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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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At least 577 records · Page 32
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NASA NTRS1984

The 41.5 day binary X-ray pulsar 4U 1223 - 62 (GX 301 - 2)

Ariel 5 and SAS 3 X-ray pulse timing data for the 700 s X-ray pulsar 4U 1223 - 62 (GX 301 - 2) are reexamined in order to deduce the orbital elements of this system. The Ariel 5/SAS 3 arrival times are first reanalyzed to obtain the best solution for an orbital period close to 41.5 days and to estimate the uncertainties in it caused by unknown variations in the underlying pulse period. Spectral measurements by OSO 8 and HEAO 1 at a variety of orbital phases are presented and the origin of an unabsorbed, unpulsed soft component is discussed. OSO 8 observations of occasions when the amplitude and shape of the pulse profile changed dramatically are discussed. The global X-ray properties of the system are explained in terms of a simple stellar wind accretion model, and the interaction of the inflowing material with the neutron star magnetosphere is considered.

White, N. E.↗
NASA NTRS1985

IUE spectroscopy, visible-band photometry, and polarimetry of HD 47732 (V641 Monocerotis)

Several high- and low-dispersion IUE spectra are described for the hot, massive close binary HD 47732. The stellar silicon lines do not show theoretically expected strength, the weakness being attributed to incipicent emission. A weak stellar wind is measurable with an expansion velocity of about 500 km/s. There is difficulty in fitting a model atmosphere to all of the IUE continuum and visible band and IR measures. These difficulties are resolved by appealing to a 22,500 K model atmosphere and a distinctive interstellar extinction law. Numerous V band measures show the polarization to be variable, but not strongly in a phased-locked way. This suggests sporadic outbursts of gas feeding the shell. Several seasonal V band light curves are discussed, and the seasonal variations among them are attributed to variable developments of a systemic shell which scatters the photospheric light and dilutes to a variable degree the light variation due to ellipticity of figure of the component stars.

Koch, R. H.↗
NASA NTRS1985

X-ray observations of Wolf-Rayet stars

X-ray observations have been made of a very luminous O8f star, four late WN stars, and eight O VI Wolf-Rayet stars. The X-ray pulse height distributions of the O8f star is analyzed to obtain information on source temperature, emission measure, and location relative to the stellar wind. Only upper limits are obtained for the X-rays from the Wolf-Rayet stars, but for the late WN stars the upper limits are well below the maximum Lx/Lbol detected in earlier surveys. For the O VI stars, the limits, used in conjunction with models for the production of the optical O VI lines, supply information about the excitation conditions in the winds.

Sanders, W. T.↗
NASA NTRS1985

The peculiar X-ray and radio star AS431

Einstein observations are reported which reveal that the highly reddened emission-line star AS431 has a highly absorbed X-ray spectrum and a relatively strong intrinsic flux of 5 x 10 to the -12th erg/sq cm/s or more. Observations at 20 cm and 6 cm with the National Radio Astronomy Observatory Very Large Array are also reported which show that AS431 is also a moderately strong radio source (about 35 mJy). These data, together with optical and infrared observations, suggest a model in which both the radio and X-ray emissions arise in a chaotic stellar wind emerging from a single luminous Wolf-Rayet star.

Caillault, J.-P.↗
NASA NTRS1985

Detection of radio continuum emission from Herbig-Haro objects 1 and 2 and from their central exciting source

The region in Orion containing HH 1 and HH 2 was observed with the VLA at 20, 6, and 2 cm on several occasions from 1981 to 1984. At lower resolution, four continuum sources were detected. Two of these sources coincide positionally with HH 1 and HH 2. At 6 cm and higher resolution, HH 1 is resolved into at least two components. The emission is probably bremsstrahlung originating in the same region where the visible line emission is produced. This is the first detection of radio continuum from classic Herbig-Haro objects. At a position closely centered between HH 1 and HH 2, an object that can be interpreted as the energy source of the system was detected. The central source spectrum is S(nu) of about nu to the alpha power, where alpha = 0.4 + or - 0.2, suggesting a stellar wind. Finally, the fourth radio continuum source coincides positionally with an H2O maser and is probably excited by an independent star. There is evidence of time variability in its radio flux. No emission was detected from the Cohen-Schwartz (1979) star at the 0.1 mJy level.

Pravdo, S. H.↗
NASA NTRS1985

Mass outflows from young stellar objects

The process of mass loss from young stellar objects is examined in a review of recent observational investigations and theoretical models. Consideration is given to the interaction of the stellar wind with surrounding molecular clouds, the high degree of collimation seen in some embedded objects, alignment of outflows from stars embedded in the same cloud complex, initially isotropic and intrinsically anisotropic models of mass outflow, and the kinds of observations needed to determine the actual mechanisms involved.

Strom, S. E.↗
NASA NTRS1985

Spectrophotometry at 10 microns of T Tauri stars

New 8-13 micron spectra of 32 T Tau, or related young, stars are presented. Silicate emission features are commonly seen. Absorptions occur less frequently but also match the properties of silicate materials. The shape of the emission feature suggests that a more crystalline grain is responsible in the T Tau stars than those of the Trapezium region. The evolution of the silicate component of the circumstellar shell around T Tau stars, and its dependence upon stellar wind activity, visual linear polarization, and extinction are investigated. Several correlations suggest that the shells are likely to be flattened, disklike structures rather than spherical.

Cohen, M.↗
NASA NTRS1985

Anatomy of a cosmic-ray neutrino source and the Cygnus X-3 system

The effects of an intense beam of ultra-high energy cosmic rays from a compact object in the Cygnus X-3 binary system hitting the companion star, and of the subsequent production of secondary neutrinos, are examined. A maximum allowable beam luminosity of about 10 to the 42nd erg/s is found for a system containing a 1-10 solar mass main sequence target star. The proton beam must heat a relatively small area of the target star to satisfy observational constraints on the resulting stellar wind. With such a model, the neutrino to gamma-ray flux ratio of about 1000 can result from a combination of gamma-ray absorption and a large neutrino to gamma-ray duty cycle ratio. It is found that the high density of the atmosphere resulting from compression by the beam leads to pion cascading and a neutrino spectrum peaking at 1-10 GeV energies.

Stecker, F. W.↗
NASA NTRS1985

Observational studies of the symbiotic stars. III High-dispersion IUE and H-alpha observations of EG Andromedae

High-dispersion IUE and optical spectra are presented for the symbiotic star EG Andromedae (HD 4174). Remarkable emission-line strength and profile variations are confirmed for the S IV, O IV, C IV, and He II ultraviolet lines as well as H-alpha. Accurate cross-correlation absorption-line velocities determined from Ti I, Ca I, and Fe I features convincingly demonstrate that EG And is a single-lined spectroscopic binary. The velocity curve suggests that the photometric ephemeris reported by Smith in 1980 should be revised by a redefinition of zero phase by about 0.08 of a period. The primary of the system may be similar to the central star of a planetary nebula embedded in a dense nebula with a mild stellar wind. The behavior of the emission lines is interpreted to indicate that the primary and its surrounding nebula suffer a partial eclipse by the cool giant secondary.

Oliversen, N. A.↗
NASA NTRS1986

Research reports: 1985 NASA/ASEE Summer Faculty Fellowship Program

A compilation of 40 technical reports on research conducted by participants in the 1985 NASA/ASEE Summer Faculty Fellowship Program at Marshall Space Flight Center (MSFC) is given. Weibull density functions, reliability analysis, directional solidification, space stations, jet stream, fracture mechanics, composite materials, orbital maneuvering vehicles, stellar winds and gamma ray bursts are among the topics discussed.

Karr, G. R.↗
NASA NTRS1986

Halos around planetary nebulae

Preliminary results of a CCD survey designed to detect and investigate faint halos around planetary nebulae are reported. A TI 800 x 800 pixel CCD was used to take deep exposures of 44 planetary nebulae. The exposures were obtained through an H-alpha filter at the Cassegrain focus of the Palomar 1.5 m telescope. Spatial resolutions of 1 to 2 arcsec were obtained across 400 arcsec wide fields. The images, which are in many cases considerably deeper than any previously taken, reveal numerous planetary nebula halos. About two-thirds of the studied nebulae possess extensive outer halos, here defined as any extended emission beyond the 10 percent isophote. Ionized sulphur electron density measurements show that in some nebulae, the mass in the halo is comparable to the mass contained in the primary H II region. The data have been used to place constraints on the mode of origin of the halos. It is likely that the halos originate either by dynamical separation of a single ejected shell of gas or by the ejection of two or more such shells from the central star. It is possible but less likely that the halos are caused by excitation of the preplanetary stellar wind and improbable that the halos represent reflection nebulae.

Jewitt, D. C.↗
NASA NTRS1985

Radio continuum emission from premain sequence stars and associated structures

VLA 6 cm (4860 MHz with 100 MHz total bandwidth) C-array observations of regions of recent star formation containing premain sequence (PMS) stars, Herbig-Haro objects, and stellar jets, are presented. Three PMS stars, HL Tau, XZ Tau and FS Tau, were definitely (6-sigma) detected and FS Tau B is possibly (5-sigma) detected. The mass loss rates implied for spherically-symmetric stellar winds with outflow velocities of 200 km/s are in the range 1-2 x 10 to the -8th solar masses/yr. HL Tau shows extended structure including a 3-sigma detection of emission possibly associated with the jet from this star. No Herbig-Haro objects were detected at a typical 3-sigma rms level of 0.12 mJy/beam.

Brown, A.↗
NASA NTRS1986

A cloud collision model for water maser excitation

High-velocity collisions between small, dense, neutral clouds or between a dense cloud and a dense shell can provide the energy source required to excite H2O maser emission. The radiative precursor from the surface of the collisional shock front rapidly diffuses through the cloud, heating the dust grains but leaving the H2 molecules cool. Transient maser emission occurs as the conditions for the Goldreich and Kwan (1974) 'hot-dust cold-gas' maser pump scheme are realized locally within the cloud. In time, the local maser action quenches due to the heating of the H2 molecules by collisions against the grains. Although this model cannot explain the very long-lived steady maser features, it is quite successful in explaining a number of the observed properties of the high-velocity features in such sources as Orion, W51, and W49. In particular, it provides a natural explanation for the rapid time variations, the narrow line widths, juxtaposition of high- and low-velocity features, and the short lifetimes which are frequently observed for the so-called high-velocity maser 'bullets' thought to be accelerated by strong stellar winds.

Tarter, T. C.↗
NASA NTRS1986

The dynamics of Herbig-Haro objects

Radial-velocity and proper-motion information on Herbig-Haro (HH) objects is analyzed for clues to the character of the supersonic flows that produce the objects. The correlations among space velocities, excitation states, internal velocity dispersions, electron densities, and positions relative to the exciting stars for the emission knots of HH 1 and HH 2 is examined. Whereas the interstellar-bullet model may account for most of the phenomena in the HH 1-HH 2 system, HH 43 is found to show characteristics of a stellar wind shock against an obstacle cloudlet. By contrast, the HH 46-HH 47 system exhibits a continuous, well-collimated jet of emission with knots that may be due to instabilities in the confined, supersonic flow.

Schwartz, R. D.↗
NASA NTRS1986

Supershells and propagating star formation

Correlated supernovae from an OB association can carve large cavities (greater than 100 pc) in the interstellar medium (ISM), and can punch holes completely through the disk of a spiral galaxy. Supernova remnant energy within such a cavity is thermalized before the shock reaches the supershell. Thus stellar wind theory may be used to model these superbubbles. We describe how the evolution of the superbubble depends on the density distribution of the galactic disk gas and the rate of supernovae in the OB association. At a radius of 100 to 300 pc, the supershell becomes gravitationally unstable, forming giant molecular clouds which are the sites for new star formation. This gravitational instability of the supershells provides a physical mechanism for propagating star formation and may account for the observation of bursts of star formation in galaxies.

Maclow, M. M.↗
NASA NTRS1986

Unstable 06.5f?p star HD 148937 and its interstellar environment

The massive, early-type star HD 148937 (spectral type 06.5?p) is surrounded by a unique set of nebulosities. A spherically symmetric Stromgren sphere (Radius approx. - 25 pc), an ellipsoidal filamentary nebulosity (semimajor axis approx. - 5 pc) interpreted as a stellar-wind-blown shell, and a bipolar nebular complex (semimajor axis approx. - 1 pc) with HD 148937 located in the apparent center of symmetry. Observations of these nebulosities are reported (narrow-band charge coupled devices imaging, image dissector scanner (IDS) spectrophotometry, high resolution spectroscopy) in an attempt to establish a consistent model of HD 148937 and its nebulosities.

Leitherer, C.↗
NASA NTRS1987

Maps of millimeter wave emission from three galactic star-forming regions

In order to investigate the gas dynamics around young stellar objects, three sources were mapped which exhibit supersonic velocities in the 115 GHZ, J = 1-0 transition of CO. The maps, made with the Owens Valley Radio Observatory Millimeter Interferometer, are the highest spatial resolution images currently available of millimeter-wave continuum and line emission from the sources S106, S87, and LkHalpha101. Observations were made in the CS (J = 2-1) and C-13O (J = 1-0) transitions. In all the sources, the observations indicate that the ionized stellar wind is sweeping up ambient molecular gas. The molecular gas is found adjacent to the outer edges of the ionized winds, which originate in embedded infrared sources. From the observations presented, it may be inferred that the outflowing ionized winds are channeled by the surrounding dense, neutral gas.

Barsony, Mary↗
NASA NTRS1986

The infrared spectrum of M8 E - Evidence for circumstellar CO

High-resolution spectroscopic observations of the compact infrared source M8 E are reported in the region from 3 to 5 microns. Very prominent CO absorption lines are observed in the v = 1-0 band at 4.7 microns. The velocity width and rotational temperature suggest that this CO absorption occurs in a highly excited region. The high background continuum flux level and the prominent appearance of the CO features suggest that the CO line-forming region must be in front of the dust emission region. A blister model for M8 E, which places most of the dust continuum emission behind the source, satisfies this requirement. According to this picture, the observed circumstellar CO spectrum shows a high rotational temperature and a large velocity dispersion because of the combined effects of the strong stellar wind and possible shock heating near the dust zone as the wind encounters the ambient molecular cloud.

Larson, H. P.↗