About the foreshortening effect on sunspot umbral dots

Using high-resolution pictures of the core of a unipolar sunspot observed with several cos values, we studied the center limb effect on the form of the bright umbral dots. The ratio of the apparent sizes in radial and tangential direction do not show the foreshortening effect typically observed in granular structures.On leave from University of Tabriz, Iran.Observational part of this work was done during a stay of S.K. at Sacramento Peak Observatory, U.S.A., as NRC Resident Research Associate.     

Some factors affecting the growth and decay of plages

The Mount Wilson coarse array magnetograph data set is analyzed to examine the dependence of growth and decay rates on the tilt angles of the magnetic axes of the regions. It is found that there is a relationship between these quantities which is similar to that found earlier for sunspot groups. Regions near the average tilt angle show larger average (absolute) growth and decay rates. Thepercentage growth and decay rates show minima (in absolute values) at the average tilt angles because the average areas of regions are largest near this angle. This result is similar to that derived earlier for sunspot groups. As in the case of spot groups, this suggests that, for decay, the effect results from the fact that the average tilt angle may represent the simplest subsurface configuration of the flux loop or loops that make up the region. In the case of region growth, it was suggested that the more complicated loop configuration should result in increased magnetic tension in the flux loop, and thus in a slower ascent of the loop to the surface, and thus a slower growth rate. In order to examine this further, the growth and decay rates of plage regions were examined as functions of the magnetic complexity of the regions. In the case of decay, the result was as expected from the model suggested above - that is, the more complex regions decayed more slowly. But for growing regions the effect is the opposite to that expected (more complex regions grow faster, even in terms of percentage growth), so the explanation of the tilt angle effect for growing regions proposed earlier may not be valid.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

A model of the supergranulation network and of active-region plages

Analysis of magnetograph recordings made simultaneously in different spectral lines have shown that the quiet-region network and active-region plages with average field strengths less than about 100 G are made up by the same type of elementary structures, each having the same physical properties. Magnetograph data are used together with continuum, line profile, and EUV data to derive a model of these subarcsec, spatially unresolved elementary structures. The field strength at the center of each basic element is about 2 kG. The temperature enhancement starts at a height of about 180 km (above the level ₀ = 1 in HSRA), and increases rapidly with height. The brightness structures are coarser than the magnetic-field structures.The magnetic field cannot be contained by either gas pressure or dynamic pressure. The magnetic pressure must be balanced by the constricting force of strong electric currents along the magnetic filaments (pinch effect). A mechanism is proposed for the amplification of the field, involving vortex motions around the downdrafts in the network and plages. Efficient heating by hydromagnetic waves builds up an excess gas pressure inside the twisted fluxropes. The excess pressure is released by the ejection of spicules, which have to move out along the helically shaped field lines and thereby will acquire a spinning motion.The continuum emission in the fluxropes, which are located in the intergranular lanes, washes out the contrast between cell interiors and cell boundaries and creates an abnormal granulation pattern. When more and more magnetic flux is brought into a given area, the interaction between the fluxropes and the granulation starts to change the physical structure of the fluxropes. This begins at an average field B _obs 100 G, with a gradual transition to pores and sunspots as b _obs is increased.     

The rotation of calcium plages in the years 1967–1970

An analysis of Ca II spectroheliograms obtained at Catania Observatory in the period 1967–1970 shows that plages rotate - in their first four days of lifetime - with a latitudinal differential rotation profile steeper than for older objects.A closer inspection reveals that plages slow down with age in some latitude strips, and accelerate in some others. That makes the profiles of old and young objects highly different from each other. In particular, the empirical laws of solar rotation usually adopted, appear to be inadequate to describe so complex a phenomenon as the rotation of these magnetic features. A close correspondence has been found between the latitudes at which plages accelerate (slow down) and the latitudes of westward (eastward) streams (Howard and LaBonte, 1980).Some implications of these results, in the light of the theory of a direct coupling of magnetic features to deep layers, are discussed.In the years concerned, Ca-plages of whatever age show differential rotation profiles steeper than in other phases of the solar cycle.     

Analysis of the magnetic structure of hale region 16398 and turbulent heating of plages

We use the Zirin-Frazier-McIntosh rules to interpret the plages and flares of Region 16398 (1979 November) as shown on H_α filtergrams taken at the Purple Mountain Observatory. The coupled equations of wave and flow fields are used to explain the vertical heating of plages. We think the observed long thin filament is the result of turbulent heating along a horizontal magnetic tube.     

Peculiar solar flares and plages of possible interest for the study of electric quadrupole lines of NaI and Mgii

Attention is drawn to flare-like plages showing the resonance lines of Nai and Mgii as strong emission lines. Spectra of such objects may prove of interest for the study of electric quadrupole lines of the type 3² S-n ²D.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

The impact of aging on the rotation rate of calcium plages in the years 1967–1977

An analysis of Ca ii spectroheliograms obtained at Catania Astrophysical Observatory throughout the years 1967–1977 has been carried out, to throw light on the complex relationship linking (Ternullo, 1986) the angular rotation rate of Ca plages with their age, as well as with solar cycle phase, and with latitude. Given the rotation law w =, a + b sin² I, solar-cycle-related oscillatory properties both of a and b coefficients are described, both for young and old Ca plages.The aging-dependent rate-increments vary, for each epoch, both in module and sign with latitude; that results in deep distortions of the differential rotation latitudinal profile, which exhibits, when old plages are taken into account, a fine structure (Ternullo, 1987). Such a fine structure is absent in the young plage differential rotation profile.Throughout the time interval under examination, the torsional waves observed by Howard and LaBonte (1980) have appeared to be in close spatial relationship with the latitude bands where aging-dependent rate increments occur.

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The effect of an interaction of magnetic flux and supergranulation on the decay of magnetic plages

This paper studies how the properties of large-scale convection affect the decay of plages. The plage decay, caused by the random-walk dispersion of flux tubes, is suggested to be severely affected by differences between the mean size of cellular openings within and around plages. The smaller cell size within a plage largely explains the smaller diffusion coefficient within plages as compared to that of the surrounding regions. Moreover, the exchange of flux tubes between the inner regions of the plage and the surrounding network is suggested to be modified by this difference in cell size, and the concept of a partially transmitting plage periphery is introduced: this periphery preferentially turns back flux parcels that are moving out of the plage and preferentially lets through flux parcels that are moving into the plage, thus confining the flux tubes to within the plage. This semi-permeability of the plage periphery, together with the dependence of the diffusion coefficient on the flux-tube density, can explain the observed slow decay of plages (predicting a typical life time of about a month for a medium-sized plage), the existence of a well-defined plage periphery, and the observed characteristic mean magnetic flux density of about 100 G. One effect of the slowed decay of the plage by the semi-permeability of the plage periphery is the increase of the fraction of the magnetic flux that can cancel with flux of the opposite polarity along the neutral line to as much as 80%, as compared to at most 50% in the case of non-uniform diffusion. This may explain why only a small fraction of the magnetic flux is observed to escape from the plage into the surrounding network.     

On the symmetric difference quotient and its application to the correction of orbits

In this paper we consider the analytical foundations of numerical applications of the symmetric difference quotient for orbits correction. From these considerations it follows that the better results obtained in numerical calculations of values of derivatives at point, obtained by replacing the ordinary difference quotient with the symmetric difference quotient, have not been obtained fortuitandy.     

On the branching in the emission relations of Ca+ in prominences

Spatially well resolved prominence spectra of the three lines Ca⁺ K, H, and Ca⁺ 8542 are analysed. It is confirmed that the branching in the emission relations of Ca⁺ versus H correlates with the magnitude of non-thermal (turbulent) broadening.     

The old calcium plages differential rotation latitudinal profile: Its gross and fine structure evolution with the solar cycle

This work is a study of the rotational properties of the solar calcium plages, during the time interval 1967–1977; only plages older than 4 days have been the object of this research. We have looked systematically for any significant change occurring during the course of the solar cycle, and any kind of ‘anomaly’ or fine structure in the differential rotation latitudinal profile. We find that such a profile undergoes a cyclic transformation, making it assume the highest steepness at the solar maximum; a sudden flattening then occurs in the first years of declining activity; the last years of the cycle, as the first years of the next one, are characterized by intermediate steepness values. Moreover, we find that, in spite of the general belief that the angular rotation rate is continuously decreasing with increasing heliographic latitude, at least two inversions do exist of such an overall tendency:

1. A narrow, minimal angular-rotation-rate strip lies very close to the equatorward margin of the plage production band; this feature shifts continuously, in a wave-like manner, throughout the solar cycle, from 15/18° to 3/6° latitude.
2. A narrow, maximal angular-rotation-rate strip has been observed lying in the neighbourhood of the poleward margin of the activity band; a process of continuous transformation of the rotation rate profile is always active, in a narrow latitude strip on the equatorward side of such a feature, generating new features of the same kind, which replace the older ones, that disappeared due to the equatorward shift of the plage zone. All that simulates an equatorward shift of the observed ‘anomalies’; we observed them until the minimum activity epoch (1976), at 15/18° latitude. Some relations of these features with both torsionai waves (Howard and LaBonte, 1980) and magnetic activity are briefly discussed.

     

Differential correction for near-stationary satellites

This paper presents a new concept for the differential correction of orbits. It is developed in detail for the case of near-stationary artificial satellites. For these satellites a few (<10) observations over a short (5–15^m,1% period) time interval allows the reacquisition of the satellite an hour later. Moreover, the addition of only a few more observations spanning a slightly longer time interval allows the production of an excellent set of orbital elements. The technique is self-starting and does not use any of the classical initial orbit determination procedures. It can be used for radar observations or extended to include angular velocity data. Its success appears to be based on the ability to find a coordinate system in which the object's motion is nearly stationary and the extensive use of analytical (instead of numerical) procedures.This work was sponsored by the Department of the Air Force.The views and conclusions contained in this document are those of the contractor and should not be interpreted necessarily representing the official policies, either expressed or implied, of the United States Government.     

On the Determination of the Quiet-Sun Center-to-Limb Variation in Ca II K Spectroheliograms

We present a method for the determination of the center-to-limb variation (CLV) for Caii K spectroheliograms. It is based on the calculation of intensity histograms for rings of constant area. Using a simple cutoff criterion in the cumulative histograms, we are able to derive CLVs of the quiet Sun regardless of the solar activity level. Using an example from the literature, we show in which way different methods of normalization of the quiet-Sun CLV may affect the results.     

On peculiarities of the H and K Ca ii lines of quiescent prominences

A study of the metallic lines in bright quiescent prominences indicates that the optical thickness in the K line of Ca ii may reach values as high as 10³. This is about 10 times larger than the optical thickness in the H line and may explain some peculiarities of the H and K lines in solar prominences.     

Time series data correction for the Chang'E-1 gamma-ray spectrometer

The main goal of the gamma-ray spectrometer(GRS) onboard Chang'E1(CE-1) is to acquire global maps of elemental abundances and their distributions on the moon,since such maps will significantly improve our understanding of lunar formation and evolution.To derive the elemental maps and enable research on lunar formation and evolution,raw data that are received directly from the spacecraft must be converted into time series corrected gamma-ray spectra.The data correction procedures for the CE-1 GRS time series...     

Settling of metal droplets in a terrestrial magma ocean: On the correction of the Stokes velocity

The formation of magma oceans on at least the major terrestrial planets is widely assumed even if the full accretion history and early evolution of terrestrial planets is discussed rather controversial. Various processes occur within these magma oceans, among them the settling of small iron drops and their chemical equilibration with the silicate environment. Different models were proposed to explain the differentiation within a magma ocean. In order to model a magma ocean and give constraints about settling time of iron droplets, a constant velocity is used in most models, which is calculated using Stokes’ famous formula. According to the other model parameters this assumption is invalid, since Stokes’ assumption of a creeping flow is violated. However, former models investigated the behaviour of a large number of droplets, which makes it is impossible to solve the flow around each single iron drop. We introduce a model, in which the flow around iron drops in a molten silicate environment is computed using the appropriate hydrodynamic equations. We investigate the terminal velocity of a single drop descending through a magma ocean and additionally study the effects of the presence of other obstacles in the neighbourhood. We determine a new mean velocity, which may serve as an input parameter for the existent models of magma oceans. Although we used a full fluid-dynamical approach, the velocity computed with our model is not very different from the simple Stokes case and thus proves that the former assumptions were legitimate and can be used in future as well as the new velocity presented here.     

A wavefront tilt correction servo for the Sydney University Stellar Interferometer

The tilt correction servo for the Sydney University Stellar Interferometer (SUSI) consists of a 'pyramid' detector and piezo-electrically controlled tilt mirrors. The system measures image position and re-centers it with a sample frequency of 1000 Hz thereby holding the two beams of the interferometer parallel with a standard deviation of 0.164 ± 0.025 arcseconds. With an aperture size of 0.06 metres this implies less than a 2% loss in the visibility measurements made by SUSI. The servo has been used to magnitude 6.5 stars and is predicted to have a limiting magnitude of 7.5 and possibly as high as 8.5. The system not only corrects for the tilt introduced by the atmosphere but will supply a good estimate of seeing conditions using the same optical path through the atmosphere as the visibility measurements of the interferometer.     

On the Shape of H and K Ca II Line Profiles in Sunspot Umbral Spectra

Emission cores of the H and K Caii lines observed in sunspot umbral spectra are mainly single-peaked, while semi-empirical umbral models predict their double-peak character. It is verified whether a single-peaked profile can be the result of the smearing of an originally double-peaked profile by macroturbulence. The integral convolution equation is solved for measured H and K profiles, and it is shown that, also after the deconvolution, they remain single-peaked even at an r.m.s. value of the macroturbulence velocity equal to 5 km s-1.