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Solar Wind Stream Interactions and the Wind Speed-Expansion Factor Relationship.
Goldstein, B. E.; Phillips, J. L.; Sheeley, N. R., Jr. +1 more
Previous studies have shown that the solar wind speed observed near Earth is inversely correlated with the divergence rate of magnetic flux tubes near the Sun. We test the global validity of this relationship by employing Ulysses wind speed measurements during 1990-1997 as well as inecliptic data for 1976-1997. When the correspondence between wind…
A two-dimensional simulation of the radial and latitudinal evolution of a solar wind disturbance driven by a fast, high-pressure coronal mass ejection
Riley, Pete; Gosling, J. T.; Pizzo, V. J.
Using a hydrodynamic simulation, we have studied the two-dimensional (symmetry in the azimuthal direction) evolution of a fast, high-pressure coronal mass ejection (CME) ejected into a solar wind with latitudinal variations similar to those observed by Ulysses. Specifically, the latitudinal structure of the ambient solar wind in the meridional pla…
Hubble Space Telescope WFPC2 Observations of the Binary Fraction among Pre-Main-Sequence Cluster Stars in Orion
Strom, Stephen E.; Padgett, Deborah L.; Ghez, Andrea
We present estimates of the binary frequency for optically visible (IHST < 19 mag) members of the dense (mean star separation ~0.05 pc) embedded stellar clusters associated with NGC 2024, NGC 2068, and NGC 2071 (distance = 460 pc) based on Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) observations. Of 99 targets,…
Adaptive Optics 0.2" Resolution Infrared Images of HL Tauri: Direct Images of an Active Accretion Disk around a Protostar
Roddier, Claude; Close, Laird M.; Roddier, François +2 more
We have obtained 0.2" FWHM images of HL Tau at K', H, and J utilizing the University of Hawaii Adaptive Optics System at the 3.6 m CFHT. These are the highest resolution deep images of HL Tau ever obtained in the infrared. They provide unique insight into HL Tau's circumstellar environment. An active accretion disk is directly resolved around HL T…
Dynamical Correlations for Globular Clusters in M31,
Djorgovski, S. G.; McCarthy, J. K.; Meylan, G. +5 more
We present internal velocity dispersion measurements for a set of 21 globular clusters in the Andromeda galaxy (M31). We combine them with structural and photometric cluster parameters measured earlier with the Hubble Space Telescope and from the ground to explore correlations of cluster properties and to compare them with the equivalent correlati…
Spectral analyses of central stars of planetary nebulae of early WC-type NGC 6751 and Sanduleak 3.
Hamann, W. -R.; Koesterke, L.
The two Wolf-Rayet type central stars of the planetary nebulae NGC 6751 and Sanduleak 3, showing the early spectral subtypes [WC4] and [WC2-3], respectively, are analyzed by means of non-LTE models for spherically expanding atmospheres. Complex model atoms of helium, carbon, oxygen and nitrogen are taken into account. For the atmospheric compositi…
First Results on it P Modes from GOLF Experiment
Baudin, F.; García, R. A.; Pérez Hernández, F. +17 more
The GOLF experiment on the SOHO mission aims to study the internal structure of the Sun by measuring the spectrum of global oscillations in the frequency range 10-7 to 10-2 Hz. Here we present the results of the analysis of the first 8 months of data. Special emphasis is put into the frequency determination of the p modes, as…
Acceleration of Solar Wind Ions by Nearby Interplanetary Shocks: Comparison of Monte Carlo Simulations with Ulysses Observations
Baring, Matthew G.; Forsyth, Robert J.; W. Ogilvie +1 more
Various theoretical techniques have been devised to determine distribution functions of particles accelerated by the first-order Fermi mechanism at collisionless astrophysical shocks. The most stringent test of these models as descriptors of the phenomenon of diffusive acceleration is a comparison of the theoretical predictions with observational …
Collimation of Astrophysical Jets: The Proto-Planetary Nebula He 3-1475
Borkowski, Kazimierz J.; Harrington, J. Patrick; Blondin, John M.
The proto-planetary nebula He 3-1475 was imaged in the [N II] λ6584 line with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image has revealed what appear to be large-scale flows being collimated into narrow bipolar jets. This is a unique object: we may be observing the actual collimation process of an astrophysical j…
On the Patterns of the Solar Granulation and Supergranulation
Title, Alan M.; Schrijver, Carolus J.; Hagenaar, Hermance J.
We study the cellular patterns of the white light granulation and of the chromospheric Ca II K supergranular network. We apply a gradient-based tessellation algorithm to define the cell outlines. The geometry of the patterns formed by the associated granular and supergranular flows are very similar, in spite of the substantial difference in length…