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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 55 records · Page 3
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NASA NTRS1996

Far-Infrared Hydrogen Lasers in the Peculiar Star MWC 349A

Far-infrared hydrogen recombination lines H15(alpha)(169.4 micrometers), H12(alpha)(88.8 micrometers), and H10(alpha)(52.5 micrometers) were detected in the peculiar luminous star MWC 349A from the Kuiper Airborne Observatory. Here it is shown that at least H15(alpha) is strongly amplified, with the probable amplification factor being greater than or about equal to 10(exp 3) and a brightness temperature that is greater than or about equal to 10(exp 7) kelvin. The other two lines also show signs of amplification, although to a lesser degree. Beyond H10(alpha) the amplification apparently vanishes. The newly detected amplified lines fall into the laser wavelength domain. These lasers, as well as the previously detected hydrogen masers may originate in the photoionized circumstellar disk of MWC 349A and constrain the disk's physics and structure.

Strelnitski, Vladimir↗
NASA NTRS1974

On the nature of the nonthermal radio emission from the galactic center

Some recent observations of the galactic center appear at first sight to have made the character of the radio source Sgr A unclear. The flatness of the usually quoted spectrum, the lack of any measured polarization, the presence of hydrogen recombination lines, and the radio-infrared luminosity ratio are all consistent with Sgr A being a rather hot H II region. It is shown here, however, that when flux measurements between 80 MHz and 91000 MHz are all included and the multiple nature of the source is accounted for, the spectral index exceeds 0.4 - much too steep to be bremsstrahlung. There is, therefore, no question that Sgr A is a nonthermal source. It is further argued on the basis of a comparison of appearance, energetics and the recent results which no longer put Sgr A exactly at the center of the galaxy that Sgr A could be a supernova remnant rather than a miniature of active extragalactic radio sources.

Jones, T. W.↗
NASA NTRS1975

The rocket-ultraviolet spectrum of the planetary nebula NGC 7027

An ultraviolet spectrum of NGC 7027, obtained with a rocket-borne telescope, is analyzed. Absolute values are presented for the observed fluxes, and upper limits are given for the strongest predicted lines that were not observed. The results are corrected for interstellar extinction using the observed and calculated line ratios between H-beta and the hydrogenic recombination line of He II at 1640 A. The corrected C IV resonance line at 1549 A is found to be in good agreement with the intensity calculated from models, but the intercombination line of C III at 1909 A is found to be too bright by a factor of 10. This discrepancy is reduced to a factor of 4 by taking dielectric recombination into account and is eliminated by using the solar carbon abundance, which implies attenuation in the C IV line. It is shown that no appreciable number of absorbing grains can exist in the C IV-producing region of the nebula since the optical depth is of the order of 10,000 at the line center.

Bohlin, R. C.↗
NASA NTRS1977

Solar photolysis of water

Hydrogen is produced by the solar photolysis of water in a first photooxidation vessel with a transparent wall in the presence of a water soluble photooxidizable reagent and an insoluble hydrogen recombination catalyst. Simultaneously oxygen is produced in a second photoreduction reactor with a transparent wall in the presence of an insoluble photoreduction reagent catalyst. When spent, the solution from the first reactor is fed into the second reactor. A reaction occurs in the dark in which the redox reagents are regenerated, and the regenerated photooxidation reagent solution is recycled to the first reactor. The photoreduction-catalyst is a bifunctional reagent catalyst including a transition metal salt together with a hydroxyl or chlorohydroxyl decomposition catalyst of high area.

Ryason, P. R.↗
NASA NTRS1976

Millimeter emission lines in Orion A

During the course of a search of Orion A for signals from three large organic molecules, several millimeter-wave lines from known interstellar molecules were observed. Results are reported for observations of methanol (CH3OH), methyl cyanide (CH3CN), methyl acetylene (CH3CCH), acetaldehyde (CH3CHO) and (Si-29)O. Emission signals from two hydrogen recombination lines (H41-alpha and H42-alpha) detected from the H II region of Orion A are also reported. Negative results were obtained for several millimeter-wave transitions of ethylene oxide, acetone, and cyclopropenone.

Lovas, F. J.↗
NASA NTRS1980

Rocket-ultraviolet imagery of the North America nebula

New ultraviolet imagery of NGC 7000 has been obtained in a sounding-rocket flight with an electrographic Schmidt camera which covers the 1230-2000 A wavelength range and has a higher angular resolution than the Apollo 16 imagery. The integrated brightness of NGC 7000 near 1450 A is unexpectedly high (three times the brightness of HD 199579 as measured by CHB), but as no emission lines were observed with a nebular spectrograph, it is concluded that the radiation observed in the UV image is nearly pure continuum. Comparison with the blue continuum image is not possible, as the latter image has dominant contributions due to night sky background, hydrogen recombination continuum, and possibly unresolved faint stars. It is suggested that the high UV brightness of NGC 7000 is due to the highly efficient dust scattering of stellar radiation.

Carruthers, G. R.↗
NASA NTRS1980

Ultraviolet observations of the Cygnus Loop

The analysis of IUE observations of a filament on the western edge of the Cygnus Loop yields a shock velocity of about 130 km/sec, significantly higher than the velocity estimated from the optical spectrum. This velocity together with the high forbidden O III/H-beta ratio reported by Miller (1974) indicates that much of the hydrogen recombination region predicted by steady flow shock models is absent. This situation may occur because this part of the supernova remnant is in the shell-formation phase that accompanies the transition from the adiabatic to the snowplow phase or because the observed filament is a recently shocked cloud.

Raymond, J. C.↗
NASA NTRS1982

The energetic molecular outflow near AFGL 961 - Millimeter-wave and infrared observations

Sensitive millimeter-wave C-12O line observations and near-infrared hydrogen recombination line observations of AFGL 961 are reported and analyzed. The observations show that the high-velocity flow has a maximum extent of at least six arcmin or 1.9 pc at the distance of AFGL 961. The flow is anisotropic and the emission profiles are asymmetric in velocity. The mass of the gas involved in the flow is determined to be approximately 19 solar masses, and the kinetic energy of this gas is estimated to be about 8 x 10 to the 46th ergs. These observations are interpreted as evidence that an energetic bipolar outflow of molecular gas is occurring near AFGL 961. Comparison of infrared recombination line data, radio continuum, and CO observations shows that a strong, ionized, stellar wind would not be a sufficient force to drive the outflow. The effects of the outflow on the surrounding molecular cloud was also investigated.

Lada, C. J.↗
NASA NTRS1983

Modeling of G333.6-0.2 as a spherical H II region

The radio and IR observations of the H II region G333.6-0.2 are matched with a detailed spherical model with a density distribution which has a uniform-density core of radius 0.05 pc, a power-law intermediate zone, and a uniform-density halo. A stellar radiation field is required that is somewhat different from those predicted by available model atmospheres. Of the stellar models of Kurucz, the Teff = 34,000 K and log g = 3.5 model best fits the observed ratio of helium to hydrogen recombination lines. A good fit to all the observations in obtained with an S(2+) ionizing flux which is a factor of 20 times less than predicted by the Kurucz atmosphere. Current model atmospheres may not be appropriate because a single stable star with Teff = 34,000 K fails by at least an order of magnitude to produce the ionizing luminosity. The small radius of the constant-density core implies a short dynamical lifetime of approximately 5000 years for this spherical model; this may indicate that a nonspherical blister geometry is more appropriate for this H II region.

Rubin, R. H.↗
NASA NTRS1984

The electron density in M82 from the S III mid-infrared line ratio

Strong detections have been made of both the 18.7 microns and 33.4 microns lines of S III in the irregular galaxy M82. This represents the first detection of the 33.4 microns line in an extragalactic object. These measurements sample the ionized gas component which dominates the observed infrared forbidden line and infrared hydrogen recombination line emission. From the ratio of the line fluxes an electron density of 120 (+ 280, - 120) per cu cm is deduced. This result is in agreement with previous estimates of the density derived from high-frequency radio continuum measurements and an assumed emitting volume. They impose further constraints on possible starburst models.

Houck, J. R.↗
NASA NTRS1986

A study of the dust distribution and extinction law in Mon R2

Observations were obtained at wavelengths from 1.5 to 7.5 microns with beams varying in diameter from 4 to 28 arcsec of infrared hydrogen recombination lines toward the Mon R2 IRS1 H II region. It is found that the data cannot be fitted with the extinction law which characterizes the interstellar medium unless the obscuring matter is clumped on a small scale of not greater than 0.3 arcsec; in which case considerable fluctuations in the amount of extinction on scales smaller than 1 arcsec are expected. The data of Simon et al. (1983) suggest a dip in the extinction about 5 arcsec from the 2-micron and radio continuum peak, and rule out models with uniform dust and clump distributions.

Natta, A.↗
NASA NTRS1986

The ionization structure of the circumstellar envelope of Alpha Orionis

The physical processes which affect the ionization of the outer circumstellar envelope of Alpha Ori are analyzed and evaluated. The ultraviolet radiation fields of the chromosphere and the interstellar medium dominate the envelope, and the most common forms of all species are neutral atoms and first ions. Hydrogen recombines just outside the chromosphere, where atoms with smaller ionization potential are essentially fully ionized. The heavier ions gradually recombine with increasing distance from the star, until the interstellar radiation field reverses this trend. The electron fraction in the outer envelope is approximately equal to the abundance of all such heavy atoms, i.e., of the order of 0.0001. The analysis is applied to the case of neutral K, whose density in the envelope has been determined by scattering experiments. The theory predicts that the slope of the K I density distribution should decrease from -1.5 to -3.5 in the outer envelope. The mass loss rate of Alpha Ori implied by the K I scattering experiments is 4 x 10 to the -6th solar mass/yr.

Glassgold, A. E.↗
NASA NTRS1987

Extragalactic infrared spectroscopy

The spectra of galaxies in the near infrared atmospheric transmission windows are explored. Emission lines were detected due to molecular hydrogen, atomic hydrogen recombination lines, a line attributed to FEII, and a broad CO absorption feature. Lines due to H2 and FEII are especially strong in interacting and merging galaxies, but they were also detected in Seyferts and normal spirals. These lines appear to be shock excited. Multi-aperture measurements show that they emanate from regions as large as 15 kpc. It is argued that starbursts provide the most plausible and consistent model for the excitation of these lines, but the changes of relative line intensity of various species with aperture suggest that other excitation mechanisms are also operating in the outer regions of these galaxies.

Joseph, R. D.↗
NASA NTRS1987

Spectrophotometery of Brackett lines in very luminous IRAS galaxies

Observation of the Brackett-alpha and Brackett-gamma hydrogen recombination lines were made in a sample of galaxies chosen from the IRAS catalog to have high luminosities at infrared wavelengths. Most have strong Brackett line emission indicating large numbers of high mass stars; the formation of these stars may hence be the underlying source for the galaxies' luminosities. However, there are at least two exceptions that may not be explained in this manner: NGC 6240 and Arp 220. Additional evidence indicates that each of these exceptions may be more closely related to Seyfert-type galaxies or other active galactic nuclei.

Depoy, D. L.↗
NASA NTRS1989

The prevalence of supernova remnants among unidentified Galactic radio sources

Nine Galactic radio sources were mapped to identify new Crab-like and composite supernova remnants. The sources were selected on the basis of existing stringent upper limits on their hydrogen recombination line fluxes. One new Cracb-like remnant, one new composite remnant, at least one, and probably two, new shell-like remnants, and a compact H II region were found, along with the expected collection of extragalactic objects. The results suggest that there are several hundred SNRs in the Galaxy which are detectable with current instruments, but which have yet to be identified.

Helfand, David J.↗
NASA NTRS1989

Spectroscopic images of NGC 7027 in the near-infrared dust emission features

Isophote maps derived from spatially resolved moderate spectral resolution images of the planetary nebula NGC 7027 in the 3.28-micron and 3.4-micron 'unidentified' emission features, and in the Br-alpha hydrogen recombination line are presented. Comparison of these images clearly shows that the 3.28-micron emission is spatially more extended than the ionized gas. Analysis and modeling of the spatial distribution of the 3.28-micron feature strength suggest that roughly equal amounts of feature emission appear to come from within the H II region and from a shell outside the H II region. The spatial distribution of the 3.4-micron feature emission is found to be similar to that of the 3.28-micron feature emission.

Woodward, C. E.↗
NASA NTRS1990

Cometary compact H II regions are stellar-wind bow shocks

Comet-shaped H II regions, like G34.3 + 0.2, are easily explained as bow shocks created by wind-blowing massive stars moving supersonically through molecular clouds. The required velocities of the stars through dense clumps are less than about 10 km/s, comparable to the velocity dispersion of stars in OB associations. An analytic model of bow shocks matches the gross characteristics seen in the radio continuum and the velocity structure inferred from hydrogen recombination and molecular line observations. The champagne flow model cannot account for these structures. VLBI observations of masers associated with the shells of cometary compact H II regions should reveal tailward proper motions predominantly parallel to the shell, rather than perpendicular. It is predicted that over a decade baseline, high signal-to-noise VLA observations of this class of objects will show headward pattern motion in the direction of the symmetry axis, but not expansion. Finally, shock-generated and coronal infrared lines are also predicted.

Van Buren, Dave↗
NASA NTRS1991

Computational fluid dynamics studies of nuclear rocket performance

A CFD analysis of a low pressure nuclear rocket concept is presented with the use of an advanced chemical kinetics, Navier-Stokes code. The computations describe the flow field in detail,including gas dynamic, thermodynamic and chemical properties, as well as global performance quantities such as specific impulse. Computational studies of several rocket nozzle shapes are conducted in an attempt to maximize hydrogen recombination. These Navier-Stokes calculations, which include real gas and viscous effects, predict lower performance values than have been reported heretofore.

Stubbs, Robert M.↗