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The Electron Pressure in the Solar Lower Transition Region Determined from O V and Si III Density-sensitive Line Ratios
Wilhelm, K.; Doschek, G. A.; Warren, H. P. +3 more
We determine the electron density at the temperatures of formation of O+4 and Si+2 ions, which are about 2.5 × 105 and 3.2 × 104 K in ionization equilibrium, respectively. These temperatures occur in the lower transition region of the Sun's atmosphere and allow a test of the often invoked assumption of c…
Planetary nebulae with ISO: A58 and A78 - nebulae with hydrogen-poor ejecta
Kimeswenger, S.; Kerber, F.; Weinberger, R.
We present ISO observations of A58 and A78. Both objects are suspected to have undergone late He flashes (`born-again' nebulae). With ISOCAM we have been able to obtain data of much higher spatial resolution over the wavelength range 4.5-18 µm than has been possible in the past. In order to extract full information from our data we have deve…
HST Spectra of the Jovian Ultraviolet Aurora: Search for Heavy Ion Precipitation
Trafton, L. M.; Waite, J. H.; Gérard, J. -C. +3 more
Ultraviolet spectra using Hubble Space Telescope sampled between 1250 and 1680 Å at spectral resolution <=0.57 Å are reported for characteristically bright regions of Jupiter's morning and afternoon northern aurora. Several observed spectra exhibit sharply enhanced resolution. We interpret this as bright auroral emission foreshortened on the mo…
Beta Hydri (G2 IV): a revised age for the closest subgiant
Lindegren, L.; Vandenberg, D. A.; Dravins, D.
The secular evolution of solar-type atmospheres may be studied through comparisons of the current Sun with old solar-type stars of known age. Among the few such stars in the solar Galactic neighborhood, beta Hydri (G2 IV) stands out as a normal single star with an advanced age. Previous age determinations ( =~ 9.5 Gy) were based on the old ground-…
The hot prominence periphery in EUV lines
Wiehr, E.; Stellmacher, G.; de Boer, C. R.
Two sets of He I and metallic lines were observed with the EUV spectrograph SUMER in a quiescent prominence. H, He, and Ca II lines were observed simultaneously with both German telescopes on Tenerife. The visible lines from elements with different atomic weights yield thermal and non-thermal broadening parameters of 7500 <= Tkin <…
Ultraviolet Spectroscopy of AB Doradus with the Hubble Space Telescope: Impulsive Flares and Bimodal Profiles of C IV lambda1549 in a Young Star
Collier Cameron, A.; Huovelin, J.; Hakala, P. +3 more
We observed AB Doradus, a young and active late-type star (K0-K2 IV-V, P = 0.514 days), with the Goddard High Resolution Spectrograph of the post-COSTAR Hubble Space Telescope with time and spectral resolutions of 27 s and 15 km s^-1, respectively (1994 November 14.08-14.30 UT). The wavelength band (1531-1565 Å) included the strong C iv doublet (1…
Confirmation of previous ground-based Cepheid P-L zero-points using HIPPARCOS trigonometric parallaxes
Sandage, Allan; Tammann, G. A.
Comparisons show agreement at the 0.1-mag level between the calibration of the Cepheid period-luminosity (P-L) relation by Feast & Catchpole (FC) using the early release of Hipparcos data and four previous ground-based calibrations, three of which are either largely or totally independent of the distance to the Large Magellanic Cloud (LMC). Ea…
Three-dimensional Solar Modulation of Cosmic Ray and Anomalous Components in the Inner Heliosphere
McKibben, R. B.
Our picture of modulation in the inner heliosphere has been greatly affected by observations from the Ulysses mission, which since 1992 has provided the first comprehensive exploration of modulation as a function of latitude from 80 deg S to 80 deg N heliographic latitude. Among the principal findings for the inner heliosphere are: a) the cosmic r…
Radiometric calibration tracking of the vacuum-ultraviolet spectrometer SUMER during the first year of the SOHO mission
Wilhelm, Klaus; Schühle, Udo; Brekke, Pål +3 more
Small-Scale Structure in the Lyα Forest at High Redshift
Impey, C. D.; Petry, C. E.; Foltz, C. B.
We have obtained spectra of the four components of the system B1422+231 with HST's Faint Object Spectrograph in order to study spatial inhomogeneities and velocity variations in the absorbers which are pierced by the four lines of sight. The four images are well resolved, and the spectra clearly show the system is a lensed quasar; a new redshift b…