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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.
| Astrometric and astrophysical discontinuities between the galactic old disk and halo stellar populations
Intermediate band, RI, and DDO photometry of the weak-lined stars in thefirst three volumes of the Michigan catalogs of spectral type arediscussed on the basis of luminosity and heavy element abundance. Theinterface between the old disk (Fe/H greater than -0.8 dex) and halo(Fe/H less than -1.2 dex) populations represents discontinuities in boththe stellar motions and the stellar physics. The CN strengths of bothevolved and unevolved halo stars decrease with decreasing temperature,in a mirror image of the increase with decreasing temperature for thedisk objects. The result for the halo giants has been attributed to deepmixing in the stellar atmospheres but the similar result for unevolveddwarfs indicates a difference in formation rather than in evolutionaryprocess of the two populations.
| Population studies. I - The Bidelman-MacConnell 'weak-metal' stars
BRVI and DDO photometry are presented for 309 Bidelman-MacConnell'weak-metal' stars. Radial velocities are calculated for most of thestars having Fe/H abundances of no more than -0.8. The photometricobservations were carried out using the 0.6-meter and 1.0-metertelescopes of the Siding Spring Observatory. Photometric taxonomy wasused to classify the stars as dwarfs, giants, red-horizontal branchstars, and ultraviolet-bright stars, respectively. It is found that 35percent of the stars are giants; 50 percent are dwarfs; and 5 percentbelong to the red-horizontal branch group. The role of selection effectsin investigations of the formation of the Galaxy is discussed on thebasis of the photometric observations and the observational constraintsproposed by Eggen et al. (1962).
| Weak-lined stars in the Michigan spectral survey. I - A-, F-, and G-type stars
Data from intermediate-band and H-beta photometric observations of 89early-type stars classified as weak-lined by Bidelman and MacConnell(1973), Houk and Cowley (1975), or Houk (1978 and 1982) are presented intables and graphs and analyzed. The group is found to comprise 55 diskstars and 34 halo stars (Fe/H less than -0.65), including 21 near themain-sequence turnoff, seven red horizontal-branch stars, one bluehorizontal-branch star, one suprahorizontal-branch object, and four bluestragglers; five of the newly identified halo stars are shown to haveradial velocities in excess of 100 km/s. Special consideration is givento the 17 early-type members of Kapetyn's star group (Eggen, 1977), andthe mean luminosity and Fe/H ratio of the four very-short-periodCepheids of this group are determined as 0.75 mag and -1.7.
| Photometry of Metal Weak Stars
Not Available
| Southern subdwarf photometry
UBV photometry and normalized UV excesses are reported for 176 southernmetal-poor stars selected from the objective-prism survey of Bidelmanand MacConnell (1973) as well as 49 other metal-deficient starsidentified in other surveys. Photometry is also presented for 32 otherstars lying near the 225 program stars (although not explicitlyidentified as such in the text, the program stars are apparentlysubdwarfs and subdwarf candidates). Previously determined spectral typesand degrees of line weakening are given for the 225 stars, andmetallicities are estimated on the basis of the degrees of lineweakening. It is noted that 33 F and G stars with extreme meannormalized UV excesses of approximately 0.22 mag have a mean Fe/H valueof -1.4 and probably represent halo subdwarfs, while 82 F and G starswith moderate UV excesses are mostly old disk stars.
| UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]
Not Available
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