Links Between Dust Disks and Exoplanets

Since 1984, roughly 100 main sequence stars within 50 parsecs of the Sun have been identified as possibly possessing replenished, circumstellar dust disks. Optical to submillimeter imaging has resolved disk-like structure around 7 main sequence stars. We review these results, and discuss how they elucidate the existence and properties of exoplanetary systems.     

Chromospheric heating by electric currents induced by fluctuating magnetic elements

We refer to two papers by Goodman (1995, 1996) on the heating of the chromosphere by large-scale electric currents, and to our paper (Lorrain and Koutchmy, 1993) on magnetic elements. Goodman assumes that the dynamo that runs a magnetic element stops operating at t = 0. From then on, the magnetic field decays exponentially, and the induced currents heat the chromosphere. The time constants calculated by Goodman disagree with the observed values, possibly because he disregards the driving dynamo. Also, he assumes static conditions, but his magnetic force density appears suddenly when the dynamo stops, and it is about equal to the gravitational force density. The magnetic force acts downward and fluctuations in the current flowing through the magnetic element should induce vertical oscillations at the photosphere. This point should be investigated further.     

Configuring Detection Wells Near Landfills

A graphical method was devised for designing contaminant detection monitoring networks in aquifers. The approach eliminates bias in detection efficiency among well pairs, thereby improving the overall efficiency of a ground water monitoring network. In the equidistant configurations derived by the graphical approach, all wells are located the same distance from a landfill, but the distance is measured parallel to ground water flow, Measured perpendicular to ground water flow, there is also an equal spacing between wells in an equidistant network. A simulation model was used to compare an equidistant network to a peripheral monitoring configuration, in which wells were spaced evenly along the downgradient boundaries of a landfill. The equidistant network yielded a 12.4% higher detection efficiency and also facilitated earlier release detection. In practice, the graphical approach that yields equidistant configurations can be used to identify candidate monitoring networks to detect potential releases from landfills.     

The solubility of aragonite in seawater—I. Effect of pH and water chemistry at one atmosphere

The effect of water chemistry on the solubility of aragonite in seawater has been defined experimentally as a series of apparent solubility products measured with respect to pH at one atmosphere.The dominant control of the apparent solubility product of aragonite is the carbonate ion concentration, and this is primarily a function of pH. In the light of this fact, we have reconciled our data with 81 other reported values of aragonite solubility by simply examining the water chemistry of the waters in which they were determined.     

On propagation of love-type waves on a spherical model with rigidity and density both varying exponentially with the radial distance

Summary The propagation of Love type waves on a spherical model' in the mantle of which the rigidity and density vary exponentially with the radial distance while in the core they remain constant — has been investigated. The frequency equation that has been worked out has been examined in detail for the existence of root in the particular cases when they involve Bessel Functions of smallest and largest orders.     

Atmospheric entry profiles from the Mars Exploration Rovers Spirit and Opportunity

Accelerometer measurements made by Spirit and Opportunity during their entries through the martian atmosphere are reported. Vertical profiles of atmospheric density, pressure, and temperature with sub-km vertical resolution were obtained using these data between 10 and 100 km. Spirit's temperature profile is ∼10 K warmer than Opportunity's between 20 and 80 km. Unlike all other martian entry profiles, Spirit's temperature profile does not contain any large amplitude, long wavelength oscillations and is nearly isothermal below 30 km. Opportunity's temperature profile contains a strong inversion between 8 and 12 km. A moderate dust storm, which occurred on Mars shortly before these two atmospheric entries, may account for some of the differences between the two profiles. The poorly known angle of attack and unknown wind velocity may cause the temperature profiles to contain errors of tens of Kelvin at 10 km, but these errors would be an order of magnitude smaller above 30 km. On broad scales, the two profiles are consistent with Mars Global Surveyor Thermal Emission Spectrometer (TES) pressure/temperature profiles. Differences exist on smaller scales, particularly associated with the near-isothermal portion of Spirit's profile and the temperature inversion in Opportunity's profile.     

Stellar Populations in Bulges of Spiral Galaxies

We present a few results of a work in progress tackling the radial spectroscopic properties of bulges of spiral galaxies. This revised version was published online in September 2006 with corrections to the Cover Date.     

The Visible Solar Spectral Irradiance from 350 to 850 nm As Measured by the SOLSPEC Spectrometer During the ATLAS I Mission

The SOLSPEC instrument has been built to carry out solar spectral irradiance measurements from 200 to 3000 nm. It consists of three spectrometers designed to measure the solar spectral irradiance in ultraviolet, visible, and infrared domains. It flew with the ATLAS I mission in March 1992. This paper is dedicated to the visible part of the solar spectrum. Comparisons with recent data are shown and differences below 450 nm are discussed.