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The Three-dimensional Coronal Magnetic Field during Whole Sun Month
Thompson, B. J.; Hoeksema, J. T.; Lazarus, A. J. +11 more
Combining models and observations, we study the three-dimensional coronal magnetic field during a period of extensive coordinated solar observations and analysis known as the Whole Sun Month (WSM) campaign (1996 August 10-September 8). The two main goals of the WSM campaign are addressed in this paper, namely, (1) to use the field configuration to…
Multiwavelength Study of the Starburst Galaxy NGC 7714. I. Ultraviolet-Optical Spectroscopy
Leitherer, Claus; Pasquali, Anna; González Delgado, Rosa M. +2 more
We have studied the physical conditions in the central 300 pc of the prototypical starburst galaxy NGC 7714. Our analysis is based on ultraviolet spectroscopy with the HST/GHRS and ground-based optical observations, and it also covers X-ray and radio data taken from the literature. The data are interpreted using evolutionary models optimized for y…
Revision and Calibration of MK Luminosity Classes for Cool Giants by HIPPARCOS Parallaxes
Keenan, Philip C.; Barnbaum, Cecilia
The Hipparcos parallaxes of cool giants are utilized in two ways in this paper. First, a plot of reduced parallaxes of stars brighter than 6.5, as a function of spectral type, for the first time separates members of the clump from stars in the main giant ridge. A slight modification of the MK luminosity standards has been made so that luminosity c…
Microwave and Extreme Ultraviolet Observations of Solar Polar Regions
Nindos, A.; Kundu, M. R.; White, S. M. +3 more
The poles of the Sun are brighter than the rest of the quiet Sun's emission in a limited range of radio frequencies from 17 GHz to 87 GHz. We have studied microwave images of the quiet Sun made with the Nobeyama radioheliograph at 17 GHz. They show that the so-called polar-cap brightening consists of two components: a diffuse component of 1500 K e…
The Radial and Angular Variation of the Electron Density in the Solar Corona
Mathioudakis, M.; Keenan, F. P.; Phillips, K. J. H. +2 more
We derive, for the first time, electron densities as a function of both radius (R) and position angle (θ) for the southwest quadrant of the off-limb corona, using the density-sensitive Si IX λ349.9/λ341.9 and Si X λ356.0/λ347.7 extreme-ultraviolet line ratios. The observations were made with the coronal diagnostic spectrometer on board the Solar a…
The Ultraviolet Peak of the Energy Distribution in 3C 273: Evidence for an Accretion Disk and Hot Corona around a Massive Black Hole
Kriss, Gerard A.; Zheng, Wei; Davidsen, Arthur F. +1 more
We present absolutely calibrated far-ultraviolet spectrophotometry of the quasar 3C 273 covering the 900-1800 Å range. Our ~3 Å resolution spectra were obtained with the Hopkins Ultraviolet Telescope (HUT) during the Astro-1 mission in 1990 December and during the Astro-2 mission in 1995 March. Both spectra exhibit a change in slope near the Lyman…
Source of Solar Acoustic Modes
Kosovichev, A. G.; Nigam, R.
Solar acoustic modes are found to be excited in a thin superadiabatic layer of turbulent convection (about 75+/-50 km below the photosphere) beneath the Sun's surface. Comparing the theoretical power spectra of both velocity and pressure oscillations of medium angular degree with that obtained from the Michelson Doppler Imager instrument on board …
The Chromosphere in Coronal Holes and the Quiet-Sun Network: an HE I (584 Å) Full-Disk Scan by SUMER/SOHO
Peter, H.
A raster scan by Solar Ultraviolet Measurements of Emitted Radiation/Solar and Heliospheric Observatory (SOHO) of the full solar disk containing over 2 million individual spectra of the He I line at 584 Å provides the possibility to study small- and large-scale variations of intensity, line shift, and line width. New striking features are the enha…
Hubble Space Telescope WFPC2 Imaging of XZ Tauri:Time Evolution of a Herbig-Haro Bow Shock
Ballester, Gilda E.; Krist, John E.; Crisp, David +13 more
We report observations of dramatic morphological changes in the extremely young Herbig-Haro object ejected by the pre-main-sequence binary XZ Tauri. Hubble Space Telescope images taken in 1995 showed a filled bubble of emission nebulosity extending 4" north-northeast of the system in the direction of a previously known jet. New images obtained in …
The D/H Ratio in Interstellar Gas toward G191-B2B
Gull, T. R.; Barstow, M. A.; Bruhweiler, F. C. +7 more
Recent analysis of Goddard High-Resolution Spectrograph (GHRS) echelle spectra suggests ~30% variations in the D/H abundance ratio along the line of sight to the nearby (69 pc) hot white dwarf (WD) G191-B2B (Vidal-Madjar et al.). Variations in the D/H ratio on such short length scales imply nonuniform production/destruction of deuterium and an ine…