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Results for “ULTRAVIOLET SPECTRA”

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NASA NTRS1981

A classification system for O-B2 stars based on the Si IV and C IV resonance lines

Low-dispersion ultraviolet spectra from Skylab Experiment S-019 are used to explore the variations of Si IV and C IV line strengths with temperature and luminosity. These considerations lead to a classification system in which the Si/C ratio is used to discriminate luminosity among the O stars and temperature among the O9-B2 stars of lower luminosity. Stars falling in these two regimes may be distinguished either by the presence of C IV emission or on the basis of C IV absorption strength. The log(Si IV/C IV) vs C IV diagram is proposed as a primary tool in such a classification system. The rapid variation in the Si IV/C IV ratio from less than 1/10 at O9 to greater than 10 at B1.5 for luminosity class III-V stars appears to be an especially useful criterion for the temperature classification of stars in this spectral range.

Henize, K. G.↗

NASA NTRS1981

IUE observations of faint comets

Ultraviolet spectra of seven comets taken with the same instrument are given. The comets P/Encke (1980), P/Tuttle (1980 h), P/Stephan-Oterma (1980 g), and Meier (1980 q) were observed in November and December 1980 with the IUE satellite, and comets P/Borrelly (1980 i) and Panther (1980 u) were observed with the IUE on March 6, 1981. The spectra of these comets are compared with one another, as well as with comet Bradfield (1978 X), which was extensively studied earlier in 1980 with the IUE. To simplify the interpretation of the data and to minimize the dependence upon a specific model, the spectra are compared at approximately the same value of heliocentric distance whenever possible. Effects arising from heliocentric velocity, geocentric distance, and optical depth are also discussed. All of the cometary spectra are found to be remarkably similar, suggesting that these comets may have a common composition and origin.

Weaver, H. A.↗

NASA NTRS1982

Ultraviolet spectroscopy of planetary nebulae in the Magellanic Clouds

Ultraviolet spectra of the high excitation planetary nebulas LMC P40, SMC N2, and SMC N5 are presented in an investigation of their chemical composition in an effort to make reliable estimates of the carbon abundance in extragalactic planetary nebulas. The carbon abundance is found to be almost 40 times more abundant in the SMC planetaries than in the SMC interstellar medium, and is about 6 times more abundant in the LMC planetary than in the LMC interstellar medium. The net result of carbon synthesis and convective dredgeup in the progenitors of planetary nebulas as reflected in the nebular carbon abundance is roughly the same in the Galaxy, the LMC, and the SMC.

Maran, S. P.↗

NASA NTRS1982

A spectrophotometric analysis of the hot helium-rich white dwarf HD 149499 B

A comprehensive analysis of the hot helium-rich white dwarf HD 149499 B is presented based on International Ultraviolet Explorer ultraviolet spectra along with available optical spectra and photometry. Line strengths, line profiles, and continuum fluxes are analyzed in terms of a new grid of hot, high-gravity stellar atmospheres of mixed composition. The line strengths furnish the strongest temperature and gravity diagnostics because they are not affected by the contamination of the white dwarf optical spectrum and photometric properties by the K0 V companion, 2.35 arcsec away. Wegner's (1978) classification of HD 149499 B as a DO star is confirmed.

Sion, E. M.↗

NASA NTRS1982

Production of CS and S in Comet Bradfield /1979 X/

High and low resolution ultraviolet spectra of carbon monosulfide (CS) in Comet Bradfield (1979 X) were obtained with the IUE satellite. The high resolution rotational profile of the (0, 0) band at 257.5 nm can be fitted with a theoretical profile derived assuming a Boltzmann temperature of 70 K. Spatial plots of the low resolution data for both S and CS show that these emissions are concentrated toward the cometary nucleus. The results that have been obtained are consistent with a Haser model for CS and S where the parent molecule is CS2. A very rapid variation of CS brightness with heliocentric distance is found.

Jackson, W. M.↗

NASA NTRS1982

The ultraviolet spectrum of an aurora 530-1520 A

Ultraviolet spectra between 530 and 1520 A of an active auroral arc were obtained at 6.5-A instrumental resolution. Several new emission features are identified, including several bands of the N2 Birge-Hopfield (1, v-double-prime) progression and numerous N I multiplets, the latter being preponderant at low altitudes. The improved instrumental resolution over previous experiments in the wavelength region below 1200 A allows for a partial resolution of the complex structure between 900 and 1100 A reported in earlier work. The ratio of O I 1356 to N2 Lyman-Birge-Hopfield is smaller than in the dayglow at a similar altitude, and this is interpreted as evidence for a depletion of atomic oxygen in the auroral ionosphere relative to mid-latitude composition.

Feldman, P. D.↗

NASA NTRS1981

Mass loss from interacting close binary systems

The three well-defined classes of evolved binary systems that show evidence of present and/or past mass loss are the cataclysmic variables, the Algols, and Wolf-Rayet stars. It is thought that the transformation of supergiant binary systems into the very short-period cataclysmic variables must have been a complex process. The new evidence that has recently been obtained from the far ultraviolet spectra that a certain subclass of the Algols (the Serpentids) are undergoing fairly rapid evolution is discussed. It is thought probable that the remarkable mass outflow observed in them is connected with a strong wind powered by accretion. The origin of the circumbinary clouds or flat disks that probably surround many strongly interacting binaries is not clear. Attention is also given to binary systems with hot white dwarf or subdwarf components, such as the symbiotic objects and the BQ stars; it is noted that in them both components may be prone to an enhanced stellar wind.

Plavec, M. J.↗

NASA NTRS1982

The low state of AM Herculis - Observations from 0.12 to 10 microns

Observations of AM Her during a low state over a wavelength range from 0.12 to 10 microns are reported. These include IUE ultraviolet spectra, light curves at U, B, V, R, J, H, K, and magnitudes at L, M, and N. The UV observations reveal a nearly Rayleigh-Jeans continuum spectral distribution and broad Lyman-alpha absorption from a hot (effective temperature = 50,000 K) white dwarf. Of the strong emission lines present in the high state, only weak C IV (1550 A) and Mg II (2800 A) features remain. The optical light curves are markedly different from the high state, while the infrared light curves are similar in appearance to the high state. The infrared variations cannot be explained solely by the ellipsoidal variations of a secondary star which is heated by an accretion column. The 10 micron flux is less than the high state, but it is not possible to tell if the excess noted during the high state is still present. The large available wavelength range is used to constrain the relative contributions of the white dwarf, the red dwarf, and the accretion columns.

Szkody, P.↗

NASA NTRS1982

UV time-dependent emission in SY Muscae

IUE ultraviolet spectra of SY Mus for September 20, 1980 and June 11, 1981 indicate a substantial enhancement of UV emission over a nine-month period. The general UV flux level appears to have increased by about one order of magnitude between the two observing epochs. The strong UV continuum evident throughout the entire IUE spectral range 1200-3200 A on June 11, 1981 is closely approximated by a star with an effective temperature of 40,000 K. On September 20, 1980, however, the continuum distribution manifested a more complex structure, which is possibly explained by a combination of thermal emission from an early type main sequence star and nebular recombination emission.

Michalitsianos, A. G.↗

NASA NTRS1983

Ultraviolet spectroscopy of the brightest supergiants in M31 and M33

Ultraviolet spectroscopy from the IUE, in combination with groundbased visual and infrared photometry, are to determine the energy distributions of the luminous blue variables, the Hubble-Sandage variables, in M31 and M33. The observed energy distributions, especially in the ultraviolet, show that these stars are suffering interstellar reddening. When corrected for interstellar extinction, the integrated energy distributions yield the total luminosities and black body temperatures of the stars. The resulting bolometric magnitudes and temperatures confirm that these peculiar stars are indeed very luminous, hot stars. They occupy the same regions of the sub B01 vs. log T sub e diagram as do eta Car, P Cyg and S Dor in our galaxy and the LMC. Many of the Hubble-Sandage variables have excess infrared radiation which is attributed to free-free emission from their extended atmospheres. Rough mass loss estimates from the infrared excess yield rates of 0.00001 M sub annual/yr. The ultraviolet spectra of the H-S variables are also compared with similar spectra of eta Car, P Cyg and S For.

Humphreys, R. M.↗

NASA NTRS1982

IUE observations of supernova remnants

Ultraviolet spectra of supernova remnants obtained with the IUE satellite provide unique information concerning the shock conditions and elemental abundances in the optically bright filaments. High temperature species such as N V provide diagnostics for shock velocities above 100 k/s, and strong lines of carbon and silicon in the IUE spectral range make it possible to study the destruction of refractory grains in shocked interstellar gas. Observations of a nonradiative shock at the edge of the Cygnus Loop provide constraints on the physics of the shock front itself. Most of the very young remnants whose optical spectra show anomalous elemental abundances are too highly reddened for IUE observations, but extensive observations of the Crab Nebula and a spectrum of the supernova remnant in NGC 4449 yield carbon to oxygen ratios from which the mass of the progenitor may be estimated.

Raymond, J. C.↗

NASA NTRS1983

The ultraviolet excess of luminous quasars. II - Evidence for massive accretion disks

This paper presents new infrared, optical, and ultraviolet spectra of three high-redshift quasars. They are analyzed along with three published quasar spectra. After accounting for other sources of radiation, the continua are fitted with spectra predicted for optically thick steady-state accretion disks which include the effects of general relativity. The two fitting parameters, the mass of the accreting black hole and the accretion rate, are determined by the data with a formal accuracy of 20 percent. The masses range from 0.2-0.5 billion solar mass for 3C 273 and PKS 0405-123 to 1-3 billion solar masses for the high-redshift quasars. The values depend on the assumed disk inclination and the angular momentum of the hole. The high luminosities of these six quasars are all within a factor of 2 of their Eddington limits, and this conclusion is not extremely sensitive to the modeling assumptions.

Malkan, M. A.↗

NASA NTRS1983

Possible evidence for the driving of the winds of hot stars by Alfven waves

Ultraviolet spectra of the supergiants Alpha Cam (09.5 Ia), HD 105056 (ON9.7 Iae), and 15 Sgr (O9.7 Iab) are compared, and it is shown that the terminal outflow velocity, TOV, of HD 105056 is one-half that of the other two stars even though HD 105056 has the highest effective temperature of the three stars. This anomaly, together with the fact that the observed TOV values for early-type stars scatter about an empirical correlation between TOV and log T(eff) by an amount which is larger than the amount expected according to the observational errors in determining TOV and log T(eff), leads to the conclusion that an agent in addition to radiation, Alfven waves, is driving the winds of early-type stars.

Underhill, A. B.↗

NASA NTRS1983

A determination of the composition of the Saturnian stratosphere using the IUE

Ultraviolet spectra of Saturn from the IUE satellite was reduced to produce a geometric albedo of the planet from 1500 to 3000 A. By matching computer models to the albedo a chemical composition consistent with the data was determined. This model includes C2H2 and C2H6 with mixing ratios and distributions of 9 + or - 3 x 10 to the -8th in the top 20 mbar of the atmosphere with none below for C2H2 and 6 + or 1 x 10 to the -6th also in the top 20 mbar with none below for C2H6. The C2H2 and C2H6 distributions and the C2H6 mixing ratio are taken directly from the Voyager IRIS model (R. Courtin et al., 1981). The Voyager IRIS model also includes PH3, which is not consistent with the UV albedo from 1800 to 2400 A. This model requires a previously unidentified absorber to explain the albedo near 1600 A. After considering several candidates, it is found that the best fit to the data is obtained with H2O, having a column density of 6 + or - 1 x 10 to the -3 cm-am.

Winkelstein, P.↗

NASA NTRS1983

Combined ultraviolet studies of astronomical sources

Ultraviolet spectra of non-radiataive shock waves grain destruction and elemental abundances in interstellar shocks, carbon abundance in M33 and M31 from supernova remnants, determination of the mass function in the large Magellanic cloud, UV spectra of white dwarf pulsars, stellar flares, availability of the double quasar Q 0957 + 56' AB, spectra of late-F dwarfs and their relation to rotation, dynamics of hot gas surrounding hybrid stars, high resolution study of epsilon coronae Austriual, active regions on solar-type dwarfs as a function of rotation rate and age, coordinated chromospheric synoptic observations of selected late-type stars, the two-component atmosphere of Lambda Andromedae, and activity in Hyades giants are discussed.

Dupree, A. K.↗

NASA NTRS1983

Evidence for a warm wind from the red star in symbiotic binaries

A systematic redshift of the high ionization resonance emission lines with respect to the intercombination lines is found from an examination of the ultraviolet spectra of symbiotic stars obtained with IUE. After consideration of other possibilities, this is most probably explained by photon scattering in an expanding envelope optically thick to the resonance lines. Line formation in a wind, or at the base of a wind is therefore suggested. Reasons are also given indicating line formation of the most ionized species in a region with an electron temperature of the order of 100,000 K, probably around the cool star. The behavior of the emission line width with ionization energy seems to support this model. The cool components of symbiotic stars appear to differ from normal red giants, which do not have winds of this temperature. An explanation in terms of a higher rotation velocity due to the binary nature of these stars is suggested.

Friedjung, M.↗

NASA NTRS1983

Ultraviolet high-resolution spectroscopy from the Space Telescope

The High Resolution Spectrograph is one of five scientific instruments which will be part of the Space Telescope observatory. The spectrograph was designed to take advantage of the imaging and pointing capabilities of the telescope to obtain ultraviolet spectra with spectral resolution comparable to large, ground-based coudeinstruments. Some of the results of the ground-based testing program will be described, along with applications of these properties to future science programs.

Ebbets, D. C.↗

NASA NTRS1984

A Far Ultraviolet Imaging Spectrograph for Shuttle

The development of the Far Ultraviolet Imaging Spectrograph (FUVIS) Shuttle sortie missions, is described. Objectives of the experiment are to obtain spatially-resolved far-ultraviolet spectra of extraterrestrial sources, including emission-line and reflection nebulae, diffuse background radiation, extragalactic objects, and comets. The use of fast focal ratio (f/1) Schmidt optics and an opaque CsI photocathode which affords high quantum efficiency in the far-UV provides the maximum possible diffuse source sensitivity. Measured emission line intensities of 5 Rayleighs (or continua of intensity 1 R/A) in 300 sec exposures are expected. The development includes a dedicated pointing platform and a low light level television camera for payload specialist use in target acquisition and guiding.

Carruthers, G. R.↗