Search Publications
Non-LTE Radiative Transfer in Model Prominences. I. Integrated Intensities of He I Triplet Lines
Labrosse, N.; Gouttebroze, P.
In this work we use new results of radiative transfer calculations out of local thermodynamical equilibrium to study the triplet lines emitted by neutral helium in solar quiescent prominences. We compare two types of prominence atmospheres: isothermal and isobaric models versus nonisothermal and nonisobaric ones. We can thus investigate the effect…
Correlated Infrared and X-ray variability of the transient Anomalous X-ray Pulsar XTE J1810-197
Covino, S.; Campana, S.; Tiengo, A. +10 more
We report on observations aimed at searching for flux variations from the proposed IR counterpart of the Anomalous X-ray Pulsar (AXP) XTE J1810-197. These data, obtained in March 2004 with the adaptive optics camera NAOS-CONICA at the ESO VLT, show that the candidate proposed by Israel et al. (\cite{Israel04}, ApJ, 603, L97) was fainter by Δ H=0.7…
Age Constraints for an M31 Globular Cluster from Main-Sequence Photometry
Ferguson, Henry C.; Brown, Thomas M.; Rich, R. Michael +5 more
We present a color-magnitude diagram (CMD) of the globular cluster SKHB 312 in the Andromeda galaxy (M31), obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. The cluster was included in deep observations taken to measure the star formation history of the M31 halo. Overcoming a very crowded field, our photometry of SKHB 31…
Magnetic Field Confinement in the Solar Corona. I. Force-free Magnetic Fields
Low, B. C.; Thomas, S.; Flyer, N. +1 more
Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value problems in an unbounded domain posed by the equilibrium equations. It is well known from virial considerations that stringent global constraints apply for a force-free field to be confined in equilibrium against expansion into the unbounde…
Obscured Star Formation in the Central Region of the Dwarf Galaxy NGC 5253
Imanishi, Masatoshi; Rieke, George H.; Alonso-Herrero, Almudena +4 more
We present Hubble Space Telescope (HST) NICMOS observations (1.1-2.2 µm) and 1.9-4.1 µm spectroscopy of the central region of the dwarf galaxy NGC 5253. The HST NICMOS observations reveal the presence of a nuclear double star cluster separated by ~=0.3"-0.4", or 6-8 pc (for a distance d=4.1 Mpc). The double star cluster, also a bright …
Modeling temporal variability of plasma conditions in the Io torus during the Cassini era
Delamere, P. A.; Bagenal, F.; Steffl, A.
Observations of ultraviolet (UV) emissions from the major ion species (S+, S++, S+++, O+, O++) of the Io plasma torus made during the Cassini flyby (October 2000 to March 2001) have revealed significant time variability. Using a homogeneous model for mass and energy flow in the torus parameter…
A Star Catalog for the Open Cluster NGC 188
Stetson, Peter B.; VandenBerg, Don A.; McClure, Robert D.
We present new BVRI broadband photometry for the old open cluster NGC 188, based on an analysis of 299 CCD images either obtained by us, donated by colleagues, or retrieved from public archives. We compare our results on a star-by-star basis with data from 11 previous photometric data sets for the cluster. We homogenize and merge the data from all…
The X-ray variability of the narrow-line type 1 Seyfert galaxy IRAS 13224-3809 from an XMM-Newton observation
Brandt, W. N.; Fabian, A. C.; Boller, Th. +5 more
We report on the XMM-Newton timing properties of the most X-ray variable, radio-quiet, narrow-line type 1 Seyfert galaxy IRAS 13224-3809. IRAS 13224-3809 continues to display the extremely variable behaviour that was previously observed with ROSAT and ASCA; however, no giant, rapid flaring events are observed. We detect variations by a factor as h…
The Highly Relativistic Kiloparsec-Scale Jet of the Gamma-Ray Quasar 0827+243
Jorstad, Svetlana G.; Marscher, Alan P.
We present Chandra X-ray (0.2-8 keV) and Very Large Array radio (15 and 5 GHz) images of the γ-ray-bright, superluminal quasar 0827+243. The X-ray jet bends sharply-by ~90°, presumably amplified by projection effects-5" from the core. Only extremely weak radio emission is detected between the nuclear region and the bend. The X-ray continuum spectr…
Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Malkan, M. A.; Hunt, L. K.
Why are the nuclei of some galaxies more active than others? If most galaxies harbor a central massive black hole, the main difference is probably in how well it is fueled by its surroundings. We investigate the hypothesis that such a difference can be seen in the detailed circumnuclear morphologies of galaxies using several quantitatively defined…