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Metallicities for Double-Mode RR Lyrae Stars in the Large Magellanic Cloud
Metallicities for six double-mode RR Lyrae stars (RRd's) in the LargeMagellanic Cloud have been estimated using the ΔS method. Thederived [Fe/H] values are in the range [Fe/H]=-1.09 to -1.78 (or -0.95to -1.58, adopting a different calibration of [Fe/H] versus ΔS).Two stars in our sample are at the very metal-rich limit of all RRd'sfor which metal abundance has been estimated, either by direct measure(for field objects) or on the basis of the hosting system (for objectsin globular clusters or external galaxies). These metal abundances,coupled with mass determinations from pulsational models and thePetersen diagram, are used to compare the mass-metallicity distributionof field and cluster RR Lyrae variables. We find that field and clusterRRd's seem to follow the same mass-metallicity distribution, within theobservational errors, strengthening the case for uniformity ofproperties between field and cluster variables. At odds to what isusually assumed, we find no significant difference in mass for RR Lyraevariables in globular clusters of different metallicity and Oosterhofftypes, or there may even be a difference contrary to the commonlyaccepted one, depending on the metallicity scale adopted to derive themasses. This ``unusual'' result for the mass-metallicity relation isprobably due, at least in part, to the inclusion of updated opacitytables in the computation of metal-dependent pulsation models. Based onobservations collected at the European Southern Observatories, Chile.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Photoelectric search for CP2-stars in open clusters. X - NGC 2232, NGC 2343, CR 140, and TR 10
One hundred stars in the regions of the four open clusters NGC 2232, NGC2343, Cr 140, and Tr 10 were measured in the Delta(a)-system (Maitzen,1976) in order to detect photometric peculiarity indicating CP2-stars.Of the total of 63 cluster member and probable member stars, only oneturned out to be photometrically peculiar (NGC 2232-9), while Cr 140-60is peculiar, but most likely a nonmember. Tr 10-19, a spectroscopicallypeculiar star according to one source (in disagreement with another),appears to be normal in the present observations.
| A spectroscopic and statistical study of Collinder 140
Results of a spectroscopic and statistical study of 140 stars in a 1.36sq deg area surrounding the extended open cluster Collinder 140 and intwo neighboring fields are presented. Stars were classified in the MKsystem based on prism and slit spectra to a completeness limit of V =14.35 - 0.65 S, where S is a numerical representation of spectral class.A statistically significant H-R diagram of Cr 140 is obtained by thesubtraction of the H-R diagrams of the neighboring field stars, and itis shown that most cluster members are of type B9 or earlier, between A0and A4 with V less than or equal to 10.3 or between F8 and K4 with Vless than 7.2 + 0.65 S, with a well-defined main sequence down to A3 anda significant number of F8 to K4 giants. The H-R diagram, B-V and U-Vcolors and membership properties of the cluster are then used toestimate a distance of 410 + or - 30 pc and an age of 20 + or - 6 Myrfor the cluster. The presence of a significant concentration of yellowgiants in the cluster is pointed out, and proper motion and radialvelocity studies are suggested as a means of confirming the clustermembership of the evolutionarily anomalous group.
| The open cluster CR 140 revisited.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978MNRAS.183...49W&db_key=AST
| The nearby open cluster Collinder 140.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978AJ.....83..278C&db_key=AST
| The Open Cluster Cr 140
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