ALBERT

Description: A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream.

Description: A weak infrared absorption feature near 4141 wavenumbers (2.415 micrometers) in the spectrum of WL5, an infrared source in the rho Ophiuchus cloud complex, has been detected. It is attributed to molecular hydrogen created by irradiation and frozen in situ into water-rich ices. A second, broader absorption at 4125 wavenumbers centimeters (2.424 micrometers) is probably due to methanol in the ices. The column densities of frozen molecular hydrogen and methanol are inferred to be about 2.5 x 10(exp 18) and 3.0 x 10(exp 19), respectively. There is about three times more frozen molecular hydrogen than frozen carbon monoxide along this line of sight.

Description: Far ultraviolet observations of the behavior of wind velocity and superionization values as a function of the phase of the (Be, B shell, B normal) pattern established by visual observations for gamma Cas and 59 Cyg are translated into a crude atmospheric model for the Be phase and several kinds of mass flux variability across the three phases.

Description: The goal of this project was to support the scientific analysis of multi-spectral astrophysical data by means of scientific visualization. Scientific visualization offers its greatest value if it is not used as a method separate or alternative to other data analysis methods but rather in addition to these methods. Together with quantitative analysis of data, such as offered by statistical analysis, image or signal processing, visualization attempts to explore all information inherent in astrophysical data in the most effective way. Data visualization is one aspect of data analysis. Our taxonomy as developed in Section 2 includes identification and access to existing information, preprocessing and quantitative analysis of data, visual representation and the user interface as major components to the software environment of astrophysical data analysis. In pursuing our goal to provide methods and tools for scientific visualization of multi-spectral astrophysical data, we therefore looked at scientific data analysis as one whole process, adding visualization tools to an already existing environment and integrating the various components that define a scientific data analysis environment. As long as the software development process of each component is separate from all other components, users of data analysis software are constantly interrupted in their scientific work in order to convert from one data format to another, or to move from one storage medium to another, or to switch from one user interface to another. We also took an in-depth look at scientific visualization and its underlying concepts, current visualization systems, their contributions, and their shortcomings. The role of data visualization is to stimulate mental processes different from quantitative data analysis, such as the perception of spatial relationships or the discovery of patterns or anomalies while browsing through large data sets. Visualization often leads to an intuitive understanding of the meaning of data values and their relationships by sacrificing accuracy in interpreting the data values. In order to be accurate in the interpretation, data values need to be measured, computed on, and compared to theoretical or empirical models (quantitative analysis). If visualization software hampers quantitative analysis (which happens with some commercial visualization products), its use is greatly diminished for astrophysical data analysis. The software system STAR (Scientific Toolkit for Astrophysical Research) was developed as a prototype during the course of the project to better understand the pragmatic concerns raised in the project. STAR led to a better understanding on the importance of collaboration between astrophysicists and computer scientists.

Description: Observational data on atmospheric structure and mass fluxes from the sun and Be stars are applied to test the adequacy of the original Parker 'hot corona' approach to predicting atmospheric structure and the size of the mass flux from only the radiative and nonradiative energy fluxes, and from gravity, and imposing the condition that thermal and escape points must coincide. Observations do not support this latter condition. It is concluded that the Parker approach is an asymptotic approximation to the very low mass flux limit in a nonvariable stellar atmosphere.

Description: Enhanced X-ray emission from an early-type runaway star would be direct evidence for the presence of a collapsed companion, and thus for its origin as the result of a supernova explosion in a massive binary. To test this idea, measurements of X-ray fluxes in the 0.5-3 keV energy range from nine O and B type runaway stars were made with the Einstein Observatory. In each case, the X-ray luminosity observed does not exceed that expected from a normal OB star. Therefore we conclude that, if the runaway stars have collapsed companions, the separations of the components must be much greater than those in normal OB binaries.

Description: Carbon monoxide fundamental lines near 4.7 microns are employed to probe the thermal structure of the atmospheres of cool stars. A new non-LTE radiation transfer code is used to analyze high-resolution infrared CO line spectra and derive observation-based stellar atmosphere models. The main results are: (1) the CO-based models developed here deviate strongly from previously published models based on UV/visible observations; (2) varying degrees of agreement between the CO empirical models and predictions based on theoretical radiative-equilibrium atmosphere models are found; and (3) the parameter used to quantify this agreement is anticorrelated with the magnitude of chromospheric activity in the observed stars. These results suggest thermally bifurcated upper atmospheres as the standard case for cool stars.

Description: An extreme ultraviolet (EUV) imaging spectrograph designed for sounding rocket flight has been used to search for velocity fields in the low solar corona. During a flight in May, 1989, we obtained emission line profile measurements along a chord through an active region on the Sun. Relative Doppler velocities were measured in emission lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km/s at 350 A. The only Doppler shift appreciably greater than this level was observed in the line of Mg IX at 368.1 A over the umbra of the large sunspot. The maximum shift measured at that location corresponded to a velocity toward the observer of 14 plus or minus 3 km/s relative to the mean of measurements in that emission line made elsewhere over the active region. The magnetic field in the low corona was aligned to within 10 deg of the line of sight at the location of maximum Doppler shift. Depending on the magnetic field geometry, this mass outflow could either re-appear as a downflow of material in distant footprints of closed coronal loops or, if along open field lines, could contribute to the solar wind. The site of the sunspot was near a major photospheric magnetic field boundary. Such boundaries have been associated with low-speed solar winds as observed in interplanetary plasmas.

Description: Most current models of matter-flux in hot stars place its origin in radiation pressure, and then model the flow explicitly to produce no chromosphere-corona. Our model of the stellar atmosphere as a transition zone between stellar interior and interstellar medium places the origin of matter-flux, chromosphere-corona, and spectral 'emission classes' in subatmospheric nonthermal kinetic energy storage, equally for all stars, hot or cold. Current observations of both hot and cold stars suggest chromospheres to be a universal phenomenon, correlated with matter-fluxes, and enhanced in 'emission-class' stars. To clarify the difference between the two kinds of models above, we reformulate the wind-tunnel analogy to stellar winds, suggesting that stars satisfy an 'imperfect,' rather than 'perfect,' such model; i.e., transonic shocks occur before the throat, corresponding to an imposed outward velocity in the storage section, or subatmosphere. We then investigate the stability of an arbitrary stellar atmosphere, hot or cold, to suggest a cause for such an outward subatmospheric velocity.