Search Publications
ISO Far-IR spectroscopy of IR-bright galaxies and ULIRGs
Malkan, M. A.; Spinoglio, L.; Lord, S. D. +16 more
Based on far-infrared spectroscopy of a small sample of nearbyinfrared-bright and ultraluminous infrared galaxies (ULIRGs) with theISO Long Wavelength Spectrometer we find adramatic progression in ionic/atomic fine-structure emission line andmolecular/atomic absorption line characteristics in these galaxiesextending from strong [O III]52,88 µ…
Hubble Space Telescope Observations of the Host Galaxies of BL Lacertae Objects
Giavalisco, Mauro; Urry, C. Megan; Scarpa, Riccardo +3 more
Six BL Lac objects from the complete 1 Jy radio-selected sample of 34 objects were observed in cycle 5 with the Hubble Space Telescope (HST) Wide-Field Planetary Camera 2 (WFPC2) to an equivalent limiting flux of µI~26 mag arcsec-2. Here we report results for the second half of this sample, as well as new results for th…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XX. The Discovery of Cepheids in the Virgo Cluster Galaxy NGC 4548
Kelson, Daniel D.; Illingworth, Garth D.; Madore, Barry F. +19 more
We report on the discovery and properties of Cepheid variable stars in the barred spiral galaxy NGC 4548, which is a member of the Virgo cluster of galaxies. This is one of the galaxies being observed as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale, which aims to determine the Hubble constant to 10% accu…
Thermal-infrared imaging of 3C radio galaxies at z~1
Simpson, Chris; Rawlings, Steve; Lacy, Mark
We present the results of a programme of thermal-infrared imaging of 19 z ~ 1 radio galaxies from the 3CR and 3CRR (LRL) samples. We detect emission at L' (3.8 µm) from four objects; in each case the emission is unresolved at 1-arcsec resolution. 15 radio galaxies remain undetected to sensitive limits of L' ~ 15.5. Using these data in tandem…
Analysis of ultraviolet and extreme-ultraviolet spectra of the DA white dwarf G 191-B2B using self-consistent diffusion models
Dreizler, S.; Wolff, B.
We present a multi-wavelength spectral analysis of the DA white dwarf G 191-B2B. The employed atmospheric models account for gravitational settling and radiative levitation, which are, for the first time, calculated self-consistently with the atmospheric structure. The resulting spectra can reproduce the complete EUVE spectrum and the ultraviolet …
Morphology and Composition of the Helix Nebula
Dufour, R. J.; Henry, R. B. C.; Kwitter, K. B.
We present new narrowband filter imagery in Hα and [N II] λ6584, along with UV and optical spectrophotometry measurements from 1200 to 9600 Å of NGC 7293, the Helix Nebula, a nearby, photogenic planetary nebula of large diameter and low surface brightness. Detailed models of the observable ionized nebula support the recent claim that the Helix is …
Post-Perihelion HST Observations of Comet Hale-Bopp (C/1995 O1)
Stern, S. A.; Feldman, P. D.; A'Hearn, M. F. +3 more
Post-perihelion observations of Comet Hale-Bopp (C/1995 O1) were made with the Hubble Space Telescope (HST) on 27 August 1997 (r=2.48 AU; Δ=2.99 AU), 11 November 1997 (r=3.38 AU; Δ=3.31 AU), and 19 February 1998 (r=4.44 AU; Δ=4.40 AU) using the newly installed Space Telescope Imaging Spectrograph (STIS). The STIS CCD was used to image the comet, a…
Astrometric and space-geodetic observations of polar wander
Vondrák, Jan; Gross, Richard S.
Optical astrometric measurements of star positions taken during the past century have been recently re-reduced using the final Hipparcos star catalog in order to determine variations in the mean location of the Earth's rotation pole with respect to the Earth's crust. This newly available polar motion series, which is the longest homogeneous polar …
A Semiempirical Model of the Infrared Universe
Tan, Jonathan C.; Silk, Joe; Balland, Christophe
We present a simple model of the infrared universe, based as much as possible on local observations. We model the luminosity and number evolution of disk and starburst galaxies, including the effects of dust, gas, and spectral evolution. Although simple, our approach is able to reproduce observations of galaxy number counts and the infrared and su…
Wolf-Rayet nebulae as tracers of stellar ionizing fluxes. I. M1-67
Schmutz, W.; Hillier, D. J.; de Koter, A. +3 more
We use WR124 (WN8h) and its associated nebula M1-67, to test theoretical non-LTE models for Wolf-Rayet (WR) stars. Lyman continuum ionizing flux distributions derived from a stellar analysis of WR124, are compared with nebular properties via photo-ionization modelling. Our study demonstrates the significant role that line blanketing plays in affec…