Rotating ‘star-in-a-box’ experiments

Using the radiation hydrodynamics code CO⁵BOLD in its ‘star-in-a-box’ setup, we have performed exploratory simulations of global convection in a rotating reference frame. The goal is to study the interaction of convection and rotation by direct numerical simulation. For these first experiments, we chose an idealized configuration (a scaled-down, fast rotating Sun) whose properties resemble those of red supergiants in some respect. We describe the setup and time evolution of these models, and discuss the particular problems we have encountered. Finally, we derive the resulting differential rotation pattern and meridional flow field by temporal and azimuthal averaging of the simulation data. We find anti-solar differential rotation for all cases studied so far. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chromospheric ‘active region loops’

Archshaped structures above or around sunspot groups are considered as tracers of the magnetic lines of force. A study of the chromospheric contribution to the 3D general pattern is necessary to quantify this relationship. The emissive features detected in nine different active regions (AR) and observed on the disk at different levels in the chromosphere have been analysed (6 maps/AR). A good spatial correspondence is found between the maxima of Ca II K₃ and H emissions. Eleven archshaped structures may be easily interpreted as loops. The footpoints are located on both sides of an inversion region in the magnetic field. They always avoid the local maxima and minima of the photospheric line-of-sight magnetic fields (H ) pattern independent of the heliographic longitude. This suggests that the magnetic lines of force may have an oblique direction relative to the solar surface.Underneath the footprints, H is about 400–500 G and V the line-of-sight component of velocity in the photosphere) is less than 100 m s^-1 (frequently involving an inversion of velocity sign, i.e., V = 0 line). The mean distance between the feet of the arches is about 30000 km. Height is variable: the arches are lower in the young AR, higher when it evolves, scarcely or not detectable when the AR is dying. The maximum peaks in K ₁ v(the blue wing of K line) are observed at the periphery of the highest values of H and K ₃ intensities, or at the periphery of the AR.There are no great morphological differences between the slowly-varying arches and the flaring ones. However, a new relation is found between these two kinds of chromospheric features: at the maximum of flares, the flaring arch has one of its footpoints in common with a closer stable, pre-existing arch.On leave from Nanjing University, China.     

‘Nomadic’ nuclei of galaxies

In this paper we discuss observational and theoretical arguments in favour of hypothesis on nomad life of active nuclei inside and outside galaxies as well as its consequences. It may be the anisotropic collapse of a supermassive star, or the disruption of a supermassive binary system after the collapse of one companion that would give birth to such nuclei. We predict the existence of veritable quasi-stellar active objects without any ghost gagalies.     

‘Prominences’ of RY Tauri

High-resolution spectroscopic monitoring of the Nai D lines in the T Tau-type star RY Tau results in the discovery of relatively cool gas clouds ascending and descending inside the stellar wind on a time-scale of few days and co-rotating with the star. Radial velocity of the clouds varies from –100 to +100 km s^–1, which is twice as large as thev sini of the star.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

‘Dead’ pulsars: Cosmic-ray sources

Dead pulsars outnumber live pulsars by a factor of 10⁴. It is estimated that there are 3×10⁹ of them in our Galaxy. The exospheres of the atmosphere of dead pulsars are characterised by cosmic-ray energies per particle, as the result of accretion of cold particles from interstellar space. Velocities of particles in the exosphere tend to be Maxwellianised by collisions there. The temperature of the exosphere from which particles escape is of the order of 10¹² K while the temperature of the photosphere closer to the surface of the pulsar is of the order of 10⁷ K. Collisions in the exosphere result in Jeans's type escape of cosmic rays with GeV energies at infinity. Two braod ranges of conditions for the exospheres are considered (a) with no magnetic fields involved, and (b) with magnetic fields. Similar conclusions are reached regarding the escape of cosmic rays. Conditions are delineated such that the exospheres of dead pulsars might be major sources of cosmic rays.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

An apparent ‘even-odd’ cycle distribution in Mt. Wilson ‘numbers of spots’ data

Mt. Wilson numbers of spots data (as defined in Howard et al., 1984) appear to be distributed according to even-odd cycle numbering. Linear fits of annual numbers of spots versus annual sunspot number for even- and odd-numbered cycles have slopes which are statistically different at the 5% level of significance. The existence of an even-odd split in Mt. Wilson numbers of spots data may be due either to a real difference in even- and odd-numbered cycles on the Sun or to a difference in weather at Mt. Wilson (perhaps, related to the 22-yr rhythm of drought in the western United States) during even- and odd-numbered cycles, or both. For cycle 22, an even-numbered cycle, the peak numbers of spots is estimated to be near 2600.     

Pitch angle scattering of solar particles: Comparison of ‘particle’ and ‘field’ approach

In the quasi-linear theory of pitch angle scattering the power spectrum of magnetic field fluctuations is related to the shape of the pitch angle diffusion coefficient D(), the absolute value of the mean free path , and the rigidity dependence of the mean free path (R). We discuss these relations in detail during the solar particle event of 11 April, 1978 which was observed on HELIOS-2 at a distance of 0.49 AU from the Sun. Magnetic field measurements obtained during the time of the event are used as a basis for the layer model in which the method of particle trajectories in an actually measured field is used to simulate pitch angle diffusion. The values of D() and based on the trajectory simulation for 100 MeV protons (field approach) are compared with results obtained from solar proton data (particle approach) and with predictions from quasi-linear theory based on the additional assumption of the slab model for magnetic field fluctuations (QLT approach). The time of the event is characterized by a high level of field fluctuations, the observed mean free path of about 0.03 AU for 100 MeV protons is smaller than the average value near 1 AU. Results from the field and particle approaches agree surprisingly well. The remaining difference in the mean free path of about a factor of 2 could be due to tangential discontinuities which are measured by the magnetometer, but not seen by the real particles traveling along the average field. The results from the field and QLT approaches based on the same set of magnetic field measurements differ by about a factor of 4. One of the reasons for this discrepancy is that the conditions for resonance scattering are only marginally valid. In addition, the wave vectors representing Alfvén-type fluctuations may not be totally field aligned. This deviation from the slab model would cause an increase of the theoretically predicted mean free path and lead to better agreement with the other two approaches.     

Generalized ‘dependencies’ and parameter variance

The autodependence, (a special case of the — now quite obsolete — dependences, which had been introduced for very specialized astrometric purposes) is proportional to the parameter variance which is the expectation of the variance of the systematic error of a function evaluated with estimated parameters.     

Three-dimensional,periodic, ‘halo’ orbits

A largely numerical study was made of families of three-dimensional, periodic, halo orbits near the collinear libration points in the restricted three-body problem. Families extend from each of the libration points to the nearest primary. They appear to exist for all values of the mass ratio , from 0 to 1. More importantly, most of the families contain a range of stable orbits. Only near L₁, the libration point between the two primaries, are there no stable orbits for certain values of . In that case the stable range decreases with increasing , until it disappears at =0.0573. Near the other libration points, stable orbits exist for all mass ratios investigated between 0 and 1. In addition, the orbits increase in size with increasing .     

The ‘critical inclination’: Another look

The occurrence and uniqueness of the critical inclination in satellite theory is discussed.An infinite set of canonical transformations in Hill variables are shown to exist whereby the first order secular part of the disturbing function can be changed into an alternative form. As a result of such a transformation the critical inclination can become (a)any other real or complex inclination or a function independent of the satellite's orbital inclination and (b) a function dependent on the semi-major axis, eccentricity and inclination of the satellite's orbit. It is also shown that all transformations of types (a) and (b) are only valid for short intervals of time of the order of a few satellite revolutions. Furthermore if such transformations are modified so that they become valid for greater intervals of time, then the resulting solutions in all cases containno singular divisor other than the critical inclination.It is concluded that the singularity at the critical inclination is unique and that it represents an actual physical resonance rather than something resulting from the method of solution or the type of variable used in the analysis. This conclusion is supported by numerical evidence which shows that a satellite's perigee height does suffer resonant changes when the orbital inclination is equal to the critical inclination of 63.°4.     

Cosmological Models with ‘Some’ Variable Constants

Various models are considered with metric type flat FRW i.e. with k = 0 whose energy-momentum tensor is described by a perfect fluid whose generic equation of state is p = ωρ and taking into account the conservation principle div(T _i ^j ) = 0, but considering some of the‘constants’ as variable. A set of solutions through dimensional analysis is trivially found. The numeric calculations carried out show that the results obtained are not discordant with those presently observed for cosmological parameters together with the electromagnetic and quantum quantities. This revised version was published online in July 2006 with corrections to the Cover Date.     

‘Swinging dipoles’ inmagnetic close binary stars

The recently discovered phenomena in polars — Magnetic Close Binary Stars (MCBS), are discussed. Asynchronous MCBS are on the propeller stage (which is analogous to the investigated one for neutron stars), and are synchronizing during t_S10³ yr, being during this stage rapidly evolving, mass ejecting systems. The accretion rate is largest when the angle between the magnetic axis and the line of centers is near zero. If 90°, then the magnetic field prevents the plasma flow, and the magnetic valve becomes closed. Near this position the oscillations of the orientation of the white dwarf's magnetic axis may be excited. This model of a swinging dipole has such observational properties: (a) the system's luminosity changes with characteristical times of some years; (b) the phase curves of light, polarization and radial velocities must be cyclically changing with a few year cycle; (c) one would observe the correlation between the phase shift of these curves, and the system's luminosity. The observational data on polars are briefly discussed. All these phenomena are observed in AM Herculis and some other polars, but subsequent studies are needed to investigate the orientation changes of the magnetic axis, and so the structure and evolution of this exotic class of our Galaxy population.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Diffuse extragalactic gamma-radiation above ‘black-body cutoff’

The possible contribution of gamma-rays predicted within the universal cosmic-ray (CR) hypothesis to the energy range of CR spectrum above black-body cutoff is calculated. These gamma-rays arise from the relativistic electromagnetic cascade generated in the field of microwave background radiation (MBR). The ultra-high energy photons and electrons that initiate the cascade are produced at the decay of -mesons created in interactions of photons with the MBR. Simple analytic expression for cascade gamma-ray spectrum is obtained from the solution of kinetic equations for electrons and photons as well as for protons propagating in the MBR field. It is shown that at certain values of magnetic field and radio-wave density in the intergalactic space te flux of cascade gamma-rays may at least partly mask the black-body cutoff in the CR spectrum.Deceased, August 13, 1989.     

Which One is the ‘GNEVYSHEV’ GAP?

Gnevyshev [Solar Phys. 1, 107, 1967] showed that in solar cycle 19 (1954 –1965), the coronal line half-yearly average intensity at 5303 Å (green line) had actually two maxima, the first one in 1957 and the second in 1959–1960. In the present communication, the structures at solar maxima were reexamined in detail. It was noted that the two-peak structure of solar indices near sunspot (Rz) maxima was only a crude approximation. On a finer time scale (monthly values), there were generally more than three peaks, with irregular peak separations in a wide range of ～12± 6 months. The sequences were seen simultaneously (within a month or two) at many solar indices (notably the 2800 MHz radio flux) at and above the photosphere, and these can be legitimately termed ‘Gnevyshev peaks’ and ‘Gnevyshev gaps’. The open magnetic flux emanating from the Sun showed this sequence partially, some peaks matching, others not. In interplanetary space, the interplanetary parameters N (number density), V (solar wind speed), B (magnetic field) showed short-time peak structures but mostly not matching with the Rz peaks. Geomagnetic indices (aa, Dst) had peaked structures, which did not match with Rz peaks but were very well related to V and B, particularly to the product VB. The cosmic ray (CR) modulation also showed peaks and troughs near sunspot maximum, but the matching with Rz peaks was poor. Hence, none of these can be termed Gnevyshev peaks and gaps, particularly the gap between aa peaks, one near sunspot maximum and another in the declining phase, as this gap is qualitatively different from the Gnevyshev gap in solar indices.     

Lunar ‘en echelon within en echelon’ structures

Some en echelon structures, tension gashes and compressional ridges may form similar patterns. The N-S compression activates diagonal conjugate zones of weakness with tension gashes in the vicinity of the compressional direction. In the case of E-W compression similar arrangements of en echelon compression ridges are generated.The global N-S compression existing at the time of fracturing of the lava-flooded Oceanus Procellarum basin is arguable. It is possible to interpret some different scale mare ridge arrangements as en echelon within en echelon structures. Major ridge ranges evidently have Riedel and opposite Riedel orientations and they consist of minor en echelon structures which may in places be intruded tension gashes but are evidently mostly sheared and compressed Riedel fractures.The en echelon withinen echelon structures of mare ridges manifest the significance of different scale strike-slip movements along the lithosphere zones of weakness indicated by present mare ridge zones. The orientation of these Riedel-fracture-like en echelon structures also points to the existence of an areal compression during shearings along the zones of weakness. The Oceanus Procellarum basin sinking caused by lava loadings and lunar internal cooling led to the lithosphere shortening and to compressional circumstances. The angle between proposed Riedel structures and the mare ridge zones varies within this area, possibly indicating differences in compression and shearing in distinct parts of the shortened basin lithosphere.     

Entropy per baryon in a ‘many-worlds’ cosmology

We imagine the universe split into infinitely many branches, or worlds, only one of which we can observe. Our world has an entropy per baryon 10⁹: other worlds can have all possible values of entropy per baryon. High-entropy worlds with >5×10¹¹ do not form galaxies, but only giant black holes. Low entropy worlds with <3×10⁵ do form galaxies, but only metal-poor dwarf galaxies with no planets. Life can evolve only in worlds with entropy per baryon in the range 3×10⁵<<5×10¹¹, and life is abundant only in a much narrower range.     

Are ‘negative bursts’ due to absorption?

Optical activity near the time of two microwave negative bursts is distinctive enough to demonstrate a real relation, but does not occur simultaneously with the radio events. Such a loose association between microwave flux decreases and H prominence or filament activity is typical of a sample of 23 negative bursts. A model of a microwave occulting cloud differs from that of an H absorber: the H dark flocculus is relatively low, dense, and compact; the microwave occulter is higher in the corona, larger, and more completely ionized. The two types of absorption are not expected to be seen simultaneously, although they could be separate phases of an ejection of chromospheric material into the corona. The association of microwave decreases with H activity in some cases, and their usual non-simultaneity, is consistent with interpretation of the decrease as absorption, but it does not rule out alternative interpretations such as an intrinsic change in the emission of the microwave source.The location of decrease-associated activity has a suggestive, though not statistically significant, bias toward east limb that leads one toward an absorption interpretation, with asymmetry introduced by a tendency for ejected material to move from the leading part of an active region toward the following part, agreeing with Liszka's observation of asymmetry in the line-of-sight velocities of prominences.     

Rapid changes in the fine structure of a coronal ‘bright point’ and a small coronal ‘active region’

A coronal bright point is resolved into a pattern of emission which, at any given time, consists of 2 or 3 miniature loops (each 2500 km in diameter and 12 000 km long). During the half-day lifetime of the bright point individual loops evolved on a time scale 6 min. A small ctive region seemed to evolve in this way, but the occasional blurring together of several loops made it difficult to follow individual changes.     

‘Active Longitudes’ in the Heliomagnetic Reference Frame

A new coordinate system – heliomagnetic reference frame – has been proposed in which the great circle passes through the solar pole and the north pole of the magnetic dipole is considered as the central meridian. It is shown that, in the new coordinate system, the active longitudes are defined much more clearly, are more stable in time, and are interlaced every 11 years.