Search Publications
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…
Deep Extragalactic Surveys around the Ecliptic Poles with AKARI (ASTRO-F)
Nakagawa, Takao; Shirahata, Mai; Oyabu, Shinki +26 more
AKARI (formerly ASTRO-F) is an infrared space telescope designed for an all-sky survey at 10-180 µm, and deep pointed surveys of selected areas at 2-180 µm. The deep pointed surveys with AKARI will significantly advance our understanding of galaxy evolution, the structure formation of the universe, the nature of buried AGNs, and the co…
Surface Brightness Profiles of Galactic Globular Clusters from Hubble Space Telescope Images
Gebhardt, Karl; Noyola, Eva
The Hubble Space Telescope (HST) allows us to study the central surface brightness profiles of globular clusters at unprecedented detail. We have mined the HST archives to obtain 38 WFPC2 images of Galactic globular clusters with adequate exposure times and filters, which we use to measure their central structure. We outline a reliable method to o…
A Lyman-α blob in the GOODS South field: evidence for cold accretion onto a dark matter halo
Fynbo, J. P. U.; Nilsson, K. K.; Møller, P. +2 more
We report on the discovery of a z = 3.16 Lyman-α emitting blob in the Great Observatories Origins Deep Survey (GOODS) South field. The discovery was made with the VLT, through narrow-band imaging. The blob has a total Lyα luminosity of ∼1043 erg s-1 and a diameter larger than 60 kpc. The available multi-wavelength data in the…
Constraints on the global structure of magnetic clouds: Transverse size and curvature
Liu, Y.; Wang, C.; Richardson, J. D. +3 more
We present direct evidence that magnetic clouds (MCs) have highly flattened and curved cross section resulting from their interaction with the ambient solar wind. Lower limits on the transverse size are obtained for three MCs observed by ACE and Ulysses from the latitudinal separation between the two spacecraft, ranging from 40° to 70°. The cross-…
Venus Express science planning
Barabash, S.; Pätzold, M.; Zhang, T. L. +20 more
Venus Express is the first European mission to the planet Venus. Its payload consists of seven instruments and will investigate the atmosphere, the plasma environment, and the surface of Venus from orbit. Science planning is a complex process that takes into account requests from all experiments and the operational constraints. The planning of the…
Forward Modeling of the Corona of the Sun and Solar-like Stars: From a Three-dimensional Magnetohydrodynamic Model to Synthetic Extreme-Ultraviolet Spectra
Peter, Hardi; Gudiksen, Boris V.; Nordlund, Åke
A forward model is described in which we synthesize spectra from an ab initio three-dimensional MHD simulation of an outer stellar atmosphere, where the coronal heating is based on braiding of magnetic flux due to photospheric footpoint motions. We discuss the validity of assumptions such as ionization equilibrium and investigate the applicability…
Type II Quasars from the Sloan Digital Sky Survey. V. Imaging Host Galaxies with the Hubble Space Telescope
Strauss, Michael A.; Brinkmann, J.; Schneider, Donald P. +7 more
Type II quasars are luminous active galactic nuclei (AGNs) whose centers are obscured by large amounts of gas and dust. In this paper we present three-band Hubble Space Telescope images of nine type II quasars with redshifts 0.2<z<0.4 selected from the Sloan Digital Sky Survey based on their emission-line properties. The intrinsic luminositi…
Size and properties of the narrow-line region in Seyfert-2 galaxies from spatially-resolved optical spectroscopy
Komossa, S.; Haas, M.; Chini, R. +2 more
Context: .While [O III] narrow-band imaging is commonly used to measure the size of the narrow-line regions (NLRs) in active galactic nuclei (AGNs), it can be contaminated by emission from surrounding starbursts. Recently, we have shown that long-slit spectroscopy provides a valuable alternative approach to probe the size in terms of AGN photoioni…
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…