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NASA NTRS1975

Ultraviolet photometry from the Orbiting Astronomical Observatory. XX - The ultraviolet extinction bump

Ultraviolet extinction bumps are investigated in the interstellar extinction curves between 1800 and 3600 A for 36 stars which have (B-V) excesses ranging from 0.03 to 0.55 and are mostly confined to the brighter OB associations distributed along the galactic plane. Each extinction curve is found to have a broad bump which peaks near 2175 A and whose position and profile appear to be constant among all the stars. It is shown that the bump is probably interstellar in origin and that the constancy of its position and shape places such severe restrictions on grain geometrical parameters that classical scattering theory cannot be used to explain the feature unless the dust grains in widely separated regions of space and with very different physical conditions are assumed to have nearly identical size and shape distributions. Three extinction curves which extend to 1100 A are examined and found to have the same general characteristics as the others. Several extinction curves are analyzed for fine structure, but no convincing evidence is found in the present interval. Some processes are discussed which may be responsible for the bumps.

Savage, B. D.↗
NASA NTRS1976

Ultraviolet photometry from the Orbiting Astronomical Observatory. XXI - Absolute energy distribution of stars in the ultraviolet

The absolute energy distribution in the ultraviolet is given for the stars alpha Vir, eta UMa, and alpha Leo. The calibration is based on absolute heterochromatic photometry between 2920 and 1370 A carried out with an Aerobee sounding rocket. The fundamental radiation standard is the synchrotron radiation from 240-MeV electrons in a certain synchrotron storage ring. On the basis of the sounding-rocket calibration, the preliminary OAO-2 spectrometer calibration has been revised; the fluxes for the three program stars are tabulated in energy per second per square centimeter per unit wavelength interval.

Bless, R. C.↗
NASA NTRS1979

Catalog of far-ultraviolet objective-prism spectrophotometry: Skylab experiment S-019, ultraviolet steller astronomy

Ultraviolet stellar spectra in the wavelength region from 1300 to 5000 A (130 to 500) were photographed during the three manned Skylab missions using a 15 cm aperture objective-prism telescope. The prismatic dispersion varied from 58 A mm/1 at 1400 A to 1600 A mm/1 at 3000 A. Approximately 1000 spectra representing 500 stars were measured and reduced to observed fluxes. About 100 stars show absorption lines of Si IV, C IV, or C II. Numerous line features are also recorded in supergiant stars, shell stars, A and F stars, and Wolf-Rayet stars. Most of the stars in the catalog are of spectral class B, with a number of O and A type stars and a sampling of WC, WN, F and C type stars. Spectrophotometric results are tabulated for these 500 stars.

Henize, K. G.↗
NASA NTRS1979

Ultraviolet photometry from the Orbiting Astronomical Observatory. XXXII - An atlas of ultraviolet stellar spectra

Ultraviolet stellar fluxes are presented in graphs and tables for 164 bright stars in the spectral region from 1200 to 3600 A. The spectra represent a subset of OAO 2 spectrometer data on file at the National Space Science Data Center. The monochromatic flux is given in units of erg per (sq cm-s-A) with a spectral resolution of about 22 A in the region from 3600 to 1850 A and of approximately 12 A in the region from 1850 to 1160 A.

Code, A. D.↗
NASA NTRS1980

Ultraviolet photometry from the Orbiting Astronomical Observatory. XXXVIII - A second atlas of ultraviolet stellar spectra

Ultraviolet stellar spectra are presented for 132 stars in the spectral region from 1200 to 1850 A and 34 stars in the region from 1800 to 3600 A in a graphical and tabular form. The spectra represent a subset of OAO 2 spectrometer data on file at the National Space Science Data Center. The monochromatic flux is given in units of ergs/sq cm s A with a spectral resolution of about 12 A in the region from 1850 to 1160 A and of about 22 A in the region from 3600 to 1800 A.

Meade, M. R.↗
NASA NTRS1984

Observations of the Ultraviolet Spectra of Helium (DB) White Dwarfs and a Study of the Ultraviolet Spectra of White Dwarfs Containing Carbon

Strong ultraviolet carbon lines were detected in the spectrum of the southern DC white dwarf BPM 11668. Observations of a number of hotter DB white dwarfs with IUE show no evidence of carbon features. Two additional DA white dwarfs were observed that have the strong unidentified absorption near 1400 A which now seems to be identified with another lower temperature feature as satellite lines to Lyman alpha radiation.

Wegner, G. A.↗
NASA NTRS1988

Simple ultraviolet calibration source with reference spectra and its use with the Galileo orbiter ultraviolet spectrometer

A simple compact electron impact laboratory source of UV radiation has been developed and is used to obtain calibrated optically thin VUV spectra and synthetic spectral models for important molecular band systems of H2, N2, and the n 1P0 Rydberg series of He. The relative spectral intensity of the electron impact source can be used as the primary calibration standard for VUV instrumentation in the 80-230 nm range and with FWHM of not less than 0.4 nm. The accuracy of the present method is 10 percent in the FUV and 20 percent in the EUV. Results for calibration of the Galileo orbiter ultraviolet spectrometer have been compared with those obtained using other methods.

Shemansky, D. E.↗
NASA NTRS1988

Far ultraviolet wide field imaging and photometry - Spartan-202 Mark II Far Ultraviolet Camera

The U.S. Naval Research Laboratory' Mark II Far Ultraviolet Camera, which is expected to be a primary scientific instrument aboard the Spartan-202 Space Shuttle mission, is described. This camera is intended to obtain FUV wide-field imagery of stars and extended celestial objects, including diffuse nebulae and nearby galaxies. The observations will support the HST by providing FUV photometry of calibration objects. The Mark II camera is an electrographic Schmidt camera with an aperture of 15 cm, a focal length of 30.5 cm, and sensitivity in the 1230-1600 A wavelength range.

Carruthers, George R.↗
NASA NTRS1991

Far-ultraviolet mapping of the Cygnus Loop with the Voyager 2 Ultraviolet Spectrometer

FUV maps of the Cygnus Loop made using spectroscopic data from the Voyager 2 Ultraviolet Spectrometer are presented. Emission line features at about 980 and about 1035 A dominate the 500-1700 A spectra of the Cygnus Loop as observed with Voyager. Maps were generated in the light of these two features. The 980 and 1035 A maps are compared with X-ray and optical images of the Cygnus Loop that have been sampled in the same manner. From this comparison it is clear that the 980 A feature arises mainly from regions of bright optical emission, whereas the 1035 A emission more closely resembles the X-ray emission. This general impression can be confirmed by inspection of the spectra as a function of position. Spectra extracted from positions corresponding to the primary shock front show the 1035 A feature to be relatively strong, while the 980 A feature is brighter when substantial optical emission is present within the aperture.

Blair, William P.↗
NASA NTRS1991

First ultraviolet spectropolarimetry of Be stars from the Wisconsin Ultraviolet Photo-Polarimeter Experiment

The first UV spectropolarimetric observations of Be stars are presented. They were obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) aboard the Astro-1 mission. WUPPE data on the Be stars Zeta Tau and Pi Aqr, along with near-simultaneous optical data obtained at the Pine Bluff Observatory (PBO). Combined WUPPE and PBO data give polarization as a function of wavelength across a very broad spectral region, from 1400 to 7600 A. Existing Be star models predicted increasing polarization toward shorter wavelengths in the UV, but this is not supported by the WUPPE observations. Instead, the observations show a constant or slightly declining continuum polarization shortward of the Balmer jump, and broad UV polarization dips around 1700 and 1900 A, which may be a result of Fe-line-attenuation effects on the polarized flux. Supporting evidence for this conclusion comes from the optical data, in which decreases in polarization across Fe II lines in Zeta Tau were discovered.

Bjorkman, K. S.↗
NASA NTRS1992

Astro-1 ultraviolet imaging of the 30 Doradus and SN 1987A fields with the Ultraviolet Imaging Telescope

A preliminary analysis of Ultraviolet Imaging Telescope (UIT) images in the 30 Doradus region is reported. Photometry was obtained for the 30 Doradus cluster and its UV-bright core, R136, in various UIT bandpasses. It is found that about 14 percent of the total FUV light and about 16 percent of the total near-UV light of the 3-arcmin diameter 30 Doradus cluster originates from the region within 5 arcsec of R136. The UV magnitudes and colors of R136 and other known O and Wolf-Rayet WN stars in the same field were measured. The UIT data, combined with published observations at longer wavelengths, indicate that R136a1, the brightest component of R136, is not a supermassive stars. A qualitative comparison between the UIT images, Einstein X-ray data, IRAS HiRes images, and ground-based CCD images in forbidden O III 5007 A, H-alpha, B, R, U, and Stromgren u is performed. The extended diffuse UV feature detected in the UIT images is correlated with the IR structure seen in the IRAS 60-micron HiRes image, which suggests the existence of large amounts of widely distributed dust in this region.

Cheng, Kwang-Ping↗
NASA NTRS1992

Ultraviolet Imaging Telescope ultraviolet images - Large-scale structure, H II regions, and extinction in M81

The study employs UV images of M81 obtained by the Ultraviolet Imaging Telescope (UIT) during the December 1990 Astro-1 spacelab mission to determine 2490- and 1520-A fluxes from 46 H II regions and global surface brightness profiles. Comparison photometry in the V band is obtained from a ground-based CCD image. UV radial profiles show bulge and exponential disk components, with a local decrease in disk surface brightness inside the inner Lindblad Resonance about 4 arcmin from the nucleus. The V profile shows typical bulge plus exponential disk structure, with no local maximum in the disk. There is little change of UV color across the disk, although there is a strong gradient in the bulge. Observed m152-V colors of the H II regions are consistent with model spectra for young clusters, after dereddening using Av determined from m249-V and the Galactic extinction curve. The value of Av, so determined, is 0.4 mag greater on the average than Av derived from radio continuum and H-alpha fluxes.

Hill, Jesse K.↗
NASA NTRS1992

Far-ultraviolet observations of the Crab Nebula using the Hopkins Ultraviolet Telescope

Observations of the FUV spectrum of the central portion of the Crab Nebula SNR using the Hopkins Ultraviolet Telescope (HUT) aboard the Astro-1 space shuttle mission in December 1990 are reported. The C IV 1549-A emission line shows two resolved components representing the front and back sides of the shell expanding at roughly +/- 1100 km/s. The He II 1640-A emission line shows only a blueshifted component corresponding to the near side of the shell. The HUT observation is compared to optical emission-line imagery and to archival IUE observations. This comparison indicates that a distribution emission component, consisting of either a number of individually faint filaments or a diffuse component, produces the bulk of the emission seen by HUT. A grid of photoionization models for the Crab Nebula filaments is calculated to infer the range of limits. The differing UV line ratios observed for these components indicates that varying carbon and/or He abundances are present in the observed material.

Blair, William P.↗
NASA NTRS1992

Far-ultraviolet observations of the supernova remnant N49 using the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope has been used to obtain the first sub-Lyman-alpha spectrum of an extragalactic SNR, N49, in the LMC. Emission from O VI 1032, 1038 has been detected in this spectral region. The measured fluxes of C IV, semiforbidden O IV, and O VI and the upper limit on N V provide stringent limits on the shocks responsible for the bulk of the O VI production. O VI cannot originate in the shocks with velocities of 140 km/s or less because the postshock temperature is not high enough. The nonradiative main blast wave cannot account for the brightness of the observed O VI emission. The majority of the O VI must originate in an optically faint system of shocks with velocities of 190-270 km/s and preshock densities of 20-40 cu cm. The emission from such high-velocity shocks is dominated by O VI.

Vancura, Olaf↗
NASA NTRS1993

Extreme ultraviolet observations of HZ 43 and the local H/He ratio with the Hopkins Ultraviolet Telescope

We present a spectrum of the hot DA white dwarf HZ 43 in the EUV, near the 504-A ionization edge of neutral helium, obtained with the Hopkins Ultraviolet Telescope (HUT) during the 1990 December Astro-1 mission. The interstellar column densities derived from this spectrum rule out the anomalous interstellar absorption model proposed by Heise et al.(1991), which required a greater column density of neutral helium than neutral hydrogen toward HZ 43 in order to explain the low EUV flux from HZ 43 reported by EXOSAT. Instead, we find the interstellar neutral H/He ratio toward HZ 43 to be consistent with the canonical cosmic abundance ratio of 10 or with the 11.6 +/- 1.0 ratio measured by HUT along the line of sight toward another DA white dwarf, G191-B2B. The HUT observations suggest that either there is a substantial calibration error in the EXOSAT spectroscopy of HZ 43, or otherwise undetected metals in the nominally pure hydrogen HZ 43 atmosphere suppress its flux between 150 and 300 A, or both.

Kimble, Randy A.↗
NASA NTRS1992

Ultraviolet observations of clusters of Wolf-Rayet stars in the SBm3 galaxy NGC 4214 and Ultraviolet and optical observations of LINER's

The purpose of the grant was to obtain and analyze IUE (UV) and ground-based (optical) spectra of the central bar of NGC 4214, which contains several bright H II regions, in order to further explore the properties of the Wolf-Rayet stars in this galaxy. Several spatially distinct regions, with widely different equivalent widths of optical Wolf-Rayet lines, could be sampled by the large IUE entrance aperture. By using newly developed extraction techniques, the spectra of these H II regions could be isolated, and differences in their stellar populations would be systematically studied. Data were obtained with IUE in late February and early March, 1992. Some of the shifts were successful, but a few were not -- apparently the blind offset from the nearby star did not work equally well in all cases. Thus, the signal-to-noise ratio is somewhat lower than we had hoped. This necessitated a more careful extraction of the spectra of individual H II regions from the two-dimensional spectra. (A program that models the point spread function in the spatial direction was used to deblend the distinct H II regions.) The IUE data are currently being analyzed in conjunction with ground-based optical spectra. There appear to be obvious variations in the stellar population over angular scales of only a few arc seconds. The second part of the research performed under this grant was a continuation of a project that uses IUE (UV) and ground-based (optical) spectra to infer the physical conditions in Low-Ionization Nuclear Emission-Line Regions (LINER's). We have obtained spectra of a few key objects that cover a representative range in LINER continuum and emission-line properties. The overall goals are to (1) separate the emission into spatially distinct components, (2) establish whether the observed nuclear ultraviolet continua indicate sufficient photoionizing fluxes to account for the emission lines, (3) determine whether the nuclear emission can be explained by hot stars alone, (4) detect and measure the strengths of UV emission lines, and (5) search for systematic differences in the UV spectra of LINER's whose other properties differ in some respects.

Filippenko, Alexei V.↗