Spectroscopy of the roAp star Alpha-Cir -- II. The bisector and equivalent-width of the H-alpha line

We present bisector measurements of the H-alpha line of the rapidly oscillating Ap (roAp) star, Alpha-Cir, obtained from dual-site observations with medium-dispersion spectrographs. The velocity amplitude and phase of the principal pulsation mode vary significantly, depending on the height in the H-alpha line, including a phase reversal between the core and the wings of the line. This supports the theory, suggested in Paper I, of a radial pulsational node in the atmosphere of the star. Blending with metal lines partially affects the H-alpha bisector results but probably not enough to explain the phase reversal. We have also detected changes in the equivalent-width of the line during the pulsation, and measured the oscillatory signal as a function of wavelength across the H-alpha region.Comment: 13 pages, 14 figures, accepted by MNRA

New Variable Stars in Open Clusters I: Methods and Results for 20 Open Clusters

We present high precision CCD photometry of 1791 objects in 20 open clusters with an age from 10 Myr to 1 Gyr. These observations were performed within the Delta a photometric system which is primarily used to detect chemically peculiar stars of the upper main sequence. Time bases range between 30 minutes and up to 60 days with data from several nights. We describe the way of time series analysis reaching a detection limit of down to 0.006 mag. In total, we have detected 35 variable objects from which four are not members of their corresponding clusters. The variables cover the entire Hertzsprung-Russell-diagram, hence they are interesting targets for follow-up observations.Comment: 4 pages, 2 figures, accepted by A&

Asteroseismology and Interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within Astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume 14, Issue 3-4, pp. 217-36

Stellar Structure and Evolution: Deductions from Hipparcos

During the last decade, the understanding of fine features of the structure and evolution of stars has become possible as a result of enormous progress made in the acquisition of high-quality observational and experimental data and of new developments and refinements in the theoretical description of stellar plasmas. The confrontation of high-quality observations with sophisticated stellar models has allowed many aspects of the theory to be validated, and several characteristics of stars relevant to Galactic evolution and cosmology to be inferred. This paper is a review of the results of recent studies undertaken in the context of the Hipparcos mission, taking benefit of the high-quality astrometric data it has provided. Successes are discussed, as well as the problems that have arisen and suggestions proposed to solve them. Future observational and theoretical developments expected and required in the field are also presented.Comment: 56 pages, including 9 figures, Ann. Rev. Astron. Astrophys. Vol. 38, September 2000 (in press

Kriminalitet i en population af patienter med sår i tolvfingertarm og mavesæk og med pseudo-ulcus

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