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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.
| Studies of large-amplitude Delta Scuti variables. 2: DY Herculis
This the second paper in a series on large-amplitude delta Scuti starsintended to determine Baade-Wesselink radii and luminosities withprecision. The first paper discussed our method of analysis and itsapplication to EH Librae; in this paper we discuss the observations andanalysis of DY Herculis. Optical and infrared photometry andcross-correlated radial-velocity data have been obtained and analyzed.Fourier representations for the UBVRIJHK light curves and for theradial-velocity curves were used to derive a value for the minimumradius for each of 60 combinations of flux and color index. From thesewe adopt a mean value for the minimum radius of Rmin = 2.77+/- 0.20 solar radii. When combined with effective temperatures fromBerger et al. (1978), we find a mean bolometric luminosity ofLb = 21.70 solar luminosity and a mean absolute magnitude ofmean value of mB = 1.41. The radial excursion is 0.149 solarradii. We use the same procedure to improve our results for EH Librae,deriving Rmin for each of 42 combinations of flux and colorindex, and obtain mean values of Rmin = 2.62 +/- 0.19 solarradii, LB = 24.56 solar luminosity and (mean value ofMB) = 1.27.
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Osservazione e dati astrometrici
| Costellazione: | Ercole |
| Ascensione retta: | 16h32m39.42s |
| Declinazione: | +11°53'15.4" |
| Magnitudine apparente: | 8.892 |
| Distanza: | 98.717 parsec |
| Moto proprio RA: | -33.9 |
| Moto proprio Dec: | 21.1 |
| B-T magnitude: | 9.37 |
| V-T magnitude: | 8.932 |
Cataloghi e designazioni:
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