Search Publications
The Nuclei of Radio Galaxies in the Ultraviolet: The Signature of Different Emission Processes
Sparks, William B.; Chiaberge, Marco; Capetti, Alessandro +3 more
We have studied the nuclei of 28 radio galaxies from the 3CR sample in the UV band. Unresolved nuclei (central compact cores: CCCs) are observed in 10 of the 13 FR I galaxies, and in five of the 15 FR II galaxies. All sources that do not have a CCC in the optical do not have a CCC in the UV. Two FR I galaxies (3C 270 and 3C 296) have a CCC in the …
Abundance Gradients and the Role of Supernovae in M87
Gastaldello, Fabio; Molendi, Silvano
We make a detailed measurement of the metal abundance profiles and metal abundance ratios of the inner core of M87/Virgo observed by XMM-Newton during the performance verification phase. We use multitemperature models for the inner regions, and we compare the plasma codes APEC and MEKAL. We confirm the strong heavy-element gradient previously foun…
Monitoring the Evolution of the X-Ray Remnant of SN 1987A
Garmire, Gordon P.; Park, Sangwook; McCray, Richard +4 more
We report on the results of our monitoring program of the remnant of SN 1987A with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. Two new observations have been performed in AO2, bringing the total to four monitoring observations over the past 2 years. Over this time period, new techniques for correction of ``…
Three-dimensional Model of the Structure and Evolution of Coronal Mass Ejections
Tokman, M.; Bellan, P. M.
We present a new three-dimensional magnetohydrodynamic (MHD) model that describes the evolution of coronal magnetic arcades in response to photospheric flows. The dynamics of the system is discussed, and it is shown that the model reproduces a number of features characteristic of coronal mass ejection (CME) observations. In particular, we propose …
The Structure and X-Ray Recombination Emission of a Centrally Illuminated Accretion Disk Atmosphere and Corona
Raymond, J. C.; Liedahl, D. A.; Jimenez-Garate, M. A.
We model an accretion disk atmosphere and corona photoionized by a central X-ray continuum source. We calculate the opacity and one-dimensional radiation transfer for an array of disk radii to obtain the two-dimensional structure of the disk and its X-ray recombination emission. The atmospheric structure is extremely insensitive to the viscosity α…
A Uniform Analysis of the Lyα Forest at z=0-5. V. The Extragalactic Ionizing Background at Low Redshift
Bechtold, Jill; Kulkarni, Varsha P.; Dobrzycki, Adam +2 more
In Paper III of our series, ``A Uniform Analysis of the Lyα Forest at z=0-5,'' we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J(ν0),…
Limits on Chromospheres and Convection among the Main-Sequence A Stars
Ayres, Thomas R.; Redfield, Seth; Simon, Theodore +1 more
In deeply convective stars, the nonthermal energy required to heat the chromosphere ultimately is supplied by turbulent magnetoconvection. Because the early and middle A stars have very shallow convective layers, they are not expected to produce enough magnetoconvective power to sustain luminous chromospheres or hot coronae. Here we describe a sea…
Fundamental Properties and Distances of Large Magellanic Cloud Eclipsing Binaries. III. EROS 1044
Fitzpatrick, Edward L.; Guinan, Edward F.; Udalski, Andrzej +2 more
We present results from a detailed analysis of a third eclipsing binary (EB) system in the Large Magellanic Cloud, EROS 1044 (~B2 IV-V+~B2 III-IV). Our study combines the ``classical'' EB study of light and radial velocity curves with detailed modeling of the observed spectral energy distribution and yields an essentially complete picture of the s…
Optically Faint Counterparts to the Infrared Space Observatory FIRBACK 170 Micron Population: Discovery of Cold, Luminous Galaxies at High Redshift
Smail, I.; Ivison, R. J.; Helou, G. +3 more
We present Keck spectroscopy and UKIRT near-IR imaging observations of two 170 µm-selected sources from the Infrared Space Observatory (ISO) FIRBACK survey that have faint counterparts in the optical and r-K~5. Both sources were expected to lie at z>1, based on their far-infrared, submillimeter, and radio fluxes, assuming a spectral energ…
Dust in I Zw 18 from Hubble Space Telescope Narrowband Imaging
Cannon, John M.; Skillman, Evan D.; Garnett, Donald R. +1 more
We present new WFPC2 narrowband imaging of the blue compact dwarf galaxy I Zw 18, which is host to the lowest metallicity H II regions known. Images at Hα and Hβ are combined with archival broadband images to allow the study of the ionized gas distribution and morphology. Analysis of the Hα/Hβ flux ratio reveals significant enhancements in some ar…