Search Publications
Ion Charge States in Halo Coronal Mass Ejections: What Can We Learn about the Explosion?
Laming, J. Martin; Rakowski, Cara E.; Lepri, Susan T.
We describe a new modeling approach to develop a more quantitative understanding of the charge state distributions of the ions of various elements detected in situ during halo coronal mass ejection (CME) events by the Advanced Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution based on observations of CMEs propagating i…
Pismis 24-1: The Stellar Upper Mass Limit Preserved
Walborn, Nolan R.; Maíz Apellániz, J.; Morrell, N. I. +2 more
Is there a stellar upper mass limit? Recent statistical work seems to indicate that there is and that it is in the vicinity of 150 Msolar. In this paper we use HST and ground-based data to investigate the brightest members of the cluster Pismis 24, one of which (Pismis 24-1) was previously inferred to have a mass greater than 200 M…
An Investigation of the Origin of Soft X-Ray Excess Emission from Ark 564 and Mrk 1044
Rao, A. R.; Dewangan, G. C.; Griffiths, R. E. +1 more
We investigate the origin of the soft X-ray excess emission from Ark 564 and Mrk 1044. Based on a long XMM-Newton observation of Ark 564, we find clear evidence for time delays such that the variations in the 4-10 kev band lag behind that in the 0.2-0.5 kev band by 1768+/-122 s. The full-band power density spectrum (PDS) of Ark 564 has a break at …
A Time Delay for the Cluster-Lensed Quasar SDSS J1004+4112
Keeton, C. R.; Kochanek, C. S.; Maoz, D. +12 more
We present 426 epochs of optical monitoring data spanning 1000 days from 2003 December to 2006 June for the gravitationally lensed quasar SDSS J1004+4112. The time delay between the A and B images is ΔtBA=38.4+/-2.0 days (Δχ2=4) in the expected sense that B leads A and the overall time ordering is C-B-A-D-E. The measured dela…
New Evidence for the Role of Emerging Flux in a Solar Filament's Slow Rise Preceding Its CME-producing Fast Eruption
Harra, Louise K.; Moore, Ronald L.; Sterling, Alphonse C.
We observe the eruption of a large-scale (~300,000 km) quiet-region solar filament leading to an Earth-directed ``halo'' coronal mass ejection (CME), using data from EIT, CDS, MDI, and LASCO on SOHO and from SXT on Yohkoh. Initially the filament shows a slow (~1 km s-1 projected against the solar disk) and approximately constant velocit…
The Suzaku Observation of the Nucleus of the Radio-loud Active Galaxy Centaurus A: Constraints on Abundances of the Accreting Material
Ptak, A.; Fukazawa, Y.; Kataoka, J. +16 more
A Suzaku observation of the nucleus of the radio-loud AGN Centaurus A in 2005 has yielded a broadband spectrum spanning 0.3-250 keV. The net exposure times after screening were 70 ks per X-ray Imaging Spectrometer (XIS) camera, 60.8 ks for the Hard X-ray Detector (HXD) PIN, and 17.1 ks for the HXD GSO. The hard X-rays are fit by two power laws of …
Embedded Star Formation in the Eagle Nebula with Spitzer GLIMPSE
Indebetouw, R.; Whitney, B. A.; Robitaille, T. P. +5 more
We present new Spitzer photometry of the Eagle Nebula (M16, containing the optical cluster NGC 6611) combined with near-infrared photometry from 2MASS. We use dust radiative transfer models, mid-infrared and near-infrared color-color analysis, and mid-infrared spectral indices to analyze point-source spectral energy distributions, select candidate…
Resolving the Stellar Populations in the Circumnuclear Ring of NGC 7469
Colina, L.; Knapen, J. H.; Díaz-Santos, T. +2 more
We investigate the stellar populations in the star-forming ring of the luminous infrared galaxy NGC 7469. We use HST multiwavelength (UV through NIR) imaging complemented with new K-band ground-based long-slit spectroscopy, and mid-IR and radio maps from the literature. SEDs and evolutionary synthesis models have been used to characterize the star…
Validation of Time-Distance Helioseismology by Use of Realistic Simulations of Solar Convection
Zhao, Junwei; Kosovichev, Alexander G.; Georgobiani, Dali +3 more
Recent progress in realistic simulations of solar convection have given us an unprecedented opportunity to evaluate the robustness of solar interior structures and dynamics obtained by methods of local helioseismology. We present results of testing the time-distance method using realistic simulations. By computing acoustic wave propagation time an…
Swift X-Ray Observations of Classical Novae
Schmitt, J. H. M. M.; Ness, J. -U.; Gehrels, N. +5 more
The new γ-ray burst (GRB) mission Swift has obtained pointed observations of several classical novae in outburst. We analyzed all the observations of classical novae from the Swift archive up to 2006 June 30. We analyzed usable observations of 12 classical novae and found 4 nondetections, 3 weak sources, and 5 strong sources. This includes detecti…