The formation of Mg i 4571 Å in the solar atmosphere

An analysis of the 4571 Å line of neutral magnesium is presented in which one-dimensional macroscopic velocity fields are included. It is shown that gradients over restricted heights in the vertical and horizontal components of the velocity field of order -0.005 s^–1 and -0.004 s^–1 (such that velocity towards the observer decreases as height increases), respectively, result in asymmetries in the computed line profile similar to those observed. The heights in the solar atmosphere at which these velocity gradients exist are shown to be very critical in reproducing the observations. It was found that the best results were obtained when the gradients existed in the height range from 200 km to 300 km below the temperature minimum. The results indicate that for the Mg i 4571 Å line model calculations that do not include one-dimensional flow velocities may safely be compared with frequency-averaged observations.     

The opposition and tilt effects of Saturn’s rings from HST observations

The two major factors contributing to the opposition brightening of Saturn’s rings are (i) the intrinsic brightening of particles due to coherent backscattering and/or shadow hiding on their surfaces, and (ii) the reduced interparticle shadowing when the solar phase angle α → 0°. We utilize the extensive set of Hubble Space Telescope observations (Cuzzi, J.N., French, R.G., Dones, L. [2002]. Icarus 158, 199–223) for different elevation angles B and wavelengths λ to disentangle these contributions. We assume that the intrinsic contribution is independent of B, so that any B dependence of the phase curves is due to interparticle shadowing, which must also act similarly for all λ’s. Our study complements that of Poulet et al. (Poulet, F., Cuzzi, J.N., French, R.G., Dones, L. [2002]. Icarus 158, 224), who used a subset of data for a single B ∼ 10°, and the French et al. (French, R.G., Verbiscer, A., Salo, H., McGhee, C.A., Dones, L. [2007b] PASP 119, 623–642) study for the B ∼ 23° data set that included exact opposition. We construct a grid of dynamical/photometric simulation models, with the method of Salo and Karjalainen (Salo and Karjalainen [2003]. Icarus 164, 428–460), and use these simulations to fit the elevation-dependent part of opposition brightening. Eliminating the modeled interparticle component yields the intrinsic contribution to the opposition effect: for the B and A rings it is almost entirely due to coherent backscattering; for the C ring, an intraparticle shadow hiding contribution may also be present.Based on our simulations, the width of the interparticle shadowing effect is roughly proportional to B. This follows from the observation that as B decreases, the scattering is primarily from the rarefied low filling factor upper ring layers, whereas at larger B’s the dense inner parts are visible. Vertical segregation of particle sizes further enhances this effect. The elevation angle dependence of interparticle shadowing also explains most of the B ring tilt effect (the increase of brightness with elevation). From comparison of the magnitude of the tilt effect at different filters, we show that multiple scattering can account for at most a 10% brightness increase as B → 26°, whereas the remaining 20% brightening is due to a variable degree of interparticle shadowing. The negative tilt effect of the middle A ring is well explained by the the same self-gravity wake models that account for the observed A ring azimuthal brightness asymmetry (Salo, H., Karjalainen, R., French, R.G. [2004]. Icarus 170, 70–90; French, R.G., Salo, H., McGhee, C.A., Dones, L. [2007]. Icarus 189, 493–522).     

The Fossil Starburst in M82

We present high-resolution optical and near-infrared HST observations of two adjacent regions in the fossil starburst region inM82, M82 B1 and B2. The presence of both the active and the fossil starburst in M82 provides a unique physical environment to study the stellar and dynamical evolution of star cluster systems. The cluster population in B2 is more heavily affected by internal extinction than that in B1, amounting to an excess extinction in B2 of A_V,excess≃1.1±0.3 mag. Preliminary age estimates date the cluster population in the fossil starburst between ∼2× 10⁸ and ∼ 10⁹ years. The radial luminosity profiles of the brightest clusters are more closely approximated by power laws than by a Gaussian model, in particular in their wings, which favours a slow star formation scenario. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heights of formation of non-magnetic solar lines suitable for velocity studies

Heights of formation of lines that do not exhibit Zeeman splitting are calculated using an LTE, partial non-LTE, and full non-LTE approach. Non-magnetic (g=0) lines are valuable for velocity investigations in quiet-Sun magnetic field regions, and a knowledge of their formation heights is useful for obtaining three dimensional velocity profiles in these regions. Presently at Sacramento Peak Observatory. Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

On the cooling of the moon by solid convection

If a molten, or partially molten, lunar core exists at present, constraints would be placed on the viscosity of the solid mantle and the distribution of radioactive heat sources. Models in which the heat sources have been concentrated near the surface would rapidly solidify if the effective viscosity was equal to, or less than, 10²² cm² s⁻¹. Retention of most of the heat sources throughout the mantle would permit present day solid convection to occur without cooling the core.     

IR calibrations for water determination in olivine,r-GeO<Subscript>2</Subscript>, and SiO<Subscript>2</Subscript> polymorphs

Mineral-specific IR absorption coefficients were calculated for natural and synthetic olivine, SiO₂ polymorphs, and GeO₂ with specific isolated OH point defects using quantitative data from independent techniques such as proton–proton scattering, confocal Raman spectroscopy, and secondary ion mass spectrometry. Moreover, we present a routine to detect OH traces in anisotropic minerals using Raman spectroscopy combined with the “Comparator Technique”. In case of olivine and the SiO₂ system, it turns out that the magnitude of ε for one structure is independent of the type of OH point defect and therewith the peak position (quartz ε = 89,000 ± 15,000 textl textmol_textH2textO^-1 textcm^-2text{l},text{mol}_{{text{H}_2}text{O}}^{-1},text{cm}^{-2}), but it varies as a function of structure (coesite ε = 214,000 ± 14,000 textl textmol_textH2textO^-1 textcm^-2text{l},text{mol}_{{text{H}_2}text{O}}^{-1},text{cm}^{-2}; stishovite ε = 485,000 ± 109,000 textl textmol_textH2textO^-1 textcm^-2text{l},text{mol}_{{text{H}_2}text{O}}^{-1},text{cm}^{-2}). Evaluation of data from this study confirms that not using mineral-specific IR calibrations for the OH quantification in nominally anhydrous minerals leads to inaccurate estimations of OH concentrations, which constitute the basis for modeling the Earth’s deep water cycle.     

AN ‘EXTENDED SOLAR CYCLE’ AS OBSERVED IN Fe XIV

Investigation of the behavior of coronal intensity above the limb in Fexiv emission (530.3 nm) obtained at the National Solar Observatory at Sacramento Peak over the last 23 years has resulted in the confirmation of a second set of zones of solar activity at high latitudes, separate from the Main Activity Zones (MAZ). Localized high-latitude intensity maxima, which I will call High-latitude Emission Features (HEF), are observed at 0.15 solar radii above the limb throughout the solar cycle. They persist long enough at a given latitude to be visible in long-term (e.g., annual) averages. I identify two types of HEF. Poleward-moving HEF, which may be identified with the Rush to the Poles phenomenon seen in polar-crown prominences, were first seen to appear in this investigation near latitude 60° in 1978. In 1979 equatorward-moving HEF branched off from the poleward-moving HEF (which continued on to reach the pole in 1980) at a latitude of 70° to 80°. They evolved approximately parallel to the MAZ. Near solar minimum, these HEF evolved into the MAZ of cycle 22, and the emission continues its path towards the equator, where it should disappear soon.Currently, it is clear that the pattern seen earlier is repeating. The poleward-moving HEF became apparent near the beginning of 1988 near 50° to 60° latitude. The northern poleward-moving HEF reached the pole and disappeared in 1990. The southern poleward-moving HEF moved more slowly, reaching the pole and disappearing in 1991. The equatorward-moving HEF that are the precursors of cycle 23 appeared in 1989 to 1990 and began to move approximately parallel to the MAZ of cycle 22. Based on inferences from previous cycles, we can expect these HEF to continue to the equator, with emission ceasing there near 2009. These recent observations increase the evidence for an extended solar cycle that begins every 11 years but lasts for approximately 19–20 years.     

The coronal disturbance of 1972, August 12

Using the observed data for metric and hectometric type III radio bursts, the dependence of burst characteristics on the solar longitude has been examined over a wide frequency range. It is found that there exists an east-west asymmetry for the extension of metric type III bursts into hectometric wavelength range. In particular, hectometric bursts are rarely observed for solar flares associated with metric bursts eastward solar longitude 60°E. Furthermore, for eastern longitudes, the low frequency radio observations show a large dispersion in drift time interval.     

Outcomes of tidal evolution for orbits with arbitrary inclination

Tides raised by a satellite on a rotating planet dissipate energy and result in an exchange of angular momentum between the orbit and the spin. A set of diagrams is constructed which shows the evolution of the angular momentum vectors. The results are applied to possible histories of the Uranus system.     

THE ELLICOTT METEORITE

Two individual specimens (total weight 15.7 kg) of a new medium octahedrite were found near Ellicott, El Paso County, Colorado. The find is only 1.2 km from the find (in 1890) of the Franceville medium octahedrite. Ellicott and Franceville are distinct meteorites, the latter exhibiting pronounced differences in shock features, kamacite band width, and Ni, Ga, Ge, and Ir contents. Ellicott is a group IA iron while Franceville is in group IIIA.