October 1998 arXiv papers — page 24

David H. Weinberg, Rupert A. C. Croft, Lars Hernquist, Neal Katz

We estimate the value of the matter density parameter Ω_0 by combining constraints from the galaxy cluster mass function with Croft et al.'s recent measurement of the mass power spectrum, P(k), from \lya forest data. The key assumption of the method is that cosmic structure formed by gravitational instability from Gaussian primordial fluctuations. For a

L. Angelini, M. J. Church, A. N. Parmar, M. Balucinska-Church

We report the discovery with BeppoSAX of a new 170.84 +/- 0.04 s X-ray pulsar, 1SAX J1324.4-6200, found serendipitously in the field of the X-ray binary X1323-619 in 1997 August. The source and periodicity are also detected in archival ASCA data taken in 1994. The X-ray spectrum is modeled by a power-law with a photon index of 1.0 +/- 0.4 and absorption of (

R. D. Jeffries

The present state of X-ray observations of cool stars in coeval open clusters is reviewed. Concentrating on ROSAT results for solar-type stars, the available observational dataset is summarized along with those details of the evolution of X-ray activity of low mass stars which have been firmly established as a result. Observational questions which are as yet

K. K. S. Wu, A. C. Fabian, P. E. J. Nulsen

Models of galaxy formation should be able to predict the properties of clusters of galaxies, in particular their gas fractions, metallicities, X-ray luminosity-temperature relation, temperature function and mass-deposition-rate function. Fitting these properties places important constaints on galaxy formation on all scales. By following gas processes in deta

Tomasz Bulik, Bronislaw Rudak

We present spectra of pulsed gamma-ray emission expected from millisecond pulsars within the framework of polar-cap models. The spectra are a superposition of three components due to curvature (CR), synchrotron (SR), and Compton upscattering (ICS) processes. The CR component dominates below $100 $GeV and the ICS component exhibits a peak at $\sim 1 $TeV. The

Bronislaw Rudak, Jaroslaw Dyks

For polar-cap models based on electromagnetic cascades induced by curvature radiation of beam particles we calculate broad-band high-energy spe ctra of pulsed emission expected for classical ($\sim 10^{12}\G$) and millisecond pulsars ($\sim 10^9\G$). The spectra are a superposition of curvature and synchrotron radiation components and most of their detailed

Andrea Cimatti, Paola Andreani, Huub Röttgering, Remo Tilanus

The nature of the extremely red galaxies is poorly known, the critical issue being whether they are old ellipticals at $z>1.5$ or distant star-forming galaxies strongly reddened by dust extinction. Here we review the little we know about them, and we present recent and preliminary results from our ongoing submillimeter -- millimeter observations.

Brad K. Gibson, Shaun M. G. Hughes, Peter B. Stetson, Wendy L. Freedman

The distance to NGC 4725 has been derived from Cepheid variables, as part of the Hubble Space Telescope Key Project on the Extragalactic Distance Scale. Thirteen F555W (V) and four F814W (I) epochs of cosmic-ray-split Wide Field and Planetary Camera 2 observations were obtained. Twenty Cepheids were discovered, with periods ranging from 12 to 49 days. Adopti

Robert A. Fesen, Christopher L. Gerardy, Kevin M. McLin, Andrew J. S. Hamilton

Near UV HST images of the remnant of SN 1885 (S And) in M31 show a 0"70 +- 0"05 diameter absorption disk silhouetted against M31's central bulge, at SN 1885's historically reported position. The disk's size corresponds to a linear diameter of 2.5 +- 0.4 pc at a distance of 725 +- 70 kpc, implying an average expansion velocity of 11000 +-

Chung-Pei Ma

I present a general discussion of the evolution and model-dependence of both the linear and nonlinear power spectrum of density fluctuations. The features of the linear power spectrum in cosmological models with cold dark matter (CDM) and cold+hot dark matter (C+HDM) are reviewed, and useful analytical approximations are summarized. Cosmological numerical si

H. Böhringer, L. Guzzo, C. A. Collins, D. M. Neumann

The paper describes the goals and first results of the ROSAT ESO Flux-Limited X-ray (REFLEX) Cluster Survey, a redshift survey of the X-ray brightest galaxy clusters in the ROSAT All-Sky Survey in the southern hemisphere conducted in the frame of an ESO key programme.