Search Publications
Does a Luminosity-dependent Continuum Shape Cause the Baldwin Effect?
Zheng, Wei; Malkan, Matthew A.
We combine ground- and space-based spectrophotometry to measure the luminosity dependence of the shape of the optical/UV continuum in 108 QSO and 37 Seyfert 1 nuclei. The UV continuum at 1250 Å in high-luminosity QSOs, compared with the optical continuum at 6500 Å, is over one magnitude higher than that in the less luminous Seyfert galaxies. In te…
Silicon and Carbon Abundances in the Orion Nebula
Dufour, Reginald J.; Rubin, Robert H.; Walter, Donald K.
We assess the gas-phase abundances of Si and C from our recent measurements of Si(2+), C(2+), and C(+) in the Orion Nebula by expanding on our earlier 'blister' models. The C and Si abundances are derived from new IUE high-dispersion spectra of the C(2+) 1907, 1909 A and Si(2+) 1883, 1892 A lines and archival IUE data. Gas-phase Si/C = 0.016 in th…
Doppler tracking of spacecraft with multi-frequency links
Comoretto, G.; Iess, L.; Bertotti, B.
We discuss the use of multi-frequency microwave links in Doppler tracking of interplanetary spacecraft for scientific purposes, especially in relation to the measurement and the elimination of the contribution due to the plasma in the solar wind and the ionosphere. We show how the two contributions in the up- and the down-link can be separately me…
Ejection of dust from Jupiter's gossamer ring
Hamilton, Douglas P.; Burns, Joseph A.
ONE of the most intriguing discoveries of the Ulysses mission so far has been the detection of periodic, collimated streams of high-velocity, submicrometre-sized dust particles emanating from Jupiter1,2. To explain the Ulysses data, Horanyi et al. showed3 that electromagnetic forces within Jupiter's magnetosphere can accelera…
SAO 244567 : a post-AGB star which has turned into a planetarey nebula within the last 40 years.
Pottasch, S. R.; Clavel, J.; de Martino, D. +5 more
SAO 244567 (Hen 1357 = CPD -59 deg 6926 = IRAS 17119-5926) is an IRAS source with far infrared colors and flux distribution similar to those of planetary nebulae. The IUE ultraviolet spectra obtained in July 1988 and April 1992 show nebular emission lines, and also the changes in the spectra suggest the formation of the planetary nebula and the ra…
Lyman-alpha emission in spectra of Herbig AE stars. an indication of accretion ?
Talavera, A.; Blondel, P. F. C.; Djie, H. R. E. T. A.
Lyman-alpha emission lines have been detected in the IUE spectra of several Herbig Ae stars, but not in those of Herbig Be stars. The shapes and positions of these lines are not consistent with those expected from a chromosphere and transition region (TR), which may be the origin of the other FUV emission lines in the spectra of these stars. The c…
High resolution UV stellar spectroscopy with the HST/GHRS, challenges and opportunities for atomic physics.
Leckrone, D. S.; Wahlgren, G. M.; Johansson, S. +1 more
The Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) is producing ultraviolet spectra of unprecedented resolution and photometric quality. The authors illustrate this with observations of the ultra-sharp-lined, chemically peculiar B-type star, χ Lupi. The photosphere of this star is rich in heavy elements, and its UV…
Discovery of an Optical Synchrotron Jet in 3C 264
Boksenberg, A.; Barbieri, C.; Weigelt, G. +17 more
Observations with the Faint Object Camera on board the Hubble Space Telescope have revealed a new optical jet in the core of the elliptical galaxy NGC 3862 (3C 264). Morphologically, this jet is similar to the synchrotron jets seen in other galaxies, as it shows knots and bifurcations. The optical spectral index [-d log I(v)/d log v = α = 1.4] is …
The Quasi-periodic Oscillations and Very Low Frequency Noise of Scorpius X-1 as Transient Chaos: A Dripping Handrail?
Scargle, Jeffrey D.; Steiman-Cameron, Thomas; Young, Karl +3 more
We present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process. We analyzed a long, high time resolution EXOSAT observation of the low-mass X-ray binary (LMXB) Sco X-1. The X-ray luminosity varies stochastically on time s…
GINGA Observations of the Coma Cluster and Studies of the Spatial Distribution of Iron
Hughes, John P.; Tanaka, Yasuo; Butcher, Jackie A. +1 more
The large area counters on the Japanese satellite Ginga have been used to determine the X-ray spectrum from the central region of the Coma cluster of galaxies over the energy range from 1.5 to 20 keV. The spectrum is well represented by an isothermal model of temperature 8.21+/-0.16 keV and a heavy element (iron) abundance of 0.212+/-0.027 relativ…