Search Publications
Quiet Sun EUV transient brightenings and turbulence. A panoramic view by EIT on board SOHO
Berghmans, D.; Clette, F.; Moses, D.
Since January 1996, the Extreme-Ultraviolet Imaging Telescope (EIT, onboard SOHO) has produced unique image sequences covering a wide field of view with a high temporal resolution, in the He Ii transition region line and in several Fe coronal emission lines. Using two sequences acquired with cadences of the order of one minute and with durations r…
Geomagnetic storms caused by coronal mass ejections (CMEs): March 1996 through June 1997
St. Cyr, O. C.; Paswaters, S. E.; Simnett, G. M. +7 more
(1) All but two geomagnetic storms with Kp ≥ 6 during the operating period (March 1996 through June 1997) of the Large Angle Spectroscopic Coronagraph (LASCO) experiment on the Solar and Heliospheric Observatory (SOHO) spacecraft can be traced to Coronal Mass Ejections (CMEs). (2) These geomagnetic storms are not related to high speed solar wind s…
Evolved Massive Stars in the Local Group. II. A New Survey for Wolf-Rayet Stars in M33 and Its Implications for Massive Star Evolution: Evidence of the ``Conti Scenario'' in Action
Massey, Philip; Johnson, Olivia
We expect the evolution of massive stars to be strongly influenced by mass loss and hence to be sensitive to metallicity. It should be possible to test this ``Conti scenario'' be comparing the populations of evolved massive stars among the Local Group galaxies, but such investigations have been hampered by incompleteness. In a previous paper, we p…
Deuterium Abundance in the Local ISM and Possible Spatial Variations
Linsky, Jeffrey L.
Excellent HST/GHRS spectra of interstellar hydrogen and deuterium Lyman-alpha absorption toward nearby stars allow us to identify systematic errors that have plagued earlier work and to measure accurate values of the D/H ratio in local interstellar gas. Analysis of 12 sightlines through the Local Interstellar Cloud leads to a mean value of D/H = (…
The Ultraviolet Spectra of LINERs: A Comparative Study
Filippenko, Alexei V.; Ho, Luis C.; Maoz, Dan +3 more
Imaging studies have shown that ~25% of LINER galaxies display a compact nuclear UV source. As part of a program to study the nature of LINERs and their connection to the active galaxy phenomenon, we compare the Hubble Space Telescope UV (1150-3200 Å) spectra of seven such UV-bright LINERs. Data for three of the galaxies (NGC 404, 4569, and 5055) …
X-ray coronal changes during Halo CMEs
St. Cyr, O. C.; Webb, D. F.; Lemen, J. R. +2 more
Using the Yohkoh soft X-ray images, we examine the coronal structures associated with “halo” coronal mass ejections (CMEs). These may correspond to events near solar disk center. Starting with a list of eleven confirmed halo CMEs over the time range from December 1996 through May 1997, we find seven with surface features identifiable in soft X-ray…
The Mass-to-Light Ratio of Early-Type Galaxies: Constraints from Gravitational Lensing in the Rich Cluster AC 114
Smail, Ian; Ellis, Richard S.; Kneib, Jean-Paul +1 more
We present a new wide-field image of the distant cluster AC 114 (z = 0.31) obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image considerably extends our knowledge of the lensing properties of the cluster beyond that derived earlier from a single WFPC1 pointing. In conjunction with published ground-based s…
Asteroids as far-infrared photometric standards for ISOPHOT
Mueller, T. G.; Lagerros, J. S. V.
Asteroids are used as far-IR calibrators for the imaging photopolarimeter ISOPHOT on board the Infrared Space Observatory ISO. For the 10 selected objects we compiled a large uniform database of 678 individual observations, ranging from 7-2 000 microns. Applying a new thermophysical model to the observations we derived thermal properties of the se…
Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars
Eyer, L.; Aerts, C.; Grenon, M. +2 more
We present a classification of 267 new variable B-type stars discovered by Hipparcos. We have used two different classification schemes and they both result in only a few new beta Cephei stars, a huge number of new slowly pulsating B stars, quite some supergiants with alpha Cyg-type variations and variable CP stars, and further some new periodic B…
Detection of intergalactic red-giant-branch stars in the Virgo cluster
Ferguson, Henry C.; von Hippel, Ted; Tanvir, Nial R.
It has been suspected for nearly 50 years that galaxy clusters contain a population of intergalactic stars ripped from the galaxies during cluster formation, or when the galactic orbits pass through the cluster centre. Observational support for theexistence of such a stellar population is provided both by measurements of the diffuse light in clust…