Search Publications
High Resolution Imaging of Galaxy Cores
Boksenberg, A.; Barbieri, C.; Weigelt, G. +17 more
Surface photometry data obtained with the Faint Object Camera of the Hubble Space Telescope in the cores of ten galaxies is presented. The major results are: (i) none of the galaxies show truly "isothermal" cores, (ii) galaxies with nuclear activity show very similar light profiles, (iii) all objects show central mass densities > 10^3^M_sun_ pc…
On the nature of rapid X-ray variability in active galactic nuclei.
McHardy, I. M.; Lehto, H. J.; Green, A. R.
We systematically analyse all (110) EXOSAT AGN medium-energy light curves of length greater than 20 ks to search for and quantify their flux variability. We also perform extensive simulations to quantify the selection effects (such as the source brightness or the length of observation) that might prevent the detection of variability. We quantify v…
Ulysses observations of a recurrent high speed solar wind stream and the heliomagnetic streamer belt
McComas, D. J.; Goldstein, B. E.; Bame, S. J. +4 more
Near-ecliptic solar wind observations by Ulysses on its way to the polar regions of the Sun, compared with those from IMP 8 at 1 AU, showed that high-speed streams decay and broaden with heliocentric distance from IMP 8 to Ulysses, as expected. In July 1992 while travelling south at ∼13°S and 5.3 AU, Ulysses encountered a recurrent high-speed stre…
Perpendicular transport in 1- and 2-dimensional shock simulations
Giacalone, J.; Jokipii, J. R.; Kota, J.
We consider the foundations of 1- and 2-dimensional shock simulations in which the physical quantities are independent of a coordinate which is not parallel to the magnetic field. We show analytically that in such simulations the ions are effectively tied to the convected magnetic lines of force because of the presence of an ignorable spatial coor…
A large nuclear accretion disk in the active galaxy NGC4261
O'Connell, Robert W.; Ferrarese, Laura; Ford, Holland C. +2 more
THE powerful emissions from the nuclei of active galaxies and quasars are thought to arise from the accretion of matter onto a massive black hole. Angular momentum will prevent matter from falling directly onto the central mass; instead, an 'accretion disk' should form, within which the gravitationally bound material will lose angular momentum and…
Stellar Kinematic Groups. I. The URSA Major Group
Soderblom, David R.; Mayor, Michel
The Ursa Major Group (UMaG) is studied as a test case for the authenticity of Stellar Kinematic Groups, using Coravel radial velocities, recent compilations of astrometric data, and new spectroscopic observations. Spectroscopic age indicators, particularly indices of the strength of chromospheric emission, are applied to solar-type candidate membe…
Lithium and Rapid Rotation in Chromospherically Active Single Giants
Fekel, Francis C.; Balachandran, Suchitra
The rotational velocities presently obtained via spectroscopic observations of a group of moderately rapidly rotating, chomospherically active single giants indicate that Gray's (1989) rotostat hypothesis requires modification. Their rapid rotation appears to be due to high Li abundances, and results in increased chromospheric activity. A scenario…
Latitudinal variation of solar wind corotating stream interaction regions: Ulysses
McComas, D. J.; Goldstein, B. E.; Bame, S. J. +4 more
Ulysses’ initial transit to high heliographic latitudes at a heliocentric distance of ∼5 AU has revealed systematic effects in the latitudinal evolution of corotating interaction regions (CIRs). At a latitude corresponding roughly to, but slightly less than, the inferred tilt of the coronal streamer belt and embedded heliospheric current sheet, th…
Detection of the hydroxyl radical in the Saturn magnetosphere
Shemansky, D. E.; Tripp, T. M.; Matheson, P. +2 more
THE magnetosphere in the vicinity of the orbits of Saturn's icy satellites consists of a low-density plasma, in which the electrons are an order of magnitude cooler than the accompanying heavy ions1. Most models2-12 neglect this fact, even though radiative cooling and diffusive loss rates are both too slow to account for the …
Hubble Space Telescope Imaging of the Narrow-Line Region of NGC 4151
Ford, H. C.; Kriss, G. A.; Evans, I. N. +3 more
We have used the Planetary Camera aboard the Hubble Space Telescope to obtain high spatial resolution [O III] λ5007 and Hα λ6563 + [N II] λλ6548, 6583 images of the nucleus of NGC 4151. Almost all of the Hα λ6563 + [N II] λλ6548, 6583 emission arises from an unresolved nuclear point source. The [O III] λ5007 image resolves the narrow-line region i…