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Results for “RADIAL VELOCITY”

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At least 487 records · Page 27

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NASA NTRS1978

An interstellar cloud density from Copernicus observations of CO in the spectrum of Zeta Ophiuchi

Interstellar CO absorption bands in Copernicus spectra of Zeta Oph have been studied. Absorption profiles, computed under the assumption that excitation is due to collisions with H2 molecules and interaction with the 3-K background radiation field, were fitted to the reduced data of nine bands. When a gas kinetic temperature of 56 K is assumed, the best-fit condition implies a hydrogen-nucleus density of 120 per cu cm, a CO column density of 1.2 by 10 to the 15th power per sq cm, and a radial-velocity dispersion of 0.9 km/s. The relevance of these results to existing ideas concerning the Zeta Oph interstellar clouds is discussed. It is suggested that the strongest interstellar component is not circumstellar in origin but is instead part of a supernova remnant. Simple calculations are made to establish the plausibility of the supernova-remnant identification. This suggestion is also supported by Heiles's (1976) 21-cm pictures.

Smith, A. M.↗

NASA NTRS1978

A viscous-inviscid interactive compressor calculation

A viscous-inviscid interactive procedure for subsonic flow is developed and applied to an axial compressor stage. Calculations are carried out on a two-dimensional blade-to-blade region of constant radius assumed to occupy a mid-span location. Hub and tip effects are neglected. The Euler Equations are solved by MacCormack's method, a viscous marching procedure is used in the boundary layers and wake, and an iterative interaction scheme is constructed that matches them in a way that incorporates information related to momentum and enthalpy thicknesses as well as the displacement thickness. The calculations are quasi-three-dimensional in the sense that the boundary layer and wake solutions allow for the presence of spanwise (radial) velocities.

Johnston, W. A.↗

NASA NTRS1978

Spectroscopy of the extreme-ultraviolet source Feige 24 - The binary orbit and the mass of the white dwarf

Results are reported for coude spectroscopy of the extreme-ultraviolet white dwarf Feige 24. Radial velocities of the H-alpha, He I 5876-A, and He I 6678-A emission lines, and the underlying M-dwarf absorption features, were determined from spectrograms obtained with the Lick 3-m telescope. The velocities show a binary period of 4.239(+ or - 0.0015) days. The emission-line and absorption-line velocities agree in phase, which indicates that the emission lines originate in the atmosphere of the M-dwarf secondary as a result of reprocessing of the EUV radiation. This effect is modeled, and the observed amplitude of the emission-line variability is used to place a lower limit on the orbital inclination. From these and other data it is shown that the mass of the white dwarf lies between 0.46 and 1.24 solar masses. Some possible implications for the evolution of binary stars are briefly discussed.

Thorstensen, J. R.↗

NASA NTRS1978

The observational status of the Beta Cephei stars

The Beta Cephei stars are a group of variables of spectral type B, whose light and radial velocity periods lie between about three and seven hours. An up-to-date summary of the observational data for individual stars considered to be members of the Beta Cephei group is provided. The general properties of Beta Cephei stars as determined from a comparison between theory and observation are considered, taking into account location in the HR diagram and evolutionary state, physical properties, statistics and galactic distribution, and period-luminosity relation and pulsation mode. Recent trends concerning the observation of Beta Cephei stars are examined, giving attention to a search for new variables, ultraviolet observations from spacecraft, and high-resolution studies of profile variations.

Lesh, J. R.↗

NASA NTRS1979

H2O masers near OB associations

Four new water masers have been found in the vicinity of three OB associations. One of these, in Cep OB3, is among the most intense sources yet discovered and may be related to the most recent epoch of star formation in the OB association. Two others, one in CMa OB1, the other in M16, have large radial velocities relative to their associated molecular clouds. These results are discussed in the context of star formation and CO line self-reversal within the individual sources.

Blitz, L.↗

NASA NTRS1979

Searching for nonsolar planets

The use of infrared techniques to search for nonsolar planets is examined and compared with other possible methods. Long focus astrometry, spectroscopic radial velocity measurements and spaceborne apodization all use visible light and need further refinement to be practical. Infrared offers an advantage of about 10 to the 5th over visible light as regards the ratio of power received from star and planet. Long baseline infrared interferometry from earth orbit could place an interferometric null on the star to enhance planetary radiation and a spinning interferometer would modulate planetary emission to permit synchronous detection; such an interferometer is illustrated. The limit to sensitivity would be set by thermal radiation to the detector and the infrared component of zodiacal light.

Bracewell, R. N.↗

NASA NTRS1979

A spectroscopic flare of YZ Canis Minoris

Observations of a spectroscopic flare in YZ Canis Minoris are reported. Emission lines of Mg I, Fe I, and Fe II were found in the spectral region 5090-5350 A. The intensity of the emission lines declined only slightly over a span of 2 hours. No significant radial-velocity difference was found between the emission and absorption lines. The turbulent velocity dispersion was less than 20 km/s. Upper limits of 7500 and 15,000 gauss can be placed on the longitudinal and transverse magnetic fields. The equal intensities of the Mg I b lines imply that the emitting region was optically thick. The intensity ratios did not change with time.

Mochnacki, S. W.↗

NASA NTRS1979

Optical counterpart of 2A0311-227

Spectrophotometric observations of the optical counterpart of the X-ray source 2A0311-227 are reported. A 1.3-m telescope associated with a photon-counting spectral scanner was used for observations in the range 4000 to 5800 A. Strong emission features are noted for H I, He II at 4686 A and the C III-N III blend at 4640-4650 A. Analyses of radial velocities show the star to be a spectroscopic binary with a period of 81.04 + or - 0.01 min, while blue and yellow light curves reveal variations in stellar color. Similarities between this binary and AM Herculis are noted and a model of a 1.2-solar mass white dwarf with a 0.2-solar mass companion at a separation of 0.7 solar radii is suggested.

Williams, G.↗

NASA NTRS1979

VV 5-32-63/64 - The 'supermassive double galaxy' in Abell 1775 revisited

Spectroscopy is presented for galaxies in A 1775, the cluster containing VV 5-32-63/64, an apparent double galaxy which has long been considered a gravitationally bound system with supermassive components (10 to the 13th solar masses). However, this model has run afoul of recent radio observations, which detected an extremely long straight radio tail emanating from the eastern galaxy in the pair. The present observations indicate that if both galaxies are members of the same cluster, the cluster radial-velocity dispersion (1522 km/sec) is large enough to account for the velocity difference between the two VV galaxies (1650 km/sec). It is therefore suggested that the VV galaxies are not gravitationally bound and need not be supermassive. The large velocity dispersion measured for A 1775 also strains suggested velocity dispersion vs X-ray luminosity relations for clusters of galaxies, as A 1775 has not yet been detected at X-ray wavelengths.

Hintzen, P.↗

NASA NTRS1979

Laser anemometer measurements in a transonic axial flow compressor rotor

A laser anemometer system employing an efficient data acquisition technique was used to make measurements upstream, within, and downstream of the compressor rotor. A fluorescent dye technique allowed measurements within endwall boundary layers. Adjustable laser beam orientation minimized shadowed regions and enabled radial velocity measurements outside of the blade row. The flow phenomena investigated include flow variations from passage to passage, the rotor shock system, three-dimensional flows in the blade wake, and the development of the outer endwall boundary layer. Laser anemometer measurements are compared to a numerical solution of the streamfunction equations and to measurements made with conventional instrumentation.

Strazisar, A. J.↗

NASA NTRS1980

Population of the lower part of the instability strip: Delta Scuti stars and dwarf Cepheids (or AI Velorum)

Some of the properties of the atmospheric variations in delta Scuti stars were investigated with emphasis on the amplitude and the shape of both light curves and radial velocity curves. It is shown that these curves are small and rapidly variable in the case of dwarf Scuti stars; for the evolved stars the situation is more complex. The relation between variables and nonvariables, and also the results on abundances in the atmospheres of these stars were surveyed with respect to the hydrodynamics of their envelopes. The abundance anomalies of Am stars were qualitatively examined. The coexistence of abundance anomalies and variability among giants were also studied. Attempts were made to relate the variability to the hydrogen ionization zone in an envelope deprived of helium. Specific results are reported.

Auvergne, M.↗

NASA NTRS1980

Pulsation and mass loss in Mira variables

The behavior of pulsation in the outer layers of a typical Mira variable was studied in the adiabatic and isothermal limits. A shock wave propagates outward once per period and the radial velocity obtained from observations of hydrogen emission lines is identified with the velocity of gas in the post shock region. In the adiabatic case, mass loss in the form of a steady stellar wind was produced. In the isothermal case, no continuous mass loss was produced but occasional ejection of shells occur. Pulsation introduced into a star undergoing steady mass loss as a result of radiation pressure acting on grains caused the mass loss rate to increase by a factor of approximately 40, while the terminal velocity of the flow was almost unaltered.

Wood, P. R.↗

NASA NTRS1980

An independent Cepheid distance scale: Current status

An independent distance scale for Cepheid variables is discussed. The apparent magnitude and the visual surface brightness, inferred from an appropriate color index, are used to determine the angular diameter variation of the Cepheid. When combined with the linear displacement curve obtained from the integrated radial velocity curve, the distance and linear radius are determined. The attractiveness of the method is its complete independence of all other stellar distance scales, even though a number of practical difficulties currently exist in implementing the technique.

Barnes, T. G., III↗

NASA NTRS1980

Documentation for the machine-readable version of the Perth 70: A catalogue of positions of 24900 stars tape B, mean values of the observation

The Perth 70 catalog contains accurate positions of 24978 stars, plus other useful data such as approximate proper motions, radial velocities, and parallaxes. The Perth 70 is a result of meridian circle observations made by the Hamburg observatory expedition to Perth as part of the international effort of Southern References Stars (SRS). Tape B, which contains mean values of the observations and corresponds to the printed catalog is described.

Warren, W. H., Jr.↗

NASA NTRS1980

Windfield retrieval from Doppler lidar observations

An approach to the retrieval of a vector wind field from Doppler lidar observations is developed in general terms. The field of radial velocity measurements from each look angle is modeled by a smooth surface, the parameters of the model being determined from the data by least squares techniques. The vector wind field and higher-order fields are obtained from the two modeled surfaces. Estimated measurement errors are taken into account, and error estimates are available for all output data sets.

Lee, R. W.↗

NASA NTRS1979

Lightman-Eardley instabilities and accretion disk thickening

After reviewing the role of Compton scattering in accretion disks around black holes, it is discussed whether Lightman-Eardley (LE) secular instabilities can trigger and maintain Pringle-Rees (PR) thermal instabilities. The radiative-transfer-equation and equation-of-state criteria for LE stability in alpha-viscosity-law disk models and dynamic viscosity criteria for more general situations is derived. On the basis of these considerations the LE instability is insufficient for inducing PR instabilities and hot thick inner regions important in accretion-disk models of compact hard X-ray sources. The density thinning due to radial velocity gradients in the accretion flow is suggested as a more likely and satisfactory mechanism.

Stoeger, W. R.↗

NASA NTRS1979

The Hercules supercluster. I - Basic data

A sample of more than 150 redshifts, the majority new, is presented for galaxies brighter than an apparent photographic magnitude of 15.8 in a 28-square-deg field in Hercules containing the clusters A2151, A2152, and A2147. This sample populates a 60,000 cu Mpc conical volume. It contains a super-cluster centered near a radial velocity of 11,000 km/sec a large void of depth approximately 100 Mpc in front of the supercluster, and foreground structure at 4700 and 2300 km/sec the former associated with Seyfert's sextet.

Tarenghi, M.↗

NASA NTRS1980

Changes in the ultraviolet spectrum of the mass-losing Be star 59 Cygni

Observations of a few selected wavelength regions in the ultraviolet spectrum of the Be star 59 Cyg, obtained in 1975 November, are compared with the complete low-resolution Copernicus scan of the same star obtained in 1972 October. Changes in the spectrum between the two times are discussed and interpreted in terms of the two distinct shell episodes revealed by optical data. A wide range of ionization exists from Fe III to N V, with a range in radial velocity of approximately 1000 km/s. Changes in the Si III, Si IV, and N V absorption arising in the stellar wind show that the velocity structure of the wind may have changed, and that the ionization balance also was altered over the 3 year interim.

Marlborough, J. M.↗