Search Publications
Periodicities in the IUE Particle Radiation Data
Arquilla, Richard
The magnetospheric charged particle flux measured serendipitously by the IUE satellite during perigee passages from February 1978 to February 1989 has been searched for periodicities using Fourier transform and correlation techniques. The analysis uncovers persistent modulations of the particle flux with periods of 28 to 33 days and 15 to 17 days.…
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…
Resolution and Noise Properties of the Goddard High Resolution Spectrograph
Ebbets, Dennis C.; Morris, Simon L.; Gilliland, Ronald L. +2 more
The Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) provides an unprecedented capability for ultraviolet spectroscopy of a wide range of astronomical targets. The combination of high resolution (to R 100,000), good sensitivity (maximum total system quantum efficiency of 1%), low background noise (order 0.01 counts s…
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…
Astrometric Performance Characteristics of the Hubble Space Telescope Fine Guidance Sensors
Benedict, G. F.; Franz, O. G.; Hemenway, P. D. +10 more
Each of the three Fine Guidance Sensors for the Hubble Space Telescope constitutes a sixth science instrument to be used for astrometry. We detail the tests and results used in choosing one of the three sensors to be the prime astrometer. The Astrometry Science team has chosen Fine Guidance Sensor (FGS) 3. FGS 3 produces position measurements on a…
A Deconvolution Technique for Hubble Space Telescope FGS Fringe Analysis
Hershey, John L.
A technique has been developed for directly transforming interferometer fringe visibility functions (``S-curves") from the HST Fine Guidance Sensors (FGSs) into intensity profiles of the program object. In a process analogous to Fourier transform image deconvolution, an S-curve from a double star yields a pair of narrow profiles containing informa…
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…
High Resolution Imaging of QSO 2305+187 (=4C 18.68)
Hutchings, J. B.; Neff, S. G.; Crabtree, D. +1 more
We present optical imaging of QSO 2305+187 with resolution ranging from 0.1 to 1.0 arcsec, in continuum and line emission. The data are from FOCAM and the HR Cam of the Canada-France-Hawaii telescope, and the Wide Field Camera of the Hubble Space Telescope. These are compared with previously published optical and radio images. The QSO host galaxy …