Search Publications
Atlas of Quasar Energy Distributions
Elvis, Martin; Wilkes, Belinda J.; McDowell, Jonathan C. +6 more
We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, an…
Dust Extinction of the Stellar Continua in Starburst Galaxies: The Ultraviolet and Optical Extinction Law
Calzetti, Daniela; Storchi-Bergmann, Thaisa; Kinney, Anne L.
We analyze the IUE UV and the optical spectra of 39 starburst and blue compact galaxies in order to study the average properties of dust extinction in extended regions of galaxies. The optical spectra have been obtained using an aperture which matches that of IUE, so comparable regions within each galaxy are sampled. The data from the 39 galaxies …
The Center of the Core-Cusp Globular Cluster M15: CFHT and HST Observations, ALLFRAME Reductions
Stetson, Peter B.
The central brightness cusps seen in some globular clusters are thought to be the relics of a gravothermal core collapse that occurred in the clusters' past. Recent observations show that the centers of such clusters are bluer than their outskirts, indicating that the stellar populations there are somehow different than those farther out, presumab…
R v-dependent Optical and Near-Ultraviolet Extinction
O'Donnell, James E.
We have derived extinctions A(lambda)/A(V) at the wavelengths of the uvby filters for 22 stars, with a range of values of Rnu, from the sample of Cardelli, Clayton, & Mathis (1989, hereafter CCM). We have fit these extinctions, and also UBVRIJHKL, IUE and ANS extinction measurements, with linear relations A(lambda)/A/(V) = a+b/R
The Hubble Space Telescope Extragalactic Distance Scale Key Project. I. The Discovery of Cepheids and a New Distance to M81
Illingworth, Garth D.; Kennicutt, Robert C.; Madore, Barry F. +12 more
We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I m…
Elemental abundances for a sample of southern galactic planetary nebulae.
Barlow, M. J.; Kingsburgh, R. L.
We present spectrophotometric observations of a sample of 80 southern galactic planetary nebulae (PN), and derive elemental abundances for 68 objects, supplementing the optical observations with Uv data in 25 cases. We define Type I PN as those objects that have experienced envelope-burning conversion to nitrogen of dredged- up primary carbon. Suc…
Detection of a γ-ray burst of very long duration and very high energy
Cline, T.; Hurley, K.; Fishman, G. J. +24 more
ALTHOUGH γ-ray bursts (GRBs) have been known for more than 20 years, their origin remains mysterious1. Suggestions have ranged from nearby colliding comets2 to merging neutron stars at cosmological distances3. The lack of any counterpart at wavelengths other than X-rays and γ-rays has posed a major problem in ident…
Distance to the Virgo cluster galaxy M100 from Hubble Space Telescope observations of Cepheids
Illingworth, Garth D.; Kennicutt, Robert C.; Madore, Barry F. +11 more
Accurate distances to galaxies are critical for determining the present expansion rate of the Universe or Hubble constant (H0). An important step in resolving the current uncertainty in H0 is the measurement of the distance to the Virgo cluster of galaxies. New observations using the Hubble Space Telescope yield a distance of…
Thick tori around active galactic nuclei: a comparison of model predictions with observations of the infrared continuum and silicate features.
Danese, L.; Granato, G. L.
The continuum expected from active galactic nuclei (AGN) surrounded by thick tori is compared to the data available for a sample of optically selected Seyfert 1 galaxies. The optical and near-IR nuclear fluxes have previously been derived for these objects, and hence the spectral energy distributions (SEDs) of their active nuclei can be analysed. …
HST FOS Spectroscopy of M87: Evidence for a Disk of Ionized Gas around a Massive Black Hole
Kriss, Gerard A.; Hartig, George F.; Ford, Holland C. +7 more
Using the Faint Object Spectrograph on the Hubble Space Telescope (HST) to observe the central region of M87, we have obtained spectra covering ~4600-6800 A at a spectral dispersion ~4.4 A per resolution element through the 0.26" diameter entrance aperture. One spectrum was obtained centered on the nucleus of M87 and two centered 0.25" off the nuc…