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Interstellar Matter and the Boundary Conditions of the Heliosphere
Frisch, Priscilla C.
The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun, and determines the boundary conditions of the heliosphere. Both the Sun and interstellar clouds move through space, so these boundary conditions change with time. Data and theoretical models now support densities in the cloud surrounding the solar sy…
An Empirical Limit on Extremely High Redshift Galaxies
Lanzetta, Kenneth M.; Yahil, Amos; Fernández-Soto, Alberto
We apply the Lyman absorption signature to search for galaxies at redshifts z ~ 6-17 using optical and infrared images of the Hubble Deep Field. The infrared images are sensitive to a point-source 5 sigma detection threshold of AB(22,000) = 23.8, which, adopting plausible assumptions to relate rest-frame ultraviolet flux densities to unobscured st…
In Situ Measurements of Interstellar Dust
Grün, E.; Landgraf, M.
We present the mass distribution of interstellar grains measured in situ by the Galileo and Ulysses space probes as cumulative flux. The derived in situ mass distribution per logarithmic size interval is compared to the distribution determined by fitting extinction measurements. Large grains measured in situ contribute significantly to the overall…
The solar neighbourhood HR diagram as a quantitative test for evolutionary time scales
Schroeder, K. -P.
The HIPPARCOS parallaxes have provided us with a precise HR diagram (HRD) of the solar neighbourhood, complete within certain limits. The scope of this work is a study of the stellar population densities in characteristic regions of the HRD to test stellar evolutionary time scales. We examine two HRDs (M_v <= 4.0), both based on the single-star…
Recovery of 29 Second Oscillations in Hubble Space Telescope Eclipse Observations of the Cataclysmic Variable UX Ursae Majoris
Horne, Keith; Long, Knox S.; Baptista, Raymundo +3 more
Low-amplitude (~=0.5%) 29 s oscillations have been detected in Hubble Space Telescope Faint Object Spectrograph eclipse observations of the nova-like cataclysmic variable UX UMa. These are the same dwarf nova-type oscillations that were originally discovered in this system by Warner & Nather in 1972. The 29 s oscillations are seen in one pair …
The Orbits of the Inner Uranian Satellites from Hubble Space Telescope and Voyager 2 Observations
Jacobson, R. A.
This article presents revised orbital elements for the 10 small Uranian satellites discovered by the Voyager 2 spacecraft. The elements have been determined from a fit to astrometric observations made with the Hubble Space Telescope and imaging data acquired by Voyager 2. An assessment of the accuracy of the orbits represented by the elements is p…
VRI CCD Photometry of Supergiant Stars in the Barred Galaxies NGC 925 and NGC 1637
Davidge, T. J.; Sohn, Young-Jong
V, R, and I CCD images obtained with the Canada-France-Hawaii Telescope are used to investigate the bright stellar content of the barred spiral galaxies NGC 925 and NGC 1637. Not counting objects located in H ii regions, we detect 295 supergiants in NGC 925 and 266 in NGC 1637. Comparisons with theoretical isochrones indicate that massive star for…
On the Multiplicity of η Carinae
Walborn, Nolan R.; Livio, Mario; Panagia, Nino +1 more
The nebula around the luminous blue variable (LBV) η Car is extremely N rich and C and O poor, which is indicative of CNO-cycle products. On the other hand, the recent Hubble Space Telescope-Goddard High-Resolution Spectrograph observation of the nucleus of η Car shows the spectrum of a star with stellar-wind lines of C II, C IV, Si II, Si IV, etc…
The Direct Amplification of Electromagnetic Waves by Electron Beams: An Alternate Explanation for Solar Type III Bursts
Huang, Guangli
The direct amplification of electromagnetic (EM) waves by the beam-plasma instability is proposed as an alternative for solar type III bursts in corona and planetary space, the main properties of type III bursts at meter bands are compared to this model, including the cutoff frequency, the timescale, the relative bandwidth, the polarization sense …
Gamma-Ray Burst Arrival Time Localizations: Simultaneous Observations by Pioneer Venus Orbiter, Compton Gamma-Ray Observatory, and ULYSSES
Hurley, K. C.; Fishman, G. J.; Kouveliotou, C. +9 more
Between the Compton Gamma Ray Observatory (CGRO) launch in 1991 April and the Pioneer Venus Orbiter (PVO) demise in 1992 October, concurrent coverage by CGRO, PVO, and Ulysses was obtained for several hundred gamma-ray bursts (GRBs). Although most of these were below the PVO and Ulysses thresholds, 37 were positively detected by all three spacecra…