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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…
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…
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…
Molecular Hydrogen in the Direction of ζ Orionis A
Jenkins, Edward B.; Peimbert, Antonio
A spectrum of ζ Ori A over the wavelength interval 950-1150 Å recorded by the Interstellar Medium Absorption Profile Spectrograph (IMAPS) on the ORFEUS-SPAS I mission shows Lyman and Werner band absorption features from molecular hydrogen in rotational levels J = 0, 1, 2, 3, and 5. Most of the molecules are found in two distinct velocity component…
The Structure of the Super-Star Clusters in NGC 1569 from Hubble Space Telescope WFPC2 Images
Leitherer, Claus; Clampin, Mark; Nota, Antonella +3 more
We present high-resolution observations of the super-star clusters in the nearby irregular galaxy NGC 1569, obtained with the WFPC2 on board the Hubble Space Telescope. Our analysis shows that the brightest of these clusters, NGC 1569A, results from the superposition of two clusters with an angular separation of ~0.2". Recent ground-based spectros…
Evolution of Cluster Ellipticals at 0.2 < z < 1.2 from Hubble Space Telescope Imaging,
Barrientos, L. Felipe; López-Cruz, Omar; Schade, David
Two-dimensional surface photometry derived from Hubble Space Telescope imaging is presented for a sample of 225 early-type galaxies (assumed to be cluster members) in the fields of nine clusters at redshifts 0.17 < z < 1.21. The 94 luminous ellipticals (MAB(B) < -20 selected by morphology alone with no reference to color) form …