Search Publications
HST synthetic spectral analysis of U GEM in early and late quiescence: A heated white dwarf and accretion belt?
Horne, Keith; Sion, E. M.; Huang, M. +3 more
We have re-examined two archival HST FOS G130H spectra of the prototype dwarf nova U Geminorum obtained during its quiescence 13 days and 70 days after a wide outburst. Using synthetic spectral fitting with two flux-emitting components, a slowly rotating white dwarf photosphere, and a rapidly spinning accretion belt (Vrot sin i=3200 km …
Near Infrared Imaging of the Hubble Deep Field with the Keck Telescope
Hogg, David W.; Matthews, K.; Soifer, B. T. +4 more
Two deep K-band (2.2 microns ) images, with point-source detection limits of K=25.2 mag (one sigma), taken with the Keck Telescope in subfields of the Hubble Deep Field, are presented and analyzed. A sample of objects to K=24 mag is constructed and V606-I814 and I814-K colors are measured. By stacking visually sele…
The Nuclear Region of M51 Imaged with the HST Planetary Camera
Lauer, Tod R.; Faber, S. M.; Grillmair, Carl J. +4 more
We present high-resolution, broad- and narrow-band, pre-refurbishment images of the central region of M51 taken with the Planetary Camera of the Hubble Space Telescope. The V-band images show a rather chaotic distribution of dust lanes, though some are oriented radially, roughly aligned with the major axis of the bar, and may be transporting gas t…
Chromospheric Emission in Metal-poor Solar-Type Stars
Schrijver, Carolus J.; Peterson, Ruth C.
Cool stars like the Sun show chromospheric activity, which is largely attributed to nonradiative sources of energy linked to rotationally driven magnetic fields. However, a nonmagnetic process, such as dissipation of acoustic waves, may operate side by side with the first process. We report detections of chromospheric emission reversals in Mg II 2…
The heliospheric modulation of galactic cosmic rays at solar minimum
Potgieter, M. S.
The observations acquired by the Ulysses spacecraft since launch, but especially during the recent fast latitude scan, have provided a comprehensive, 3-dimensional view of the inner heliosphere. Together with the observations by IMP 8, Pioneer 10 and the two Voyagers, a wealth of new observations on particles and fields enables us to improve signi…
Simulation of the Morphology of the Jovian UV North Aurora Observed with the Hubble Space Telescope
Waite, J. H.; Grodent, D.; Gladstone, G. R. +2 more
A model simulating Earth views of UV auroral arcs and diffuse emissions in the Jovian north polar region is described. It assumes a Chapman profile of vertical brightness distribution and various horizontal structures. Simple geometric cases are described to illustrate the dependence on the altitude, atmospheric scale height, and central meridian …
Determination of the Formation Temperature of Si IV in the Solar Transition Region
Wilhelm, K.; Schühle, U.; Lemaire, P. +4 more
Using spectra obtained with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we deduce the temperature of formation of the Si IV ion in the solar transition region from the Si IV ultraviolet spectral line intensity ratio, 3p 2P3/2-3d …
Subarcsec structures in the double nucleus of NGC6240 disclosed with HST at 370, 430 and 500 NM
Barbieri, C.; Komossa, S.; Rafanelli, P. +4 more
We present an analysis of three medium band width (FWHM ~ 400 - 450 Angstroms) images of the nuclear region of NGC6240 taken with the pre-COSTAR Faint Object Camera (FOC) on board of the Hubble Space Telescope. The first filter band comprises the [OII]lambda 3727 doublet, the second measures the blue continuum around 4400 { Angstroms} and the thir…
Testing the X-ray variability of active galactic nuclei with the non-linear prediction method
Czerny, Bozena; Lehto, Harry J.
The analysis of eight EXOSAT X-ray light curves of six active galactic nuclei by non-linear prediction methods indicates that the observed variability is truly stochastic and is not caused by deterministic chaos. This result favours X-ray emission models with multiple centres of production of hot, possibly relativistic, electrons.
Ultraviolet Spectroscopy of Hot Compact Stars.
Rauch, T.; Werner, K.; Dreizler, S. +4 more