Electron density and temperature measurements, and abundance anomalies in the solar atmosphere

Using spectra obtained from the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric Observatory), we investigate the height dependence of electron density, temperature and abundance anomalies in the solar atmosphere. In particular, we present the behaviour of the solar FIP effect (the abundance enhancement of elements with first ionization potential < 10 eV in the corona with respect to photospheric values) with height above an active region observed at the solar limb, with emphasis on the so-called transition region lines.     

Electron density and temperature in the Io plasma torus from Ulysses thermal noise measurements

During the Ulysses flyby of Jupiter, the spacecraft crossed the outer part of the Io plasma torus along a basically North-to-South trajectory at a Jovicentric distance of about 8R_J. The quasi-thermal noise measured by the Unified Radio and Plasma Wave (URAP) experiment is used to deduce the electron density and temperature along the trajectory. The density is deduced from the upper hybrid frequency line and the temperature from the spin modulation of Bernstein waves. These results are used to build a simplified Gaussian model of the torus. The density profile is roughly symmetric with respect to the centrifugal equator, with a scale height of about 0.9R_J. The density at equator crossing is twice as large as that expected from the Divine-Garrett Voyager-based model at the same radial distance. The density scale height is lower than that found by Voyager 1; it is consistent with an ion temperature of about 5 × 10⁵K, assuming an effective mass of about 20 proton masses. The fitting of the pressure distribution, symmetric with respect to the centrifugal equator, yields a cold electron temperature of about 1.4 × 10⁵K at the equator, which is of the same order of magnitude as found by Voyager 1.     

Rocket measurements of electric fields,electron density and temperature during different phases of auroral substorms

On 27 January 1979, three rocket payloads were launched from Kiruna, Sweden into different phases of two successive auroral substorrns. Among other experiments, the payloads carried the RIT double probe electric field experiments providing electric field, electron density and temperature data which are presented here. These data supported by rocket particle observations are discussed mainly in association with ground-based observations (magnetometer, TV) and very briefly with GEOS electric field data. The motions of the auroral forms as obtained from auroral pictures are compared with $\text{E × B}\text{/B}{}^2$ drifts and the currents calculated from the rocket electric field and density measurements with the equivalent current system deduced from ground-based magnetometer data (Scandinavian Magnetometer Array).     

Coronal density and temperature gradients

Mean density models of the solar corona show evidence for two distinctive density regimes characterized by different density gradients. High density gradients are identified with regions of predominantly open magnetic lines of force and low density gradients are identified with regions of predominantly closed magnetic lines of force. Spectroscopic data yielding equivalent widths of forbidden lines of Fe x and Fe xiv strongly suggest that the coronal temperature for r > 2.5 R decreases considerably less rapidly in equatorial regions than r ^–2/7, which is the decrease predicted by conduction models with open field lines.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Determination of wave characteristics of VLF-waves by means of multicomponent electromagnetic field measurements

The multicomponent data of the electromagnetic field obtained on the Aureol-3 satellite were studied. On the basis of the application of the multispectral analysis, nonlinear interactions on the harmonics of the proton gyro-frequency were determined. By the power spectra of the low frequency radiation components, the principal regulations of behaviour of the vectors of the wave normal and of the wave distribution function from the frequency and the invariant latitude L were found. It is noted, that at frequencies below the proton gyro-frequency there often arises the second maximum in the form of a wave distribution function, that can be interpreted as a reflected wave.     

Properties of spherical galaxies and clusters with an NFW density profile

Using the standard dynamical theory of spherical systems, we calculate the properties of spherical galaxies and clusters whose density profiles obey the universal form first obtained in high-resolution cosmological N -body simulations by Navarro, Frenk & White (NFW). We adopt three models for the internal kinematics: isotropic velocities, constant anisotropy and increasingly radial OsipkovMerritt anisotropy. Analytical solutions are found for the radial dependence of the mass, gravitational potential, velocity dispersion, energy and virial ratio and we test their variability with the concentration parameter describing the density profile and amount of velocity anisotropy. We also compute structural parameters, such as half-mass radius, effective radius and various measures of concentration. Finally, we derive projected quantities, the surface mass density and line-of-sight as well as aperture-velocity dispersion, all of which can be directly applied in observational tests of current scenarios of structure formation. On the mass scales of galaxies, if constant mass-to-light is assumed, the NFW surface density profile is found to fit HubbleReynolds laws well. It is also well fitted by Sérsic R ^{1/ m} laws, for     but in a much narrower range of m and with much larger effective radii than are observed. Assuming in turn reasonable values of the effective radius, the mass density profiles imply a mass-to-light ratio that increases outwards at all radii.     

Universal gas density and temperature profile

We explore possibilities of collapse and star formation in Population III objects exposed to the external ultraviolet background (UVB) radiation. Assuming spherical symmetry, we solve self-consistently radiative transfer of photons, non-equilibrium H₂ chemistry and gas hydrodynamics. Although the UVB does suppress the formation of low-mass objects, the negative feedback turns out to be weaker than previously suggested. In particular, the cut-off scale of collapse drops significantly below the virial temperature T _vir∼10⁴ K at weak UV intensities ( J ₂₁≲10⁻²) , owing to both self-shielding of the gas and H₂ cooling. Clouds above this cut-off tend to contract highly dynamically, further promoting self-shielding and H₂ formation. For plausible radiation intensities and spectra, the collapsing gas can cool efficiently to temperatures well below 10⁴ K before rotationally supported and the final H₂ fraction reaches ∼ 10⁻³.
Our results imply that star formation can take place in low-mass objects collapsing in the UVB. The threshold baryon mass for star formation is ∼ 10⁹ M_⊙ for clouds collapsing at redshifts z ≲3 , but drops significantly at higher redshifts. In a conventional cold dark matter universe, the latter coincides roughly with that of the 1 σ density fluctuations. Objects near and above this threshold can thus constitute 'building blocks' of luminous structures, and we discuss their links to dwarf spheroidal/elliptical galaxies and faint blue objects. These results suggest that the UVB can play a key role in regulating the star formation history of the Universe.     

Visual measurements of southern double stars,III

A total of 198 micrometric observations of 103 double stars are reported, which form the third series of a program started at Córdoba with a 30-cm refractor. The WDS pairs observed are largely neglected wide systems mostly south of –60°, many of them having only one previous observation. Internal errors are estimated, and all existing measurements of the pairs are used to study the personal equation. Catalogue proper motions are employed to investigate the motion and nature of many of these stars.     

The Jovian temperature structure obtained by inversion of infrared spectral measurements

The results of inversions of infrared spectral measurements indicate that there exist temperature structures in the region of the temperature minimum at ～0.1 bar which are significantly different from radiative models. We demosntrate that this difference can be accounted for in terms of errors in the retrieved temperature structures caused by the lack of observations which adequately define the thermal structure in the lower stratosphere.     

Correlation of interplanetary scintillation and spacecraft plasma density measurements

Interplanetary scintillation and spacecraft measurements of proton density are observed to be strongly correlated. This result confirms the association between corotating sectors of enhanced scintillation and compression regions located at the interface between fast and slow solar wind streams; it also suggests that scintillation observations provide a means of predicting, several days in advance, the arrival at the Earth, of solar plasma of enhanced density.     

Rocket measurements of lower ionosphere electron density by propagation characteristics of VLF waves

The electron density profile in the lower ionosphere was determined from the right- and left-handed circularly polarized wave fields of a 40 kHz ground based signal observed by means of a rocket born receiver. Estimation of the electron density profile from 70 km up to 100 km was made under the condition for the values calculated by the full wave analysis to agree with the observed values. Results are presented for two rockets launched soon after sunset.     

Electron density and temperature structure of two limb active regions observed by SOHO-CDS

The analysis of two active regions on the limb using observations from SOHO-CDS allows us to determine the electron density and temperature distribution of the coronal emission. We find that the active regions have hot cores (3×10⁶ K) with larger cooler (10⁶ K) loop structures extending above the limb. The electron number density, determined using the Si X diagnostic line ratio, is found to be highest in the active region core (greater than 2.3×10⁹ cm^–3). Electron number density values are determined for a range of spectral lines from different ions and are found to increase with temperature between 0.8 and 2.5×10⁶ K. These results are consistent with recent models of enhanced heating along the compact core of active regions, where the magnetic field shear is strongest.     

An evaluation of ionospheric probe performanc—II. The influence of vehicle wake effects on electron density and temperature measurements

The theoretical performance and accuracy of the Sayers type of R.F. capacitance electron density probe are discussed in some detail, and results from two ionospheric flights of this probe are given. After a brief survey of current satellite wake theories, the broad features of a sounding rocket wake are postulated, and its likely extent calculated by a method applicable to almost any rocket and probe configuration. Both electron density and temperature data are shown to correlate well with the rocket attitude and the postulated wake, confirming the existence of a wake and its importance to probe measurements. Evidence for prolonged outgassing from the rocket motors was also found.     

Gluon polarization at finite temperature and density

We calculate the gluon self-mass and the QCD coupling constant at finite temperature in the real-time formalism up to the first loop level. The expressions are derived in a form that is valid for all temperature ranges in QCD. Using these results the dynamically generated mass of gluons and the plasma screening length can be determined from their effective potential.     

CCD measurements of visual double stars at Calar Alto

342 CCD measurements of relative positions and magnitude differences for 145 visual double stars are presented. Observations were carried out at the 1.23m telescope of the German‐Spanish Astronomical Center at Calar Alto (Spain), all of them in V and R photometric bands.     

Micrometer measurements of visual double stars at Calar Alto

We present 93 micrometer measurements of 55 double stars observed with the 152 cm telescope at the Spanish observatory at Calar Alto (Almeria, Spain).     

Physical properties of Martian meteorites: Porosity and density measurements

Abstract— Martian meteorites are fragments of the Martian crust. These samples represent igneous rocks, much like basalt. As such, many laboratory techniques designed for the study of Earth materials have been applied to these meteorites. Despite numerous studies of Martian meteorites, little data exists on their basic structural characteristics, such as porosity or density, information that is important in interpreting their origin, shock modification, and cosmic ray exposure history. Analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planet's surface. We present new data relating to the physical characteristics of twelve Martian meteorites. Porosity was determined via a combination of scanning electron microscope (SEM) imagery/image analysis and helium pycnometry, coupled with a modified Archimedean method for bulk density measurements. Our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample. Preliminary interpretation of the data demonstrates good agreement between porosity measured at 100× and 300× magnification for the shergottite group, while others exhibit more variability. In comparison with the limited existing data for Martian meteorites we find fairly good agreement, although our porosity values typically lie at the low end of published values. Surprisingly, despite the increased data set, there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency. Further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations.     

A calculation of structural parameters of spherical stellar systems by means of characteristic functions method. I. Theory

To calculate structural parameters of stellar systems such as an effective radius and central space (or surface) density, the method of characteristic functions is suggested. The characteristic function of the system is a Fourier image of their normalized space density profile f₃(r). In the case of spherical symmetry the probability distribution of r (Q₃(r) = (3/a³)r²f₃(r)) and its orthogonal projections have the same characteristic functions. This fact is used to calculate the effective radii of a few star cluster models (King law, Plummer model and Gausian profile). It is shown, that the characteristic function for King law clusters tends to a finite generalised function if the concentration parameter c is large. The expression for the effective radius (at c ≫ 1) is given. The formula of the effective radius in the Plummer model as well as the relation between the one-dimensional central velocity dispersion and the root mean square velocity are obtained. It is shown, that in the Gaussian model and for King law clusters the effective radius (half-mass visual radius) can differ from the effective (harmonic) radius a few times. This fact should be taken into account in estimating the mass-to-light ratio from the virial mass of such systems using the King radius.     

Evolution of density perturbations in double exponential quintessence models

In this work we investigate the evolution of matter (linear) density perturbations for quintessence models with a self-interaction potential that is a combination of exponentials. One of the models is based on the Einstein theory of gravity, while the other is based on the Brans-Dicke scalar tensor theory. We constrained the parameter space of the models by using the determinations of the growth rate of perturbations derived from data of the 2-degree Field Galaxy Redshift Survey.      

Effects of spherical geometry and two temperature electrons on dust acoustic waves

The nonlinear dust acoustic waves in dusty plasmas with two temperature electrons and the combined effects of bounded spherical geometry and the transverse perturbation are studied. Using the perturbation method, a spherical Kadomtsev-Petviashvili (SKP) equation that describes the dust acoustic waves is deduced.