Search Publications
A Catastrophic Flux Rope in a Quadrupole Magnetic Field for Coronal Mass Ejections
Wang, J. -X.; Zhang, Y. -Z.
We propose a flux-rope model for the initiation of flare-associated CMEs. The model triggers the eruption with a catastrophic loss of MHD equilibrium and then requires magnetic reconnection to sustain the eruption's acceleration. We carry out 2.5-dimensional time-dependent resistive MHD simulations, choosing the initial state such that a flux rope…
The Frequency of Mid-Infrared Excess Sources in Galactic Surveys
Indebetouw, R.; Benjamin, R. A.; Wolfire, M. G. +27 more
We have identified 230 Tycho-2 Spectral Catalog stars that exhibit 8 µm mid-IR extraphotospheric excesses in the MSX and Spitzer GLIMPSE surveys. Of these, 183 are either OB stars earlier than B8 in which the excess plausibly arises from a thermal bremsstrahlung component or evolved stars in which the excess may be explained by an atmospheri…
Circumnuclear Star Clusters in the Galaxy Merger NGC 6240, Observed with Keck Adaptive Optics and the Hubble Space Telescope
Schneider, G.; Max, C. E.; Pollack, L. K.
We discuss images of the central ~10 kpc (in projection) of the galaxy merger NGC 6240 at H and K' bands, taken with the NIRC2 narrow camera on Keck II using natural guide star adaptive optics. We detect 28 star clusters in the NIRC2 images, of which only 7 can be seen in the similar spatial resolution, archival WFPC2 Planetary Camera data at eith…
Observational Consequences of the Hypothesized Helium-rich Stellar Population in ω Centauri
Terndrup, D. M.; Newsham, G.
In response to the proposed high-helium content stars as an explanation for the double main sequence observed in ω Centauri, we investigated the consequences of such stars elsewhere on the color-magnitude diagram. We concentrated on the horizontal branch, where the effects of high helium are expected to show themselves more clearly. In the process…
Photometric Properties of the Most Massive High-Redshift Galaxies
Hernquist, Lars; Cox, Thomas J.; Hopkins, Philip F. +2 more
We calculate the observable properties of the most massive high-redshift galaxies in the hierarchical formation scenario where stellar spheroid and supermassive black hole growth are fueled by gas-rich mergers. Combining high-resolution hydrodynamical simulations of the hierarchical formation of a z~6 quasar, stellar population synthesis models, t…
The 1-200 keV X-Ray Spectrum of NGC 2992 and NGC 3081
Gehrels, N.; Beckmann, V.; Tueller, J.
The Seyfert 2 galaxies NGC 2992 and NGC 3081 have been observed by INTEGRAL and Swift. We report the results and a comparison of the spectrum above 10 keV based on INTEGRAL IBIS/ISGRI, Swift/BAT, and BeppoSAX/PDS. A spectrum can be extracted in the X-ray energy band ranging from 1 up to 200 keV. Although NGC 2992 shows a complex spectrum below 10 …
Structure of the Near-Surface Layers of the Sun: Asphericity and Time Variation
Basu, Sarbani; Antia, H. M.; Bogart, Richard S.
We present results on the structure of the near-surface layers of the Sun obtained by inverting frequencies of high-degree solar modes from ``ring diagrams.'' We have results for eight epochs between 1996 June and 2003 October. The frequencies for each epoch were obtained from ring diagrams constructed from Michelson Doppler Imager (MDI) Dopplergr…
MS 2053.7-0449: Confirmation of a Bimodal Mass Distribution from Strong Gravitational Lensing
Limousin, Marceau; de Diego, J. A.; Verdugo, T.
We present the first strong-lensing study of the mass distribution in the cluster MS 2053-04 based on HST archive data. This massive, X-ray luminous cluster has a redshift z=0.583 and is composed of two structures that are gravitationally bound to each other. The cluster has one multiply imaged system composed of a double gravitational arc. We hav…
Isophotal Structure and Dust Distribution in Radio-loud Elliptical Galaxies
Macchetto, F. D.; Capetti, A.; Sparks, W. B. +4 more
We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxies, imaged in the optical and near-infrared as part of Hubble Space Telescope snapshot surveys. We present a sample-wide trend between host galaxy isophotal structure and the inclination of dusty circumnuclear disks at the centers of 13 of these object…
Radio and White-Light Coronal Signatures Associated with the RHESSI Hard X-Ray Event of 2002 July 23
Krucker, S.; Kaiser, M. L.; Gary, D. E. +3 more
Simultaneous radio, white-light, and hard X-ray (HXR) observations for the 2002 July 23 γ-ray flare event are used to establish the relationship of a complex type III-like burst to the corresponding coronal mass ejection (CME) and the coronal electron acceleration signatures observed in the decimeter/microwave (dm-cm) emissions and X-rays. We find…