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New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The domain of γ Doradus variables in the Hertzsprung-Russell diagram
70 new γ Doradus candidates were identified from Hipparcosphotometry, which represents more than a doubling of the presently knownnumber. Selecting the objects with good evidence for multiperiodicity,it is found that these stars, together with bona fide members of theclass, occupy a well-defined region in a colour-magnitude diagram. Thisdomain corresponds to a range of 7200-7700K on the zero-age mainsequence (ZAMS) and 6900-7500K one magnitude above it, which partlyoverlaps with the instability strip of δ Scuti stars. For thefirst time, γ Doradus stars can be discussed as a group. They canbe found over a significant fraction of the main sequence lifetimes forobjects in the relevant temperature range. An upper limit on the surfacemetallicity of γ Doradus stars is apparent, which may guide thesearch for their pulsation driving mechanism. The importance of possibleobjects exhibiting both γ Doradus and δ Scuti-typepulsations is discussed.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Interstellar reddening in the Southern Hemisphere. I - The UVBY beta observations
The uvby-beta photometric data obtained from a Southern Hemisphereobservational project is presented. A uvby-beta photometric network ofnearly 3900 A and early F stars has been established with the intentthat the stars serve as 'space probes' for measurements of interstellarreddening.
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
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