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Young star clusters in the Antennae: a clue to their nature from evolutionary synthesis
Fritze-v. Alvensleben, Uta
We analyse the population of bright star clusters in the interacting galaxy pair NGC 4038/39 detected with HST WFPC1 by Whitmore & Schweizer (1995). Making use of our spectrophotometric evolutionary synthesis models for various initial metallicities we derive the ages of these star clusters and calculate their future luminosity evolution. This…
On the Latitude Variation of Ammonia, Acetylene, and Phosphine Altitude Profiles on Jupiter from HST Faint Object Spectrograph Observations
Simon, A. A.; Edgington, S. G.; Atreya, S. K. +5 more
Ultraviolet spectra in the spectral region from 160 to 230 nm were taken with the Hubble Space Telescope Faint Object Spectrograph in May 1992. We analyze these data to obtain the altitude distribution of ammonia and its variation with latitude from 6°N to 25°N. Ammonia condenses below the 150-mbar level, above which it departs from saturation due…
Multiwavelength properties of blazars
Urry, C. Megan
The multiwavelength spectra of blazars appear to be dominated by nonthermal emission from a relativistic jet oriented close to the line of sight. The recent detection of many blazars at gamma-ray energies strongly supports this scenario. High quality multiwavelength monitoring data for the brightest one or two blazars suggest the optical through X…
Waves in the solar transition region
Doyle, J. G.; Banerjee, D.; O'Shea, E. +1 more
The power spectra for line intensities of several lines formed in the upper transition region around 100000 to 250000 K are presented. A period of ∼5 min is clearly present in lines due to Oiii, Oiv, and Ov. In one dataset a period approaching 10 min is present for ∼40 min. The size of the emitting features is limited to ∼7 arc sec squared. In all…
The Southern Proper Motion Program. I. Magnitude Equation Correction
Kozhurina-Platais, Vera; Girard, Terrence M.; van Altena, William F. +2 more
As with virtually all photographic plate material, the astrograph plates from which the Southern Proper Motion (SPM) catalog is being compiled suffer from magnitude-dependent systematic shifts in the image positions, i.e., a magnitude equation. If left uncorrected, these would adversely affect both the primary goals of the SPM catalog, the absolut…
The Optical Spectrum of the Planetary Nebula NGC 2440
Hyung, Siek; Aller, Lawrence H.
Wavelengths and identifications have been provided for approximately 300 lines between 3660 and 10125 Å in the spectrum of the bipolar planetary nebula NGC 2440. These lines measured with the Hamilton echelle spectrograph at Lick Observatory and supplemented by published IUE results are used to construct diagnostic diagrams and derive ionic concen…
Random Damping and Frequency Reduction of the Solar F Mode
Kosovichev, A. G.; Murawski, K.; Duvall, T. L., Jr.
We present observations showing that the frequency of the high-degree f-mode is significantly lower than the frequency given by the simple dispersion relation, ω2=gk , and that the line width grows with the wavenumber k. We attempt to explain that this behavior is the result of the interaction with granulation, which we model as a rando…
Differences between the Optical/Ultraviolet Spectra of X-Ray Bright and X-Ray Faint QSOs
Green, Paul J.
We contrast measurements of composite optical and ultraviolet (UV) spectra constructed from samples of QSOs defined by their soft X-ray brightness. X-ray bright (XB) composites show stronger emission lines in general, but particularly from the narrow-line region. The difference in the [O III]/Hβ ratio is particularly striking, and is even more so …
Tomographic Analysis of Hα Profiles in HDE 226868/Cygnus X-1
Shafter, A. W.; Gies, D. R.; Bagnuolo, W. G. +3 more
We present high-quality Hα spectra of the massive X-ray binary HDE 226868 = Cyg X-1 that were made in 1985 and 1986. We measured radial velocities using the He I λ6678 line, and we use the resulting orbital solution together with a Hipparcos light curve of the ellipsoidal variation to arrive at a revised period estimate of P = 5.59977 +/- 0.00002 …
Hubble Space Telescope Observations of an Accreted Silicon SPOT on the White Dwarf in V471 Tauri
Bond, Howard E.; Sion, Edward M.; Saffer, Rex A. +2 more
We have used the Hubble Space Telescope's (HST) Goddard High-Resolution Spectrograph to detect a photospheric metallic absorption line, Si III λ1206, in the spectrum of the magnetic white dwarf component of the Hyades precataclysmic binary V471 Tauri. The Si III feature is modulated on the soft X-ray/EUV/optical 9.25 minute rotational period of th…