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HD 207691


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A search for previously unrecognized metal-poor subdwarfs in the Hipparcos astrometric catalogue
We have identified 317 stars included in the Hipparcos astrometriccatalogue that have parallaxes measured to a precision of better than 15per cent, and the location of which in the(MV,(B-V)T) diagram implies a metallicitycomparable to or less than that of the intermediate-abundance globularcluster M5. We have undertaken an extensive literature search to locateStrömgren, Johnson/Cousins and Walraven photometry for over 120stars. In addition, we present new UBV(RI)C photometry of 201of these candidate halo stars, together with similar data for a further14 known metal-poor subdwarfs. These observations provide the firstextensive data set of RCIC photometry ofmetal-poor, main-sequence stars with well-determined trigonometricparallaxes. Finally, we have obtained intermediate-resolution opticalspectroscopy of 175 stars. 47 stars still lack sufficient supplementaryobservations for population classification; however, we are able toestimate abundances for 270 stars, or over 80 per cent of the sample.The overwhelming majority have near-solar abundance, with theirinclusion in the present sample stemming from errors in the colourslisted in the Hipparcos catalogue. Only 44 stars show consistentevidence of abundances below [Fe/H]=-1.0. Nine are additions to thesmall sample of metal-poor subdwarfs with accurate photometry. Weconsider briefly the implication of these results for clustermain-sequence fitting.

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Gözlemler ve gökölçümü verileri

Takýmyýldýz:Oglak
Sað Açýklýk:21h51m22.55s
Yükselim:-21°45'02.3"
Görünürdeki Parlaklýk:9.326
özdevim Sað Açýklýk:13.9
özdevim Yükselim:-34
B-T magnitude:9.879
V-T magnitude:9.372

Kataloglar ve belirtme:
Özgün isimleri   (Edit)
HD 1989HD 207691
TYCHO-2 2000TYC 6375-655-1
USNO-A2.0USNO-A2 0675-36676926
HIPHIP 107873

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