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uvby Hβ CCD photometry and membership segregation of the open cluster NGC 2548; gaps in the Main Sequence of open clusters
Deep CCD photometry in the uvby-Hβ intermediate-bandsystem is presented for the cluster NGC 2548 (M 48). A completemembership analysis based on astrometric and photometric criteria isapplied. The photometric analysis of a selected sample of stars yields areddening value of E(b-y)= 0.06±0.03, a distance modulus ofV_0-M_V= 9.3±0.5 (725 pc) and a metallicity of [ Fe/H] = - 0.24±0.27. Through isochrone fitting we find an age of log t = 8.6±0.1 (400 Myr). Our optical photometry and JHK from 2MASS arecombined to derive effective temperatures of cluster member stars. Theeffective temperature distribution along the main sequence of thecluster shows several gaps. A test to study the significance of thesegaps in the main sequence of the HR diagram has been applied. The methodis also applied to several other open clusters (Pleiades, Hyades, NGC1817 and M 67) to construct a sequence of metallicities and ages. Thecomparison of the results of each cluster gives four gaps with highsignificance (one of them, centred at 4900 K, has not been previouslyreported).
| A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters
As part of our continuing search for peculiar A-type stars, especiallyλ Bootis stars, in open clusters of all ages, we have obtainedclassification spectra of 130 late B, A, and early F-type stars in 12intermediate-age open clusters, including NGC 1039, 2281, 2548, 6633,7039, 7063, 7092, and 7209, IC 4665, IC 4756, Stock 2, and Praesepe. Thespectra were obtained with resolutions of 1.8 and 3.6 Å on the 0.8m telescope of Appalachian State University and were classified on theMK system. Numerous classical Ap and Am stars were found among the 130,including two new Ap stars in NGC 7092. In addition, three emission-linestars and two candidate λ Bootis stars were found. Neither ofthese λ Bootis candidates turned out to be members of theirrespective clusters. Combined with 184 stars previously classified in 10other intermediate-age open clusters, also devoid of λ Bootisstars, a statistically significant null result is obtained. We discussthe implications of this null result for our understanding of theλ Bootis mechanism.
| Determination of proper motions and membership of the open star cluster NGC 2548
Absolute proper motions, their corresponding errors and membershipprobabilities of 501 stars in the intermediate-age open cluster NGC 2548region are determined from MAMA measurements of 10 photographic plates.The plates have the maximum epoch difference of 82 years and they weretaken with the double astrograph at Zô-Sèstation ofShanghai Observatory, which has an aperture of 40 cm and a plate scaleof 30 arcsec mm-1. The average proper motion precision is1.18 mas yr-1. These proper motions are used to determine themembership probabilities of stars in the region. The number of starswith membership probabilities higher than 0.7 is 165. Table 5 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/381/464, and by e-mail requestto Lola.Balaguer@am.ub.es MAMA (Machine Automatique àMesurer pourl'Astronomie, http://dsmama.obspm.fr) is developed and operated byINSU/CNRS and Observatoire de Paris.
| 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
| Galactic cluster star radial velocities obtained with a focal reducer field spectrograph. I - The clusters IC 1805, NGC 2287, NGC 2548, IC 4665, NGC 6633, NGC 6940 and NGC 7092
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...62..301G&db_key=AST
| Photometric and Objective Prism Observations in Three Galactic Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961ApJ...134..602P&db_key=AST
| Proper Motions in the Galactic Cluster NGC 2548.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1939ApJ....90..689E&db_key=AST
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Наблюдательные данные и астрометрия
| Созвездие: | Гидра |
| Прямое восхождение: | 08h13m08.55s |
| Склонение: | -05°38'35.7" |
| Видимая звёздная величина: | 9.217 |
| Собственное движение RA: | -0.6 |
| Собственное движение Dec: | 1.1 |
| B-T magnitude: | 9.303 |
| V-T magnitude: | 9.225 |
Каталоги и обозначения:
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