Search Publications
An Ionized Accretion Disk in Cygnus X-1
Done, C.; Mulchaey, J. S.; Mushotzky, R. F. +1 more
Results of an analysis of archival Exosat and HEAO 1-A2 observations of Cyg X-1 are presented. It is found, in agreement with Ebisawa (1991), that the X-ray spectrum of Cyg X-1 exhibits a 'high-energy excess' above 8 keV, similar to that seen in Ginga spectra of AGN. It is shown, on the basis of a likelihood ratio test, that the data are significa…
Correlated Hard X-Ray and Ultraviolet Variability in NGC 5548
Nandra, K.; Clavel, J.; Reichert, G. A. +7 more
We present the result of a series of contemporaneous (within one day) hard X-ray (Ginga) and ultraviolet (IUE) observations of the Seyfert 1 galaxy NGC 5548. Nine of these observations were carried out over a period of 51 days in 1990 May-July, and two in 1989. An additional simultaneous IUE-EXOSAT observation obtained on 1984 May 21 is also analy…
The Abundance of Boron in Three Halo Stars
Lambert, David L.; Lemke, Michael; Duncan, Douglas K.
B abundances for three halo stars: HD 140283, HD 19445, and HD 201891 are presented. Using recent determinations of the Be abundance in HD 140283, B/Be of 10 +5/-4 is found for this star, and similar ratios are inferred for HD 19445 and HD 201891. This ratio is equal to the minimum value of 10 expected from a synthesis of B and Be by high-energy c…
Ultraviolet Observations of the Gas Phase Abundances in the Diffuse Clouds toward zeta Ophiuchi at 3.5 Kilometers per Second Resolution
Savage, Blair D.; Sofia, Ulysses J.; Cardelli, Jason A.
Goddard High Resolution Spectrograph echelle mode measurements at 3.5 km/s resolution are presented for interstellar absorption produced by C II, O I, Mg I, Mg II, Al III, P II, Cr II, Mn II, Fe II, Ni II, Cu II, Zn II, Ga II, Ge II, and Kr I. The absorption line measurements are converted into representations of apparent column density per unit v…
Analysis of the Photospheric Epoch Spectra of Type IA Supernovae SN 1990N and SN 1991T
Kirshner, Robert P.; Leibundgut, Bruno; Sonneborn, George +3 more
An analysis of the photospheric epoch optical and UV spectra (obtained with the IUE satellite) of Type Ia supernovae SN 1990N and SN 1991T is presented. To perform the analysis, synthetic spectra calculated using an LTE radiative transfer procedure and white dwarf explosion models of Type Ia supernovae were fitted to the observations. For both sup…
A Multiwavelength Study of the Supernova Remnant N49 in the Large Magellanic Cloud
Blair, William P.; Raymond, John C.; Long, Knox S. +1 more
Using the 2.5 m du Pont telescope at Las Campanas, the International Ultraviolet Explorer satellite, and archival high-resolution imager X-ray data from the Einstein Observatory, we present a detailed imaging and spectroscopic study of the supernova remnant (SNR) N49 in the Large Magellanic Cloud. Although the X-ray and optical morphology of N49 a…
Combined Infrared and Analytical Electron Microscope Studies of Interplanetary Dust Particles
Bradley, J. P.; Humecki, H. J.; Germani, M. S.
Ultramicrotomed thin sections (less than 100 nm thick) of eight chondritic interplanetary dust particles (IDPs) were studied by analytical electron microscopy and IR microspectroscopy with the objective of identifying IDPs or their specific components with IR spectral transmission characteristics at 10 microns similar to those of comets. Two IDPs …
The Cepheid Distance to IC 4182: Calibration of M V(max) for SN IA 1937C and the Value of H 0
Saha, A.; Panagia, Nino; Sandage, Allan +2 more
Cepheid variables with periods from 2 to more than 50 days have been found in IC 4182 from observations with the Hubble Space Telescope over a time interval of 47 days, comprised of 20 epochs. The period-luminosity relation from photometry of 27 Cepheids in the F555W HST magnitude system gives an apparent V distance modulus of (m - M)_AV_ = 28.47 …
Improved Calculations for the C III lambda lambda 1907,1909 and SI III lambda lambda 1883,1892 Electron Density Sensitive Emission-Line Ratios, and a Comparison with IUE Observations
Feibelman, W. A.; Keenan, F. P.; Berrington, K. A.
Atomic data are used in conjunction with the statistical equilibrium code of Dufton (1977) to calculate relative C III and Si III level populations, and hence emission-line strengths for a range of electron temperatures and densities. It is assumed that photoexcitation and deexcitaton rates are negligible in comparison with the corresponding colli…
EXOSAT X-Ray Spectra of Quasars
Comastri, Andrea; Setti, Giancarlo; Zamorani, Giovanni +4 more
We have measured the X-ray spectra in the 0.1-10 keV energy range for 17 AGNs (mostly PG quasars) using the EXOSAT Low and Medium Energy arrays. The sample has been selected on the basis of soft X-ray flux and includes all the AGNs in the 1981 Zamorani et al. and 1986 Tananbaum et al. publications with an Einstein flux greater than 6x10^-12^ ergs …