Search Publications
XMM-Newton Observations of Radio Pulsars B0834+06 and B0826-34 and Implications for the Pulsar Inner Accelerator
Haberl, F.; Zhang, B.; Gil, J. +3 more
We report the X-ray observations of two radio pulsars with drifting subpulses, B0834+06 and B0826-34, using XMM-Newton. PSR B0834+06 was detected with a total of 70 counts from the three EPIC instruments over 50 ks exposure time. Its spectrum is best described as that of a blackbody (BB), with temperature Ts = (2.0+ 2.0-…
Characterizing the Near-UV Environment of M Dwarfs
Hawley, Suzanne L.; Johns-Krull, Christopher M.; Walkowicz, Lucianne M.
We report the results of our Hubble Space Telescope (HST) snapshot survey with the ACS HRC PR200L prism, designed to measure the near-UV emission in a sample of nearby M dwarfs. Thirty-three stars were observed, spanning the mass range from 0.1 to 0.6 solar masses (Teff ~ 2200-4000 K) where the UV energy distributions vary widely betwee…
Rotational Feature of Vega Revealed from Spectral Line Profiles
Takeda, Yoichi; Kawanomoto, Satoshi; Ohishi, Naoko
In order to establish Vega's absolute rotational velocity, ve, as distinct from the inclination angle, i, we conducted a detailed profile study on a large number (~200) of weak lines based on very high signal-to-noise ratio spectrum data, making use of the fact that the lines' characteristic shapes may contain information about rotation…
Solar Cycle Related Changes at the Base of the Convection Zone
Basu, Sarbani; Baldner, Charles S.
The frequencies of solar oscillations are known to change with solar activity. We use principal component analysis to examine these changes with high precision. In addition to the well-documented changes in solar normal mode oscillations with activity as a function of frequency, which originate in the surface layers of the Sun, we find a small but…
SWAS Observations of Water in Molecular Outflows
Bergin, Edwin A.; Neufeld, David A.; Kaufman, Michael J. +4 more
We present detections of the ground-state 110→ 101 transition of ortho-H2O at 557 GHz in 18 molecular outflows based on data from the Submillimeter Wave Astronomy Satellite (SWAS). These results are combined with ground-based observations of the J = 1-0 transitions of 12CO and 13CO obtained at…
Titan's Tropical Storms in an Evolving Atmosphere
McKay, Christopher P.; Griffith, Caitlin A.; Ferri, Francesca
The Huygens probe landed in a damp lake bed fed by fluvial channels, indicative of past rainfall. Such washes, interspersed with vast dunes, are typical of Titan's tropical landscape. Yet, Cassini-Huygens measurements reveal a highly stable tropical atmosphere devoid of deep convective storms, and the formation of washes in dune fields is not unde…
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…