Search Publications
Star Formation in the NICMOS HDF
Thompson, Rodger I.
This contribution discusses the rate of star formation in the galaxies observed in the NICMOS Hubble Deep Field. A combination of the earlier fluxes from the WFPC II HDF measurements and the NICMOS near infrared measurement produces a superb data base for the application of photometric redshift techniques. By capitalizing on the extended wavelengt…
Kinematics and Morphology of the Resolved Narrow Line Region in NGC 4151
Gull, T. R.; Kraemer, S. B.; Crenshaw, D. M. +6 more
A complement of HST narrow band images, STIS slitless and long-slit spectra have been employed to probe the morphology, kinematics, dynamics, and ionization structure of the near-nuclear region in NGC 4151. The images illustrate the inner biconical cloud distribution which exhibits recessional velocities relative to the nucleus to the NE and appro…
On the Lyman α and O VI Line Profiles in Streamers and Coronal Holes
Poletto, G.; Noci, G.; Nicolosi, P. +1 more
The profiles of the Lyα line at 1215.6 Å and of the O VI doublet at 1031.9 Å and 1037.6 Å in the extended solar corona have been analyzed vs. latitude and radial direction, performing observations with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (Solar and Heliospheric Observatory). The results show t…
Implications of Increased Perpendicular Diffusion on the Tilt Angle Depedence of Electron Modulation in the Heliosphere
Ferreira, S. E. S.; Potgieter, M. S.; Burger, R. A.
For numerical solutions of Parker's cosmic ray transport equation to be compatible with the small latitudinal gradients observed for protons by Ulysses, enhanced perpendicular diffusion seems needed in the polar regions of the heliosphere. The role of enhanced perpendicular diffusion was further investigated by examining electron modulation as a f…
Relationship between X-ray and ultraviolet emission in 3C 273
Paltani, S.; Walter, R.; Courvoisier, T. J. -L. +1 more
In 3C 273, ultraviolet flux and X-ray flux measured by BATSE are not well correlated, contrarily to predictions of several models, unless the X-ray flux lags the UV emission by 1.75 yr. The absence of observed correlation at small lag cannot be due to spectral variability. A Comptonizing corona model is however compatible with all UV and X-ray obs…
Ulysses/BeppoSAX observations of cosmic gamma-ray bursts
Piro, L.; Frontera, F.; Orlandini, M. +5 more
BeppoSAX has been added to the 3rd Interplanetary Network of gamma-ray burst detectors. Of the 8 events observed to date by Ulysses and the BeppoSAX Gamma Ray Burst Monitor (GRBM), four have been localized by triangulation, resulting in annuli whose 3σ widths are as small as 63''. These data give error boxes whose sizes are sometimes smaller than …
The Morphological Evolution of Field Galaxies
Ellis, Richard S.
I review two observational programs which, together, promise to unravel the detailed astrophysical evolution of normal field galaxies over the last 5–7 Gyr. Systematic ground-based spectroscopy of faint galaxies have revealed an increasing faint end slope for the luminosity function with redshift. The trend is strongest for galaxies undergoing int…
Solar Energetic Particle Events in the Rising Phase of Solar Cycle 23: Observations at 1 and 5 AU
Lario, David
We present energetic particle observations by the Ulysses and WIND spacecraft during the years 1997-1998. This period corresponds to the onset of the new solar cycle (23) when the increasing level of solar activity started to produce solar energetic proton (SEP) events. Several large and long-lasting SEP events were observed by both spacecraft dur…
Pleiades luminosity function: fine structure and new Pre-MS models
Piskunov, A. E.; Schilbach, E.; Belikov, A. N.
In order to study a model-dependence of the results achieved in the previous investigations of the Pleiades luminosity function using D'Antona and Mazzitelli (1994) evolutionary tracks, we repeated the computations with the new track system by D'Antona and Mazzitelli (1997). T h e following main conclusions can be drawn: the new models agree bette…
Calibration of the Faber--Jackson relation for M31 globular clusters using HIPPARCOS data
Paturel, G.; Lanoix, P.; Di Nella-Courtois, H.
In this paper we present data analysis regarding globular clusters as possible extragalactic distance indicators. For this purpose, we collected all velocity dispersion measurements published for Galactic and M31 globular clusters. The slope and zero-point of the Faber--Jackson relation were calibrated using Hipparcos distance measurements, and th…