Showing papers in "The Astrophysical Journal in 1966"

Non-Axisymmetric Responses of Differentially Rotating Disks of Stars

Abstract: Stability and dynamical response of small portions of differentially rotating stellar disks, noting decaying nonaxisymmetrical instabilities, epicyclic frequency, surface density, etc

Profiles of strong lines in K- dwarfs

Abstract: A study of the profiles of strong lines in two stars € Eridani and Gmb 1830 has been done. The following lines were investigated: Hα; D 1 and D 2 lines of Na I ; H- and K-lines of Ca II ; and the infrared triplet lines of Ca II . Model atmospheres were constructed in the majority of cases investigated, using a scaled solar (T-τ) relation. Line profiles were then constructed. For € Eridani, all the profiles could be explained well with the use of solar composition and with effective temperature, T e = 5050° K. For Gmb 1830, all the profiles except Hα could be explained well with T e = 5000° K and hydrogen-to-metal ratio of twenty times the solar value, with sodium depleted more with respect to that of the solar value by a factor of 2. For Hα, the effect of convection is shown to have some effect. In a parallel calculation, it was found that the calculated and the observed profiles for the Sun do not agree if the Bohm-Vitense (T-τ) relation is used.

Observer time as a coordinate in relativistic spherical hydrodynamics.

Abstract: Retarded observer time as coordinate in relativistic spherical hydrodynamic equations prevents Schwarzschild surface formation

Omnidirectional inverse compton and synchrotron radiation from cosmic distributions of fast electrons and thermal photons.

Abstract: Diffuse omnidirectional inverse Compton and synchrotron X and gamma radiation from cosmic distributions of fast electrons and thermal photons

A study of pulsation in RR Lyrae models.

Abstract: Non-linear calculations of intermediate amplitude to investigate stability have been carried out for one hundred RR Lyrae models of varying composition, mass, luminosity, and effective temperature. Of these, the calculations have been extended to the maximum amplitude for fifty models. The dependence of the location of the instability strip on composition, mass, and luminosity has been explored. In particular, the high-temperature boundary of the strip increases by 500° K for each 15 per cent increase in the mass fraction of helium. The dependence on effective temperature of the phase shift, the ratio of radius and luminosity amplitudes, and the shape of the light-curve has been explored, and the correlations of these three measures have been found. These measures may then be applied to observed variables to determine their location in the instability strip and the helium content of their envelopes. The examples studied give best agreement at about 30 per cent helium by mass. The calculations reveal many details of the shapes of the light- and velocity-curves which may be compared to observation. A number of features of these curves of known variables are discussed, and the underlying explanation is investigated. The sources of the driving energy of these models have been explored. In the models of the most favored composition, 30 per cent helium, the hydrogen ionization region is almost as important to the driving as is the He II ionization. The effects that cause the amplitude to cease growing and level off at the observed maximum amplitude are explored: they appear to involve several non-linear effects, particularly a steep velocity front, in the He II ionization zone. A new kind of period-luminosity relation has been discovered. The shortest period at which the fundamental mode persists, before it changes to the first harmonic, has been found to be independent of mass and composition and to depend only on the luminosity. This relation was found to be Ptr = 0 057 (L/L☉)0.6 days. This has been used to interpret the varying period distributions of RR Lyrae stars in clusters and in the field with the result that the luminosities are found to vary from Mbol = 0.57 for very metal-weak clusters to Mbol = 0.96 for clusters only slightly weak in metals. Metal-rich variables are slightly less luminous still. These results lead to the conclusion that the masses of RR Lyrae stars are near 0.5 M☉, which must imply a significant mass loss. These conclusions appear to be consistent with the possible interior models.

Stellar evolution. III - The evolution of a 5 solar masses star from the main sequence through core helium burning.

Abstract: Evolution of 5 solar masses star model from main sequence through core helium burning compared to 3 solar masses model, noting Hertzsprung-Russell diagram

The stability of supermassive stars.

Abstract: Dynamic stability of supermassive stars with nuclear-energy generation, noting rotation and limiting mass for hydrogen burning

On the optical identification of Sco X-1

Abstract: Optical identification of position of X-ray astronomical source Sco X-1, noting similarity of certain properties with old novae

Measurements of Solar Magnetic Fields

Abstract: The photographic technique of Leighton (1) has been used to obtain high resolution measurements of photospheric magnetic fields with the following chief results: 1. "Source fluxes", Φ(defined as the average of the absolute values of the total fluxes of positive and negative polarity in a bipolar magnetic region on the day when this average is largest), of bipolar magnetic regions (BMRs) have been measured as a function of the "size", Am, of the associated sunspot activity. [Am is defined to be the area covered by all of the sunspots of a group (umbras plus penumbras of both leading and following parts) on the day when this area is largest.] The source fluxes were found to satisfy Φ = 1.2 Am within about ± 50%, where Φ is in "solar flux units" (1 SFU = 1021 maxwells) and Am is in units of 1018 cm2. Within measurement accuracy there was no imbalance of flux of positive and negative magnetic polarity in the BMRs observed, provided that the photographically-obtained fluxes were supplemented by the fluxes in the umbras of sunspots, as calculated from Mount Wilson observations. 2. Two BMRs were traced for the first few months following their birth. The development of each was semi-quantitatively what one would expect if the random-walk (2) plus solar differential rotation were the only means of flux transport on the solar surface. 3. In quiet regions of the solar surface, magnetic flux is distributed in small bits and fragments, and in the quietest regions, in tiny points less than 3000 km in diameter. Measurements for eight small features yielded fluxes ranging from 0.05 SFU for the very small points to 0.4 SFU for typical network fragments. The corresponding magnetic fields ranged from 200 gauss for the points to 700 gauss for the network fragments, showing that magnetic fields of a few hundred gauss are not at all uncommon for small magnetic features. 4. Polar faculae curves (3) have been calibrated to give magnetic flux on the polar caps of the sun as a function of time during the period 1905-1964. The fluxes vary cyclicly with time approximately 90° out of phase with the variation of the sunspot number for the whole solar disk with time during this same period (provided the sunspot number is given a polarity corresponding to the magnetic polarity of the following sunspots of the relevant hemisphere). The maxima of the polar fluxes vary considerably from cycle to cycle (just as the maxima of the sunspot number vary considerably from cycle to cycle), maximum fluxes ranging from 6 SFU to 21 SFU with 12 SFU being a typical maximum polar flux during the 1905-1964 period. The principal conclusion is that these measurements are consistent with the hypothesis that all of the magnetism on the sun's surface originates in BMRs, and that it is gradually spread about the surface by the random-walk (2, 4) and differential rotation, eventually causing the cancellation and reversal of the polar fields.

Franck-Condon factors for observed transitions in N sub 2 above 6 ev.

Abstract: Wave functions and Franck-Condon factors for transitions in molecular nitrogen obtained by Numerov integration of Schroedinger equation

RADIATIVE LIFETIMES OF ULTRAVIOLET MULTIPLETS IN Si, P, S, O, Ne II, AND Ar II.

Abstract: Radiative lifetimes of UV multiplets in Si, P, S, O, Ne 2 and Ar 2 measured via phase shift method, correcting for transition cascading

The Rotation of the Planet Mercury

Abstract: Mercury rotational period as consequence of solar torques and equatorial asymmetry, based on radar data and model developing superharmonic resonance