Search Publications
HST study of Lyman-alpha emission in star-forming galaxies: the effect of neutral gas flows
Mas-Hesse, J. M.; Terlevich, E.; Terlevich, R. +3 more
We present high dispersion HST GHRS UV spectroscopic observations of 8 H II galaxies covering a wide range of metallicities and physical properties. We have found Lyalpha \ emission in 4 galaxies with blueshifted absorption features, leading to P Cygni like profiles in 3 of them. In all these objects the O I and Si II absorption lines are also blu…
The Ultraviolet Spectroscopic Properties of Local Starbursts: Implications at High Redshift
Robert, Carmelle; Heckman, Timothy M.; Leitherer, Claus +2 more
We report the results of a systematic study of the vacuum ultraviolet (λ ~= 1150-2000 Å) spectra of a sample of 45 starburst and related galaxies observed with the IUE satellite. These span broad ranges in metallicity (from 0.02 to 3 times solar), bolometric luminosity (~107-4 × 1011 L⊙), and galaxy properties (e.g…
An ultraviolet, optical and infrared study of Herbig Ae/Be stars
Waelkens, C.; Malfait, K.; Bogaert, E.
We have selected a list of 45 Herbig Ae/Be-type candidates on the base of their IRAS colors and their spectral types. We propose the presence of a broad infrared excess as a defining criterion for these stars, rather than the detection of circumstellar nebulosity. In this way, our selection also includes more evolved young stars, that are no longe…
Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279
Maraschi, L.; Ghisellini, G.; Pian, E. +69 more
The blazar 3C 279, one of the brightest identified extragalactic objects in the γ-ray sky, underwent a large (factor of ~10 in amplitude) flare in γ-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 January-February. The flare peak represents the highest γ-ray intensity ever recorded for this object. During …
Starburst-like Dust Extinction in the Small Magellanic Cloud
Gordon, Karl D.; Clayton, Geoffrey C.
The recent discovery that the ultraviolet (UV) dust extinction in starburst galaxies is similar to that found in the Small Magellanic Cloud (SMC) motivated us to reinvestigate the UV extinction found in the SMC. We have been able to improve significantly on previous studies by carefully choosing pairs of well-matched reddened and unreddened stars.…
A spectral decomposition of the variable optical, ultraviolet and X-ray continuum of NGC 5548
Zdziarski, Andrzej A.; Smith, David A.; Johnson, W. Neil +2 more
We present an analysis and decomposition of the broad-band optical/UV/X-ray/gamma-ray spectrum of the Seyfert 1 galaxy NGC 5548. The spectrum consists of an average of simultaneous optical/IUE/Ginga observations accompanied by ROSATCGRO/OSSE data from non-simultaneous observations. We show that the overall optical/UV/X-ray/gamma-ray spectrum can b…
Classical monopoles: Newton, NUT space, gravomagnetic lensing, and atomic spectra
Lynden-Bell, D.; Nouri-Zonoz, M.
This article reviews the dynamics and observational signatures of particles interacting with monopoles, beginning with a scholium in Newton'sPrincipia. The orbits of particles in the field of a gravomagnetic monopole, the gravitational analog of a magnetic monopole, lie on cones; when the cones are slit open and flattened, the orbits are the ellip…
Quantitative spectroscopy of Wolf-Rayet stars in HD97950 and R136a - the cores of giant HII regions
Crowther, P. A.; Dessart, Luc
We present quantitative analyses of Wolf-Rayet stars in the cores of two giant Hii regions - HD97950 in NGC3603 and R136a in 30 Doradus - based on archive Hubble Space Telescope (HST) spectroscopy. We confirm previous WN6h+abs classifications for components A1, B and C in HD97950, while classifications for R136a1-3 are revised from O3If^*/WN6 to W…
The EC 14026 stars - VIII. PG 1336-018: a pulsating sdB star in an HWVir-type eclipsing binary
O'Donoghue, D.; Kilkenny, D.; Lynas-Gray, A. E. +2 more
The sdB star PG 1336-018 is found to be a very short-period eclipsing binary system, remarkably similar to the previously unique system HW Vir. In addition, and unlike HW Vir, the sdB star in the PG 1336 system shows rapid oscillations of the type found in the recently discovered sdB pulsators, or EC 14026 stars. The orbital period, 0.101 0174 d, …
Spectral analyses of PG 1159 star: constraints on the GW Virginis pulsations from HST observations
Dreizler, S.; Heber, U.
We present the results of a quantitative analysis of UV and optical spectra of nine PG 0122+200ls, very hot hydrogen-deficient [pre-] white dwarfs, by means of line blanketed NLTE model atmospheres. Four programme stars constitute the GW Vir variables, a class of non-radial g-mode pulsators. Precise effective temperatures, carbon, nitrogen and oxy…