Search Publications
Errors Associated with Fitting Gaussian Profiles to Noisy Emission-Line Spectra
Ayres, Thomas R.; Lenz, Dawn D.
Landman, Roussel-Dupre, and Tanigawa developed prescriptions to predict profile fitting errors for Gaussian emission lines perturbed by white noise. We show that their scaling laws can be generalized to more complicated signal-dependent "noise models" of common astronomical detector systems. (SECTION: Instrumentation and Data Analysis)
Variability of Emission Lines in the Planetary Nebulae IC 4997 and NGC 6572
Feibelman, Walter A.; Hyung, Siek; Aller, Lawrence H.
We compare the new IUE high dispersion data and recent ground-based spectra of the planetary nebulae IC 4997 and NGC 6572 with equivalent IUE observations taken in 1980 and optical data taken in 1974-1990. Significant changes are detected in many emission line fluxes in IC 4997, and primarily in He II and C IV for NGC 6572. We interpret these chan…
Outbursts by Low-Mass White Dwarfs in Symbiotic Variables
Sion, Edward M.; Ready, Christian J.
We have investigated the nature of P Cygni-like features in the high resolution IUE spectra of the symbiotic variables BF Cyg and EG And by looking for orbital phase-dependent variations in the structure and velocity of the C IV (1550 A) resonance doublet in 10 archival IUE high-dispersion spectra of these systems and by comparing their profiles w…
The Ionization Conditions in the Milky Way Halo: Infalling Gas toward the North Galactic Pole
Danly, Laura
The observations of gas in the Milky Way are reviewed with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown which indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Besides being interesting in its own right, …
A Search for Weak Ultraviolet Interstellar Absorption Features in IUE Spectra of rho Ophiuchi and zeta Ophiuchi
York, D. G.; Welty, D. E.; Hobbs, L. M. +1 more
We have applied procedures designed to reduce substantially the non-random, so-called "fixed-pattern" noise present in IUE spectra to archival long-wavelength light-dispersion spectra of rho Ophiuchi and zeta Ophiuchi. Substantial elimination of the fixed-pattern noise via flat fielding can yield 2-sigma equivalent width limits of 5-10 mA from the…
The Ultraviolet Spectrum of HH 24A and its Relation to Optical Spectra
Noriega-Crespo, A.; Brugel, E. W.; Boehm, K. H. +1 more
We have studied the spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 in the short wavelength (1300 A The ultraviolet spectrum is definitely detected in three observations with exposure times of 560 to 680 min. It is, however, sufficiently faint that corrections for the IUE "artifact spectrum" (as described by Crensha…
Ultraviolet Colors of Old LMC Clusters
Cowley, A. P.; Hartwick, F. D. A.
New ultraviolet spectra for five red LMC globular clusters have been obtained with IUE. These have been supplemented with archival spectra for eleven old LMC clusters. These data strengthen and extend the UV-color vs. age relation for clusters older than 10^9 years, but do not offer much precision in age determination, presumably because the ultra…
The Composite Nature of the Peculiar Star HR 6560 (HD 159870)
Wegner, Gary; Cowley, Charles R.
Ground based high dispersion photographic spectra and ultraviolet spectra obtained with the International Ultraviolet Explorer (IUE) satellite are described and employed to determine the nature of the peculiar star HR 6560 (HD 159870). Previously this object had been described as both a composite system and a strong Fm star. We inter-compare the U…