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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.
| Mining the Metal-rich Stars for Planets
We examine the correlation between stellar metallicity and the presenceof short-period planets. It appears that approximately 1% of dwarf starsin the solar neighborhood harbor short-period planets characterized bynear-circular orbits and orbital periods P<20 days. However, amongthe most metal-rich stars (defined as having [Fe/H]>0.2 dex), itappears that the fraction increases to 10%. Using the Hipparcos databaseand the Hauck & Mermilliod compilation of Strömgren uvbyphotometry, we identify a sample of 206 metal-rich stars of spectraltype K, G and F which have an enhanced probability of harboringshort-period planets. Many of these stars would be excellent candidatesfor addition to radial velocity surveys. We have searched the Hipparcosepoch photometry for transiting planets within our 206 star catalog. Wefind that the quality of the Hipparcos data is not high enough to permitunambiguous transit detections. It is, however, possible to identifycandidate transit periods. We then discuss various ramifications of thestellar metallicity-planet connection. First, we show that there ispreliminary evidence for increasing metallicity with increasing stellarmass among known planet-bearing stars. This trend can be explained by ascenario in which planet-bearing stars accrete an average of 30M⊕ of rocky material after the gaseous protoplanetarydisk phase has ended. We present dynamical calculations which suggestthat a survey of metallicities of spectroscopic binary stars can be usedto understand the root cause of the stellar metallicity-planetconnection.
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