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Results for “RADIAL VELOCITY”

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At least 505 records · Page 28

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NASA NTRS1979

Radar observations of asteroids

Radar observations of asteroids use simple CW waveforms, the transmissions lasting for the duration of the round-trip delay. The echo is received, spectrum-analyzed, and integrated for a similar period. Since radar coherently illuminates the target, the surface scattering properties at radio wavelengths are directly determined as a function of angle and polarization. The distance and radial velocity obtained with radar complement the angular position of the object as determined from telescope measurements. Radar cross sections, scattering law, and radius are given for radar-observed asteroids.

Pettengill, G. H.↗

NASA NTRS1980

Laser anemometer measurements in a transonic axial flow compressor rotor

A laser anomometer system employing an efficient data acquisition technique has been 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

A solution of the variational equations for elliptic orbits in rotating coordinates

For elliptic reference orbits, formulas are given for the perturbation state transition matrix of the two-body problem. The formulas relate perturbations expressed in a local vertical rotating coordinate system and are valid for motion in the linear neighborhood of reference orbits with e in the range of 0 to 1. The elements of the state transition matrix are expressed in terms of natural parameters (horizontal and radial velocity, radius, eccentricity, true anomaly, etc.) at the initial and final points. In addition to the general form, a simplified version, valid for small eccentricity orbits, is given.

Jones, J. B.↗

NASA NTRS1980

Highly-ionized species in the interstellar medium

Interstellar absorption lines have been observed toward 25 stars with the International Ultraviolet Explorer satellite. Results are presented for observations of interstellar lines of C III, C IV, N V, Si III, and Si IV. Strong lines of Si IV or C IV are seen toward 11 stars. The strengths of these lines are inconsistent with their formation in the same hot gas responsible for the interstellar O IV lines observed with the Copernicus ultraviolet spectrometer. Comparison with simple models of the ionization structures of H II regions around hot stars suggests that the observed column densities of Si III, Si IV, and C IV are in harmony with those expected in normal photoionized nebulae. The line of sight to HD 93250, and O3 V star near Eta Carinae, passes through highly ionized gas that shows features spanning 250 km/s in radial velocity. Stellar wind velocities are presented for 21 of the stars observed in this survey of interstellar absorption lines.

Black, J. H.↗

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 NTRS1980

Analytical investigation of efficiency and performance limits in klystron amplifiers using multidimensional computer programs; multi-stage depressed collectors; and thermionic cathode life studies

An extensive parametric investigation was performed of the extraction of energy in output gaps of klystron amplifiers, using 3-D computer programs. Due to complexity of the program which used a hydrodynamic, axially and radially deformable disk ring model and the resulting long computing time, the investigation was limited to the output gap, by far the most important and difficult part of the klystron interaction. Results show that, for a confined flow focused beam throughout the penultimate cavity, radial velocities remain very small and the beam is highly laminar. It was, therefore, concluded that possible errors resulting from treating only the output cavity in 3-D would remain small.

Kosmahl, H. G.↗

NASA NTRS1981

Fluorescence equilibrium in the ultraviolet spectra of Comets Seargent (1978 m) and Bradfield (1979 l)

Detailed fluorescence calculations for OH including the Swings effect were performed. These calculations were used to reproduce the high resolution spectra of Comets Seargent and Bradfield taken with IUE. The calculations also provide the OH fluorescence efficiencies (g factors), as a function of heliocentric radial velocity, which are needed to derive OH abundances from measured fluxes. A close examination of the spectra shows no sign of the corresponding emission bands of OD allowing upper limits to be placed on the ratio N(OD)/N(OH). Preliminary attempts to reproduce the CO+ band structure by fluorescence are discussed.

Donn, B.↗

NASA NTRS1981

Satellite To Satellite Doppler Tracking (SSDT) for mapping of the Earth's gravity field

Two SSDT schemes were evaluated: a standard, low-low, SSDT configuration, which both satellites are in basically the same low altitude nearly circular orbit and the pair is characterized by small angular separation; and a more general configuration in which the two satellites are in arbitrary orbits, so that different configurations can be comparatively analyed. The standard low-low SSDT configuration is capable of recovering 1 deg X 1 deg surface anomalies with a strength as low as 1 milligal, located on the projected satellite path, when observing from a height as large as 300 km. The Colombo scheme provides an important complement of SSDT observations, inasmuch as it is sensitive to radial velocity components, while keeping at the same performance level both measuring sensitivity and measurement resolution.

Colombo, G.↗

NASA NTRS1980

Thermal convection of an internally heated infinite Prandtl number fluid in a spherical shell

A Galerkin technique is used to study the finite-amplitude axisymmetric steady convective motions of an infinite Prandtl number Boussinesq fluid in a spherical shell. Two types of heating are considered: in one case, convection is driven both by internal heat sources in the fluid and by an externally imposed temperature drop across the shell boundaries; in the other case, only internal heat sources drive convection and the lower boundary of the shell is adiabatic. Two distinct classes of axisymmetric steady states are found to be possible: states characterized by temperature and radial velocity fields that are symmetric about an equatorial plane; and a class of solutions that does not possess any symmetry properties about the equatorial plane.

Schubert, G.↗

NASA NTRS1980

Interstellar gas in the Gum Nebula

A survey of the interstellar gas near the Gum Nebula by optical observation of 67 stars at Ca II, 42 stars at Na I, and 14 stars in the UV with the Copernicus satellite provided radial velocities and column densities for all resolved absorption components. Velocity dispersions for gas in the Gum Nebula are not significantly larger than in the general interstellar medium; the ionization structure is predominantly that of an H II region with moderately high ionization. Denser, more highly ionized clouds are concentrated toward the Gum Nebula; these clouds do not show the anomalously high ionization observed in the Vela remnant clouds.

Wallerstein, G.↗

NASA NTRS1981

Phase-correlated P Cygni profile variations of the C III multiplet in UW Canis Majoris

The interacting close binary system UW CMa has been observed, in the wavelength range from 1161 to 1188 A, continuously during a complete orbital cycle in 1979 with the Copernicus (OAO-3) U2 spectrometer. The C III multiplet at 1175 A, observed as a P Cygni feature, exhbits a clear dependence on the orbital phase of the binary; the radial velocity variation of this feature lags behind that of the O7 primary component by 0.1 orbital phase, which agrees with the anticipations in an earlier study by the same authors. The radiation-driven matter, flowing out of the binary, originates in the primary component.

Drechsel, H.↗

NASA NTRS1981

Rapid oscillations in cataclysmic variables. V - H2252-035, a single-sideband X-ray and optical pulsar

Photometric and spectroscopic observations of the optical counterpart of the X-ray source H2252-035 reveal the existence of stable periodicities of 3.59 hr and 14.31 min. Both radial velocity and photometric variations occur at the longer period, suggesting that it is the true orbital period of the underlying cataclysmic binary. The shorter period appears as a 10% modulation in the light curve, superposed on the 3.59 hr variation. The frequency is the lower orbital sideband of the X-ray pulsation frequency, suggesting that the optical pulses arise from reprocessing in the atmosphere of the secondary. Unlike the majority of X-ray pulsars, H2252-035 appears to contain a white dwarf rather than a neutron star.

Patterson, J.↗

NASA NTRS1980

Molecular clouds in Orion and Monoceros

A 1.2-m millimeter-wave telescope has been used to survey CO in the constellations of Orion and Monoceros. Many new molecular clouds have been found. The distribution of molecular material shows two striking characteristics: (1) Most of the molecular clouds in this region appear to be connected by continuous extensions and filaments. To judge from continuity in radial velocity, most of these connections appear to be real, and are not merely the result of projection along the line of sight; (2) There are at least two slender filamentary features longer than 10 deg in angular extent. These filaments may connect the molecular clouds lying well out of the Galactic plane to clouds lying in the plane. Their shape and orientation suggest that magnetic fields may play a role in their evolution. The observed velocity gradients may be explained by accelerated gas flow along the filament.

Morris, M.↗

NASA NTRS1981

Continuing changes in the peculiar nebulous object PV Cephei

Changes in the nebular structure, optical spectrum and stellar brightness of the faint star PV Cephei and the nebulosity associated with it are discussed. Iris photometry of the starlike object at the tip of the fan-shaped nebula reveals irregular variability of approximately 4 magnitudes in the red. Stellar spectra in the region 4300-6750 A taken from December 1976 to April 1980 are similar to the richest emission line spectra of T Tauri stars, while nebular spectra indicate a lack of spherical symmetry. Observations obtained in the infrared reveal a source offset by a few arcsec from the apex of the fan, which is identified with the illuminating star. Radial velocities of CO emission indicate that PV Cep is at the same distance as NGC 7023, and independent estimates lead to an estimated value of 500 pc. Such a distance corresponds to a bolometric luminosity approximately 100 times that of the sun. It is suggested that PV Cep is a T Tauri star that has recently broken through its circumstellar cocoon at a time when highly erratic variability and a strong stellar wind characterize the star.

Cohen, M.↗

NASA NTRS1981

The dynamics of superclusters - Initial determination of the mass density of the universe at large scales

The radial velocities of cluster members of two rich, large superclusters have been measured in order to probe the supercluster mass densities, and simple evolutionary models have been computed to place limits upon the mass density within each supercluster. These superclusters represent true physical associations of size of about 100 Mpc seen presently at an early stage of evolution. One supercluster is weakly bound, the other probably barely bound, but possibly marginally unbound. Gravity has noticeably slowed the Hubble expansion of both superclusters. Galaxy surface-density counts and the density enhancement of Abell clusters within each supercluster were used to derive the ratio of mass densities of the superclusters to the mean field mass density. The results strongly exclude a closed universe.

Ford, H. C.↗

NASA NTRS1981

Prediction of swirling reacting flow in ramjet combustors

Numerical computations have been undertaken for a basic two-dimensional axisymmetric flowfield which is similar to that found in conventional gas turbine and ramjet combustors. A swirling flow enters a larger chamber via a sudden or gradual expansion. The calculation method involves a staggered grid system for axial and radial velocities, a line relaxation procedure for efficient solution of the equations, a two-equation turbulence energy-turbulence dissipation rate turbulence model, a stairstep boundary representation of the expansion flow, and realistic accommodation of swirl effects. The results include recirculation zone characterization and predicted mean streamline patterns. Predictions with and without chemical reaction are obtained. An associated isothermal experimental flow study is providing a useful data base. Successful outcomes of the work can be incorporated into the more combustion- and hardware-oriented activities of industrial concerns.

Lilley, D. G.↗

NASA NTRS1981

On the computation of acceleration parallaxes

Rigorous formulas are derived with which one can compute from three observed (coplanar) directions the proper-motion components and the product of parallax and radial velocity of an object (star) which moves uniformly with respect to the observer (earth). The errors of the determination of distance by parallactic acceleration are analyzed and the possibility of determining distances by this method is discussed.

Eichhorn, H.↗

NASA NTRS1981

Changes in the high state of AM Herculis - A simultaneous X-ray, optical, polarimetric, and spectroscopic study

Simultaneous UBVR photometry, circular polarimetry, and high resolution spectroscopy observations (during May, 1979), coordinated with a monitor proportional counter and a solid state spectrometer, are reported for the cataclysmic variable AM Her, when it was in its normal 'high' state, where the mean visual magnitude was 12.5 mag versus 15 mag for the infrequent 'low' state. The circular polarization was always negative and had the smallest peak to peak amplitude yet reported. The emission lines He II 4686, H-beta, N III 4634, N III 4640-4641, C III 4650-4651, and He I 4713 present at least two components identified with the broad and sharp components of Greenstein at al. (1977). The radial velocity curve of the broad component shows a 50% reduction of amplitude in comparison to their values, and a third very broad component in 4686 is identified. No correlation between the optical photometry and 1-10 keV X-ray intensity was found on flickering time scales. Results of the observations are discussed within the framework of models with accretion onto one or both magnetic poles of the white dwarf.

Crosa, L.↗