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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1994

A Hubble Space Telescope ultraviolet spectrum of SN 1993J

We obtained a Hubble Space Telescope (HST) ultraviolet spectrum of the Type II supernova SN 1993J in M81 on 1993 April 15. The approximately 1650-2900 A region is smoother than observed for SN 1987A and SN 1992A and lacks strong P Cygni absorptions caused by iron peak element lines. Synthetic spectra calculated using a parameterized Local Thermodynamic Equilibrium (LTE) procedure and a simple model atmosphere do not fit the UV region. Radio observations suggest that SN 1993J is embedded in a thick circumstellar envelope. The UV spectra of other supernovae that are believed to have thick circumstellar envelopes also have approximately 1650-2900 A regions lacking in strong P Cygni absorptions. Interaction of supernova ejecta and circumstellar matter may cause the smooth UV spectrum. If so, UV observations of supernovae will provide insight into the circumstellar environment of the supernova progenitors.

Jeffery, David J.↗
NASA NTRS1990

A plasma radiation model for the prompt radio emission of supernova 1987 A

It is proposed that the prompt radio emission of supernova 1987a a few days after the explosion is the result of a plasma interaction between the ejecta and the presupernova circumstellar matter. The emission frequency then is determined by the electron density in the front of the ejecta, and the radio flux density mainly depends on the velocity of the ejecta and the circumstellar electron density. Free-free absorptions in the interaction region and by the circumstellar medium limit the emission on the high, respectively low, frequency side and inhibit observable emission in the first two days.

Benz, A. O.↗
NASA NTRS2011

Molecular Gas in Young Debris Disks

Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old > or approx.8 Myr), gaseous dust disks. From our results, neither primordia1 origin nor steady secondary production from icy planetesima1s can unequivocally explain the presence of CO gas in the disk ofHD21997.

Moor, A.↗
NASA NTRS1994

The Circumstellar Imager: Direct detection of extra-solar planetary systems

The Astrometric Imaging Telescope (AIT) is designed to probe the circumstellar environment by both direct imaging and indirect astrometric measurements. The Circumstellar Imager (CI) is a coronagraphic camera and is the direct imaging component of the AIT. The CI is designed to obtain high-sensitivity images of the circumstellar region. It provides crucial non-inferential information relating to the frequency, origin, and evolution of planetary systems and all forms of circumstellar matter. Such imaging is usually limited by the scattered and diffracted light halos of the star itself, which are greatly suppressed in the CI by mating a novel high-efficiency coronagraph with a phase-compensated optical system. For faint point sources in the circumstellar region, the CI will have a sensitivity in excess of 5 magnitudes fainter than the as-designed Hubble Space Telescope (HST). Laboratory data are shown for the coronagraph, which, in a diffraction-limited environment, is capable of suppressing the stellar diffraction sidelobes by several orders of magnitude without significant sacrifice of field of view. In order to realize the high rejection levels inherent in the coronagraph design, it is necessary to limit scatter in the optical systems, imposing a mid-spatial frequency figure error requirement an order of magnitude smaller than that of the HST. Experimental data directed toward meeting this requirement are also shown.

Ftaclas, Christ↗
NASA NTRS1975

Electromagnetic pulse from supernovae

Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

Colgate, S. A.↗
NASA NTRS1975

Soft X-ray observations of Centaurus X-3 from Copernicus

We have detected soft X-ray emission from Centaurus X-3 in the 0.6-1.9 keV band, using the focusing telescope aboard OAO Copernicus. The flux is compatible with an extrapolation of the harder X-ray spectrum, attenuated by (3-4) times 10 to the 22nd atoms per sq cm of interstellar and/or circumstellar matter. The data are consistent with the distance estimate of 5-10 kpc derived from the spectroscopic modulus of the optical component, and obviate the need to postulate the primary to be an anomalously subluminous hot star. There is currently no compelling evidence that such models must be invoked to explain any of the observed compact X-ray sources.

Margon, B.↗
NASA NTRS1979

Ultraviolet and optical spectroscopic studies of Lambda Andromedae - The chromosphere and interstellar medium

Chromospheric lines of, and interstellar lines toward, the spectroscopic binary Lambda And (primary component G7-G8 III-IV) have been observed in the ultraviolet with the spectrometer and telescope on board the Copernicus satellite. An extensive, high-resolution spectroscopic study of the Ca II H and K profiles has also been undertaken. Some of these optical spectra were obtained simultaneously with the ultraviolet data. The ultraviolet emission lines of Lamba And are compared to the sun and to stars of similar spectral type. The star Lamba And resembles the active sun in surface brightness of chromospheric emissions and in appearance of the Mg II and Ca II profiles. The largest variations in the integrated calcium emission cores amount to an 80% increase in the K core and a corresponding 40% increase in the H core between observations two years apart. Variations in the cores may show a dependence on spectroscopic phase, and may be contributed to by circumstellar matter in the binary system. Previously unreported, transient emission features have also been observed, at a velocity of -70 km/s with respect to the Ca II emission cores.

Baliunas, S. L.↗
NASA NTRS1979

Mass flow in close binaries - Results of optical and ultraviolet observations

Observational data provide information regarding mass flow in close binaries. Data about origin, condition, and development of circumstellar matter can also be obtained. The investigations are based on an evaluation and correlation of photometric observations and simultaneously made photoelectric and spectrographic observations in the visible spectral range and, in addition, also on satellite observations in the ultraviolet range. Supplementary information concerning the mass flow in close binaries is obtained on the basis of observations related to the X-ray, infrared, and radio range. Suitable theoretical models are employed to interpret the observational data.

Rahe, J.↗
NASA NTRS1979

Infrared observations of NGC 2071/IRS/ and AFGL 490 - Two low-luminosity young stars

Infrared observations are presented of two compact sources associated with molecular clouds. Photometry from 2 to 200 microns of the source associated with an OH maser in NGC 2071, OH 205.1-14.1, shows a steep increase in flux from 2 to 50 microns. Scans at several wavelengths fail to resolve the source. Photometry at 50-200 microns of the other object, GL 490, when combined with earlier 2-20-micron spectrophotometry, shows an infrared energy distribution that is much broader than that of the NGC 2071 source. Both sources are interpreted as young, possibly pre-main-sequence objects with differences in energy distributions due principally to differences in the distribution of circumstellar matter.

Harvey, P. M.↗
NASA NTRS1984

Optically-thick, highly-variable plasma in interacting binaries

The interacting binaries HD 207739 and R Arae were observed by IUE. The ultraviolet spectrum of HD 207739 undergoes complex variations in both the lines and the continuum. Considerable circumstellar matter is present; R Arae (B9p + ?) exhibits SiIV, CIV and even NV absorption features. Both the lines and continuum are variable. An unusual secondary eclipse which is deeper in the ultraviolet than in the visible is present near phase 0.6. The CII line has a P cygni profile with emission present at all observed phases. These systems are probably in a relatively short-lived phase of evolution which is not often observed.

Kondo, Y.↗
NASA NTRS1983

Infrared observations of RS CVn stars

The paper presents infrared photometry of the RS CVn binary stars AR Lac (1.2-10 microns) and MM Her (1.2-3.5 microns) as they egressed from their primary and secondary eclipses; of the eclipsing systems RS CVn and Z Her at maximum light (1.2-10 microns) and of the non-eclipsing systems UX Ari and HR 1099 (1.2-10 microns). An analysis of these and published V data based on flux ratio diagrams (linear analogues of color-color diagrams) shows that G and K stars supply the infrared light of these systems. In AR Lac, the combined light of a G5-K0 subgiant and either a late F dwarf or an early F subgiant can account for the observed visual and infrared light curves. None of these systems shows infrared emission from circumstellar matter. This result is simply understood: dust grains would not be expected to form in the physical conditions surrounding the subgiant, and the corona and chromosphere (whose properties have been deduced from spectroscopic X-ray observations) should not produce appreciable infrared emission.

Berriman, G.↗
NASA NTRS1985

Ultraviolet spectroscopic observations of HD 77581(Vela X-1 = 4U 0900-40)

Ultraviolet spectra of HD 77581 obtained with the IUE satellite in December 1982 and January 1983 are analyzed. The effective temperature is found to be 25,000 + or - 1000 K by comparing its photospheric absorption lines with those in four well-studied B0-B1 supergiants. The distance of 1.9 + or - 0.2 kpc is derived from its luminosity log L/solar-L = +5.53, which is obtained from the effective temperature and from its radius. Circumstellar matter is detected not only in the C IV and Si IV lines but also in Al III, Fe III, C II, and Mg II lines. Profiles of the C IV and Si IV lines show a similar dependence on the orbital phase as in 1978. Two distinct sharp components are found in the shortward-shifted absorptions of the Al III and Fe III lines. Once component is present only in the second half of the orbital period, and its origin may be a 'trailing wake' behind the neutron star. The other component is seen all over the period, and it can be interpreted as originating in a cool expanding region of gas in the orbital plane.

Sadakane, K.↗
NASA NTRS1989

A second supernova inside Puppis A?

Narrow-band images of an unusual swirl structure located near the center of the Puppis A supernova remnant are presented which reveal three overlapping filamentary systems of highly diverse composition. One is dominated by emission lines of nitrogen, one by oxygen, and one by sulfur. Spectra indicate that these small rings have high velocities and a corresponding kinematic age of less than 800 yr. Heavy-element abundances are extremely high and different in each system, some reminiscent of knots in Cas A, and others of circumstellar matter observed surrounding supernova 1987A. The youth and unusual chemistry lead to the suggestion that a second supernova has exploded within the shell of Puppis A, giving rise to the swirl structure.

Winkler, P. F.↗
NASA NTRS1989

X-ray emission from O-type stars - Parameters which affect it

As a result of previous analyses of the X-ray fluxes of O-type stars, it has been established that, surprisingly, there is no correlation between X-ray flux and such basic parameters as M, R, v(rot), T(eff), mass accretion rate v(infinity), L(w) = mass accretion rate v(infinity), and wind energy. In this paper, other factors influencing the X-ray flux of the hottest stars are sought. As a result of the present analysis, it is found that stars embedded in dense clouds are often X-ray brighter, runaway stars are fainter in X-rays, massive binaries emit more X-rays than single stars, and radio-bright stars are also more active in X-rays. All these correlations lead to the conclusion that the stellar environment and the interaction of the stellar wind with circumstellar matter (possible remnants of protostellar clouds) play a dominant role in the production of the X-ray flux.

Chlebowski, T.↗
NASA NTRS1988

Supernova 1987A

Supernova 1987A (February 23, 1987) in the Large Magellanic Cloud is the brightest supernova to be observed since SN 1604 AD (Kepler). Detection of a burst of neutrinos indicates that a neutron star was formed. Radioactive decay of about 0.07 solar mass of Co-56 is responsible for the observed optical light as well as hard X-rays and gamma-ray lines. Ultraviolet, optical, and infrared 'light echoes' and soft X-rays provide information on the distribution of circumstellar matter and the evolution of the progenitor star.

Mccray, Richard↗
NASA NTRS1989

500-3200 A observations of the interacting binary stars V356 Sgr and Beta Lyr

Results on VG356 Sgr and Beta Lyr are presented from the Voyager UV spectrometers and the IUE. The observations of V356 Sgr cover two eclipses in which the total strength of the UV emission lines were invariant. At wavelengths shorter than 1600 A, an uneclipsed UV continuum was found. A model for the origin of the circumstellar matter in V356 Sgr is given. The UV observations of Beta Lyr show a strong far-UV continuum down to 912 A. The spectral shape fo the far-UV continuum closely resembles that of a UX Uma-type cataclysmic variable. Analysis of the Beta Lyr data indicates that the central object is small, with a radius on the order of 1 solar radius or less.

Polidan, R. S.↗
NASA NTRS1989

The carbon chemistry of meteorites: Relationships to comets

The carbonaceous meteorites exhibiting alteration by liquid water bear a strong relationship to comets. Not only is their elemental composition closer to solar in relative abundances than other meteorites, they are water rich; and they contain isotopic compositions among refractory and volatile elements indicative of presolar components. Some of these isotopic anomalies occur in organic compounds and carbonaceous grains signifying the presence of discrete and identifiable carbon components derived from interstellar and circumstellar matter. Insofar as comets and meteorites are ultimately formed from interstellar gas and dust, and comets have been subjected to considerably less aqueous and thermal evolution than carbonaceous meteorites, the interstellar imprint should be much stronger and better preserved in comets.

Chang, S.↗