Die Medienvertreter, die Politiker, die Soziologen, die Informatiker und die Hardware- und Software-Anbieter werden nicht müde zu behaupten, daß wir heute im Zeitalter der Information und Kommunikation leben. Ist dies tatsächlich so? Und was bedeutet dies?
Using a combination of near-infrared and optical photometry, along with multi-object spectroscopy, we have confirmed the existence of a high-redshift cluster of galxies at z = 0.96. The cluster was found using a wide-angle tailed radio source selected from the VLA FIRST survey as a cluster signpost. These types of radio sources are often found in clusters, and are thought to attain their C-shaped morphologies from the relative motion between the radio source host galaxy and the intracluster medium. We present optical/near-infrared color-magnitude diagrams which show a concentration of cluster galaxies in color space. We also include spectroscopic results obtained from the Keck II LRIS. Ten galaxies are confirmed at the cluster redshift, with a line-of-sight velocity dispersion of 530 +190/-90 km/s, typical of an Abell richness class 0 cluster. Using data from the ROSAT public archive, we limit the X-ray luminosity for the cluster to less than 3 x 10^{44} erg/s, consistent with the value expected from the L_X - sigma relation.
Abstract Prior to conducting a survey of the galactic plane at 327 MHz using the VLA, we have imaged four fields near galactic longitude of 20 degrees. Each image will cover a 2.5 degree field with ∼1 arcmin resolution. The fields have been chosen to include the remnants G20.0-0.2, G21.5-0.9, and G24.7+0.6. The first two are isolated Crab-like objects, that is, there is no discernible associated shell. Since such shells have relatively steep spectra, images at 327 MHz will be more sensitive to their presence. The absence of a shell can constrain the density of the ISM in the vicinity of the SNR (Reynolds and Aller 1985 A.J. 90 , 2312). Since ∼50% of Crabs are naked, the implications can be extended to a significant fraction of the ISM.
This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J104459.6+365605, covering the rest wavelength range from 2260 to 2900 Å. The line of sight toward the QSO contains two clusters of outflowing clouds that give rise to broad blue-shifted absorption lines. The outflow velocities of the clouds range from -200 to -1200 km s-1 and from -3400 to -5200 km s-1, respectively. The width of the individual absorption lines ranges from 50 to more than 1000 km s-1. The most prominent absorption lines are those of Mg II, Mg I, and Fe II, and Mn II is also present. The low-ionization absorption lines occur at the same velocities as the most saturated Mg II lines, showing that the Fe II, Mg I, and Mg II line-forming regions must be closely associated. Many absorption lines from excited states of Fe II are present, allowing a determination of the population of several low-lying energy levels. The populations of the excited levels are found to be considerably smaller than expected for LTE and imply an electron density in the Fe II line-forming regions of ne ~ 4 × 103 cm-3. Modeling the ionization state of the absorbing gas with this value of the electron density as a constraint, we find that the distance between the Fe II and Mg I line-forming region and the continuum source is ~7 × 102 pc. From the correspondence in velocity between the Fe II, Mg I, and Mg II lines we infer that the Mg II lines must be formed at the same distance. The Mg II absorption fulfills the criteria for broad absorption lines defined by Weymann and coworkers. Therefore, the distance we find between the Mg II line-forming region and the continuum source is surprising, since BALs are generally thought to be formed in outflows at a much smaller distance from the nucleus.
view Abstract Citations (91) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A 5.57 hour modulation of the X-ray flux from 4U 1822-37. White, N. E. ; Becker, R. H. ; Boldt, E. A. ; Holt, S. S. ; Serlemitsos, P. J. ; Swank, J. H. Abstract The X-ray flux of 4U 1822-37 is shown to be modulated with the 5.57 hr period of its optical counterpart. The X-ray light curve is two component, with a smooth sinusoidal-like 25% semiamplitude modulation and a 30 minute dip of approximately 0.2 in phase following the other minimum; the dip center occurs 0.04 in phase after the optical minimum. The X-ray spectrum is a relatively flat power law up to 17 keV, above which it steepens; iron emission is detected at 6.7 keV with a 4 keV FWHM and an equivalent width of 1100 eV. An excess below 2 keV is consistent with either a 0.25 keV thermal component of 350 eV equivalent width iron L emission. Modeling the eclipse for a 0.5-0.7 solar radius companion gives a system inclination of 70-79 deg and a spherical cloud radius of 0.2-0.3 solar radius. Models for the long-term modulation are considered, and a comparison of the properties of 4U 1822-37 with those of Cyg X-3 shows that they are similar systems. Publication: The Astrophysical Journal Pub Date: August 1981 DOI: 10.1086/159109 Bibcode: 1981ApJ...247..994W Keywords: Binary Stars; Blue Stars; Modulation; Stellar Radiation; X Ray Sources; Heao 1; Light Curve; Stellar Magnitude; X Ray Spectra; Astronomy full text sources ADS | data products SIMBAD (3)
view Abstract Citations (171) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of radio continuum emission from Herbig-Haro objects 1 and 2 and from their central exciting source. Pravdo, S. H. ; Rodriguez, L. F. ; Curiel, S. ; Canto, J. ; Torrelles, J. M. ; Becker, R. H. ; Sellgren, K. Abstract The region in Orion containing HH 1 and HH 2 was observed with the VLA at 20, 6, and 2 cm on several occasions from 1981 to 1984. At lower resolution, four continuum sources were detected. Two of these sources coincide positionally with HH 1 and HH 2. At 6 cm and higher resolution, HH 1 is resolved into at least two components. The emission is probably bremsstrahlung originating in the same region where the visible line emission is produced. This is the first detection of radio continuum from classic Herbig-Haro objects. At a position closely centered between HH 1 and HH 2, an object that can be interpreted as the energy source of the system was detected. The central source spectrum is S(nu) of about nu to the alpha power, where alpha = 0.4 + or - 0.2, suggesting a stellar wind. Finally, the fourth radio continuum source coincides positionally with an H2O maser and is probably excited by an independent star. There is evidence of time variability in its radio flux. No emission was detected from the Cohen-Schwartz (1979) star at the 0.1 mJy level. Publication: The Astrophysical Journal Pub Date: June 1985 DOI: 10.1086/184486 Bibcode: 1985ApJ...293L..35P Keywords: Herbig-Haro Objects; Nebulae; Radio Sources (Astronomy); Water Masers; Bremsstrahlung; Continuous Radiation; Orion Constellation; Astrophysics full text sources ADS | data products SIMBAD (18)
