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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…
The Hubble Space Telescope Quasar Absorption Line Key Project. II. Data Calibration and Absorption-Line Selection
Turnshek, David A.; Schneider, Donald P.; Savage, Blair D. +10 more
We present the observational and data processing aspects of the Hubble Space Telescope Quasar Absorption Line Key Project. Topics discussed include the observational technique, calibration of the data, software that simulates the data, the automated procedure used to identify and characterize the absorption features, and the determination of the s…
The Ionization Cones in the Seyfert Galaxy NGC 5728
Krolik, J. H.; Wilson, A. S.; Heckman, T. M. +2 more
We report high-resolution (0.1") observations of the Seyfert 2 galaxy NGC 5728 with the Hubble Space Telescope. Images have been obtained in the light of [O III] λλ4959, 5007, Hα+[N II] λλ6548, 6583 and green and red continua. The emission-line images reveal a spectacular biconical structure with overall extent 1.8 kpc. The two cones share a commo…
Abundance of Interstellar Carbon toward zeta Ophiuchi
Ebbets, Dennis C.; Savage, Blair D.; Cardelli, Jason A. +1 more
We report on the detection of the weak intersystem transition of semiforbidden C II 2325 A in the sight line toward Zeta Oph using the Ech-B mode of the Goddard High-Resolution Spectrograph. The measured equivalent width of the semiforbidden C II line is W(lambda) = 0.52 +/- 0.12 mA, implying a C II column density of 1.80 (+/- 0.42) x 10 exp 17 at…
Disappearance of the heliospheric sector structure at Ulysses
Balogh, A.; Tsurutani, B. T.; Forsyth, R. J. +6 more
In May, 1993, the heliospheric current sheet (HCS) ceased to be seen by the Ulysses spacecraft at a heliocentric latitude of ∼30° S and distance of 4.7 AU. The disappearance of the HCS coincided with the solar wind speed remaining >560 km/s and with the disappearance of one of four interaction regions previously seen on each solar rotation. The…