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Huchra, J. P.

Publications and source records attributed to Huchra, J. P..

48 records · Page 3
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NASA NTRS1984

Observational and theoretical studies of rich clusters with multiple subcondensations

Observational and theoretical studies of the formation and evolution of clusters of galaxies are investigated. The relationship between the properties of individual galaxies and their environment is examined. Perphaps the most remarkable physical result derived from these is the apparent substructure in redishift position space. The distribution of spiral galaxies is quite different from the distribution of the ellipticals. The velocity distribution for the spirals is also substantially broader than the distribution for the ellipticals.

Geller, M. J.↗
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 NTRS1983

Star formation in blue galaxies. I - Ultraviolet, optical, and infrared observations of NGC 4214 and NGC 4670

NGC 4214 and NGC 4760 have been observed between 1150 A and 1950 A with the IUE satellite, and new infrared and optical broad-band photometry have been obtained. The spectra of both galaxies are dominated by O stars, and, in the spectrum of NGC 4214, the C IV 1550 A line exhibits a P Cygni profile indicative of hot stars with large mass-loss rates. Although the optical spectra of both galaxies are dominated by strong narrow emission lines, no strong emission lines are seen in the UV (the observed Ly-alpha flux is dominated by geocoronal emission). Both galaxies contain giant H II region complexes in which the energy (in particular, the H-beta luminosity and the ultraviolet continuum) is provided by several hundred O stars. The comparison of the observed UVOIR energy distributions with evolutionary population models indicates that the regions observed consist of young 'bursts' of star formation superposed on an underlying old population. The initial mass function for this epoch of star formation is constrained to be similar in slope to or flatter than the Salpeter function.

Geller, M. J.↗
NASA NTRS1983

Combined ultraviolet studies of astronomical sources

Ultraviolet spectra of non-radiataive shock waves grain destruction and elemental abundances in interstellar shocks, carbon abundance in M33 and M31 from supernova remnants, determination of the mass function in the large Magellanic cloud, UV spectra of white dwarf pulsars, stellar flares, availability of the double quasar Q 0957 + 56' AB, spectra of late-F dwarfs and their relation to rotation, dynamics of hot gas surrounding hybrid stars, high resolution study of epsilon coronae Austriual, active regions on solar-type dwarfs as a function of rotation rate and age, coordinated chromospheric synoptic observations of selected late-type stars, the two-component atmosphere of Lambda Andromedae, and activity in Hyades giants are discussed.

Dupree, A. K.↗
NASA NTRS1983

Optical and X-ray observations of faint quasars in an optically selected sample

The confirmation of six quasars from spectrographic observations made in 1981 using the Multiple Mirror Telescope, and the characterization of 10 quasars from 1980 Einstein-Observatory X-ray observations (using both imaging proportional counter and high-resolution imager), are reported. The candidates had been selected by Formiggini et al. (1980) in a 1.72-sq-deg region centered on 13h 6 deg, on the basis of ultraviolet excess and a limiting B magnitude of 19.20. A total sample of 10 UV-excess quasars of this magnitude has now been confirmed, for an integral surface density of 5.8 + or - 1.8 per sq deg. Confirmation of three objects from another sample with B less than 18.25 as quasars yielded a surface density of 0./59 + or - 0.13 per sq deg at that magnitude. Data from the complete samples were used to compute the number-flux relation, found to be described by a power law with a 2.25 index for quasars with B between 17.0 and 19.2. From the X-ray observations it was determined that quasars with z less than 2.2 and B less than 19.20 contribute about 15 percent to the cosmic 2-keV background.

Marshall, H. L.↗
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

Galaxy clusters with multiple components. II - Abell 115

Abell 115 is a galaxy cluster with two large enhancements in X-ray surface brightness. A map of the galaxy distribution over an extended region reveals the presence of three primary clumps of galaxies. Two of these correspond to the peaks in the X-ray surface brightness. A third clump, 7 arcmin to the east of the pair, has no X-ray emission detected by the Einstein Observatory. Redshifts are measured for 29 galaxies in the region; 10 are certainly members of foreground groups. A115, at z approximately 0.2, is the highest redshift cluster for which any extensive attempt has been made to study the system dynamics.

Beers, T. C.↗
NASA NTRS1982

Galaxy clusters with multiple components. I - The dynamics of Abell 98

The nature and evolution of rich galaxy clusters containing multiple condensations is studied. Velocities for 13 members of A98 are presented and the determination of dynamical properties of the individual subclusters is substantially improved. The application of techniques for quantifying gravitational scale lengths are stressed without invocation of the symmetry arguments demanded by the usual parameter fitting procedures. The entire A98 cluster is modeled as a two-body system. The probability that A98 is bound is found to be 98 percent. From this model and the results of previous N-body simulations, it is shown that the most likely description of the system is that it reached maximum expansion about 3.5 billion years ago and is presently in a state of collapse. The subclusters will merge in another three billion years.

Beers, T. C.↗
NASA NTRS1982

Abell 2069 - An X-ray cluster of galaxies with multiple subcondensations

X-ray and optical observations of the cluster Abell 2069 are presented. The cluster is at a mean redshift of 0.116. The cluster shows multiple condensations in both the X-ray emission and in the galaxy surface density and, thus, does not appear to be relaxed. There is a close correspondence between the gas and galaxy distributions which indicates that the galaxies in this system do map the mass distribution, contrary to what might be expected if low-mass neutrinos dominate the cluster mass.

Gioia, I. M.↗
NASA NTRS1982

Combined ultraviolet studies of astronomical sources

Ultraviolet studies of astronomical sources are discussed. Some studies utilized IVE data. Non-radiative shock at the edge of the Cygnses Loop, stellar flares, local interestellar medium, hot galaxies, stellar mass ejection, contact binaries, double quasars, and stellar chromosphere and coronae are discussed.

Dupree, A. K.↗
NASA NTRS1978

Contribution of intermediate luminosity X-ray galaxies to the background - Anon 0945-30

Evidence that the galaxy A0945-30 is a new extragalactic X-ray source was found from an analysis of rotating modulation collimator quick-look data collected from the SAS 3 X-ray observatory. A strong piece of evidence was the hydrogen column density of 3 plus or minus 1 times 10 to the 22nd power per sq cm for a power law spectrum extending to about 35 keV inferred from HEAO 1 data. Observations indicate that the galaxy is an early type spiral with a bright nucleus. A faint star alongside the galaxy within the 90% confidence X-ray source error circle is an F dwarf with no indication of emission features. Spectra of the galaxy in the red and blue show sharp, intermediate strength emission lines of forbidden O III, forbidden N II, and H-alpha together with strong Mg, Fe, Ca absorption features characteristic of a normal stellar continuum in the galactic nucleus.

Schnopper, H. W.↗