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Anticipating High-Resolution STIS Spectra of Four Multiphase Mg II Absorbers: A Test of Photoionization Models
Charlton, Jane C.; Churchill, Christopher W.; Rigby, Jane R. +1 more
In this paper we propose a test of the validity of a photoionization modeling technique that is applicable when a combination of high- and low-resolution spectra are available for various chemical transitions. We apply this technique to the four Mg II systems along the line of sight toward the zem=1.335 quasar PG 1634+706 to infer the p…
Rotation and evolution of A stars: looking for progenitors of cool Ap stars
Hubrig, S.; North, P.; Medici, A.
We explore to what extent the study of the projected rotational velocities of normal A stars might reveal the existence of progenitors of cool Ap stars, i.e. of slowly rotating normal young A stars. Since according to a recent work, magnetic Ap stars with masses ranging from 1.7 to 2.5 M_sun are never found on the ZAMS in the HR diagram, but have …
The Crossings of Saturn Ring Plane by the Earth in 1995: Ring Thickness
Sicardy, Bruno; Dumas, Christophe; Poulet, François +2 more
The crossings of Saturn's ring plane by Earth were observed in the near infrared on May 22 and August 10, 1995, from the 2.2-m telescope of the University of Hawaii, the 2-m telescope at Pic du Midi, France, and with the Adonis adaptive optics camera at the 3.6-m telescope of the European Southern Observatory in Chile. Images from the Hubble Space…
The ISO spectra of Uranus and Neptune between 2.5 and 4.2 mu m: constraints on albedos and H_3+
Lellouch, E.; Feuchtgruber, H.; Atreya, S. K. +3 more
Spectra of Uranus and Neptune were recorded in May 1997, between 2.5 and 4.2 mu m, using the ISOPHOT-S instrument. The two planets were detected at 2.75 mu m, with geometric albedos of 0.0015 and 0.0052 for Uranus and Neptune respectively. In the case of Uranus, the shape of the CH_4 absorption is consistent with a reflection over the 3 bar-level …
EUV brightness variations in the quiet Sun
Solanki, S. K.; Harrison, R. A.; Fludra, A. +5 more
The Coronal Diagnostic Spectrometer (CDS) onboard the SOHO satellite has been used to obtain movies of quiet Sun regions at disc centre. These movies were used to study brightness variations of solar features at three different temperatures sampled simultaneously in the chromospheric He I 584.3 Ä (2 * 104 K), the transition region O V 6…
Measuring the Ionization of O Star Winds
Sonneborn, George; Hutchings, J. B.; Bianchi, Luciana +6 more
We present an analysis of wind line profiles from Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of two O7 supergiants in the Large and Small Magellanic Clouds (Sk -67°111 and AV 232, respectively). Model fits yield the column densities of S IV, S VI, P IV, P V, N III, and N IV, providing the first direct measurement of the ionization balan…
Heliospheric 3d Structure and CME Propagation as Seen from SOHO: Recent Lessons for Space Weather Predictions
Schwenn, R.
Observations from Skylab, Helios, Ulysses, and SOHO have demonstrated how closely the 3D heliosphere is related to the underlying coronal structure. Around solar activity minimum, the large polar coronal holes dominate the major part of the heliosphere, through the high-speed solar wind streams emanating from them. A distinctively different type o…
A Grid of Non-LTE Model Atmospheres for White Dwarfs in Cataclysmic Variables
Baron, E.; Barman, Travis S.; Hauschildt, Peter H. +1 more
We have calculated a grid of non-LTE (NLTE) line-blanketed model atmospheres for white dwarfs in cataclysmic variable (CV) systems using our stellar atmosphere code PHOENIX. The grid covers the temperature range 20,000-500,000 K for solar abundances and 10-2 and 10-4 solar metal abundance. The effective temperature resolution…
Modelling Short-Term Spectral Irradiance Variations
Solanki, S. K.; Unruh, Y. C.; Fligge, M.
On time-scales of the solar rotation most of the solar irradiance variations are caused by the changing distribution of solar surface magnetic features. We model these short-term irradiance variations using calculations of sunspot and facular contrasts as a function of wavelength and limb angle on the Sun. The position of active regions on the sol…
Structural Characteristics of Faint Galaxies Serendipitously Discovered with the Hubble Space Telescope WFPC2
Impey, C. D.; Bothun, G. D.; O'Neil, Karen
Utilizing the F814W and F300W filters, Hubble Space Telescope Wide Field Planetary Camera-2 (WFPC2) images were taken of four low surface brightness galaxies in the direction of the Virgo Cluster--V7L3, V2L8, V1L4, and Malin 1. The high resolution of the WFPC2 combined with the extremely diffuse nature of the four galaxies makes them essentially t…