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Testing the hypothesis of the morphological transformation from field spiral to cluster S0
Smail, Ian; Kodama, Tadayuki
Hubble Space Telescope observations of distant clusters have suggested a steep increase in the proportion of S0 galaxies between clusters at high redshifts and similar systems at the present day. It has been proposed that this increase results from the transformation of the morphologies of accreted field galaxies from spirals to S0s. We have simul…
Modelling of thunderclouds and lightning generation on Titan
Lammer, H.; Molina-Cuberos, G. J.; Tokano, T. +1 more
The likelihood of lightning generation in Titan's troposphere is investigated by theoretical consideration and a numerical one-dimensional time-dependent thundercloud model. The main cloud electrification hypotheses proposed for terrestrial thunderstorms are examined taking into account recent knowledge concerning Titan's atmospheric state, especi…
Coordinated 1996 HST and IRTF Imaging of Neptune and Triton. III. Neptune's Atmospheric Circulation and Cloud Structure
Baines, K. H.; Sromovsky, L. A.; Fry, P. M. +2 more
The first coordinated multispectral imaging of Neptune and Triton, using both the Hubble Space Telescope and the NASA Infrared Telescope Facility in August 1996 (L. A. Sromovsky et al., 149, 416-434, 435-458), provides new insights into Neptune's atmospheric circulation and cloud structure. From our 1996 data we derived cloud-tracked winds for 18 …
Cassiopeia A: On the origin of the hard X-ray continuum and the implication of the observed O Viii Ly-alpha /Ly-beta distribution
Kaastra, J. S.; Vink, J.; Aschenbach, B. +4 more
We present the first results on the hard X-ray continuum image (up to 15 keV) of the supernova remnant Cas A measured with the EPIC cameras onboard XMM-Newton. The data indicate that the hard X-ray tail, observed previously, that extends to energies above 100 keV does not originate in localised regions, like the bright X-ray knots and filaments or…
The origin of the runaway high-mass X-ray binary HD 153919/4U1700-37
Kaper, L.; de Bruijne, J. H. J.; Hoogerwerf, R. +3 more
Based on its Hipparcos proper motion, we propose that the high-mass X-ray binary HD 153919/4U1700-37 originates in the OB association Sco OB1. At a distance of 1.9 kpc the space velocity of 4U1700-37 with respect to Sco OB1 is 75 km s-1. This runaway velocity indicates that the progenitor of the compact X-ray source lost about 7 Ms…
Star Formation History in the Solar Vicinity
Bertelli, G.; Nasi, E.
The star formation history in the solar neighborhood is inferred by comparing a sample of field stars from the Hipparcos catalog with synthetic color-magnitude diagrams. We consider separately the main sequence and the red giant region of the H-R diagram. The criteria for our best solutions are based on the χ2 minimization of star distr…
Detection of High-Latitude Waves of Solar Coronal Activity in Extreme-Ultraviolet Data from the Solar and Heliospheric Observatory EUV Imaging Telescope
Kosovichev, A. G.; Benevolenskaya, E. E.; Scherrer, P. H.
We present the results of an investigation of EUV coronal structures in 1996-2000 using the Solar and Heliospheric Observatory EIT data in 171, 195, 284, and 304 Å lines. During this period, poleward- and equatorward-migrating waves of solar activity have been found in axisymmetrical distributions of EUV intensity in all four lines. In the axisymm…
Color-Magnitude Diagram and Luminosity Function of M4 near the Hydrogen-burning Limit
Anderson, Jay; Bedin, Luigi R.; Piotto, Giampaolo +1 more
A proper-motion separation of M4 members from field stars, using deep Hubble Space Telescope observations separated by a time baseline of 5 yr, allows us to study a pure sample of cluster main-sequence stars almost to the minimum mass for hydrogen burning. High-precision photometry shows how badly current theoretical models fail to reproduce the c…
The Multitude of Unresolved Continuum Sources at 1.6 Microns in Hubble Space Telescope Images of Seyfert Galaxies
Rieke, G. H.; Alonso-Herrero, A.; Quillen, A. C. +4 more
We examine 112 Seyfert galaxies observed by the Hubble Space Telescope at 1.6 µm. We find that ~50% of the Seyfert 2.0 galaxies which are part of the Revised Shapely-Ames (RSA) Catalog or the CfA redshift sample contain unresolved continuum sources at 1.6 µm. All but a couple of the Seyfert 1.0-1.9 galaxies display unresolved continuum…
Kinematics of the Narrow-Line Region in the Seyfert 2 Galaxy Markarian 3
Gull, T. R.; Kraemer, S. B.; Crenshaw, D. M. +5 more
We present measurements of radial velocities for the narrow-line region gas in the Seyfert 2 galaxy Mrk 3 out to ~1 kpc from the nucleus. The observations consist of two data sets, both using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope: (1) an [O III] slitless spectrum with the G430M grating of the inner 3" around …