Positions and motions of solar bursts at decameter wavelengths

The positions and motions of solar bursts in the range 20 to 60 MHz have been measured by the means of a sweep-frequency grating interferometer with angular resolution of 5 arc at 60 MHz decreasing to 15 arc at 20 MHz. The positional characteristics of the decameter wavelength bursts are discussed in terms of the commonly accepted theories of the origin of radio bursts from plasma and synchrotron radiations.     

Eclipse Observations of Compact Sources in the Outer Solar Corona

We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°2612 E, lat.: 13°3612 N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size 2.5 arc min in the outer solar corona.     

Structure and evolution of solar radio bursts at 26.4 MHz

Two dimensional source brightness distributions at 26.4 MHz for solar bursts of spectral type II, III, IV, and V are derived from observations with a multiple-baseline, time-sharing interferometer system. It was designed explicitly to study the large angle (40 halo) component of low frequency solar bursts first reported by Weiss and Sheridan (1962). Thirty-two bursts occurring in the interval of June–August, 1975, were fit with a circular gaussian core and an elliptical gaussian halo component. Half-power halo diameters (E-W×N-S) averaged 30×28 for type III bursts and 42×27, 28×37, 30×25 for type V, II and IV bursts respectively. Typical core sizes fell in the range of 10±4 giving 31 halo to core size ratio. All burst types were found to have some large angle structure: the specific intensity was 10% compared to the core but the total power in each component was comparable. Two processes for producing the core-halo structure of type III bursts are compared: scattering and refraction of a point source and refraction from many sources over an extended region. It is concluded that the core can be explained by either model but the halo is more consistent with emission from an extended source region of 40° in longitude.     

Spectroscopic Studies of the Solar Corona – V. Physical Properties of Coronal Structures

Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec^–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec^–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures.     

Supergranule and Mesogranule Evolution

The MDI instrument on the SOHO satellite obtained a nearly continuous 45.5-hr run in high-resolution mode on 17–18 January 1997, collecting continuum, Dopplergram, and magnetogram images once per minute. This is one of the longest data sets yet obtained in this mode and shows significant evolution of the supergranulation pattern. After allowing for solar rotation within the fixed field of view, an area spanning 17° in latitude and 11° in longitude was extracted that covers the same area of the solar surface for the entire run. From the de-rotated continuum images, we computed flow maps of photospheric motions using local correlation techniques (LCT). Horizontal divergence maps constructed from the flow maps show local maxima of the size of mesogranules (5–10). We interpret these as mesogranules although the LCT flow map resolution (4.8 FWHM) may not completely resolve smaller mesogranules. Movies made from the divergence maps clearly show the outward convection (advection) of these mesogranules within each supergranule, and narrow boundaries of negative divergence outlining the supergranules. Several new supergranules are observed forming. These appear as areas of strong divergence that pop up between pre-existing supergranules and grow, pushing their neighbors apart. Others seem to perish between growing neighbors. We also computed the vertical component of vorticity from the flow maps. Movies of this vorticity do not show any obvious patterns.     

The Gauribidanur Radioheliograph

A new radio heliograph for obtaining two-dimensional images of the solar corona sequentially at many frequencies in the range 40–150 MHz has been built by the Indian Institute of Astrophysics at the Gauribidanur Radio Observatory (lat. 13°3612 N and long. 77°2707 E) about 100 km north of Bangalore, India. This paper describes various aspects of the antenna system, receiver front end, digital hardware, the data acquisition and the calibration procedure. The performance of the instrument is illustrated with maps of the continuum emission from the undisturbed corona at different frequencies.     

The dust grains in the coma of Comet West

The observed variation of reddening as function of the heliocentric distance and the spatial variation of reddening within the coma of Comet West in the visual wavelength range have been considered to infer the properties of the cometary dust grains. The relevant model incorporates the variation in the size distribution function as well as the composition of the spherical grains. The real part of the complex index of refraction (m = m – im) is chosen such thatm = 1.6. The imaginary part is required to vary from m = 0.2 to 0.05 over the wavelength range 0.4 to 0.7 m. This choice of refractive index corresponds to dirty silicate grains. As a by-product, the model also satisfies the observed polarization and albedo for the Comet West.     

Interferometer observations of a radio burst at 8.6 mm associated with a polarized hard X-ray event

Observations of a radio burst at 8.6 mm wavelength on 1970 November 5, are described with the particular interest on the correspondence between radio and polarized X-ray events. The radio observations were carried out using an interferometer with a half power width of 2.9 at the Dept. of Physics, Nagoya University, and indicated that the location of the radio burst coincided with preceding sunspots and the size of the burst source must be very small, less than about 1. Mechanisms of radio and X-ray emissions are discussed briefly.     

Observations of prominences at 3.5 millimeter wavelength

At 3.5 mm wavelength absorption features are observed in correspondence with H dark filaments on the disk; beyond the limb the prominences correspond to emissive regions. The absorption features are larger (2–3 arc) than the corresponding H dark filaments; the emissive regions at the limb have similar angular sizes. The emissive regions at the limb have electron temperatures of 5500±500 K; the amount of absorption observed on the disk leads to mean electron densities of about 5 × 10¹⁰ per cm³.     

Angular sizes of stria-burst sources in the range 24–26 MHz

The UTR-2 antenna has been used to measure angular sizes of sources of narrow-band short-lived solar stria-bursts at frequencies 24–26 MHz. The majority of these sources have apparent diameters between 20 and 40. According to this parameter they do not differ noticeably from that of type III bursts at the same frequency. The short duration of the stria-bursts prevents explanation of the large diameter by scattering in the solar corona.     

Rayleigh-Cabannes scattering in planetary atmospheres III. The Milne problem in conservative atmospheres

The discrete ordinale method by Chandrasekhar is used to solve the conservative Milne problem in a homogeneous plane-parallel atmosphere which scatters the radiation according to the Rayleigh-Cabannes law.The approximate solution which is supposed to converge uniformly to an exact one when increasing the order of approximation is obtained explicitly. In addition to a tabulation of the Hopf vector for different factors of depolarization, the extrapolation distance, the values of c, q and the Rubenson degrees of polarization at the limb are given.     

Fine structure of the Solar Chromosphere: Arch-Shaped Mottles

We analyze a time series of high resolution observations near the solar limb, obtained in H and the Mg b1 line. We identified arch-shaped dark mottles, which are thin, faint H structures observable under very good seeing conditions, best seen in H +0.75 Å. Their mean length is about 15, their mean height about 6 and indicative lifetimes is of the order of 5 min. They show negative (away from the observer) line-of-sight velocities. A possible interpretation is that material flows from the apex towards the feet of the arches.     

Effects of mass transfer on the unsteady free convection flow past an accelerated vertical porous plate with variable suction

An exact analysis of the effects of mass transfer on the flow of a viscous incompressible fluid past an uniformly accelerated vertical porous and non-porous plate has been presented on taking into account the free convection currents. The results are discussed with the effects of the Grashof number Gr, the modified Grashof number Sc, the Schmidt number Sc, and the suction parametera for Pr (the Prandtl number)=0.71 representating air at 20°C.Nomenclature a suction parameter - C species concentration - C species concentration at the free stream - g acceleration due gravity - Gc modified Grashof number (vg^*(C –C )/U ₀ ³ ) - Pr Prandtl number (C _p/K) - T temperature of the fluid near the plate - T dimensionless temperature near the plate ((T-T )/(T -T )) - U(t) dimensionless velocity of the plate (U/U ₀) - v normal velocity component - v ₀ suction/injection velocity - x, y coordinate along and normal to the plate - v kinematic viscosity (/gr) - C _p specific heat at constant pressure - C _w species concentration at the plate - C non-dimensional species concentration ((C-C )/(C _w -C )) - Gr Grashof number (g(T _w -T )/U ₀ ³ ) - D chemical molecular diffusivity - K thermal conductivity - Sc Schmidt number (/D) - T _w temperature of the plate - T free stream temperature - t time variable - t dimensionless time (tU ₀ ² /) - U ₀ reference velocity - u velocity of the fluid near the plate - u non-dimensional velocity (u/U ₀) - v dimensionless velocity (v/U ₀) - v ₀ non-dimensionalv ₀ (v ₀ /U₀)=–at^–1/2 - y dimensionless ordinate (yU ₀/) - density of the fluid - coefficient of viscosity     

Hydromagnetic cylindrical shock in self-gravitating gas

Chisnell-Chester-Whitham method has been used to study the propagation of diverging hydromagnetic cylindrical shock through an infinitely electrically conducting self-gravitating gas having an initial density distribution ₀= r^-w where is the density at the axis of symmetry andw is a constant, simultaneously for the two cases, viz.: (i) when the shock is weak and (ii) when it is strong. The magnetic field is taken to be axial and initially of constant strength. Analytical relations for shock velocity and shock strength have been obtained. the expressions for the pressure, the density and the particle velocity immediately behind the shock have also been derived.     

Satellite theory

In this paper dynamical characteristics of satellites are outlined by classifying the satellites into three categories according to the values of the solar tidal factor (n/n)² which is the disturbing factor due to the sun and the oblateness factor of the primary planetJ ₂/a ². For inner satellites (n/n)² is much smaller thanJ ₂/a ² and there are several pairs among them, for which the mean motions are commensurable to each other, and for some of them secular accelerations in the mean longitudes have been detected. For outer satellites (n/n)² is much larger and the solar perturbations are dominant. For intermediary satellites the motion of the pole of the orbital plane is not so simple as those of the satellites of the other categories.     

Free-convection flow of water at 4°C past an infinite vertical porous plate with constant heat flux

An analysis of the two-dimensional flow of water at 4°C past an infinite porous plate is presented, when the plate is subjected to a normal suction velocity and the heat flux at the plate is constant. Approximate solutions are derived for the velocity and temperature fields and the skin-friction. The effects ofG (Grashof number) andE (Eckert number) on the velocity and temperature fields are discussed.Nomenclature u, v velocity components of the fluid inx, y direction - g acceleration due to gravity - coefficient of thermal expansion of water at 4°C - v kinematic viscosity - density - T temperature inside thermal boundary layer - T free-stream temperature - k thermal conductivity - C _p specific heat at constant pressure     

A plasma-emission mechanism for type I solar radio emission

A theory for type I emission is developed based on fundamental plasma emission due to coalescence of Langmuir waves with low-frequency waves. The Langmuir waves are attributed to energetic electrons trapped in a magnetic loop over an active region. It is argued that the low-frequency waves should be generated in connection with the heating of the region. The continuum can be explained in terms of Langmuir waves generated by a gap distribution formed through collisional losses over a timescale of several tens of minutes. Bursts are attributed to local enhancements in the Langmuir turbulence associated with a loss-cone instability. No triggering mechanism for the bursts is identified. It is predicted that if the continuum is due to a large source then its brightness temperature should rise over several tens of minutes to a value which is roughly independent of frequency and of position across the source and which should not exceed 3 × 10⁹ K. For bursts, it is predicted that a fainter second harmonic component should accompany bright bursts.     

Effects of Hall current on hydromagnetic free-convective flow through a porous medium

An analysis of the effects of Hall current on hydromagnetic free-convective flow through a porous medium bounded by a vertical plate is theoretically investigated when a strong magnetic field is imposed in a direction which is perpendicular to the free stream and makes an angle to the vertical direction. The influence of Hall currents on the flow is studied for various values of .Nomenclature c _p specific heat at constant pressure - e electrical charge - E Eckert number - E electrical field intensity - g acceleration due to gravity - G Grashof number - H ₀ applied magnetic field - H magnetic field intensity - (j _x , j _y , j _z ) components of current densityJ - J current density - K permeability of porous medium - M magnetic parameter - m Hall parameter - n _e electron number density - P Prandtl number - q velocity vector - (T, T _w , T ) temperature - t time - (u, v, w) components of the velocity vectorq - U ₀ uniform velocity - v ₀ suction velocity - (x, y, z) Cartesian coordinates Greek Symbols angle - coefficient of volume expansion - _e cyclotron frequency - frequency - dimensionless temperature - thermal conductivity - coefficient of viscosity - magnetic permeability - kinematic viscosity - mass density of fluid - _e charge density - electrical conductivity - _e electron collision time     

Hydrogen and helium spectra in large magnetic fields

The energy levels and wave functions of hydrogen and helium atoms in the presence of large (10⁷G) magnetic fields are found by assuming that the eigenvalues and eigenvectors may be approximated by those of a truncated Hamiltonian matrix. In these atoms, fields of this size produce, in addition to the usual Paschen-Back effect, a quadratic Zeeman effect. This contributes an upward shift to the energy of all levels, which at sufficiently high fields dominates the Paschen-Back splitting.The behavior of a number of eigenvalues and wave functions as a function of magnetic field is presented. The effects of the field on the wavelengths and strengths of the components of H and the helium lines 4471, 4026 and 4120 as well as the forbidden 4025 are examined. In hydrogen the lines are split into components attributed to the now nondegenerate transitionsnlm _lnlm_l. In helium forbidden lines are excited, which may develop strengths larger than those of the allowed lines.     

On a transformation of the differential equations of the lunar theory

This work contains a transformation of Hill-Brown differential equations for the coordinates of the satellite to a type which can be integrated in a literal form using an analytical programming language. The differential equation for the parallax of the satellite is also established. Its use facilitates the computation of Hill's periodic intermediary orbit of the satellite and provides a good check for the expansion of the coordinates and frequencies. The knowledge of the expansion of the parallax facilitates the formation of differential equations for terms with a given characteristic. These differential equations are put into a form which favors the solution by means of iteration on the computer. As in the classical theory we obtain the expansions of the coordinates and of the parallax in the form of trigonometric series in four arguments and in powers of the constants of integration. We expand the differential operators into series in squares of the constants of integration. Only the terms of order zero in these expansions are employed in the integration of the differential equations. The remaining terms are responsible for producing the cross-effects between the perturbations of different order. By applying the averaging operator to the right sides of the differential equations we deduce the expansion of the frequencies in powers of squares of the constants of integration.Basic Notations f the gravitational constant - E the mass of the planet - M the mass of the satellite - t dynamical time - x, y, z planetocentric coordinates of the satellite - u x+y–1 - s x–y–1 - the planetocentric distance of the satellite - w 1/ - ₀ the variational part of - w ₀ the variational part ofw, - n the mean daily sidereal motion of the satellite - a the mean semi-major axis of the satellite defined by means of the Kepler relation:a ³ n ²=f(E+M) - a the mean semi-major axis defined as the constant factor attached to the variational solution - e the constant of the eccentricity of the satellite - the sine of one half the orbital inclination of the satellite relative to the orbit of the sun - c(n–n) the anomalistic frequency of the satellite - c ₀ the part ofc independent frome,e, and - g(n–n) the draconitic frequency of the satellite, - g ₀ the part ofg independent frome,e, and - exp (n–n)t–1 - D d/d - e the eccentricity of the solar planetocentric orbit - a the semi-major axis of the solar orbit - n the mean daily motion of the sun in its orbit around the planet - m n/(n–n) - a/a-the parallactic factor - the disturbing function