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HD 157321


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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 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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Gözlemler ve gökölçümü verileri

Takýmyýldýz:Sunak
Sað Açýklýk:17h27m19.05s
Yükselim:-65°00'07.5"
Görünürdeki Parlaklýk:8.024
Uzaklýk:181.488 parsek
özdevim Sað Açýklýk:4
özdevim Yükselim:-4.7
B-T magnitude:8.413
V-T magnitude:8.057

Kataloglar ve belirtme:
Özgün isimleri   (Edit)
HD 1989HD 157321
TYCHO-2 2000TYC 9061-207-1
USNO-A2.0USNO-A2 0225-27655205
HIPHIP 85420

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