Search Publications
Dynamical Evidence for Environmental Evolution of Intermediate-Redshift Spiral Galaxies
Smith, Graham P.; Treu, Tommaso; Ellis, Richard S. +2 more
Combining resolved optical spectroscopy with panoramic HST imaging, we study the dynamical properties of spiral galaxies as a function of position across two intermediate-redshift clusters, and we compare the cluster population to field galaxies in the same redshift range. By modeling the observed rotation curves, we derive maximal rotation veloci…
Time-Distance Imaging of Solar Far-Side Active Regions
Zhao, Junwei
It is of great importance to monitor large solar active regions on the far side of the Sun for space weather forecasting, in particular, to predict their appearance before they rotate into our view from the solar east limb. Local helioseismology techniques, including helioseismic holography and time distance, have successfully imaged solar far-sid…
Spectral and Rotational Changes in the Isolated Neutron Star RX J0720.4-3125
Mori, Kaya; Pavlov, George G.; Kaplan, David L. +1 more
RX J0720.4-3125 is an isolated neutron star that, uniquely in its class, has shown changes in its thermal X-ray spectrum. We use new spectra taken with Chandra's Low Energy Transmission Grating Spectrometer, as well as archival observations, to try to understand the timescale and nature of these changes. We construct light curves, which show both …
A Photoionization Model for the Soft X-Ray Spectrum of NGC 4151
Turner, T. J.; Kraemer, S. B.; Armentrout, B. K.
We present an analysis of archival data from multiple XMM-Newton observations of the Seyfert 1 galaxy NGC 4151. Spectral data from the RGS instruments reveal several strong soft X-ray emission lines, chiefly from hydrogen-like and helium-like oxygen, nitrogen, neon, and carbon. Radiative recombination continua (RRC) from oxygen and carbon are also…
Dominant Nuclear Outflow Driving Mechanisms in Powerful Radio Galaxies
O'Dea, Christopher P.; Axon, David J.; Koekemoer, Anton +4 more
In order to identify the dominant nuclear outflow mechanisms in active galactic nuclei, we have undertaken deep, high-resolution observations of two compact radio sources (PKS 1549-79 and PKS 1345+12) with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope. Not only are these targets known to have powerful emission-line outflo…
A Deep Chandra, Very Large Array, and Spitzer Infrared Array Camera Study of the Very Low Luminosity Nucleus of the Elliptical NGC 821
Elvis, M.; Pellegrini, S.; Baldi, A. +5 more
The relatively nearby (distance = 24.1 Mpc) elliptical galaxy NGC 821 hosts an extreme example of a quiescent central massive black hole, for which deep Chandra observations revealed a nuclear source for the first time, with L2-10keV/LEdd~10-8. We present here a multiwavelength study of this nucleus, including Very…
Compton Telescope with a Coded Aperture Mask: Imaging with the INTEGRAL/IBIS Compton Mode
Laurent, P.; Lebrun, F.; Limousin, O. +1 more
Compton telescopes provide good sensitivity over a wide field of view in the difficult energy range from a few hundred keV to several MeV. Their angular resolution is, however, poor and strongly energy dependent. We present a novel experimental design associating a coded mask and a Compton detection unit to overcome these pitfalls. It maintains th…
Triggering Mechanism for the Filament Eruption on 2005 September 13 in NOAA Active Region 10808
Shibata, Kazunari; Okamoto, Takenori J.; Yokoyama, Takaaki +3 more
On 2005 September 13 a filament eruption accompanied by a halo coronal mass ejection (CME) occurred in the most flare-productive active region, NOAA 10808, in solar cycle 23. Using multiwavelength observations before the filament eruption on September 13, we investigate the processes leading to the catastrophic eruption. We find that the filament …
Helioseismic Test of Nonhomologous Solar Radius Changes with the 11 Year Activity Cycle
Kosovichev, A. G.; Lefebvre, S.; Rozelot, J. P.
Recent models of variations of the Sun's structure with the 11 year activity cycle by Sofia et al. predict strong nonhomologous changes of the radius of subsurface layers, due to subsurface magnetic fields and field-modulated turbulence. According to their best model, the changes of the surface radius may be 1000 times larger than those at the dep…
Thermal and Nonthermal Infrared Emission from M87
Egami, E.; Gordon, K. D.; Rieke, G. H. +2 more
We discuss images of M87 from 3.6 to 160 µm obtained with Spitzer. As found previously, there is an excess in the far-infrared over a simple power-law interpolation from the radio to the resolved nonthermal features in the mid-infrared and optical. We show that this excess is most likely due to warm dust in the galaxy itself and that the pro…