Effective temperatures,radii and bolometric magnitudes of Ap and Am stars

The effective temperatures radii and bolometric magnitudes of Ap, Am and normal A stars have been estimated from their energy distribution curves between 478 nm and 680 nm. All the Am stars and one Ap star (i.e. CrB) were found to be affected by line blanketing, a rough estimation of which in the respective (B-V) colours has been found out in each case.The range in effective temperature is 0.45–0.60 in terms of (=5040/T _e), while it is 1.8–4.8R in the case of radius, that in bolometric magnitude being from-0^m.67 to+1^m.61. An approximate estimate of the masses shows that they are between 1.5 and 3.0M . All these estimates are in agreement with those of the normal A stars. The Ap and Am stars are found to be slightly evolved and, therefore, are probably in the hydrogen shell-burning phase.     

Reflectance spectra for sodium and potassium doped ammonia frosts: Implications for Io's surface

This paper reports measurements of the reflection spectra of sodium and potassium doped ammonia frosts as a function of alkali metal concentration which cover the wavelength range 0.35–2.5 μm. The purpose of the measurements was to determine whether or not the reflection spectra for such a solid was compatible with the spectral albedo of Io. The data show that with a sufficiently large alkali metal concentration, the reflection spectra of the doped ammonia frost do not display the characteristic ammonia features at 2.0 and 2.25 μm. The high reflectance of the more concentrated samples and the character of the observed reflection spectrum make it difficult to rule out sodium doped ammonia frost as a surface constituent on Io on the basis of existing data.     

Formation of whistler ducts

A theory of whistler duct formation is presented. By means of order of magnitude calculations it is shown that, when the ring current overlaps the outer plasmasphere, irregularities will cause field-aligned currents to flow, which are below the threshold sensitivity of satellite-borne magnetometers. These currents must be continuous with horizontal ionospheric currents, which produce horizontal electric fields. These fields map up to the equatorial plane and are large enough to produce flux tube interchange and hence the formation of whistler ducts in the outer plasmasphere.     

Linear force-free fields in the lower corona

We have computed the surface Green's function for linear force-free magnetic fields, where × B = B and is a constant, for application to low coronal levels of the solar atmosphere. Boundary conditions are imposed on the normal component of B on two parallel planes which delineate the force-free volume. This procedure ensures that the magnetic field energy remains bounded, and that the field lines have a smooth behavior. A simple bipolar source distribution is treated and representative field line tracings are shown.     

The relationship of electron plasma oscillations to type III radio emissions and low-energy solar electrons

An extensive study of the IMP-6 and IMP-8 plasma and radio wave data has been performed to try to find electron plasma oscillations associated with type III radio noise bursts and low energy solar electrons. This study shows that electron plasma oscillations are seldom observed in association with solar electron events and type III radio bursts at 1.0 AU. In nearly four years of observations only one event was found in which electron plasma oscillations are clearly associated with solar electrons. Numerous cases were found in which no electron plasma oscillations with field strengths greater than 1 V/m could be detected even though electrons from the solar flare were clearly detected at the spacecraft.For the one case in which electron plasma oscillations are definitely produced by the electrons ejected by the solar flare, the electric field strength is very small, only about 100 V/m. This field strength is about a factor of ten smaller than the amplitude of electron plasma oscillations generated by electrons streaming into the solar wind from the bow shock. Electromagnetic radiation, believed to be similar to the type III radio emission, is also observed coming from the region of more intense electron plasma oscillations upstream of the bow shock. Quantitative calculations of the rate of conversion of the plasma oscillation energy to electromagnetic radiation are presented for plasma oscillations excited by both solar electrons and electrons from the bow shock. These calculations show that neither the type III radio emissions nor the radiation from upstream of the bow shock can be adequately explained by a current theory for the coupling of electron plasma oscillations to electromagnetic radiation. Possible ways of resolving these difficulties are discussed.     

Observations of coronal polarization at the solar eclipse of 7 March, 1970

Polarigraphic observations of the 7 March, 1970 eclipse were made at Miahuatlán (Mexico) with a camera of 120 cm focal length. A polarizing filter in front of the objective could be adjusted at 8 different positions, 22.5° apart. Reduction of eight photographs of the white light corona yields polarization at 72 position angles and from r = 1.1 up to 2.1. High polarization which cannot be explained with Thomson scattering was not observed. An analysation of the measuring accuracy shows, that it is not possible to determine exactly the direction of polarization in the outer corona with the classical method of measuring polarization with a small number of photographs. The coronal hole in the south-west quadrant is analysed. The low intensity and polarization can be explained by a hole with an extent in longitude between 1 and 2 times its extent in latitude and with a minimum electron density between 0 and 0.3 of that outside the hole.Astronomische Mitteilungen der Eidgenössischen Sternwarte Zürich, No. 347.     

Variations in composition and δ18O values within the Kaffo albite—Riebeckite granite of Liruei Complex,Younger Granites of Nigeria

The peralkaline Kaffo albite—riebeckite granite is an albitised, low-temperature intrusion in Liruei Complex, one of the oldest of the ring-complexes in the Younger Granite province of Nigeria. Analyses of borehole samples from different parts of the intrusion show it to be compositionally heterogeneous, especially in respect of Si, Al, Na, K and F distribution and this, in part, can be correlated with the variable degree of albitisation. Isotopically the granite is a normal plutonic type with δ¹⁸ O values of $\text{+ 8.1 ± 0.2‰}$, and albitisation does not seem to have been accompanied by exchange of isotopes between albitising fluid and the granite. Co-existing riebeckitic-arfvedsonite and aegirine pairs from borehole samples show extreme enrichment in Na and Fe; the amphibole also shows considerable substitution of Fe by Ti, Zn and Mn, and of OH by F. Isotopically the amphibole and pyroxene are different from others, having low, variable δ¹⁸ O values (+5.3–+6.4 and $\text{+4.4–+5.1‰}$, respectively), and the fractionation value Δ Px — Am is always large, negative and constant (—$\text{1.2 ± 0.2‰}$). The low δ¹⁸ O values are considered to be due to special features of the crystal chemistry of the alkali amphiboles and pyroxenes, and the spread of each set of values may be due to sub-solidus isotope exchange between the minerals and albitising fluid.     

The determination of calcium and magnesium in carbonate rocks by atomic-absorption spectrophotometry after acetic-acid decomposition

An atomic-absorption spectrophotometric method is described for the determination of Ca and Mg in carbonate rocks after an acetic-acid decomposition. KCl is used as a releasing agent instead of the more commonly used LaCl₃. Results obtained using both releasing agents compare favourably in accuracy and precision, KCl having the advantage that it is much less expensive.     

Epstein weight functions for non-radial oscillations of polytropes

Weight functions for the determination of the periods of linear adiabatic non-radial oscillations have been calculated in the same manner as Epstein's classic treatment of purely radial oscillations. Quadrupole (l=2) oscillations for thef and lower orderp andg-modes were considered. One group of static models were polytropes in the range 1.0n4.0 with ; thus included were configurations that were convectively stable, unstable and neutrally stable throughout. Another group consisted ofn=3.0 polytropes with convective shells or convective cores; ₁ was set at different values in each region in order to produce stability ( ) or instability ( ). The weight function provides a pictorial means for assessing the relative importance of each region of a given static model with respect to generating a given non-radial mode.