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At least 1,747 records · Page 97
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NASA NTRS1974

Galactic X-ray sources

Data on galactic X-ray sources from rocket and balloon experiments and the UHURU satellite are reported. The outline emphasizes general discrete source models and begins with some a priori considerations about X-ray emission mechanisms and their applicability, after which contemporary data are interpreted according to these models. Topics covered include the production of X-rays by various mechanisms, source regimes, observational parameters, stellar distributions, individual stars, flare stars, supernovae and pulsars, the Crab nebula, old and young remnants, binary systems, and others.

Holt, S. S.↗
NASA NTRS1974

Multicolour far infrared photometry of galactic H2 regions

Results are presented of far infrared photometric measurements of H2 regions in the galactic plane between longitudes 350 and 40 degrees. The results are combined from balloon flights in 1972 and 1973 carried out in cooperation with CNES in the south of France.

Olthof, H.↗
NASA NTRS1975

Energy spectrum of galactic electrons in the energy range 2 x 10 to the 10 power - 2 x 10 to the 11th power eV

New experimental data on the energy spectrum of galactic electrons up to the energies approximately 2 x 10 to the 11th power eV were obtained in the summer of 1967 by a scintillation telescope lifted to the stratosphere at 32 km. The geometrical factor of the telescope was 1200 sq cm steradians, i.e., three times as great as the geometrical factor of previously employed installations. The results confirm previous measurements.

Zatsepin, V. I.↗
NASA NTRS1974

SAS-2 observations of gamma rays from the galactic plane

Preliminary data are given for the SAS-2 high energy galactic gamma ray observation. These data include both latitude and longitude distributions. The longitude distribution shows a high density region. The latitude distributions toward the center and the anti-center are markedly different, the former showing a two-component structure of half-widths of approximately 3 and 6 deg. The energy spectrum in the range 35 to 200 MeV is hard, consistent with cosmic ray interactions with interstellar matter, including neutral pions decay and emission from energetic electron interactions. The data is consistent with an interpretation in terms of the confinement of the cosmic rays in the spiral arms.

Thompson, D. J.↗
NASA NTRS1974

Monte Carlo analysis of the solar-wind modulation of galactic C-N-O at solar maximum

A previous (Moss and Giuli, 1971) Monte Carlo analysis of the solar-wind modulation of galactic cosmic-ray rigidity spectra is extended to include particles in the C-N-O group. A solar cavity 'radius' of 7 AU is found to be consistent with observations of the C-N-O component at solar maximum. The variation in modulation between solar maximum and solar minimum may be explained solely by variation of the solar cavity size, with no change in the scattering mean free path.

Moss, T. A.↗
NASA NTRS1975

Sources of excitation of the interstellar gas and galactic structure

The excitation of the interstellar gas is discussed in the light of recent evidence from gamma-ray, molecular, and 21-cm line observations. Previous studies of the excitation of the interstellar gas have not taken into account the substantial density contrast that exists between spiral arms and interarm regions. We examine the role played by the galactic distribution of three sources of excitation (supernovae, OB stars, and ultraviolet stars) in determining the physical state of the interstellar gas in arm and interarm regions.

Cowan, J. J.↗
NASA NTRS1975

The extra-galactic contribution to the primary cosmic-ray flux

In previous studies it has been shown that a good case can be made for supposing that a large fraction of the primary cosmic rays is of extra-galactic origin. These ideas are reviewed here, and the most recent observations and theoretical suggestions bearing on the problem are described.

Burbidge, G. R.↗
NASA NTRS1975

The distribution of stars in galactic nuclei - Loaded polytropes

We consider the structure of a galactic nucleus in which a compact supermassive object (e.g., a black hole or spinar) is embedded. The surrounding stars are assumed to satisfy a polytropic or isothermal equation of state. The density distribution of these loaded polytropes has a sharp central spike in which the time scale for stellar collisions can be short. Other properties of loaded polytropes, such as their masses, radii, projected density distribution, relaxation times, and stability, can also differ significantly from those of normal polytropes.

Huntley, J. M.↗
NASA NTRS1975

The Celescope survey and the galactic distribution of interstellar absorption

The instrumentation and data-reduction techniques used in the Celescope experiment conducted on board OAO-2 are reviewed. A brief summary is presented of the principles of UV astronomy, the Celescope optical package and bay E4 electronic module assembly are described, and the distribution of the Celescope pictures is plotted in galactic coordinates. Described data-reduction techniques include the determination of the U-B and B-V colors, removal of interstellar extinction effects, and construction of model atmospheres for the observed stars. Some difficulties and apparent contradictions encountered in the data interpretation are noted.

Davis, R. J.↗
NASA NTRS1975

Metal abundances of RR Lyrae stars in galactic globular clusters

Results are reported for image-tube scanner measurements of Preston's (1959) metal-abundance indicator and metallic-line absorption in the G-band region (4285 to 4317 A) of 47 RR Lyrae stars in 12 galactic globular clusters and 67 RR Lyrae field stars. The relationship (Fe/H) is defined and determined from curve-of-growth analyses of 13 RR Lyrae field stars, while a comparison of metal-abundance vs metallic-line absorption relationships derived for the field and cluster stars indicates that both groups can be calibrated in the same way. Based on this calibration, (Fe/H) values are deduced for the globular-cluster stars and the clusters themselves. It is found that the alpha-rich phenomenon is present in these stars and is confined to calcium and titanium.

Butler, D.↗
NASA NTRS1975

Copernicus observations of a number of galactic X-ray sources

The Copernicus satellite was launched on 21 August 1972. The main experiment on board is the University of Princeton UV telescope. In addition a cosmic X-ray package of somewhat modest aperture was provided by the Mullard Space Science Laboratory (MSSL) of University College London. Following a brief description of the instrument, a list of galactic sources observed during the year is presented. Although the X-ray detection aperture is small, the ability to point the satellite for long periods of time with high accuracy makes Copernicus an ideal vehicle for the study of variable sources.

J. L. Culhane↗
NASA NTRS1976

The 'other' galactic X-ray sources

There is a standard model for X-ray sources comprising a binary system containing a compact star and powered by mass accretion. It can be argued that the majority and perhaps all the galactic X-ray sources are of this kind. Three kinds of sources which may be qualitatively different from these are discussed: namely, low luminosity sources such as 3U0352 + 30, the sources associated with the globular clusters, and the transient X-ray sources.

Gursky, H.↗
NASA NTRS1976

Galactic distribution of pulsars

The density distributions of pulsars in luminosity, period, Z-distance, and galactocentric distance were derived using a uniform sample of pulsars detected during a 408 MHz pulsar survey at Jodrell Bank. There are indications of a fine scale structure in the spatial distribution and evidence that there is a general correlation with other galactic populations and the overall spiral structure. The electron layer in the galaxy is shown to be wider than the pulsar layer and uniform on a large scale. The number of pulsars in the galaxy was estimated and used to derive the pulsar birthrate.

Seiradakis, J. H.↗
NASA NTRS1976

Gamma rays and large scale galactic structure

Many theoretical models were developed in an attempt to explain the spatial structure in the observed emission which results from interactions of energetic cosmic rays with the interstellar gas. The peaks in the observed distribution are remarkably well correlated with longitudes corresponding to tangential directions to known spiral arm features. Based on theoretical and experimental arguments, it is assumed that on the scale of galactic arms the cosmic rays are more intense where the mass of the gas to which they are coupled is greatest. Refining this model with the results of recent surveys of the interstellar gas, a good fit to the observations is obtained whether the cosmic rays are confined to the spiral arms in the disk or are more evenly confined as in a flat halo model.

Kniffen, D. A.↗
NASA NTRS1975

Rotational interpretation of recombination line widths in the galactic nucleus

The widths of the radio recombination lines observed in the direction of the galactic center are interpreted as due to pure rotation. This interpretation leads to a mass estimate for the inner 1.6-pc region of our Galaxy. It is noted that recent observations of M 31 suggest the existence of a distinct dynamic entity at its center - the nucleus. The rotational interpretation of the recombination line widths is shown to be consistent with the existence of a nucleus at the center of our own Galaxy which is similar in nature to the nucleus of M 31.

Kellman, S. A.↗
NASA NTRS1975

A comparison of X-ray sources in globular clusters and in the galactic bulge

A hypothesis is advanced that the X-ray sources of the galactic bulge and those in globular clusters are of the same type. This is supported by the similarity of the respective stellar populations and the observed incidence of luminous sources. Evolutionary considerations suggest that it is the high stellar density that favors X-ray source formation in those regions. If the correspondence is correct, there must be about 100 additional weak sources in the bulge which have so far eluded detection because of source confusion.

Canizares, C. R.↗
NASA NTRS1975

Galactic evolution. I - Single-zone models

The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

Thuan, T. X.↗
NASA NTRS1975

Galactic evolution. II - Disk galaxies with massive halos

Models of galactic evolution are computed in which matter shed by dying halo stars accumulates in a smaller, more rapidly rotating disk. The models are simpler and more successful than one-zone (pure disk) models in that (1) the observed absence of low-metal-abundance low-mass dwarfs is expected, not anomalous and (2) the relative birthrate function (or IMF) need not be a strongly variable function of time in agreement with recent interpretations of observed stellar populations and neutral hydrogen in our own and other galaxies. Even a simple 'Salpeter' IMF for both disk and halo will produce an acceptable model. The model with a halo 'Salpeter' IMF, roughly one-quarter of the mass in the secondary disk, and approximately half the metals produced in the halo seems most compatible with observations of the metal abundance in low-mass stars, the deuterium abundance, halo planetary nebulae, and light from Population II stars, as well as with arguments on the stability of the disk.

Ostriker, J. P.↗