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…
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 …
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…
M31's Undisturbed Thin Disk of Globular Clusters
Harding, Paul; Morrison, Heather L.; Perrett, Kathy +1 more
We show that there is a subsystem of the M31 globular clusters with thin-disk kinematics. These clusters span the entire metallicity range of the M31 globular cluster system, in contrast to the (thick) disk globular clusters in the Milky Way, which are predominantly metal-rich. Disk globular clusters are found across the entire disk of M31 and for…
Fragmentation Hierarchy of Bright Sungrazing Comets and the Birth and Orbital Evolution of the Kreutz System. I. Two-Superfragment Model
Sekanina, Zdenek; Chodas, Paul W.
A back-and-forth orbit integration technique, developed for our previous investigation of the splitting of the parent of the sungrazers C/1882 R1 and C/1965 S1, is now applied in an effort to understand the history and orbital evolution of the Kreutz sungrazer system, starting with the birth of two subgroups, which show prominently among the brigh…
Transient Relativistically Shifted Lines as a Probe of Black Hole Systems
Turner, T. J.; Kraemer, S. B.; Reeves, J. N.
X-ray spectra of Seyfert galaxies have revealed a new type of X-ray spectral feature, one that appears to offer important new insight into the black hole system. XMM revealed several narrow emission lines redward of Fe Kα in NGC 3516. Since that discovery the phenomenon has been observed in other Seyfert galaxies, e.g., NGC 7314 and ESO 198-G24. W…
The X-Ray Jet of 3C 120: Evidence for a Nonstandard Synchrotron Spectrum
Harris, D. E.; Walker, R. C.; Mossman, A. E.
We report on archival data from the Chandra X-Ray Observatory for the radio jet of 3C 120. We consider the emission process responsible for the X-rays from four knots using spectra constructed from radio, optical, and X-ray intensities. While a simple synchrotron model is adequate for three of the knots, the fourth (``k25''), which was previously …