu cm with a Gaussian scale height perpendicular to the plane of about 350 pc, as derived from high latitude stars.
2,625 citations
TL;DR: In this article, a new mechanism is proposed for acceleration of a power-law distribution of cosmic rays with approximately the observed slope, where high-energy particles in the vicinity of a shock are scattered by Alfven waves carried by the converging fluid flow leading to a first-order acceleration process in which the escape time is automatically comparable to the acceleration time.
Abstract: A new mechanism is proposed for acceleration of a power-law distribution of cosmic rays with approximately the observed slope. High-energy particles in the vicinity of a shock are scattered by Alfven waves carried by the converging fluid flow leading to a first-order acceleration process in which the escape time is automatically comparable to the acceleration time. Shocks from supernova explosions propagating through the interstellar medium can account for the acceleration of galactic cosmic rays. Similar processes occurring in extragalactic radio sources can lead to efficient in situ acceleration of relativistic electrons.
1,776 citations
TL;DR: In this paper, a method of abundance determination based on reddening independent properties of low-resolution spectral scans is described and applied to 177 red giants in 19 globular clusters, most of which are at galactocentric distances in excess of 8 kpc.
Abstract: A method of abundance determination based on reddening-independent properties of low-resolution spectral scans is described and applied to 177 red giants in 19 globular clusters, most of which are at galactocentric distances in excess of 8 kpc. The general properties of the halo-cluster system inferred from the abundance results are examined. It is found that the distribution over abundance of the halo globular clusters is independent of galactocentric distance for distances exceeding 8 kpc and that the clusters exhibit differences in the morphology of their color-magnitude diagrams that are uncorrelated with metal abundance. The characteristics of the system of halo clusters are compared with implications of some simple conceptual schemes for the formation of the Galaxy. It is suggested that the halo clusters originated within transient protogalactic fragments that gradually lost gas while undergoing chemical evolution and continued to fall into the Galaxy after the collapse of its central regions had been completed.
1,568 citations
TL;DR: In this article, the authors derived a period determination technique that is well suited to the case of nonsinusoidal time variation covered by only a few irregularly spaced observations and applied it to the doublemode Cepheid BK Cen.
Abstract: We derive a period determination technique that is well suited to the case of nonsinusoidal time variation covered by only a few irregularly spaced observations. A detailed statistical analysis allows comparison with other techniques and indicates the optimum choice of parameters for a given problem. Application to the double-mode Cepheid BK Cen demonstrates the applicability of these methods to difficult cases. Using 49 photoelectric points, we obtain the two primary oscillatory components as well as the principal mode-interaction term; the derived periods are in agreement with previous estimates.
1,536 citations
TL;DR: In this paper, an analytical model for the quiescent inhomogeneous solar corona is developed on the basis of the hypothesis that looplike structures are the basic coronal building blocks.
Abstract: An analytical model for the quiescent inhomogeneous solar corona is developed on the basis of the hypothesis that looplike structures are the basic coronal building blocks. By assuming that quiescent loop structures observed in X-rays are in hydrostatic equilibrium, it is demonstrated that such loops must have their temperature maximum located near their apex and that substantial nonradiative energy deposition must occur along most of their length. The calculations yield a unique relation among loop temperature, pressure, and size, which fits the X-ray observations of quiescent structures well and is consistent with the initial assumption of hydrostatic equilibrium. The results suggest that the coronal loops visible in X-rays represent a relatively steady-state equilibrium of the confined plasmas and that fluctuations in such quantities as the local heating rate can lead to dynamically unstable states in which the loop plasma does not attain a temperature sufficient for X-ray emission. A parameterization of various proposed coronal heating theories is also developed within the context of the analytical model.
1,409 citations
TL;DR: The work described here is still in progress as discussed by the authors, hence this paper will be a brief sampling of the results to date, as well as a summary of the work described in this paper.
Abstract: The work described here is still in progress; hence this paper will be a brief sampling of the results to date.
811 citations
TL;DR: In this paper, a program of two-color photometry of very distant (z greater than or equal to 0.4) clusters of galaxies, using the KPNO ISIT vidicon, is presented.
Abstract: First results are presented of a program of two-color photometry of very distant (z greater than or equal to 0.4) clusters of galaxies, using the KPNO ISIT vidicon. It is demonstrated that the ISIT system is capable of accurate photometry of faint (V approx. 23.5) galaxies in exposure times of about 1 hour on a 2.1-m telescope. Photometry is presented for two clusters, Cl 0024 + 1654 (z = 0.39) and the cluster around 3C 295 (z = 0.46). Both clusters are rich, centrally condensed systems similar to the Coma cluster. However, in contrast to nearby clusters of this type, which contain only elliptical and S0 galaxies, between one-third and one-half of the galaxies in these two distant clusters have the colors of spiral galaxies. The possible implications of this result for the evolutionary history of S0 galaxies are discussed. 17 figures, 3 tables.
656 citations
645 citations
TL;DR: In this paper, a numerical model that incorporates both implicit hydro-dynamics and a detailed treatment of nuclear reactions was proposed for population I stars of 15 M/sub sun/ and 25 M/ sub sun/ with photospheric radii of 3.9 x 10/sup 13/ cm and 6.7 x 10 /sup 13 / cm, respectively.
Abstract: Population I stars of 15 M/sub sun/ and 25 M/sub sun/ have been evolved from the zero-age main sequence through iron core collapse utilizing a numerical model that incorporates both implicit hydro-dynamics and a detailed treatment of nuclear reactions. The stars end their presupernova evolution as red supergiants with photospheric radii of 3.9 x 10/sup 13/ cm and 6.7 x 10/sup 13/ cm, respectively, and density structures similar to those invoked to explain Type II supernova light curves on a strictly hydrodynamic basis. Both stars are found to form substantially neutronized ''iron'' cores of 1.56M/sub sun/ and 1.61 M/sub sun/, and central electron abundances of 0.427 and 0.439 moles g/sup -1/, respectively, during hydrostatic silicon burning. Just prior to collapse, the abundances of the elements in the 25 M/sub sun/ star (excluding the neutronized iron core) have ratios strikingly close to their solar system values over the mass range from oxygen to calcium, while the 15 M/sub sun/ star is characterized by large enhancements of Ne, Mg, and Si. It is pointed out on nucleo-synthetic grounds that the mass of the neutronized core must represent a lower limit to the mass of the neutron star or black hole remnant thatmore » stars in this mass range can normally produce.« less
639 citations
TL;DR: In this article, a first-order mass and energy-balance model is developed for steady-state EUV 'coronal rain' loops that are not associated with postflare events and are often seen over sunspot umbrae.
Abstract: A first-order mass- and energy-balance model is developed for steady-state EUV 'coronal rain' loops that are not associated with postflare events and are often seen over sunspot umbrae. The model disregards variations in a loop's thermodynamic and magnetic properties along magnetic-field lines and yields average properties of the resonant absorption sheath, the boundary layer, and the loop's interior. Both irreversible heating by Alfvenic surface waves and energy transport via induced boundary-layer convection are taken into account in the analysis. Results that include predictions of the temperatures of the sheath and the boundary-layer plasma, the temperature of the interior plasma, the radiative output of the loop, and the filling factor associated with this radiation are given in terms of the period and velocity amplitude of the relevant surface wave as well as various parameters that characterize a typical 'coronal rain' loop. These results are shown to be consistent with the observed minimum and maximum temperatures as well as the radiative output of typical 'coronal rain' loops.
595 citations
TL;DR: For a sample of 10 high-luminosity spiral galaxies, Sa through Sc, this article obtained accurate rotation curves which extend to about 80% of the de Vaucouleurs radii.
Abstract: For a sample of 10 high-luminosity spiral galaxies, Sa through Sc, we have obtained accurate rotation curves which extend to about 80% of the de Vaucouleurs radii.
TL;DR: In this paper, the authors considered the effect of gravity and viscosity on the stability of rotating self-gravitating fluids and found that all rotating stars are unstable or marginally unstable to gravitational radiation, and the corresponding stability criterion is involved the canonical energy in a rotating frame, E/sub c/,R, a functional invariant under gauge transformations associated with the trival displacements.
Abstract: The effect of gravitational radiation and of viscosity on the stability of rotating self-gravitating fluids is considered. Previous cirteria governing secular stability to radiation are shown to fail as a result of the trival displacements introduced in a previous paper (1). The required modification is obtained by describing perturbations in terms of canonical displacements (displacements orthogonal to the trivials). There nevertheless remain physical perturbations having angular dependence e/sup i/mphi which, for sufficiently large m, make the stability functional (the canonical energy E/sub c/) negative, and it follows that all rotating stars are unstable or marginally unstable to gravitational radiation. In the case of stability against viscosity, the corresponding stability criterion is shown to involve the the canonical energy in a rotating frame, E/sub c/,R, a functional invariant under gauge transformations associated with the trival displacements. By using the functional E/sub c/,R to analyze local stability, it is found that a star is locally stable against viscosity if and only if the special entropy increases outward (in the sense of decreasing pressure). Finally, the behavior of normal modes is discussed and used to elucidate the generic radiation-induced instability; and certain orthogonality properties are derived.
TL;DR: In this article, the stellar wind from a red giant produces an extensive circumstellar cool nebula of appreciable mass, and it is shown that such a shell, when ionized by radiation from the central star, has the characteristics of a planetary nebula.
Abstract: The stellar wind from a red giant produces an extensive circumstellar cool nebula of appreciable mass. We suggest that in some cases mass loss continues until the hot core of the star is exposed, and that the stellar wind from the remnant star collides with the circumstellar nebula, producing a relatively dense shell of gas which increases in mass and radius at a constant rate. It is shown that such a shell, when ionized by radiation from the central star, has the characteristics of a planetary nebula. V 1016 Cygni is used as an example of a star which has recently undergone the transition from a red giant to a young low-mass planetary nebula.
TL;DR: The cooling produced by line emission from a variety of molecular and atomic species, including those observed as well as theoretically expected in dense interstellar clouds, was analyzed in detail in this article, and the contribution of a number of gas heating machanisms which may be present in interstellar clouds including heating by cosmic rays, H/sub 2/ formation, gravitational collapse, and magnetic ion-neutral slip heating.
Abstract: We analyze in detail the cooling produced by line emission from a variety of molecular and atomic species, including those observed as well as theoretically expected in dense interstellar clouds. At molecular hydrogen densities less than 3 x 10/sup 4/ cm/sup -3/ and kinetic temperatures between 10 K and 40 K, /sup 12/CO is the dominant coolant. At n (H/sub 2/) =3 x 10/sup -3/, however, C c, O/sub 2/, and the rarer isotopic species of carbon monoxide together contribute half of the total cooling. As n (H/sub 2/) is increased beyond 3 x 10/sup 4/ cm/sup -3/, a large number of species including water, hydrides, molecular ions, and less abundant diatomic molecules collectively dominate the cooling. The cooling per H/sub 2/ molecule, ..lambda../n (H/sub 2/), is only very weakly density-dependent for n (H/sub 2/) greater than a few times 10/sup 2/ cm/sup -3/. At a density of 4 x 10/sup 3/ cm/sup -3/, ..lambda..=2.6 x 10/sup -26/T/sub kin//sup 2.2/ ergs cm/sup -3/ s/sup -1/. The rate of energy transfer by dust-gas collisions results in infrared emission by dust grains being a significant coolant for the gas only for n (H/sub 2/) >1.5 x 10/sup 4/ cm/sup -3/. We evaluatemore » the contribution of a number of gas heating machanisms which may be present in interstellar clouds including heating by cosmic rays, H/sub 2/ formation, gravitational collapse, and magnetic ion-neutral slip heating. For clouds with kinetic temperatures approx.10 K, cosmic ray heating alone may be sufficient to balance the gas cooling for 3 x 10/sup 2/< or =n (H/sub 2/) < or =10/sup 4/ cm/sup -3/, these conditions being in good agreement with the observationally determined characteristics of dark clouds.« less
TL;DR: In this article, the authors present further results of the Hercules X-1 balloon observation on 1976 May 3 which confirm the existence of a strong line feature at approx.58 keV in the pulsed (1.24s) X-ray spectrum.
Abstract: We present further results of our Hercules X-1 balloon observation on 1976 May 3 which confirm the existence of a strong line feature at approx.58 keV in the pulsed (1.24s) X-ray spectrum we reported earlier. The spectral excess in the line region over the extrapolated continuum is 5-6 sigma. Our best estimates of the line flux and line width are 3 x 10/sup -3/ photons cm/sup -2/ s/sup -1/ and less than approx.12 keV, respectively. The most likely interpretation of this line is electron cyclotron emission at the basic frequency from the hot polar plasma of the rotating neutron star. The corresponding magnetic field strength is 5.3 x 10/sup 12/ gauss. We have searched for the second-harmonic cyclotron emission line in that part of our data showing the highest signal-to-noise ratio and find a 3.3 sigma spectral enhancement near the predicted energy (110 keV). We discuss implications of the line width and the line intensity ratio for the physical conditions of the emitting plasma and the beaming geometry.
TL;DR: In this paper, a near-infrared survey has been conducted of nearly 20 square degrees of the Taurus dark cloud complex, showing that recently formed stars are spread throughout the cloud and that these stars are primarily T Tauri stars or TTauri-like stars.
Abstract: A near-infrared survey has been conducted of nearly 20 square degrees of the Taurus dark cloud complex. Additional observations have been made of selected objects detected in this survey. These observations show that recently formed stars are spread throughout the cloud and that these stars are primarily T Tauri stars or T Tauri-like stars. Two luminous objects are identified embedded in the reflection nebulae IC 359 and IC 2087. A new Herbig-Haro object is also described. The reddening law of the dark cloud material is discussed; it does not appear to be unusual in the infrared. Comparison of the young stellar population in Taurus with that in Ophiuchus suggests that the star formation mechanisms in the two regions are qualitatively different
TL;DR: In this paper, a model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed description of matter flow in the transition region between the disk and the magnetosphere.
Abstract: A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed description of matter flow in the transition region between the disk and the magnetosphere. It is shown that the disk plasma cannot be completely screened from the stellar magnetic field and that the resulting magnetic coupling between the star and the disk exerts a significant torque on the star. On the assumption that the distortion of the residual stellar field lines threading the disk is limited by reconnection, the total accretion torque on the star is calculated. The calculated torque gives period changes in agreement with those observed in the pulsating X-ray sources and provides a natural explanation of why a fast rotator like Her X-1 has a spin-up rate much below the conventional estimate for slow rotators. It is shown that for such fast rotators, fluctuations in the mass-accretion rate can produce fluctuations in the accretion torque about 100 times larger. For sufficiently fast rotators or, equivalently, for sufficiently low accretion rates, the star experiences a braking torque even while accretion continues and without any mass ejection from its vicinity.
TL;DR: The linear X-ray polarization of the Crab Nebula has been precisely measured at 2.6 keV and 5.2 keV with the OSO 8 graphite crystal polarimeters as discussed by the authors.
Abstract: The linear X-ray polarization of the Crab Nebula has been precisely measured at 2.6 keV and 5.2 keV with the OSO 8 graphite crystal polarimeters. The 1.4 ms time resolution of these instruments permitted the removal of any contribution to the polarization from the pulsar. The nebular polarization is 19.2% plus or minus 1.0% at a position angle of 156.4 plus or minus 1.4 deg at 2.6 keV. At 5.2 keV the corresponding results are 19.5% plus or minus 2.8% at 152.6 plus or minus 4.0 deg.
TL;DR: In this article, the classical theory of scattering under the Coulomb potential of both charged and neutral particles is used to derive formulae for the energy deposition rate and mean scattering of a beam of charged particles interacting with a cold hydrogen target of arbitrary ionization level as a function of the column density traversed by the beam.
Abstract: The classical theory of scattering under the Coulomb potential of both charged and neutral particles is used to derive formulae for the energy deposition rate and mean scattering of a beam of charged particles interacting with a cold hydrogen target of arbitrary ionization level as a function of the column density traversed by the beam. These general results hold for any form of stable injection energy spectrum, and their relevance to the existing literature on chromospheric heating during solar flares is discussed.
TL;DR: In this article, infrared photometric observations of the central regions of 51 early-type galaxies and of the integrated light of five globular clusters are compared with selected optical observations and with various model predictions, and the observed parameters for the brighter galaxies, particularly the CO index and the V-K color, agree with the predictions of stellar synthesis models characterized by giant-dominated populations with mass/visual luminosity ratios less than 10.
Abstract: Multiaperture infrared photometric observations of the central regions of 51 early-type galaxies and of the integrated light of five globular clusters are presented. These data are compared with selected optical observations and with various model predictions. The main results of the work are: (1) the observed parameters for the brighter galaxies, particularly the CO index and the V-K color, agree with the predictions of stellar synthesis models characterized by giant-dominated populations with mass/visual luminosity ratios less than 10; (2) the galaxian broad-band colors tend to redden with increasing luminosity and decreasing aperture size; (3) for the globular clusters, there is evidence that the integrated colors become redder with increasing metallicity; and (4) in bright galaxies the relative changes of U-V, V-J, and J-K as functions of radius may differ from the relative changes as functions of luminosity at a fixed radius.
TL;DR: In this paper, it is suggested that a stable, massive, neutral lepton may dominate the present mass density in the universe, and an analysis of extended gauge theories as they apply to a lepton with a few GeV/sq cm.
Abstract: It is suggested that a stable, massive, neutral lepton may dominate the present mass density in the universe. To investigate this assumption, attention is given to an analysis of extended gauge theories as they apply to a lepton with a mass of a few GeV/sq cm. A critical factor in the accuracy of the hypothesis is the actual mass of the lepton, and it is noted that the more massive the individual particle, the smaller the particle's aggregate contribution to the universal mass density. High energy accelerators could prove a useful tool in an empirical determination of the lepton's mass. It is further suggested that the lepton considered might provide the material in galactic halos, or supply the mass necessary to bind galactic clusters. A study of intergalactic annihilation radiation is expected to yield more data pertaining to the lepton's existence.
TL;DR: In this paper, the three-dimensional galaxy distribution in the region of space surrounding the two rich clusters Coma and A1367 is analyzed by using a nearly complete redshift sample of 238 galaxies with m, 20 h-l Mpc where there appear to be no galaxies whatever.
Abstract: The three-dimensional galaxy distribution in the region of space surrounding the two rich clusters Coma and A1367 is analyzed by using a nearly complete redshift sample of 238 galaxies with m, 20 h-l Mpc where there appear to be no galaxies whatever. Since tidal disruption is probably responsible for the isolated component of supercluster galaxies, the observations suggest that all galaxies are (or once were) members of groups or clusters. A number of related topics with more general significance are also discussed. (1) The size-to-separation ratio for foreground groups indicates that the redshift of group formation is z 8 9. (2) There is a general correlation between the volume mass density of a galaxy system and the morphologies of the component galaxies. (3) Finally, we speculate that all clusters of richness class z 2 2 are located in superclusters. Subject headings: galaxies : clusters of galaxies: redshifts
TL;DR: In this article, a finite-amplitude circularly-polarized Alfven wave is shown to be unstable in a MHD fluid, and the wave decays by a four-wave coupling process in which the daughter waves are forward propagating random density and magnetic fluctuations and a backward-propagating magnetic wave.
Abstract: A demonstration is presented that a finite-amplitude circularly-polarized Alfven wave is generally unstable in a MHD fluid. The wave decays by a four-wave coupling process in which the daughter waves are forward propagating random density and magnetic fluctuations and a backward-propagating magnetic wave. For parameters typical of the solar corona and the solar wind (thermal to magnetic energy density ratios between 0.1 and 1, and values between 0.1 and 0.9 for the ratio of magnetic energy density of the initial Alfven wave to that of the background magnetic field), large decay rates are found.
TL;DR: In this paper, the emission-line spectra of the galaxies are analyzed, emphasizing line intensities, reddening, temperatures, densities, line strength correlations, line widths, and redshift differences.
Abstract: Results are reported for a spectrophotometric survey of several Seyfert 2 galaxies, intermediate Seyferts, and narrow-line radio galaxies. The emission-line spectra of the galaxies are analyzed, emphasizing line intensities, reddening, temperatures, densities, line strength correlations, line widths, and redshift differences. The continuous spectra are examined, and possible ionization sources are considered. It is found that: (1) there are no distinguishing differences between the spectra of Seyfert 2 galaxies and narrow-line radio galaxies; (2) the emission spectra are rich in lines from a wide range of ionization levels; (3) the continuum is starlight diluted by an underlying continuous spectrum; (4) the line widths of both classes of galaxies have the same distribution; (5) there appear to be regions of high and low ionization in the Seyfert 2 and narrow-line radio galaxies; (6) photoionization seems quite likely as the energy input to the gas; and (7) all the galaxies show a UV excess in their spectra.
TL;DR: In this paper, a time-dependent redistribution of angular momentum and chemical composition of rotating stars due to gas-dynamical instabilities has been studied, and it has been shown that the most important mechanisms for changing the angular momentum distribution are convection and Eddington circulation.
Abstract: Calculations have been performed for the evolution of rotating stars with realistic, time-dependent redistribution of angular momentum and chemical composition due to gas-dynamical instabilities. Convection and Eddington circulation are found to be the most important mechanisms for changing the angular momentum distribution, while the dynamical shear and Solberg-Hoiland instabilities produce chemical mixing in regions which remain unmixed in nonrotating calculations. The calculations indicate that ignoring the finite time scales associated with angular momentum redistribution is a poor and, often, misleading approximation.The primary results of the calculations are: (1) evolved stellar cores develop nonaxisymmetric instabilities corresponding to the bifurcation of the Maclaurin sequence before they reach critical (Keplerian) rotational velocities; (2) for the 7 M/sub sun/ star, the instability point is reached prior to carbon ignition, indicating that catastrophic carbon detonation may be avoided by rotating stars; (3) the hydrodynamic events associated with violent stellar death will generally involve rapidly rotating, triaxial or fissioning cores. In addition to radically altering the nature of these events, this indicates that stellar collapse may be a strong source of gravitational wave radiation.
TL;DR: In this article, a class of displacements that leave the physical variables unchanged is identified; these define "gauge" transformations of the initial data in the Lagrangian picture.
Abstract: In this paper the conventional description of adiabatic perturbations of stationary fluids in terms of a Lagrangian displacement is reexamined, to take account of certain difficulties that have been overlooked in other treatments. A class of displacements: called trivials: that leave the physical variables unchanged is identified; these define ''gauge'' transformations of the initial data in the Lagrangian picture. The conserved canonical energy E/sub c/ (Hamiltonian) and angular momentum J/sub c/ (in the case of axisymmetric unperturbed fluids) associated with the dynamical equations are shown not to be invariant under these gauge transformations. Since E/sub c/ has formed the basis of previous criteria for secular stability of stars, it is necessary to eliminate the gauge freedom in order to regain a meaningful criterion. To this end a conserved inner product (the symplectic structure) is introduced and used to define a dynamically invariant class of ''canonical'' displacements orthogonal to the trivials. In general, canonical displacements obey the extra restriction that the Lagrangian change in rho/sup -/1delsxdel x V vanish; in fluids with uniform entropy s they obey the more restrictive condition that the Lagrangian change in rho/sup -/1del x V vanish. Restricting consideration to canonical displacements guarantees that E/sub c/ andmore » J/sub c/ will be invariant under any residual gauge freedom. For nonaxisymmetric perturbations of axisymmetric fluids, to every physical perturbation corresponds a unique canonical displacement.In an appendix the relationship between E/sub c/ and J/sub c/ and the (gauge-invariant) second-order changes in the total energy and angular momentum of the fluid is derived. Another appendix, dealing with uniformly rotating fluids, reexpresses the gauge-invariant combination E/sub c/-..cap omega..J/sub c/ in terms of Eulerian changes in the fluid variables. A subsequent paper applies these results to the study of secular instability in stars.« less
TL;DR: In this article, it was pointed out that the convective heat transport in the magnetic field swept into the downdrafts in the junctions of supergranule boundaries is strongly suppressed by magnetic field.
Abstract: The remarkable concentration of the general field of the Sun into isolated intense flux tubes at the visible surface must be a direct consequence of conditions immediately beneath the surface. It is pointed out that the convective heat transport in the magnetic field swept into the downdrafts in the junctions of supergranule boundaries is strongly suppressed by the magnetic field. The net heat transport is reduced to such a degree that the temperature of the downdraft within the field increases nearly adiabatically below the visible surface, and hence is significiantly cooler than the surrounding ambient gas. The reduced temperature enhances the downdraft within the field and permits the gravitational field to evacuate the flux tube. The magnetic field is then strongly compressed by the external gas pressure, leading to the extraordinary observed strengths of 1500 gauss or more. It is suggested that the magnetic knots found in active regions are formed wholly or partly by the same effect.The general occurrence of superadiabatic temperature gradients and convective heat transport in the dwarf and subdwarf main-sequence stars suggests that their magnetic fields are generally broken up and concentrated by this effect, much as in the Sun.
TL;DR: In this article, the extinction at the galactic poles, as determined by galaxy counts, is reexamined by using a new method to analyze galaxy counts and a compilation of reddenings for RR Lyrae stars and globular clusters.
Abstract: We reanalyze the interrelationships among Shane-Wirtanen galaxy counts, H I column densities, and reddenings, and resolve many of the problems raised by Heiles. These problems were caused by two factors: subtle biases in the reddening data and a variable gas-to-dust ratio in the galaxy. We present a compilation of reddenings for RR Lyrae stars and globular clusters which are on the same system and which we believe to be relatively free of biases. The extinction at the galactic poles, as determined by galaxy counts, is reexamined by using a new method to analyze galaxy counts. This new method partially accounts for the nonrandom clustering of galaxies and permits a reasonable estimate of the error in log N/sub gal/ as a function of latitude. The analysis shows that the galaxy counts (or galaxy cluster counts) are too noisy to allow direct determination of the extinction, or variation in extinction, near the galactic poles. From all available data, we conclude that the reddening at the poles is small (< or =0.02 mag in E (B--V) over much of the north galactic pole) and irregularly distributed. We find that there are zero offsets in the relations between E (B--V) and H I, andmore » between galaxy counts and H I, which are at least partly the result of an instrumental effect in the radio data. We also show that the gas-to-dust ratio can vary by a factor of 2 from the average, and we present two methods for correcting for this variability in predicting the reddening of objects which are located outside of the galactic absorbing layer. We present a prescription for predicting these reddenings; in the area of sky covered by the Shane-Wirtanen galaxy counts, the error in these predictions is, on average, less than 0.03 mag in E (B--V).« less