Search Publications
The Aptly Named Phoenix Dwarf Galaxy
Dolphin, Andrew E.; Skillman, Evan D.; Weisz, Daniel R. +1 more
The Local Group galaxy Phoenix has the properties of a dwarf spheroidal galaxy, but an adjacent H I cloud has been recently found to be at the same radial velocity as the stars. The proximity suggests that this cloud is associated with the most recent (<=100 Myr) star formation in Phoenix. We have obtained relatively high sensitivity and high r…
Joint Analysis of Cluster Observations. I. Mass Profile of Abell 478 from Combined X-Ray, Sunyaev-Zel'dovich, and Weak-Lensing Data
Hoekstra, Henk; Babul, Arif; Mahdavi, Andisheh +3 more
We provide a new framework for the joint analysis of cluster observations (JACO) using simultaneous fits to X-ray, Sunyaev-Zel'dovich (SZ), and weak-lensing data. Our method fits the mass models simultaneously to all data, provides explicit separation of the gaseous, dark, and stellar components, and-for the first time-allows joint constraints on …
Magnetic Helicity Injection in Active Regions
Chae, Jongchul; Jeong, Hyewon
Magnetic helicity is now regarded as an important physical quantity in understanding solar magnetic activities. We have studied the injection of magnetic helicity through the photosphere of four active regions during the long periods of their lifetimes. The rate of helicity injection was determined as a function of time in each active region by ap…
Preferential Perpendicular Heating of Coronal Hole Minor Ions by the Fermi Mechanism
Isenberg, Philip A.; Vasquez, Bernard J.
We present a kinetic mechanism for the preferential perpendicular heating of minor ions in coronal holes, which may be responsible for the consistent observation in fast solar wind that the heavy ions are hotter and flow faster than the proton population. The basis of this mechanism is the familiar resonant cyclotron interaction between ions and p…
On the Absence of Wind Signatures in GRB Afterglow Spectra: Constraints on the Wolf-Rayet Winds of GRB Progenitors
Foley, Ryan J.; Ramirez-Ruiz, Enrico; Chen, Hsiao-Wen +3 more
We investigate available constraints on the circumstellar medium (CSM) around long-duration γ-ray burst (GRB) progenitors from afterglow spectra. We first establish a statistical sample of five GRB afterglow spectra that have been collected and analyzed with no prior knowledge of the line-of-sight properties. This sample is then adopted for a unif…
Static and Dynamic Modeling of a Solar Active Region
Winebarger, Amy R.; Warren, Harry P.
Recent hydrostatic simulations of solar active regions have shown that it is possible to reproduce both the total intensity and the general morphology of the high-temperature emission observed at soft X-ray wavelengths using static heating models. These static models, however, cannot account for the lower temperature emission. In addition, there i…
X-Ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth
Camilo, F.; Gotthelf, E. V.; Halpern, J. P. +1 more
The 105 ms X-ray pulsar J1852+0040 is the central compact object (CCO) in supernova remnant Kes 79. We report a sensitive upper limit on its radio flux density of 12 µJy at 2 GHz using the NRAO Green Bank Telescope. Timing using the Newton X-Ray Multi-Mirror Mission (XMM-Newton) and the Chandra X-Ray Observatory over a 2.4 yr span reveals no…
The Black Hole Mass and Extreme Orbital Structure in NGC 1399
Filippenko, Alexei V.; Ho, Luis C.; Gebhardt, Karl +12 more
The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescope kinematics for NGC 1399, the central galaxy in Fornax. We find the best-fit model contains a black hole of (5.1+/-0.7)×108 Msolar …
Detailed Far-Ultraviolet to Optical Analysis of Four [WR] Stars
Pereira, C. B.; Hillier, D. J.; Marcolino, W. L. F. +1 more
We present far-UV to optical analyses of four hydrogen-deficient central stars of planetary nebulae: BD +30 3639, NGC 40, NGC 5315, and NGC 6905. Using the radiative transfer code CMFGEN, we determined new physical parameters and chemical abundances for these stars. The results were analyzed in the context of the [WR]-->PG 1159 evolution via th…
First X-Ray Observations of the Young Pulsar J1357-6429
Zavlin, Vyacheslav E.
The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided indications of a tail-like pulsar wind nebula associated with this object as well as pulsations of its X-ray flux with a pulsed fraction pf>~50% and a thermal component dominating at energies E<~2 keV. The putative nebula is v…