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At least 973 records · Page 54
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NASA NTRS1987

Atomic hydrogen in planetary nebulae

The authors searched for neutral atomic hydrogen associated with 22 planetary nebulae and three evolved stars in the 21 cm line at the Arecibo Observatory. Objects whose radial velocities permitted discrimination from Galactic H I were chosen for observation. Hydrogen was detected in absorption from IC 4997. From the measurements new low limits are derived to the mass of atomic hydrogen associated with the undetected nebulae. Radio continuum observations were also made of several of the nebulae at 12.6 cm. The authors reexamine previous measurements of H I in planetary nebulae, and present the data on a consistent footing. The question of planetary nebula distances is considered at length. Finally, implications of the H I measurements for nebular evolution are discussed and it is suggested that atomic hydrogen seen in absorption was expelled from the progenitor star during the final 1000 yr prior to the onset of ionization.

Schneider, Stephen E.↗
NASA NTRS1987

Rotation and kinematics of the premain-sequence stars in Taurus-Auriga with Ca II emission

Radial velocities and v sin i values for the stars in the Taurus-Auriga region that were found to have strong Ca II H and K emission by Herbig, Vrba, and Rydgren 'HVR', (1986) are reported. Most of the velocities are determined to better than 2 km/s precision. The kinematic properties of the Ca II emission stars with strong Li are found to be indistinguishable from conventional T Tauris in Taurus-Auriga, contrary to HVR. These Li-rich stars also rotate like T Tauris. Most of the stars that lack Li are probable or possible members of the Hyades, in the foreground, and are among the brightest and most active stars in that cluster for their spectral types. It is suggested following Jones and Herbig (1979), that the apparent absence of low-mass stars older than 10 Myr in Taurus-Auriga is real, and is due to the finite lifetime of the cloud.

Hartmann, Lee W.↗
NASA NTRS1986

The convective noise floor for the spectroscopic detection of low mass companions to solar type stars

The threshold mass for the unambiguous spectroscopic detection of low mass companions to solar type stars is defined here as the time when the maximum acceleration in the stellar radial velocity due to the Doppler reflex of the companion exceeds the apparent acceleration produced by changes in convection. An apparent acceleration of 11 m/s/yr in integrated sunlight was measured using near infrared Fourier transform spectroscopy. This drift in the apparent solar velocity is attributed to a lessening in the magnetic inhibition of granular convection as solar minimum approaches. The threshold mass for spectroscopic detection of companions to a one solar mass star is estimated at below one Jupiter mass.

Deming, D.↗
NASA NTRS1986

MHD simulation of the 'geoeffectiveness' of interplanetary disturbances

A series of examples is used to evaluate the 'geoeffectiveness' prediction technique that is based on the classical, initial boundary value problem of MHD. For the nonplanar simulation of a corotating stream, it is shown that the technique can compute relevant solar wind parameters at the earth's location. For the nonplanar simulation of a complex series of events, qualitative agreement is found for large-scale structures, but the phasing and amplitudes are not satisfactory. Preliminary work with a fully three-dimensional, time-dependent simulation of a flare-generated interplanetary shock wave shows that the effect of the latitudinal variation produces attenuation of the heliolongitudinal component of the IMF and of the radial velocity.

Dryer, M.↗
NASA NTRS1987

The radio spectrum of cyclopropene

Twenty-eight millimeter-wave lines in the rotational spectrum of the three-membered hydrocarbon ring cyclopropene, C3H4, have been measured in the laboratory to high precision. When combined with previous measurements, these determine the rotational and centrifugal distortion constants of C3H4 sufficiently well to allow its entire radio spectrum to be calculated to an accuracy adequate for foreseeable astronomical applications, i.e., to an equivalent radial velocity of 0.1 km/s or better. With the recent discovery that the related ring C3H2 is widespread in the Galaxy, cyclopropene has become a plausible candidate for astronomical detection. Upper limits in Sgr B2 and TMC-1 indicate that in these sources C3H4 cannot be much more abundant than C3H2.

Vrtilek, J. M.↗
NASA NTRS1986

Two component laser velocimeter measurements of turbulence parameters downstream of an axisymmetric sudden expansion

Simultaneous two-component laser velocimeter measurements were made in an axisymmetric sudden expansion flowfield. A specially designed correction lens was employed to correct optical aberrations introduced by the circular tube. This lens system allowed the accurate simultaneous measurement of axial and radial velocities in the test section. The experimental measurements were compared to predictions generated by a code which employed the k-epsilon turbulence model. Possible sources of differences observed between model predictions and the measurements are discussed.

Gould, Richard D.↗
NASA NTRS1987

1E 1751 + 7046 - A new FK comae candidate

1E 1751 + 7046 is a star that was serendipitously detected by the Einstein Observatory Medium Sensitivity Survey. X-ray, optical, and radio observations of this star show it to have characteristics similar to the RS CVn binaries. However, repeated high-resolution spectroscopic observations fail to detect any significant radial-velocity variations. The possibility of the star being pre-main-sequence is dismissed because of its location and lack of photospheric Li I. This makes 1E 1751 + 7046 an attractive candidate for the recently proposed class of FK Comae stars. Although there is disagreement over the evolutionary status of these evolved stars, they are nonetheless interesting as exhibitors of extreme chromospheric and coronal activity.

Fleming, Thomas A.↗
NASA NTRS1987

Studies of calcium emission stars. I - HD 158393 a giant star in a binary system

HD 158393 is a giant star of spectral type late G or early K which has moderately strong Ca II H and K emission cores. UBVRIJHK photometry and IUE spectra reveal a companion of type F0-F2, luminosity class IV or V. Radial velocity data yield an orbit with a period of 31 day. The K and F stars have nearly equal mass, with a minimum value of 1.7 solar masses if i of less than 72 deg is adopted, as required by the absence of eclipses. The strong Ca II emission indicates the enhanced chromospheric activity which is typical of giant stars in a binary system of this period, and the light is variable in a 31-day period, indicative of synchronous rotation as well as on a long time-scale. Analysis of the 31-day light period by fitting a spot model indicates the presence of two spots in 1975 and 1976; the major spot appears to have been present throughout the observing period (1973-1981). The potential confusion caused by the presence of the second spot for part of the observing period emphasizes the importance of fitting a model if the photometric period is to be understood in terms of the synchronous rotation. The two spots showed different periods and were at different latitudes, suggesting differential rotation of the giant star.

Evans, T. Lloyd↗
NASA NTRS1987

CAL 83 - A puzzling X-ray source in the Large Magellanic Cloud

Spectroscopic observations of the X-ray point source no. 83 in the Columbia Astrophysics Laboratory Einstein survey of the Large Magellanic Cloud have been accumulated over 4 yr. The optical spectrum shows no stellar absorption features, but only emission lines typical of an accretion disk. Radial velocity measurements reveal a small (K = 30 km/s) velocity variation modulated at 0.93 d, which appears to be the orbital period. No strong constraints can be put on the mass of the collapsed object, but its companion must be a low-mass, evolved star. Evidence for a precessing disk with a possible period of 69 days is presented. Exosat X-ray observations reveal no short-term (less than 6 hr) periodicities, although erratic, random variations were observed. The X-ray spectrum is very soft, reminiscent of some of the candidate black-hole sources. IUE ultraviolet spectra show only weak emission lines of N V and He II. The UV flux is variable with a mean effective temperature of about 19,000 K. Optical B, V photometry during November 1985 showed random variations of about 0.2 mag with a mean V = 17.3 mag.

Crampton, David↗
NASA NTRS1987

Airborne Doppler lidar observations of convective phenomena in Oklahoma

On 30 June 1981, the wind fields around a variety of convective clouds, ranging from large thunderstorm complexes to isolated cumulus congestus, were observed in Oklahoma using an airborne Doppler lidar operated by NASA. By steering the pulsed infrared laser beam alternately along differing horizontal directions, a network of independent radial velocity measurements is obtained, which permits high-resolution synthesis of the full horizontal wind vector field in a swath adjacent to the aircraft flight track. The bright reflections of the laser signal by cloud surfaces permit direct identification of the locus of cloud edges, information which is prerequisite to detailed study of the relationships between the winds inside and outside clouds. The horizontal wind fields derived from the lidar data reveal waves and vortices along the gust front of a storm which eventually produced a gust-front tornado, and cloud-scale convergence patterns around an isolated cumulus congestus. Despite the presence of some questionable data associated with undersampling and delayed recording of certain aircraft motion parameters, most of the lidar results appear consistent with cloud photographs made during the experiment, with surface meteorological data, with aircraft flight-level wind data, and with previous observational and theoretical work.

Mccaul, Eugene W., Jr.↗
NASA NTRS1988

Vortex breakdown in an axisymmetric flow

The breakdown for both an isolated vortex and a vortex flow in a tube is studied by means of a numerical solution of the axisymmetric Navier-Stokes equations for an unsteady, incompressible, and laminar flow. Results are compared to those of other authors and to experiments. Various numerical solution methods and various physical boundary conditions are used in order to explain the existence of different solutions. The computational results reveal that the existence of different solutions is due to slightly different inflow conditions. The numerical problem for the isolated vortex becomes ill-posed at a certain time for the inflow condition of zero axial gradient of the radial velocity component. Different inflow conditions yield breakdown flowfields containing different features of the experimentally observed breakdown structure.

Menne, Stefan↗
NASA NTRS1988

The outer atmospheres of the coolest M giants - Ultraviolet spectra of Rho Persei, 2 Centauri, g Herculis, Theta Apodis, and R Lyrae

New IUE observations of five M giants cooler than most studied previously have been obtained in order to study the variation of chromospheric properties with effective temperature. The ultraviolet spectrum lines of one of these stars, Rho Persei, are identified. The properties of the spectra of of the five stars are examined in detail, including the line widths and turbulence, the radial velocities of groups of lines, the structure in the Mg II resonance lines, and the fluorescent lines. The physical properties of the M giants' chromospheres are considered, including the formation of Fe II, the electron density, the degree of ionization of iron, magnesium, silicon, and carbon, the hydrogen ionization and energy balance, and the creation and destruction of photons.

Eaton, Joel A.↗
NASA NTRS1988

High-resolution forbidden Ne II observations of the ionized filaments in the Galactic center

The forbidden Ne II 12.8 micron emission from the central 10 arcsec of the Galaxy has been observed with 1.5 arcsec resolution. The broad lines previously observed in this region are resolved into separate features associated with the filaments and knots of radio continuum emission present. The radial velocity varies rapidly and continuously with position along the filaments, with gradients of up to 30 km/s. The emission along the 'eastern arm' is mapped. The velocities are consistent with streams of gas orbiting about the center. A simple model of gravitationally dominated orbits fits the data; the masses estimated to lie within the orbits suggest the presence of a central mass of about 2.5 million solar. The implications of this model and possible objections to it are considered.

Serabyn, E.↗
NASA NTRS1988

Phase-resolved IUE observations of AM Herculis system E1405-451

The first phase-resolved IUE observations of the AM Herculis system E1405-451 is reported. The spectra show bright emission lines from N V, C IV, and He II, whose centroids vary drastically during the 101.5 minute period. The radial velocities measured from the line centroids show a sinusoidal variation with a semiamplitude of 300 km/s. An explanation for the observed emission line velocities is considered using a model for the system having inclination i = 60 deg and magnetic colatitude Delta = 20 deg.

Takalo, L. O.↗
NASA NTRS1988

Analysis of spectra using correlation functions

A novel method is presented for the quantitative analysis of spectra based on the properties of the cross correlation between a real spectrum and either a numerical synthesis or laboratory simulation. A new goodness-of-fit criterion called the heteromorphic coefficient H is proposed that has the property of being zero when a fit is achieved and varying smoothly through zero as the iteration proceeds, providing a powerful tool for automatic or near-automatic analysis. It is also shown that H can be rendered substantially noise-immune, permitting the analysis of very weak spectra well below the apparent noise level and, as a byproduct, providing Doppler shift and radial velocity information with excellent precision. The technique is in regular use in the Atmospheric Trace Molecule Spectroscopy (ATMOS) project and operates in an interactive, realtime computing environment with turn-around times of a few seconds or less.

Beer, Reinhard↗
NASA NTRS1987

The mass of the classical Cepheid SU Cygni

Radial velocity differences between the classical Cepheid SU Cyg and a hot companion were measured from IUE high dispersion spectra. The blue star is itself a close binary. The triple system solution provides the mass ratio of the Cepheid to the masses of the pair of companions. The masses of the companions are inferred from the low dispersion IUE spectra. The mass derived for the Cepheid is 6.3 solar masses, with a range from 7.0 to 5.9 solar masses, which is very close to the evolutionary mass.

Evans, Nancy Remage↗
NASA NTRS1988

Orbital and photometric properties of SZ Lyncis

New photometric results based on 3760 observations made on the Johnson BVRI system and 69 new radial-velocity measurements of the large-amplitude Delta Scuti binary SZ Lyncis are reported. Using these data and previous observations from the literature, improved values for the pulsation and orbital parameters are derived. The pulsation period is found to be 0.12052115 days, which is shorter than earlier determinations. The pulsation period is undergoing a secular period change of 3 X 10 to the -12th days/cycle. The orbital period of the binary is found to be 1181.1 days, with an orbital eccentricity of 0.188. A new ephemeris is given, which accurately predicts the times of light maximum and is consistent with the spectroscopic orbit. The mass function is 0.101 solar, which, together with other known properties of SZ Lyn, indicates that the unseen companion is most likely on the main sequence with a spectral type between F2 and K3.

Moffett, Thomas J.↗
NASA NTRS1988

An experimental study of air-assist atomizer spray flames

It is noted that air-assisted atomizer spray flames encountered in furnaces, boilers, and gas turbine combustors possess a more complex structure than homogeneous turbulent diffusion flames, due to the swirling motion introduced into the fuel and air flows for the control of flame stability, length, combustion intensity, and efficiency. Detailed comparisons are presented between burning and nonburning condition measurements of these flames obtained by nonintrusive light scattering phase/Doppler detection. Spray structure is found to be drastically changed within the flame reaction zone, with changes in the magnitude and shape of drop number density, liquid flux, mean drop size diameter, and drop mean axial velocity radial distributions.

Mao, Chien-Pei↗