Search Publications
Observing the Unobservable? Modeling Coronal Cavity Densities
de Toma, G.; Gibson, S. E.; Fan, Y. +1 more
Prominence cavities in coronal helmet streamers are readily detectable in white-light coronagraph images, yet their interpretation may be complicated by projection effects. In order to determine a cavity's density structure, it is essential to quantify the contribution of noncavity features along the line of sight. We model the coronal cavity as a…
Seismic Halos around Active Regions: A Magnetohydrodynamic Theory
Hanasoge, Shravan M.
Comprehending the manner in which magnetic fields affect propagating waves is a first step toward constructing accurate helioseismic models of active region subsurface structure and dynamics. Here we present a numerical method for computing the linear interaction of waves with magnetic fields embedded in a solar-like stratified background. The ide…
Disk-dominated States of 4U 1957+11: Chandra, XMM-Newton, and RXTE Observations of Ostensibly the Most Rapidly Spinning Galactic Black Hole
Homan, Jeroen; Wilms, Jörn; Canizares, Claude R. +4 more
We present simultaneous Chandra High-Energy Transmission Gratings (HETG) and Rossi X-ray Timing Explorer (RXTE) observations of a "soft state" of the black hole candidate 4U 1957+11. These spectra, having limited hard X-ray excess, are an excellent test of disk atmosphere models that include effects of black hole spin. The HETG data show, by model…
The Horizontal Branch of NGC 1851: Constraints on the Cluster Subpopulations
Salaris, M.; Pietrinferni, A.; Cassisi, S.
We investigate the distribution of stars along the horizontal branch of the Galactic globular cluster NGC 1851, to shed light on the progeny of the two distinct subgiant-branch populations harbored by this cluster. On the basis of detailed synthetic horizontal-branch modeling, we conclude that the two subpopulations are distributed in different re…
High-excitation OH and H2O Lines in Markarian 231: The Molecular Signatures of Compact Far-infrared Continuum Sources
Smith, Howard A.; Ashby, Matthew L. N.; González-Alfonso, Eduardo +3 more
The ISO LWS far-infrared spectrum of the ultraluminous galaxy Mrk 231 shows OH and H2O lines in absorption from energy levels up to 300 K above the ground state, and emission in the [O I] 63 µm and [C II] 158 µm lines. Our analysis shows that OH and H2O are radiatively pumped by the far-infrared continuum emission…
Deep Spectroscopy of Systematically Surveyed Extended Lyα Sources at z ~ 3-5
Ouchi, Masami; Shimasaku, Kazuhiro; Ueda, Yoshihiro +4 more
Spatially extended Lyα sources that are faint and/or compact in continuum are candidates for extremely young (lesssim107 yr) galaxies at high redshifts. We present medium-resolution (R ~ 2000) VLT/VIMOS spectroscopy of 18 such extended Lyα sources found in our previous study at z ~ 3-5. The deep spectroscopy showed that all 18 objects h…
Hard X-Ray Emission of the Microquasar GRO J1655-40 during the Rise of Its 2005 Outburst
Joinet, A.; Kalemci, E.; Senziani, F.
We present an analysis of the high-energy emission of the Galactic black hole GRO J1655-40 at the beginning of its 2005 outburst. The data from 458 ks of INTEGRAL observations, spread over 4 weeks, are analyzed, along with the existing simultaneous RXTE and Swift data. The high-energy data allow us to detect the presence of a high-energy cutoff an…
On the Origin of Bimodal Horizontal Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441
Joo, Seok-Joo; Han, Sang-Il; Ree, Chang H. +3 more
Despite the efforts of the past decade, the origin of the bimodal horizontal branch (HB) found in some globular clusters (GCs) remains a conundrum. Inspired by the discovery of multiple stellar populations in the most massive Galactic GC, ω Centauri, we investigate the possibility that two distinct populations may coexist and are responsible for t…
Observation and Modeling of Coronal "Moss" With the EUV Imaging Spectrometer on Hinode
Winebarger, Amy R.; Warren, Harry P.; Doschek, George A. +2 more
Observations of transition region emission in solar active regions represent a powerful tool for determining the properties of hot coronal loops. We present the analysis of new observations of active region moss taken with the Extreme Ultraviolet Imaging Spectrometer (EIS) on the Hinode satellite. EIS observations of a density sensitive Fe XII lin…
X-Ray Emission from Active Galactic Nuclei with Intermediate-Mass Black Holes
Rao, A. R.; Dewangan, G. C.; Mathur, S. +1 more
We present a systematic X-ray study of eight active galactic nuclei (AGNs) with intermediate-mass black holes (MBH ~ 8-95 × 104 M⊙) based on 12 XMM-Newton observations. The sample includes the two prototype AGNs in this class—NGC 4395 and POX 52 and six other AGNs discovered with the Sloan Digitized Sky Survey. The…