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We present a new method, using Bayesian estimation, to determine stellar ages and their uncertainties from observational data and theoretical isochrones. The result for an individual star is obtained as the relative posterior probability density as function of the age ("G function"). From this can be derived the most probable age and confidence intervals. The convoluted morphology of isochrones an
Aims. To investigate the astrometric effects of stellar surface structures as a practical limitation to ultra-high-precision astrometry (e.g. in the context of exoplanet searches) and to quantify the expected effects in different regions of the HR-diagram. Methods. Stellar surface structures (spots, plages, granulation, non-radial oscillations) are likely to produce fluctuations in the integrated
We present time-resolved optical spectrophotometry of the pulsatinghydrogen atmosphere (DA) white dwarf G 117-B15A. We find threeperiodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all ofwhich have been found in earlier studies. By comparing the fractionalwavelength dependence of the pulsation amplitudes (chromatic amplitudes)with models, we confirm a previous report that the stronge
We present the first ultraviolet and optical images of η Car and itscircumstellar Homunculus nebula, obtained with the Advanced Camera forSurveys/High Resolution Camera (ACS/HRC) on board the Hubble SpaceTelescope (HST). Compared to those at visual wavelengths, UV imagesreveal excess emission 0.1"-0.6" from the central source along the minoraxis that may emanate from the outer parts of η Car's non
The exceptionally high luminosities of gamma-ray bursts (GRBs), gradually emerging as extremely useful probes of star formation, make them promising tools for exploration of the high-redshift Universe. Here we present a carefully selected sample of Swift GRBs, intended to estimate in an unbiased way the GRB mean redshift (z(mean)), constraints on the fraction of high-redshift bursts and an upper l
We report abundance excesses of 1.2 and 2.6 dex, respectively, for vanadium and bromine in the hot, peculiar star 3 Cen A. Abundances for these two odd-Z elements have not been previously reported for this star. Taken with previous work, they strengthen the case of the origin of the abundance peculiarities by diffusion.
In this article we present a downscaled laboratory setup emulating five natural guide stars, a layered static atmosphere and a 7.5-m aperture telescope equipped with dual-conjugate adaptive optics at a wavelength of 2.2 mum. Three reconstruction alternatives were evaluated; conventional adaptive optics, field-averaged conventional adaptive optics and dual-conjugate adaptive optics. The results wer
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
We determine the properties of the binary star V106 in the old open cluster NGC6791. We identify the system to be a blue straggler cluster member by using a combination of groundbased and Kepler photometry and multi-epoch spectroscopy. The properties of the primary component are found to be Mp ~ 1.67M⊙, more massive than the cluster turn-off, with Rp ~ 1.91R⊙ and Teff = 7110 ± 100 K. The secondary
Context. Aims. The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Mage
We consider the origin of the anomalously high intensity of theultraviolet Fe II lambda 2507/2509 A lines observed with high spatialand spectral resolutions from gas blobs (GBs) near Carinae. This rareeffect in stellar spectra is attributable to a combination of severalfactors: (1) the high hydrogen density (>10^{8} cm^{-3}) that ensuresthe blocking of the Lyman continuum by GBs and, accordingly,
The European Gaia astrometry mission is due for launch in 2011. Gaia will rely on the proven principles of the ESA Hipparcos mission to create an all-sky survey of about one billion stars throughout our Galaxy and beyond, by observing all objects down to 20 mag. Through its massive measurement of stellar distances, motions and multicolour photometry, it will provide fundamental data necessary for
Visual observations of Perseid meteors carried out in 1953-83 at the Onsala Space Observatory are analyzed to study the fine structure of the Perseid meteor stream maximum. Observed hourly rates are corrected for weather conditions and to a zenithal value. The Perseid activity curve is studied (1) for all observed Perseids, (2) for Perseids of app. magnitude 2.0 or brighter. The activity curve for
We investigate the observed depletion of red giants in the cores ofpost-core-collapse globular clusters. In particular, the evolutionaryscenario we consider is a binary consisting of two low-mass stars whichundergoes two common-envelope phases. The first common-envelope phaseoccurs when the primary is a red giant resulting in a helium white dwarfand main-sequence star in a detached binary. The sec
We present deep Hubble Space Telescope ACS observations of the G1 clump, a distinct stellar overdensity lying at similar to 30 kpc along the southwestern major axis of M31, close to the G1 globular cluster ( from the work of Ferguson and coworkers). Our well-populated color-magnitude diagram reaches similar to 7 mag below the red giant branch tip with 90% completeness, and allows the detection of
Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD)simulations of time-dependent compressible convection, we have studiedthe dynamics and thermal structure of the convective surface layers of aprototypical late-type M-dwarf (Teffapprox 2800 K, log g=5.0,solar chemical composition). The RHD models predict stellar granulationqualitatively similar to the familiar solar patt
We present a detailed analysis of time-resolved optical spectra of the ZZ Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed mode amplitudes, we deduce the spherical degree, , of the modes, most of which have . The presence of a large number of combination frequencies (linear sums or differences of the real modes) enabled us not only to test theoretical predictions but al
