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At least 199 records · Page 11
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NASA NTRS1982

X-ray properties of the Be/X-ray systems 2S0114+650 = LSI+65 deg 010

Results are presented from experiments on the Einstein Observatory, HEAO-1 and OSO-8 on the temporal and spectral properties of 2S0114+650. In a 12 hour Einstein MPC and SSS observation two episodes of flaring occurred by an order of magnitude over about 1 hour. Variability on shorter time scales showed a preferred period of 14.9 minutes, but periodic pulsations were not seen in the HEAO-1 and OSO-8 data. There is some evidence that the spectrum is steeper when the source is quiescent at low luminosity, but no large spectral changes attended the flares. Absorption column densities were consistent with interstellar reddening of the proposed companion, the Be star LSI+65 deg 010. In the minute and hour variability and in the spectral character, 2S0114+650 is similar to other Be star-neutron star binary X-ray sources. Variations over several days in the OSO-8 data suggest orbital effects.

Koenigsberger, G.↗
NASA NTRS1983

Axions and the evolution of structure in the universe

A cosmological scenario where axions provide the dark matter in the universe is considered. Fluctuations in the axion-field energy denisty produced by domain walls and strings cause the appearance of 'axion clumps' of masses of order 10 to the 6th solar masses which most likely collapse to black holes by or at the time that the universe becomes axion dominated at T approximately 10 eV. These objects form the building blocks for the clustering hierarchy theory of galaxy and supercluster formation on scales up to about 10 Mpc and 10 to the 15th solar masses.

Stecker, F. W.↗
NASA NTRS1983

Studies of BL Lacertae objects with the Einstein X-ray observatory - The absolute volume density

It is estimated that the local volume density of BL Lac objects which emit greater than 10 to the 44th ergs/s in the 0.5-4.5 keV band is about 10 to the -7th/cu Mpc. This is based on identifications of bright X-ray sources, and the fact that Einstein X-ray observations detect BL Lac objects over a wide, continuous range of flux up to the thresholds of the all-sky X-ray surveys. Since this density is of the same order of magnitude as the local density of Seyfert galaxies, or local density of optically selected quasars, emitting X-rays at the same luminosity, we argue that the difference between these particular astronomical classifications is not solely due to the orientation of a relativistic beam.

Schwartz, D. A.↗
NASA NTRS1983

X-ray and ultraviolet observations of extragalactic H II regions

The dwarf galaxies NGC 5204, NGC 5474, and NGC 5585 have been shown by Sandage and Tammann (1974) to be physically associated with M101 (distance 7.2 Mpc). The present investigation is concerned with observations of the dwarf galaxies in the M101 group conducted with the aid of the Einstein satellite. Upon detection of X-ray emission from NGC 5204, it was found possible to observe this galaxy also with the International Ultraviolet Explorer (IUE). It is now feasible to compare the predictions on the stellar population of the galaxy inferred from the X-ray data with a more direct measure concerning this population. It is found that the hypothesis regarding the responsibility of binary X-ray sources of Population I progenitors for most of the X-ray emission is strengthened by the IUE short-wavelength spectrum of NGC 5204.

Fabbiano, G.↗
NASA NTRS1983

VLBI observations of the nucleus of Centaurus A

VLBI observations of the nucleus of Centaurus A made at 2.3 GHz on baselines with minimum fringe spacings of 0.15 and 0.0027 arcsec are presented. Results show that the nuclear component is elongated with a maximum extent of approximately 0.05 arcsec which is equivalent to a size of approximately 1 pc at the 5 Mpc distance of Centaurus A. The position angle of the nucleus is found to be 30 + or - 20 degrees, while the ratio of nuclear jet length to width is less than or approximately equal to 20. The nuclear flux density is determined to be 6.8 Jy, while no core component is found with an extent less than or approximately equal to 0.001 (less than or approximately equal to 0.02 pc) with a flux density of greater than or approximately equal to 20 mJy. A model of the Centaurus A nucleus composed of at least two components is developed on the basis of these results in conjunction with earlier VLBI and spectral data. The first component is an elongated source of approximately 0.05 arcsec (approximately 1 pc) size which contains most of the 2.3 GHz nuclear flux, while the second component is a source of approximately 0.0005 arcsec (approximately 0.01 pc) size which is nearly completely self-absorbed at 2.3 GHz but strengthens at higher frequencies.

Preston, R. A.↗
NASA NTRS1983

X-ray observations of the southern cluster CA 0340-538 and the Horologium supercluster

X-ray observations of the Horologium supercluster are examined. Results show that the optically Coma-like cluster CA 0340-538 has a smooth X-ray structure which also resembles that of Coma. The density structure of its X-ray emitting gas, determined in a model-independent way, is found to be remarkably featureless, being consistent with a nearly isothermal polytrope out to approximately 2 Mpc from the cluster center. The total mass of the gas is determined to exceed 10% of the cluster virial mass and may contribute a substantial fraction of the cluster binding mass. Although CA 0329-527 is found to be an X-ray double cluster, its structure appears to be confused. CA 0325-539 is found to show no substantial X-ray emission. An upper limit of 1.3 x 10 to the 44th erg/s is determined for any diffuse 2-10 keV emission from the Horologium supercluster.

Ku, W. H.-M.↗
NASA NTRS1983

Radioactive models of type 1 supernovae

In recent years, considerable progress has been made toward understanding Type I supernovae within the context of radioactive energy input. Much effort has gone into determining the peak magnitude of the supernovae, particularly in the B-band, and its relation to the Hubble constant. If the distances inferred for Type I events are at all accurate, and/or the Hubble constant has a value near 50 km per s per Mpc, it is clear that models must reach a peak magnitude approximately -20 in order to be consistent. The present investigation is concerned with models which achieve peak magnitudes near this value and contain 0.8 solar mass of Ni-56. The B-band light curve declines much more rapidly after peak than the bolometric light curve. The mass and velocity of Ni-56 (at least for the A models) are within the region defined by Axelrod (1980) for configurations which produce acceptable spectra at late times. The models are consistent with the absence of a neutron star after the explosion. There remain, however, many difficult problems.

Schurmann, S. R.↗
NASA NTRS1983

The Cancer Cluster - An unbound collection of groups

A surface density contour map of the Cancer Cluster derived from galaxy counts in the Zwicky catalog is presented. The contour map shows that the galaxy distribution is clumpy. When this spatial distribution is combined with nearly complete velocity information, the clumps stand out more clearly; there are significant differences in the mean velocities of the clumps which exceed their internal velocity dispersions. The Cancer Cluster is not a proper 'cluster' but is a collection of discrete groups, each with a velocity dispersion of approximately 300 km/s, separating from one another with the cosmological flow. The mass-to-light ratio for galaxies in the main concentration is approximately 320 solar masses/solar luminosities (H sub 0 = 100 km/s Mpc).

Geller, M. J.↗
NASA NTRS1983

Very large spiral galaxies

As a first step in the systematic study of large spirals, which may be useful in cosmological tests and studies of galaxy evolution, a catalog of the 107 largest known spiral galaxies is presented. Catalog galaxies have isophotal diameters greater than 90 kpc, assuming an H(zero) value of 50 km/sec per Mpc. UBVR photoelectric photometry is presented for 20 of these galaxies, and absolute magnitudes are derived for all galaxies in the catalog by transforming Zwicky magnitudes to the B(T) system.

Romanishin, W.↗
NASA NTRS1983

The X-ray emission of the old Nova V603 Aquilae (1918)

X-ray observations of the old Nova V603 Aql have been obtained with the IPC and MPC instruments aboard the Einstein Observatory during 1.7 consecutive orbital cycles. Periodic orbital phase-dependent flux variations are detected with large-amplitude flickering superimposed on the sinusoidal X-ray light curve. The spectrum is hard, characterized by a temperature of 20-30 keV, and the maximum X-ray luminosity observed was about 3 x 10 to the 33rd erg/s. The X-ray measurements are compared with recent optical photometric observations, and origin of the periodic modulation of the optical and X-ray flux is discussed.

Drechsel, H.↗
NASA NTRS1984

1E 0104.2 + 3153 - A broad absorption-line QSO viewed through a giant elliptical galaxy

The optical identification of the X-ray source 1E 0104.2 + 3153 is complicated by the close projection of a broad absorption-line (BAL) QSO (z = 2.027) 10 arcsec from a giant elliptical galaxy (z = 0.111) at the center of a compact group of galaxies. At only 1.2 de Vaucouleur radii (16 kpc for H sub 0 = 100 km/s Mpc) this QSO-galaxy projection is the closest yet discovered. Based upon current observations, the source of the X-ray emission cannot be conclusively determined. Present in the BAL QSO spectrum are extremely strong Ca II H and K absorption lines due to the intervening galaxy, the first optical detection of the cold interstellar medium in an elliptical galaxy. The strength of these lines (EW = 2 and 1 A) requires observation through several interstellar clouds in the line of sight to the QSO. By its proximity to the central regions of the elliptical galaxy and the relative distances of the galaxy and QSO, this QSO is a particularly good candidate for observing dramatic transient gravitational lensing phenomena due to halo stars in the foreground galaxy.

Stocke, J. T.↗
NASA NTRS1984

The central X-ray source in SS 433

Numerous observations of SS 433 were obtained with the Einstein X-ray Observatory over an 18 month period from 1979 March through 1980 October. MPC (as well as imaging) data from these observations show that the central object in SS 433 is variable in intensity and spectrum on a wide range of time scales. Flares appear to be correlated with the 13 day binary period, and may be more numerous at particular phases of the 164 day period. No evidence for variability on time scales less than 5 minutes is seen, suggesting the central X-ray source is extended and that the compact object itself is not directly visible. A model for SS 433 is suggested wherein the companion star has a spin misaligned with the orbital angular momentum. The volume of the Roche lobe reaches a minimum twice per binary orbit, giving rise to enhanced accretion which results in X-ray and radio flares. Additional constraints imposed by the X-ray and optical data suggest the compact object in SS 433 is an approximately 10-solar-mass black hole.

Band, D.↗
NASA NTRS1984

Discovery of the first carbon star in NGC 6822

A new photometric technique has been developed for detecting carbon and M stars in distant stellar systems, leading to isolation of carbon-star candidates in a number of Local-Group galaxies. One of the brighter candidates in NGC 6822 has been confirmed spectroscopically; at a distance of approximately 0.5 Mpc, it is the first truly extragalactic carbon star to be positively identified. The star has M(I) = about -5.7 mag, placing it near the upper-luminosity end of known carbon stars in the Magellanic Clouds.

Aaronson, M.↗
NASA NTRS1984

When clusters are superclusters

Recent research on substructure in clusters and superclusters of galaxies is critically surveyed, with an emphasis on the distinction (based on physical size and dynamic state) between the two classes of structures. The cosmological and large-scale structural implications of substructure in rich clusters are analyzed, using N-body-simulation results, and illustrated for the clusters A98 and A548. Consideration is also given to gravitational lensing of distant quasars by intervening clusters and the interpretation of the matter distribution on scales larger than about 5 Mpc. It is determined that A98 and A548 are superclusters.

Geller, M. J.↗
NASA NTRS1984

The ACTS Flight System - Cost-Effective Advanced Communications Technology

The multibeam communications package (MCP) for the Advanced Communications Technology Satellite (ACTS) to be STS-launched by NASA in 1988 for experimental demonstration of satellite-switched TDMA (at 220 Mbit/sec) and baseband-processor signal routing (at 110 or 27.5 Mbit/sec) is characterized. The developmental history of the ACTS, the program definition, and the spacecraft-bus and MCP parameters are reviewed and illustrated with drawings, block diagrams, and maps of the coverage plan. Advanced features of the MPC include 4.5-dB-noise-figure 30-GHz FET amplifiers and 20-GHz TWTA transmitters which provide either 40-W or 8-W RF output, depending on rain conditions. The technologies being tested in ACTS can give frequency-reuse factors as high as 20, thus greatly expanding the orbit/spectrum resources available for U.S. communications use.

Holmes, W. M., Jr.↗
NASA NTRS1983

The value of Ho

A brief discussion of the systematic effects of selection bias on the extragalactic distance scale is given. Distance indicators with intrinsic scatter yield only upper limits to Ho, unless the true intrinsic scatter is either small or well determined. Several distance indicators (luminosity index, diameters, globular clusters, 21 cm line widths) are discussed. It is concluded that type I supernovae, calibrated through brightest M supergiants, yield presently the most reliable determination of the large-scale value of the Hubble constant, i.e., 50 + or - 7 km/s Mpc.

Tammann, G. A.↗
NASA NTRS1984

A redshift survey of the poor cluster A1142

A nearly complete redshift survey of the galaxy cluster A1142 over a 2 sq deg region which includes the central 0.7 Mpc of the cluster is presented which includes 63 new redshifts. Of the 60 galaxies in the region brighter than m(v) = 16.5, about 40 percent are either foreground or background to the cluster. For the 35 cluster members, a mass-to-light ratio of 520 solar masses/solar luminosities is derived, consistent with the results for other well-studied systems.

Geller, M. J.↗
NASA NTRS1984

Large-scale inhomogeneities and galaxy statistics

The density fluctuations associated with the formation of large-scale cosmic pancake-like and filamentary structures are evaluated using the Zel'dovich approximation for the evolution of nonlinear inhomogeneities in the expanding universe. It is shown that the large-scale nonlinear density fluctuations in the galaxy distribution due to pancakes modify the standard scale-invariant correlation function xi(r) at scales comparable to the coherence length of adiabatic fluctuations. The typical contribution of pancakes and filaments to the J3 integral, and more generally to the moments of galaxy counts in a volume of approximately (15-40 per h Mpc)exp 3, provides a statistical test for the existence of large scale inhomogeneities. An application to several recent three dimensional data sets shows that despite large observational uncertainties over the relevant scales characteristic features may be present that can be attributed to pancakes in most, but not all, of the various galaxy samples.

Schaeffer, R.↗