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GHRS Observations of Cool, Low-Gravity Stars. V. The Outer Atmosphere and Wind of the Nearby K Supergiant λ Velorum
Harper, Graham M.; Bennett, Philip D.; Brown, Alexander +3 more
UV spectra of λ Velorum taken with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope are used to probe the structure of the outer atmospheric layers and wind and to estimate the mass-loss rate from this K5 Ib-II supergiant. VLA radio observations at λ=3.6 cm are used to obtain an independent check on the wind velocity a…
The Taylor-Proudman Balance and the Solar Rotational Data
Durney, Bernard R.
For the Sun (and because of the presence of buoyancy), the implications of the Taylor-Proudman balance (TPB, a balance between the pressure, Coriolis, and buoyancy forces in the radial and latitudinal momentum equations) differ fundamentally from those of an incompressible fluid. The TPB now only determines the latitudinal variations of the solar …
Forming the Dusty Ring in HR 4796A
Wood, Kenneth; Wolff, Michael J.; Kenyon, Scott J. +1 more
We describe planetesimal accretion calculations for the dusty ring observed in the nearby A0 star HR 4796A. Models with initial masses of 10-20 times the minimum-mass solar nebula produce a ring with a width of 7-15 AU and a height of 0.3-0.6 AU at 70 AU in ~10 Myr. The ring has a radial optical depth of ~1. These results agree with limits derived…
[Fe II] Bubbles in the Young Planetary Nebula Hubble 12
Woodward, Charles E.; Frank, A.; Forrest, W. J. +2 more
We have obtained narrowband images of the young planetary nebula Hubble 12 showing [Fe II] line emission in bipolar bubbles near the core. Bright [Fe II] emission is strong evidence for shocks, suggesting the presence of a high-velocity wind emanating from the central star. We compare our data to previously published images of Hubble 12--finding s…
Evolution of Chromospheric Structures: How Chromospheric Structures Contribute to the Solar HE II 30.4 Nanometer Irradiance and Variability
Woods, Thomas N.; Worden, John; Neupert, Werner M. +1 more
The bright He II 30.4 nm solar emission is an important energy source for ionization and heating of the Earth's upper atmosphere. The analysis of the Solar and Heliospheric Observatory (SOHO) Extreme-Ultraviolet Imaging Telescope (EIT) He II 30.4 nm images provides an improved understanding of how the solar surface structures, i.e., plage, enhance…
Nonthermal Radio Signatures of Coronal Disturbances with and without Coronal Mass Ejections
Thompson, B. J.; Andrews, M. D.; Mann, G. +3 more
This study presents data on two events from the Extreme-UV Imaging Telescope (EIT) and the Large Angle and Spectroscopic Coronagraph instruments (C1, C2, and C3), Geostationary Operational Environmental Satellite (GOES) soft X-ray data, and 40-800 MHz radio spectra of the Astrophysical Institute Potsdam. At first glance, the two events appear simi…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XIX. The Discovery of Cepheids in and a New Distance to NGC 3198
Kelson, Daniel D.; Illingworth, Garth D.; Huchra, John P. +17 more
We report the detection of Cepheid variable stars and a new distance to the Sc spiral NGC 3198. NGC 3198 is one of 25 galaxies that have been observed with the WFPC2 of the Hubble Space Telescope (HST) for the purpose of measuring Cepheid distances. Eighteen of these galaxies were targeted by the HST Key Project on the Extragalactic Distance Scale…
Ultraviolet Imaging Polarimetry of Narrow-Line Radio Galaxies
Antonucci, Robert; Hurt, Todd; Cohen, Ross +2 more
In an examination of the unification of radio galaxies and quasars, we obtained UV polarization images of eight narrow-line radio galaxies (NLRGs) with the Faint Object Camera on board the Hubble Space Telescope (HST). By observing in the rest ultraviolet, we can measure the polarization of the active nucleus with little contamination from unpolar…
GHRS and ORFEUS II Observations of the Highly Ionized Interstellar Medium toward ESO 141-055
Sembach, Kenneth R.; Savage, Blair D.; Hurwitz, Mark
We present Goddard High Resolution Spectrograph (GHRS) and ORFEUS II measurements of Si IV, C IV, N V, and O VI absorption in the interstellar medium of the Galactic disk and halo toward the nucleus of the Seyfert galaxy ESO 141-055. The high-ionization absorption is strong, with line strengths consistent with the spectral signature expected for h…
Analysis of Extreme-Ultraviolet Off-Limb Spectra Obtained with SUMER/SOHO: Ne VI-Mg VI Emission Lines
Wilhelm, Klaus; Dwivedi, Bhola N.; Curdt, Werner
We present results from a study of extreme-ultraviolet (EUV) off-limb spectra. These were obtained on 1996 June 20 with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory (SOHO). With the capabilities of SUMER, we rastered the emitting source from 40" off the limb outward, and secur…