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Low-energy solar electrons and ions observed at Ulysses February-April, 1991: The inner heliosphere as a particle reservoir
Simnett, G. M.; Tappin, S. J.; Lanzerotti, L. J. +3 more
Ulysses observations at 2.5 AU of 38-315 keV electrons and 61-4752 keV ions during February-April 1991 suggest in several ways that, during periods of sustained high solar activity, the inner heliosphere serves as a “reservoir” for low-energy solar particles. Particle increases were not associated one-to-one with large X-ray flares because of thei…
The Cepheid Distance to IC 4182: Calibration of M V(max) for SN IA 1937C and the Value of H 0
Saha, A.; Panagia, Nino; Sandage, Allan +2 more
Cepheid variables with periods from 2 to more than 50 days have been found in IC 4182 from observations with the Hubble Space Telescope over a time interval of 47 days, comprised of 20 epochs. The period-luminosity relation from photometry of 27 Cepheids in the F555W HST magnitude system gives an apparent V distance modulus of (m - M)_AV_ = 28.47 …
Hubble Space Telescope Planetary Camera Images of R136
Lauer, Tod R.; Faber, S. M.; Holtzman, Jon A. +9 more
The Planetary Camera of the Hubble Space Telescope has been used to obtain broad and narrowband images of R136, the core of the massive star cluster 30 Doradus in the Large Magellanic Cloud. R136a, the brightest component of R136, is shown to have at least 12 separate components, including the eight originally identified by speckle interferometry.…
Improved Calculations for the C III lambda lambda 1907,1909 and SI III lambda lambda 1883,1892 Electron Density Sensitive Emission-Line Ratios, and a Comparison with IUE Observations
Feibelman, W. A.; Keenan, F. P.; Berrington, K. A.
Atomic data are used in conjunction with the statistical equilibrium code of Dufton (1977) to calculate relative C III and Si III level populations, and hence emission-line strengths for a range of electron temperatures and densities. It is assumed that photoexcitation and deexcitaton rates are negligible in comparison with the corresponding colli…
EXOSAT X-Ray Spectra of Quasars
Comastri, Andrea; Setti, Giancarlo; Zamorani, Giovanni +4 more
We have measured the X-ray spectra in the 0.1-10 keV energy range for 17 AGNs (mostly PG quasars) using the EXOSAT Low and Medium Energy arrays. The sample has been selected on the basis of soft X-ray flux and includes all the AGNs in the 1981 Zamorani et al. and 1986 Tananbaum et al. publications with an Einstein flux greater than 6x10^-12^ ergs …
Globular Cluster Photometry With the Hubble Space Telescope. I. Description of the Method and Analysis of the Core of 47 TUC
Schneider, Donald P.; Yanny, Brian; Bahcall, John N. +1 more
Accurate photometry for individual post-main-sequence stars in the core of the Galactic globular cluster 47 Tuc is presented and analyzed using an empirical point spread function model and Monte Carlo simulations. A V vs. V-I color-magnitude diagrams is constructed which shows several distinct stellar types, including RGB and HB stars. Twenty-four…
Jupiter's Magnetosphere: Plasma Description from the Ulysses Flyby
Goldstein, Bruce E.; Neugebauer, Marcia; Thomsen, Michelle F. +7 more
Plasma observations at Jupiter show that the outer regions of the Jovian magnetosphere are remarkably similar to those of Earth. Bow-shock precursor electrons and ions were detected in the upstream solar wind, as at Earth. Plasma changes across the bow shock and properties of the magnetosheath electrons were much like those at Earth, indicating th…
Relationship between wave energy and free energy from pickup ions in the Comet Halley Environment
Johnstone, A. D.; Huddleston, D. E.
The free energy available from the implanted heavy ion population at comet Halley is calculated by assuming that the initial unstable velocity space ring distribution of the ions evolves toward a bispherical shell. Ultimately this free energy adds to the turbulence in the solar wind. We obtain upstream and downstream free energies separately for t…
Possible cataclysmic variable in the core of the globular cluster 47 Tucanae
Ferraro, Francesco R.; Paresce, Francesco; de Marchi, Guido
SEVERAL globular clusters have low-luminosity X-ray sources at their cores1-3, of which X0021.8-7221 in 47 Tucanae (NGC104) is one of the brightest. The nature of these sources is a mystery, and attempts to detect optical counterparts have been frustrated by the overcrowding of stars in cluster cores. The resolution of ground-based obse…
A Magnitude-limited Survey of Cepheid Companions in the Ultraviolet
Evans, Nancy R.
Results of a magnitude-limited survey of classic Cepheids brighter than 8th mag carried out to search for hot main-sequence companions are presented. Spectra of 76 stars obtained with the IUE satellite in the 2000-3200-A region were compared with the spectra of nonvariable supergiants and also the single Cepheid Delta Cep to search for excess flux…