Search Publications
Cepheid Calibration of the Peak Brightness of Type IA Supernovae. X. SN 1991T in NGC 4527
Panagia, N.; Saha, A.; Labhardt, Lukas +5 more
Repeated imaging observations have been made of NGC 4527 with the Hubble Space Telescope between 1999 April and June, over an interval of 69 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the Type Ia supernova SN 1991T, which showed relatively unusual behavior by having both an abn…
IRAS 09425-6040: A carbon star surrounded by highly crystalline silicate dust
Loup, C.; Yamamura, I.; Molster, F. J. +4 more
We present infrared spectroscopy and millimeter photometry and spectroscopy of the peculiar carbon star IRAS 09425-6040. The 2-15 mu m spectrum, as well as the CO millimeter line observations are typical for a (J-type) carbon star with moderate mass-loss rate. The 15-45 mu m spectrum is dominated by strong emission bands from Mg-rich and Fe-poor c…
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…