Search Publications
Newly Synthesized Elements and Pristine Dust in the Cassiopeia A Supernova Remnant
Dwek, E.; Arendt, R. G.; Moseley, S. H.
Spectroscopic observations at 2.4-45 µm of the young supernova remnant Cas A with the Infrared Space Observatory (ISO) Short Wavelength Spectrometer reveal strong emission lines of O, Ne, Si, S, and Ar. These lines are observed at high velocities (several 103 km s-1) and are therefore associated with the supernova eject…
Morphology of the Quiet Solar Upper Atmosphere in the 4×104<Te<1.4×106 K Temperature Regime
Warren, H. P.; Feldman, U.; Widing, K. G.
Studies on the morphology of the solar upper atmosphere began over three decades ago. Early models assumed that the temperature structure of the solar upper atmosphere was continuous with a thin transition region connecting the chromosphere with the corona. Over the years it became apparent that the original depiction of the solar upper atmosphere…
Seyfert 1 Mutation of the Classical Seyfert 2 Nucleus NGC 7582
Kunth, D.; Aretxaga, Itziar; Terlevich, R. J. +2 more
We report the transition toward a type 1 Seyfert experienced by the classical type 2 Seyfert nucleus in NGC 7582. The transition, found at most 20 days from its maximum peak, presents a unique opportunity to study these rare events in detail. At maximum, the Hα line width is about 12,000 km s-1. We examine three scenarios that could pot…
Water Ice, Silicate, and Polycyclic Aromatic Hydrocarbon Emission Featuresin the Infrared Space Observatory Spectrum of the Carbon-richPlanetary Nebula CPD -56°8032
Barlow, M. J.; Liu, X. -W.; Cox, P. +5 more
Combined Infrared Space Observatory Short-Wavelength Spectrometer and Long-Wavelength Spectrometer spectroscopy is presented of the late WC-type planetary nebula nucleus CPD -56°8032 and its carbon-rich nebula. The extremely broad coverage (2.4-197 µm) enables us to recognize the clear and simultaneous presence of emission features from both…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XV. A Cepheid Distance to the Fornax Cluster and Its Implications
Illingworth, Garth D.; Madore, Barry F.; Freedman, Wendy L. +13 more
Using the Hubble Space Telescope, 37 long-period Cepheid variables have been discovered in the Fornax Cluster spiral galaxy NGC 1365. The resulting V and I period-luminosity relations yield a true distance modulus of µ0=31.35+/-0.07 mag, which corresponds to a distance of 18.6+/-0.6 Mpc. This measurement provides several routes fo…
Seismic Images of a Solar Flare
Braun, D. C.; Lindsey, C.; Donea, A. -C.
We have used helioseismic holography to render seismic images of the solar flare of 1996 July 9, whose helioseismic signature was recently reported by Kosovichev & Zharkova. We computed time series of ``egression power maps'' in 2 mHz bands centered at 3.5 and 6 mHz. These images suggest an oblong acoustic source associated with the flare some…
Highly Ionized High-Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?
Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin +1 more
In the course of our studies of the gaseous halo surrounding the Milky Way, we have recently identified several high-velocity clouds (HVCs; VLSR<-100 km s-1) in the directions of Mrk 509 and PKS 2155-304 that have unusual ionization properties. The clouds exhibit strong C IV absorption with little or no detectable low ion …
The Origin of the Narrow-Line Region of Markarian 3: An Overpressured Jet Cocoon
Marconi, A.; Macchetto, F. D.; Capetti, A. +2 more
We have obtained Hubble Space Telescope (HST) Faint Object Camera (FOC) f/48 long-slit optical spectroscopy of the inner 2" of the narrow-line region (NLR) of the Seyfert 2 galaxy Mrk 3 with a spatial resolution of 0.06". Spectra were taken in six locations with the slit approximately perpendicular to the radio axis. In the region cospatial with t…
The PG X-Ray QSO Sample: Links between the Ultraviolet-X-Ray Continuum and Emission Lines
Ferland, G. J.; Wilkes, B. J.; Wills, D. +4 more
Two sets of relationships relate QSO UV to soft X-ray continua with the broad-line region. These are (i) the Baldwin relationships, which are inverse relationships between the broad-line equivalent width and the continuum luminosity, and (ii) Boroson & Green's optical ``Principal Component 1'' relationships, linking steeper soft X-ray spectra …
A Determination of H0 with the CLASS Gravitational Lens B1608+656. II. Mass Models and the Hubble Constant from Lensing
Koopmans, L. V. E.; Fassnacht, C. D.
We present mass models of the four-image gravitational lens system B1608+656, based on information obtained through VLBA imaging, VLA monitoring, and Hubble Space Telescope (HST) WFPC2 and NICMOS imaging. We have determined a mass model for the lens galaxies that reproduces (1) all image positions within the observational errors, (2) two out of th…