Search Publications
The Diversity of High- and Intermediate-Velocity Clouds: Complex C versus IV Arch
Richter, Philipp; Tripp, Todd M.; Jenkins, Edward B. +5 more
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS) observations of interstellar ultraviolet absorption lines in the Galactic high-velocity cloud Complex C and the Intermediate-Velocity Arch (IV Arch) in the direction of the quasar PG 1259+593 (l=120.6d, b=+58.1d). Absorption lines from C II, N …
Hemispheric Helicity Trend for Solar Cycle 23
Pevtsov, Alexei A.; Canfield, Richard C.; Latushko, Sergei M.
Applying the same methods we used in solar cycle 22, we study active region vector magnetograms, full-disk X-ray images, and full-disk line-of-sight magnetograms to derive the helicity of solar magnetic fields in the first 4 years of solar cycle 23. We find that these three data sets all exhibit the same two key tendencies-significant scatter and …
The Variable Diffuse Continuum Emission of Broad-Line Clouds
Goad, Michael R.; Korista, Kirk T.
We investigate the wavelength-dependent intensity and reverberation properties of the UV-optical diffuse continuum emission expected from broad emission line gas. The ``locally optimally emitting clouds'' picture is adopted, with the cloud distribution functions in gas density and distance from the ionizing source determined by a fit to the mean U…
The Importance of Einstein Rings
Keeton, C. R.; Kochanek, C. S.; McLeod, B. A.
We develop a theory of Einstein rings and demonstrate it using the infrared Einstein ring images of the quasar host galaxies observed in PG 1115+080, B1608+656, and B1938+666. The shape of an Einstein ring accurately and independently determines the shape of the lens potential and the shape of the lensed host galaxy. We find that the host galaxies…
Broadband Observations of the Afterglow of GRB 000926: Observing the Effect of Inverse Compton Scattering
Piro, L.; Frontera, F.; Price, P. A. +23 more
GRB 000926 has one of the best-studied afterglows to date, with multiple X-ray observations, as well as extensive multifrequency optical and radio coverage. Broadband afterglow observations, spanning from X-ray to radio frequencies, provide a probe of the density structure of the circumburst medium, as well as of the ejecta energetics, geometry, a…
Deriving the Electron Density of the Solar Corona from the Inversion of Total Brightness Measurements
Howard, R. A.; Vourlidas, A.; Hayes, A. P.
Usually, the electron density structure of the white-light solar corona is estimated from the inversion of polarized brightness measurements. The inversion technique was developed in the 1950s and has remained largely unchanged since. Here, for the first time, we expand this technique to total brightness observations to take advantage of the exten…
Supermassive Black Holes in Bulges
Filippenko, Alexei V.; Ho, Luis C.; Shields, Joseph C. +5 more
We present spatially extended gas kinematics at parsec-scale resolution for the nuclear regions of four nearby disk galaxies and model them as rotation of a gas disk in the joint potential of the stellar bulge and a putative central black hole. The targets were selected from a larger set of long-slit spectra obtained with the Hubble Space Telescop…
Star Formation in the Field and Clusters of NGC 5253
Heckman, Timothy M.; Calzetti, Daniela; Leitherer, Claus +1 more
We investigate the star formation history of both the bright star clusters and the diffuse ``field star'' population in the dwarf starburst galaxy NGC 5253 using long-slit ultraviolet spectroscopy obtained with the Space Telescope Imaging Spectrograph. The slit covers a physical area of 370 pc×1.6 pc and includes eight apparent clusters and severa…
Structure of the X-Ray Emission from the Jet of 3C 273
Murray, S. S.; Mathur, S.; Drake, J. J. +12 more
We present images from five observations of the quasar 3C 273 with the Chandra X-Ray Observatory. The jet has at least four distinct features that are not resolved in previous observations. The first knot in the jet (A1) is very bright in X-rays. Its X-ray spectrum is well fitted with a power law with α=0.60+/-0.05 (where Sν~ν-α
The Distance to the Vela Pulsar Gauged with Hubble Space Telescope Parallax Observations
Caraveo, P. A.; Bignami, G. F.; De Luca, A. +1 more
The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed to be 500 pc. Although affected by a significant uncertainty, this value stuck to both the pulsar and the supernova remnant. In an effort to obtain a model-free distance measurement, we have applied high-resolution astrometry to the pulsar V~23.6 optical counterpart. Usi…