Search Publications
Determining Central Black Hole Masses in Distant Active Galaxies and Quasars. II. Improved Optical and UV Scaling Relationships
Peterson, Bradley M.; Vestergaard, Marianne
We present four improved empirical relationships useful for estimating the central black hole mass in nearby AGNs and distant luminous quasars alike using either optical or UV single-epoch spectroscopy. These mass scaling relationships between line widths and luminosity are based on recently improved empirical relationships between the broad-line …
The surprising magnetic topology of τ Sco: fossil remnant or dynamo output?
Bouret, J. -C.; Donati, J. -F.; Howarth, I. D. +9 more
We report the discovery of a medium-strength (~0.5 kG) magnetic field on the young, massive star τ Sco (B0.2V), which becomes the third-hottest magnetic star known. Circularly polarized Zeeman signatures are clearly detected in observations collected mostly with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m Canada-France-Hawaii …
Damped Lyα Systems at z<1.65: The Expanded Sloan Digital Sky Survey Hubble Space Telescope Sample
Turnshek, David A.; Rao, Sandhya M.; Nestor, Daniel B.
We present results of our Hubble Space Telescope Cycle 11 survey for low-redshift (z<1.65) damped Lyα (DLA) systems in the UV spectra of quasars selected from the Sloan Digital Sky Survey (SDSS) Early Data Release. These quasars have strong intervening Mg II-Fe II systems that are known signatures of high column density neutral gas. In total, i…
The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
Hamann, W. -R.; Gräfener, G.; Liermann, A.
Context: .Very massive stars pass through the Wolf-Rayet (WR) stage before they finally explode. Details of their evolution have not yet been safely established, and their physics are not well understood. Their spectral analysis requires adequate model atmospheres, which have been developed step by step during the past decades and account in their…
Physical parameters and wind properties of galactic early B supergiants
Crowther, P. A.; Lennon, D. J.; Walborn, N. R.
We present optical studies of the physical and wind properties, plus CNO chemical abundances, of 25 O9.5-B3 Galactic supergiants. We employ non-LTE, line blanketed, extended model atmospheres, which provide a modest downward revision in the effective temperature scale of early B supergiants of up to 1-2 kK relative to previous non-blanketed result…
Keplerian discs around post-AGB stars: a common phenomenon?
Waters, L. B. F. M.; Dejonghe, H.; de Ruyter, S. +3 more
Aims.We aim at showing that the broad-band SED characteristics of our sample of post-AGB stars are best interpreted, assuming the circumstellar dust is stored in Keplerian rotating passive discs.Methods.We present a homogeneous and systematic study of the Spectral Energy Distributions (SEDs) of a sample of 51 post-AGB objects. The selection criter…
First detection of Lyman continuum escape from a local starburst galaxy. I. Observations of the luminous blue compact galaxy Haro 11 with the Far Ultraviolet Spectroscopic Explorer (FUSE)
Östlin, G.; Zackrisson, E.; Bergvall, N. +3 more
Context: .The dominating reionization source in the young universe has not yet been identified. Possible candidates include metal poor dwarf galaxies with starburst properties.Aims.We selected an extreme starburst dwarf, the Blue Compact Galaxy Haro 11, with the aim of determining the Lyman continuum escape fraction from UV spectroscopy.Methods.Sp…
Reduced Wolf-Rayet line luminosities at low metallicity
Crowther, P. A.; Hadfield, L. J.
New NTT/EMMI spectrophotometry of single WN2-5 stars in the Small and Large Magellanic Clouds are presented, from which He ii λ4686 line luminosities have been derived, and compared with observations of other Magellanic Cloud Wolf-Rayet stars. SMC WN3-4 stars possess line luminosities which are a factor of 4 times lower than LMC counterparts, inco…
Quantitative spectroscopy of BA-type supergiants
Butler, K.; Kudritzki, R. P.; Przybilla, N. +1 more
Luminous BA-type supergiants have enormous potential for modern astrophysics. They allow topics ranging from non-LTE physics and the evolution of massive stars to the chemical evolution of galaxies and cosmology to be addressed. A hybrid non-LTE technique for the quantitative spectroscopy of these stars is discussed. Thorough tests and first appli…
Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks around Sun-like Stars
Wolf, S.; Pascucci, I.; Carpenter, J. M. +17 more
We have carried out a sensitive search for gas emission lines at IR and millimeter wavelengths for a sample of 15 young Sun-like stars selected from our dust disk survey with Spitzer. We have used mid-IR lines to trace the warm (300-100 K) gas in the inner disk and millimeter transitions of 12CO to probe the cold (~20 K) outer disk. We …