Search Publications
Signal-to-Noise Ratios in IUE SWP-LO Spectra of Chromospheric Emission-Line Sources
Ayres, Thomas R.
The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the noise levels in flat-field images are several times higher. The exaggerated noise can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral im…
Ultraviolet Spectra of Field Horizontal Branch A-Type Stars. II.
Adelman, Saul J.; Philip, A. G. Davis; Hayes, D. S.
The spectra of six additional A-type stars have been obtained at low resolution between 1200 and 1900 A with the IUE. The energy distributions of four of the stars match that of the field horizontal branch (FHB) distribution in Huenemoerder et al. (1984) while those of the other two do not. Three of the FHB stars fall above a line in the C(19 - V)…
The MG II H and K Interstellar Lines in the Spectrum of the G-Type Giant HD 156854
Kondo, Y.; Shore, Steven N.; Gurzadian, G. A. +2 more
The results of the measurements and analysis of the IUE observations of the 2800 Mg II doublet in the spectrum of HD 156854, a G9 III star, are presented. The relative power of the magnesium chromosphere, R(Mg) = 0.00001, is in agreement with the known data for giants of the same class. The emission profiles of this doublet present absorption core…
He 2-104: A Link Between Symbiotic Stars and Planetary Nebulae
Shaw, Richard A.; Lutz, Julie H.; Kaler, James B. +2 more
Ultraviolet, optical and infrared observations of He 2-104 are presented, and estimates for some of the physical properties of the nebular shell are made. It is argued that He 2-104 is in transition between the D-type symbiotic star and bipolar planetary nebula phases and, as such, represents a link between subclasses of these two types of objects…
Ultraviolet Observations of the Planetary Nebula NGC 2242
Garnett, Donald R.; Dinerstein, Harriet L.
We present IUE observations of the high-ionization planetary nebula NGC 2242. The ultraviolet spectrum exhibits stong emission lines of C IV, He II, C III], and [Ne IV], plus weaker emission from O IV and N IV. We have also obtained narrow-band imaging of NGC 2242 in the He II 4686 A emission line; comparison of the λ 4686 flux from this image wit…
Systematic Errors in Spectral Features Introduced by Random Noise
Joseph, Charles L.
A common IUE computer routine for measuring equivalent widths is shown to introduce systematic errors in data containing large amounts of noise. During statistical tests using simulations of synthetic spectral features with noise characteristics similar to those of the IUE, the routine was found to overestimate the true strength of an absorption l…
Two Compact Planetary Nebulae of Moderate Excitation: NGC 6565 (3-4.5) and NGC 6644 (8-7.2)
Aller, Lawrence H.; Feibelman, Walter; Keyes, Charles D.
Data obtained with an image-tube scanner at the 3-m Shane telescope are combined with IUE data to obtain plasma diagnostics and chemical compositions for two planetary nebulae of moderately high excitation. Theoretical nebular models were calculated using stellar fluxes given by Husfeld et al. (1984) for T(asterisk) = 85,000 K, log g = 4.72, and e…
White Dwarfs in Cataclysmic Variables: Low State IUE Observations of V794 Aquilae, MR Serpentis, and an Ursae Majoris
Szkody, Paula; Mateo, Mario; Downes, Ronald
The authors have obtained IUE low dispersion observations of one nova-like system (V794 Aql) and two AM Her systems (MR Ser and AN UMa) during low or intermediate low accretion rate states. The decreased UV emission during these times was used to place limits on the white dwarf temperatures. When these results are added to the existing data on whi…
Ultraviolet Spectra of the Narrow-Lined Seyfert Galaxies Markarian 573 and Markarian 1388
MacAlpine, Gordon M.
Ultraviolet spectra, obtained with the IUE satellite, are presented for the unusually narrow-lined Seyfert galaxies Mrk 573 and Mrk 1388. The data support class 2 identifications for both galaxies and also suggest the need for more energetic ionizing radiation in the most recently published Seyfert 2 galaxy photoionization calculation.
Optical and Ultraviolet Activity in RT Lacertae During 1985 and 1986
Huenemoerder, David P.
Continued monitoring of optical spectra of RT Lac, a peculiar RS CVn system, showed a large range of activity in the H-alpha line. At times, there was no excess emission or absorption, and at others, much. During active times, the excess emission varied greatly with phase and seemed to come from an extended region. Two UV observations, taken conte…