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NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of

Context. The Gaia satellite will measure highly accurate absolute parallaxes of hundreds of millions of stars by comparing the parallactic displacements in the two fields of view of the optical instrument. The requirements on the stability of the "basic angle" between the two fields are correspondingly strict, and possible variations (on the microarcsec level) are therefore monitored by an on-boar

The new generation of extremely large telescopes will have adaptive optics. Due to the complexity and cost of such systems, it is important to simulate their performance before construction. Most systems planned will have Shack-Hartmann wavefront sensors. Different mathematical models are available for simulation of such wavefront sensors. The choice of wavefront sensor model strongly influences c

mass close-in planets, despite the latter being exceedingly common. Two migration channels for hot Jupiters have been proposed: through a protoplanetary gas disk or by tidal circularization of highly eccentric planets. We show that highly eccentric giant planets that will become hot Jupiters clear out any low-mass inner planets in the system, explaining the observed lack of such companions to hot

Our aim is to provide as clean and as complete a sample as possible of red giant branch stars that are members of the Hercules dSph galaxy. With this sample we explore the velocity dispersion and the metallicity of the system. Stromgren photometry and multi-fibre spectroscopy are combined to provide information about the evolutionary state of the stars (via the Stromgren c_1 index) and their radia

Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope. Aims. A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (v sin i) for representative samples of Galactic stars, which will complement information obtained by the Gaia astrometry satellite. Methods. We present an analysis to e

We discuss the tracing of star formation histories with ESAs spaceastrometry mission GAIA, emphasizing the advantages of AGB stars for thepurpose. GAIAs microarcsecond-level astrometry, multi-band photometryand spectroscopy will provide individual distances, motions,T_eff, log g and [M/H for vast numbers of AGB stars in theGalaxy and beyond. Reliable ages of AGB stars can be determined t

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This paper describes a long term, high-resolution study of the activityof the Perseid meteor stream based on visual and radar observations atthe Onsala Space Observatory in Sweden. The data consists of 147 visualhourly rates and 1368 radar hourly rates. In a previous paper (Lindblad2000) a high-resolution study of the visual zenithal hourly rates ofbright Perseid meteors versus solar longitude was

We have traced the Galactic thick disk to its, to date, highest metallicities. Based on high-resolution spectroscopic observations of 187 F and G dwarf stars that kinematically can be associated either with the thin disk (60 stars) or with the thick disk (127 stars), we find that the thick disk stars reach at least solar metallicities, and maybe even higher. This finding is independent of the U_LS