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Semiempirical Two-dimensional MagnetoHydrodynamic Model of the Solar Corona and Interplanetary Medium

Guhathakurta, Madhulika; Sittler, Edward C., Jr.

We have developed a two-dimensional semiempirical MHD model of the solar corona and solar wind. The model uses empirically derived electron density profiles from white-light coronagraph data measured during the Skylab period and an empirically derived model of the magnetic field which is fitted to observed streamer topologies, which also come from…

Dust in an Extremely Metal-Poor Galaxy: Mid-infrared Observations ofSBS 0335-052

Sauvage, Marc; Madden, Suzanne; Thuan, Trinh X.

The metal-deficient (Z=Z_solar/41) blue compact dwarf galaxy SBS 0335-052 was observed with ISOCAM between 5 and 17 µm. With an L_12µm/L_B ratio of 2.15, the galaxy is unexpectedly bright in the mid-infrared for such a low-metallicity object. The mid-infrared spectrum shows no sign of the unidentified infr…

The Metagalactic Ionizing Radiation Field at Low Redshift

Shull, J. Michael; Giroux, Mark L.; Penton, Steven V. +2 more

We compute the ionizing radiation field at low redshift, arising from Seyferts, QSOs, and starburst galaxies. This calculation combines recent Seyfert luminosity functions, extrapolated ultraviolet fluxes from our IUE-AGN database, and a new intergalactic opacity model based on Hubble Space Telescope and Keck Lyα absorber surveys. At z=0 for AGNs …

Hubble Space Telescope Observations of the CFA Seyfert 2 Galaxies: The Fueling of Active Galactic Nuclei

Pogge, Richard W.; Martini, Paul

We present an investigation of possible fueling mechanisms operating in the inner kiloparsec of Seyfert galaxies. We analyze visible and near-infrared Hubble Space Telescope images of 24 Seyfert 2 galaxies from the CfA Redshift Survey sample. In particular, we are searching for the morphological signatures of dynamical processes responsible for tr…

Decay of the GRB 990123 Optical Afterglow: Implications for the Fireball Model

Hjorth, Jens; Walter, Fabian; Hippelein, Hans +49 more

Cepheid Calibration of the Peak Brightness of Type IA Supernovae. IX. SN 1989B in NGC 3627

Panagia, N.; Saha, A.; Labhardt, Lukas +3 more

Repeated imaging observations have been made of NGC 3627 with the Hubble Space Telescope in 1997-1998 over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the prototypical, ``Branch normal,'' type Ia supernova SN 1989B. A total of 83 variables have been found, of w…

An ultra-deep ISOCAM observation through a cluster-lens

Altieri, B.; Aussel, H.; Elbaz, D. +10 more

We present results of ultra-deep ISOCAM observations through a cluster-lens at 7mu m and 15mu m with the Infrared Space Observatory (ISO) satellite. These observations reveal a large number of luminous Mid-Infrared (MIR) sources. Cross-identification in the optical and Near-Infrared (NIR) wavebands shows that about half of the 7 mu m sources are c…

Search for antihelium in cosmic rays.

Finelli, F.; Santos, D.; Usoskin, I. +207 more

The alpha magnetic spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 in a 51.7° orbit at altitudes between 320 and 390 km. A total of 2.86×10⁶ helium nuclei were observed in the rigidity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to…

A review of discontinuities and Alfvén waves in interplanetary space: Ulysses results

Tsurutani, Bruce T.; Ho, Christian M.

The Ulysses mission is the first to explore our heliosphere at all latitudes up to +/-80° and therefore is an ideal mission to study potential gradients in heliolatitude (and radial distance) of discontinuity occurrence rates and types. Directional discontinuities (DDs) are shown to be dependent on the type of solar wind streams that they are embe…

The properties of field elliptical galaxies at intermediate redshift - I. Empirical scaling laws

Treu, T.; Stiavelli, M.; Møller, P. +2 more

We present measurements of the Fundamental Plane (FP) parameters (the effective radius, the mean effective surface brightness, and the central velocity dispersion) of six field elliptical galaxies at intermediate redshift. The imaging is taken from the Medium Deep Survey of the Hubble Space Telescope, while the kinematical data are obtained from l…