Search Publications
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…
Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. I. Observations toward δ Orionis by the Interstellar Medium Absorption Profile Spectrograph
Tripp, Todd M.; Jenkins, Edward B.; Sofia, Ulysses J. +2 more
Studies of the abundances of deuterium in different astrophysical sites are of fundamental importance to answering the question about how much deuterium was produced during big bang nucleosynthesis and what fraction of it was destroyed later. With this in mind, we used the Interstellar Medium Absorption Profile Spectrograph (IMAPS) on the ORFEUS-S…
An Abundance Analysis for Five Red Horizontal-Branch Stars in the Extremely Metal-rich Globular Cluster NGC 6553
Cohen, Judith G.; Carretta, Eugenio; Gratton, Raffaele G. +1 more
We provide a high-dispersion line-by-line abundance analysis of five red horizontal-branch (HB) stars in the extremely metal-rich Galactic globular cluster NGC 6553. These red HB stars are significantly hotter than the very cool stars near the tip of the giant branch in such a metal-rich globular cluster, and hence their spectra are much more amen…