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Ultraviolet Color-Magnitude Diagram Studies of Intermediate Age Large Magellanic Cloud Star Clusters.I.NGC 1783

Cole, Andrew A.; Freedman, Wendy L.; Gallagher, John S., III +1 more

We have imaged the billion-year-old Large Magellanic Cloud star cluster NGC 1783 with the Wide Field/Planetary Camera 2 (WFPC2) in order to obtain broadband photometry at 1600 and 3300 Angstroms. We have identified for the first time the individual stars responsible for the unexpectedly strong ultraviolet light of intermediate-age stellar systems.…

Parallaxes and Proper Motions of Prototypes of Astrophysically Interesting Classes of Stars. I. R Coronae Borealis Variables

Kundu, Arunav; Trimble, V.

Hipparcos data were obtained under the 1982 announcement of opportunity for the seven brightest R CrB stars then known. None of the parallax measurements is different from zero in a statistically significant way, though most of the proper motions are. The body of the data nevertheless suggest that the stars belong to two rather different populatio…

Ulysses observations of energetic H₃⁺ ions in Jupiter's magnetosphere

Krupp, N.; Woch, J.; Keppler, E. +3 more

Ulysses was the fifth spacecraft to visit Jupiter. In this paper measurements of energetic H_3^+-ions in the Jovian magnetosphere made by the EPAC (Energetic Particle Composition) instrument onboard Ulysses are presented and compared with formerly published findings from the HI-SCALE instrument also onboard Ulysses.

Probing Galactic Center Black Hole Candidates with Far-Infrared Spectroscopy

Hollenbach, David J.; Colgan, Sean W. J.; Maloney, Philip R.

The narrow positron annihilation line source in the Galactic center has been identified with the X-ray source 1E 1740.7-2942, which is coincident in projection with a Galactic center molecular cloud and exhibits synchrotron jets in the radio spectrum. It has been suggested that the source is powered by Bondi-Hoyle accretion from the cloud onto a c…

Anomalous Cosmic-Ray Helium, Nitrogen and Oxygen in 1996 - Measurements of the ERNE Instrument on-board SOHO

Vainio, R.; Valtonen, E.; Riihonen, E. +4 more

The energy spectra of the anomalous components of helium, nitrogen and oxygen have been measured by the ERNE experiment on board the SOHO spacecraft. During February 28-April 30, 1996, the maximum intensity of anomalous helium was found to be 3.8 × 10^-5 cm^-2 sr^-1 s^-1 (MeV nucl^-1)^-1 …

Understanding some moving groups in terms of a global spiral shock.

Figueras, F.; Torra, J.; Comeron, F.

We present a schematic model to interpret the kinematics of some major moving groups in the solar neighbourhood. The origin of these groups is assumed to lie in large scale spiral shocks which may be responsible for the spiral arms in the galactic disk, which provide the initial conditions in the velocities of stars formed as a consequence of them…

Observation of interplanetary particles in a corotating interaction region and of energetic water group ions from comet Grigg-Skjellerup

Coates, A. J.; Neubauer, F. M.; Daly, P. W. +2 more

During the flyby of the Giotto S/C with comet Grigg-Skjellerup (G-S) (9-11 July 1992) energetic particles ( E_{H 2O > 60 keV, Ep > 30 keV, Eα > 3.5 MeV), magnetic fields and plasma ions were measured by three different detectors on board Giotto. The flyby period was characterized by high magnetic field …}

Optical emission in the radio lobes of Cygnus A.

Nilsson, K.; Jones, L. R.; Lehto, H. J. +2 more

Deep optical imaging and spectroscopy of stellar objects in the radio lobes of Cygnus A have been carried out. Brighter optical objects close to the radio hotspots are either confirmed or suspected Galactic stars. Very faint optical emission is found coinciding with hotspot D (R~23.1) and hotspot B (V~25.4). The implications of these observations …

Opportunities for Magnetospheric Research with Coordinated Cluster and Ground-Based Observations

Lockwood, M.; Opgenoorth, H. J.

HST observations of IP Pegasi in quiescence: the pre-eclipse spectrum

Eracleous, Michael; Szkody, Paula; Horne, Keith +5 more

We present time-resolved HST ultraviolet (UV) spectroscopy and ground-based optical photometry of the dwarf nova IP Pegasi in a quiescent state. The observations were obtained prior to an eclipse, when the bright spot caused by the impact of the accretion stream with the edge of the disc dominates the light output. The optical light curve is fairl…