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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Physical associations between quasi-stellar objects and galaxies.

Evaluation of evidence pertaining to apparent associations between galaxies and quasi-stellar objects. It is shown that for the five 3C QSOs which lie very close to bright galaxies the QSO-galaxy angular separations are inversely proportional to the redshifts of the galaxies. This lends additional support to the association hypothesis. However, an analysis of an essentially disjoint sample of QSOs identified from the Parkes radio catalog, and fainter galaxies in the catalog of Zwicky and his associates, reveals no statistically significant tendency toward pairing of QSOs and galaxies. The results can be explained in one of two ways. One is that, despite the evidence to the contrary, the 3C results are due to chance. The other is that real associations in the second sample are masked by selection effects. It is shown that several selectional biases do indeed discriminate against the detection of QSO-galaxy pairs, especially for fainter objects. Finally, on the assumption that the 3C QSO-galaxy associations are real, the relationship of QSOs to galaxies is discussed.

Burbidge, G. R.↗
NASA NTRS1972

Relativistic stellar stability: An empirical approach

The PPN formalism which encompasses the post-Newtonian limit of nearly every metric theory of gravity is used to analyze stellar stability. This analysis enables one to infer, for any given gravitation theory, the extent to which post-Newtonian effects induce instabilities in white dwarfs, in neutron stars, and in supermassive stars. It also reveals the extent to which our current empirical knowledge of post-Newtonian gravity (based on solar-system experiments) actually guarantees that relativistic instabilities exist. In particular, it shows that: (1) for conservative theories of gravity, current solar-system experiments guarantee that the critical adiabatic index, for the stability of stars against radial pulsations exceeds the Newtonian value of 4/3 and (2) for nonconservative theories, current experiments do not permit any firm conclusion about the sign of the critical adiabatic index, and (3) in the PPN approximation to every metric theory, the standard Schwarzschild criterion for convection is valid.

Ni, W.↗
NASA NTRS1973

Temperature distribution in a stellar atmosphere diagnostic basis

A stellar chromosphere is considered a region where the temperature increases outward and where the temperature structure of the gas controls the shape of the spectral lines. It is shown that lines which have collision-dominated source sink terms, like the Ca(+) and Mg(+) H and K lines, can be used to obtain the distribution of temperature with height from observed line profiles. Intrinsic emission lines and geometrical emission lines are found in spectral regions where the continuum is depressed. In visual regions, where the continuum is not depressed, emission core in absorption lines are attributed to reflections of intrinsic emission lines.

Jefferies, J. T.↗
NASA NTRS1973

Mechanical heating in stellar chromospheres using the sun as a test case

The shock dissipation hypothesis for solar atmospheric heating is extended to stellar chromospheres of late type stars which have significant convective envelopes. Principle wave modes are studied for their generation, propagation, and heating properties in the presence of a magnetic field, and various approximations on when a sound wave becomes strong enough to produce heating in the atmosphere are presented.

Jordan, S. D.↗
NASA NTRS1973

Celescope catalog of ultraviolet stellar observations

The catalog contains the observational results obtained by the Celescope Experiment during the first 16 months of operation of NASA's Orbiting Astronomical Observatory (OAO-2). It lists the results of the stellar observations, along with selected ground-based information obtained from the available literature. Lunar observations (Ahmad and Deutschman, 1972), as well as other analyses of the data, are being published as separate papers. These data are available in two forms: (1) magnetic tapes and the necessary utility programs for reading and printing the contents of the tapes; and (2) this catalog, transcribed from the magnetic-tape catalog. The magnetic tape version contains not only the compiled results but also the results of the individual observations from which these averaged data were compiled.

Davis, R. J.↗
NASA NTRS1973

Stellar figure sensor

A compilation of analytical and experimental data is presented concerning the stellar figure sensor. The sensor is an interferometric device which is located in the focal plane of an orbiting large space telescope (LST). The device was designed to perform interferometry on the optical wavefront of a single star after it has propagated through the LST. An analytical model of the device was developed and its accuracy was verified by an operating laboratory breadboard. A series of linear independent control equations were derived which define the operations required for utilizing a focal plane figure sensor in the control loop for the secondary mirror position and for active control of the primary mirror.

Peters, W. N.↗
NASA NTRS1973

Relativistic stellar stability: Preferred-frame effects

Possible preferred-frame effects on stellar stability were examined and no new instabilities were found. In particular, it is shown that: (1) Although terms linear in the preferred-frame velocity w (time-odd terms, analogous to viscosity and energy generation) change the shapes of the normal modes, their symmetry properties prevent them from changing the characteristic frequencies. Thus, no new vibrational or secular instabilities can occur. (2) Terms quadratic in w do not change either the shapes of the normal modes or the characteristic frequencies for radial pulsations. Thus, they have no influence on radial stability. (3) Terms quadratic in w do change both the normal modes and the characteristic frequencies of nonradial pulsations; but in the limit of a neutral mode these changes vanish. Hence, there is no modification of the criterion for convective stability, i.e., the standard Schwarzschild criterion remains valid.

Ni, W.↗
NASA NTRS1973

The redshift-magnitude relation for quasi-stellar objects.

It is shown that the best-fitting slope of the redshift-magnitude relation for the most luminous quasi-stellar object in each redshift range is 4.3 plus or minus 0.4. However, the steepness of this slope is due primarily to the lowest redshift range including 3C 273, without which it is 2.1 plus or minus 0.6. The slopes of the second and third brightest QSOs are 3.1 plus or minus 0.6 and 3.2 plus or minus 0.6, respectively, markedly less than the slope of 5 which is expected for a Friedmann universe with q(0) = +1. Although the departure of the slope from 5 mag per decade is statistically significant at about 95% confidence, due to the heterogeneity and incompleteness of the sample there may be a systematic selectional bias not accounted for either in this analysis or in that of Bahcall and Hills. Consequently, no definite pronouncement can be made until a complete sample of adequate size is examined.

Burbidge, G. R.↗
NASA NTRS1973

Linear convective modes and the energy transport in stellar convection zones.

Model stars whose convection zones had been prepared in accordance with the standard mixing-length theory were used as a basis for the computation of unstable convective modes. It was found that no superposition of statistically independent, nonviscous, adiabatic, convective modes can reproduce the radial dependence of the convective flux of the model. This implies that the representation of a stellar convection zone as a superposition of unstable adiabatic linear modes is inconsistent with the mixing-length theory, and that conclusions based upon such a representation should be regarded with caution. It is also shown that if the linear scale of convective motions is greater than (or of the same order as) the pressure scale height, then the fractional deviation of the pressure from equilibrium will generally not be negligible, as assumed in the mixing-length theory, but will be at least of the same order as the fractional deviation of the density from equilibrium.

Hart, M. H.↗
NASA NTRS1973

Cosmic soft gamma-ray bursts and the stellar super-flare hypothesis

Possible alternatives to the supernovae theory on the orgin of cosmic ray bursts are examined. In particular, the possibility that these outbursts are simply giant versions of the X-ray burst typically seen in solar flares is investigated. It was suggested that the outbursts are caused by the bresstrahlung of electrons accelerated to high energies in a stellar flare event.

Stecker, F. W.↗
NASA NTRS1973

Studies of hydrodynamic events in stellar evolution. 3: Ejection of planetary nebulae

The dynamic behavior of the H-rich envelope (0.101 solar mass) of an evolved star (1.1 solar mass) as the luminosity rises to 19000 solar luminosity during the second ascent of the red giant branch. For luminosities in the range 3100 L 19000 solar luminosity the H-rich envelope pulsates like a long-period variable (LPV) with periods of the order of a year. As L reaches 19000 solar luminosity, the entire H-rich envelope is ejected as a shell with speeds of a few 10 km/s. The ejection occurs on a timescale of a few LPV pulsation periods. This ejection is associated with the formation of a planetary nebula. The computations are based on an implicit hydrodynamic computer code. T- and RHO-dependent opacities and excitation and ionization energies are included. As the H-rich envelope is accelerated off the stellar core, the gap between envelope and core is approximated by a vacuum, filled with radiation. Across the vacuum, the luminosity is conserved and the anisotropy of the radiation is considered as well as the solid angle subtended by the remnant star at the inner surface of the H-rich envelope. Spherical symmetry and the diffusion approximation are assumed.

Sparks, W. M.↗
NASA NTRS1973

A comparison of the recently observed soft gamma-ray bursts with solar bursts and the stellar super-flare hypothesis

The possibility that soft gamma ray bursts are versions of X-ray bursts typically seen in solar flares and not products of supernovae events is investigated. Results show that the bursts have longer time scales that those predicted for supernovae events. It was suggested that the bursts result from the acceleration of electron bremsstrahlung to high energies in a stellar flare event.

Stecker, F. W.↗
NASA NTRS1974

Stellar occultations

It is important that future occultations by Titan be predicted well in advance, and imperative that they be observed adequately. Stellar occultations can yield reliable temperature/number density profiles of Titan's upper atmosphere near the density level. The temperature profiles can be used to discriminate between atmospheric compositions having high mean molecular weights, and those having low mean molecular weights. Detection of spikes at several wavelengths with high time resolution gives useful limits on the helium content of the atmosphere.

Veverka, J.↗
NASA NTRS1973

Stellar winds driven by Alfven waves

Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds.

Belcher, J. W.↗