Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue
Context: A new reduction of the astrometric data as produced by theHipparcos mission has been published, claiming that the accuracies fornearly all stars brighter than magnitude Hp = 8 are improved, by up to afactor 4, compared to the original catalogue. As correlations betweenthe underlying abscissa residuals have also been reduced by more than anorder of magnitude to an insignificant level, our ability to determinereliable parallaxes and proper motions for open clusters should beimproved. Aims: The new Hipparcos astrometric catalogue is usedto derive mean parallax and proper motion estimates for 20 openclusters. The HR-diagrams of the nearest clusters are compared andcombined to provide future input to sets of observational isochrones. Methods: Three different methods are applied, according to theproximity of the cluster, to compensate, where needed, for projectioneffects, spread in position along the line of sight, and the internalvelocity dispersion of the cluster stars. Results: The newparallaxes have accuracies between 2 and 2.5 times higher than what hadbeen derived from the original Hipparcos catalogue. At least two tothree groups of clusters, mostly of similar ages, are observed to eachoccupy their own specific space in the HR diagram. A significantdiscrepancy in distance moduli from those obtained with isochrone-basedmain-sequence fitting remains, in particular for one of these groups,containing the Pleiades, NGC 2516, and Blanco 1. The difference inabsolute magnitudes between this group and one containing the Hyades andPraesepe clusters appears to be correlated with systematic differencesin the Strömgren ? c0 index between those groups.The same dependency has been known to exist for a long time, and isagain confirmed by the Hipparcos data, in variations in absolutemagnitudes for field stars of the same effective temperature. Conclusions: The positions of the cluster HR diagrams are consistentwithin different groups of clusters shown for example by thenear-perfect alignment of the sequences for the Hyades and Praesepe, forComa Ber and UMa, and for the Pleiades, NGC 2516, and Blanco 1. Thegroups are mutually consistent when systematic differences in ?c0 are taken into account, where the effect of thesedifferences on the absolute magnitudes has been calibrated usingfield-star observations.
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uvby - β Photoelectric Photometry of the Open Cluster α Per
Absolute photoelectric photometry of stars in the direction of the OpenCluster α Per has been secured and is presented along with ananalysis reinforced with all the available data in Strömgrenuvby-β photometry compiled from the literature. Cluster membershipis analyzed and the physical characteristics of the stars have beendeduced. The membership determined in this paper is compared with thatof proper motion studies and Hipparcos.
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Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
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Metal abundances of A-type stars in galactic clusters. III. alpha Persei: new results
We complete our study (Hui-Bon-Hoa et al. 1997) of the abundances of Mg,Ca, Sc, Cr, Fe, and Ni in alpha Per cluster stars using new spectra oftwo stars of the previous sample and also adding two more objects. Thenew spectra of BD +48°894 and HD 21527 show that the former has analmost solar composition whereas the latter is an Am star with the ironpeak elements being all enhanced and Ca marginally underabundant. As forthe additional stars of this study, HD 19954 has a pattern very close tosolar, and HD 20135 is an SB2 system where both components seem to be Amstars: Ca and Sc are strongly deficient; Cr and Ni are overabundant inone component. A more thorough study is needed for confirmation. Basedon observations collected at the Observatoire de Haute-Provence (France)
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Metal abundances of A-type stars in three galactic clusters.
Investigations have been carried out for 11 A stars in young openclusters (α Per, Coma, and Praesepe) and three field stars bymeans of high resolution spectroscopy. Detailed abundance analyses havebeen made for Mg, Ca, Sc, Cr, Fe, and Ni. The results are discussed inthe framework of element stratification processes as invoked bytime-dependent diffusion mechanisms in Am stars. The youngest cluster ofour sample, α Per, seems to show some untypical abundance patternswhich might be identified as early Am phases.
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ROSAT Pointed Observations of the Alpha Persei Cluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1570P&db_key=AST
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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Membership of low-mass stars in the open cluster Alpha Persei
The results of a combined astrometric, photometric, and spectroscopicsearch for low-mass members in the intermediate-age open cluster AlphaPersei are presented. Over 130 low-mass new members have been identifiedto M(v) about 12.5, almost doubling the previous number of knownmembers. The new membership information suggests a slight upwardrevision of Alpha Per's age to about 8 x 10 exp 7 yr. Alpha Per isnoticeably spatially elongated in a direction parallel to the Galacticplane, most likely due to tidal deformation. Analysis of thedistribution of relative H-alpha emission strengths among Alpha Permembers confirms the view that the mean H-alpha strength decreases inincreasingly older systems. Allowing for survey incompleteness, onecannot reject the idea that the luminosity function is consistent withthe field luminosity function to M(v) about 9 or 10.
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Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
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Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
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Catalog of AP and AM stars in open clusters
The previous results of Raab (1922), Markarian (1951), and Collinder(1931) have been used to catalog Ap and Am stars that are in the fieldof open clusters. Tabular data are presented for the clusterdesignation, the HD or HDE number, the right ascension (1900), thedeclination (1900), and the magnitude. Also listed are the spectraltypes and, for certain stars, the probability of cluster membership.
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Effects of rotation on the colours and line indices of stars. I - The Alpha Persei Cluster
Analysis of the available observational data for the Alpha-Perseicluster members shows that rotation effects on the intermediate-bandindices c1 and (u-b) are considerable. In c1, rotation produces areddening of 0.040 magnitudes per 100 km/s. In (u-b), the effect for Bstars is found to be 0.06 magnitudes per 100 km/s of V sin i. Thebinaries and peculiar stars are found to behave differently in the colorexcess (due to rotation) versus V sin i diagrams. These empiricaleffects can be utilized to recalibrate these color indices and also toseparate members that are either chemically peculiar or in binarysystems.
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Chemically peculiar stars in open clusters. I - The catalog
The largest existing compilation is presented of Ap and Am open clusterstars. The catalog contains information on 381 chemically peculiar (CP)stars of the upper main sequence in 79 open clusters. The catalog iscomposed of the following tables: (1) the main body, which lists CP (orsuspected CP) stars which are kinematical (or suspected kinematical)members of open clusters; (2) the list of CP (or suspected CP) starssometimes numbered among cluster members but which are actuallykinematical nonmembers; (3) the list of stars sometimes designated as'peculiar' but, in fact, probably not CP; (4) references for numberingsystems of cluster stars; (5) references for membership; and (6)references for spectral and/or peculiarity types.
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Measurements of 258 radial velocities in two fields near Alpha Per
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..515F&db_key=AST
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Lists of photometric AM candidates
The Geneva photometric m parameter (Nicolet and Cramer, 1982) is used inorder to select Am photometric candidates from the Rufener (1981)catalogue. Two lists are given, the first containing field stars and thesecond cluster stars. According to the photometric criteria thediffusion process probably responsible for the Am phenomenon takes placerather quickly as Am candidates are present in young clusters. It isconfirmed that the phenomenon is enhanced by low rotational velocity andhigh metallicity. The age seems to slightly affect the Am phenomenon.
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Empirical Calibrations of the UVBY, Beta Systems - Part Three - the A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84.1858C&db_key=AST
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A photometric survey of the Alpha Persei cluster for Delta Scuti variables
To investigate the incidence of Delta Scuti variables in the AlphaPersei cluster, a program of differential photometry was undertakenwhich included 24 A- and F-type stars (V no more than 9.48) in or nearthe Delta Scuti instability strip. All stars in the sample weredetermined to have a high probability of cluster membership on the basisof multiple criteria, including proper motions, radial velocities, andextensive photometric data. Three variables were detected (BD +48 deg894, BD +48 deg 905, and BD +47 deg 842). These are located in theregion of the instability strip and have periods close to thosepredicted from the period-color-luminosity relation. The relativeincidence of Delta Scuti variables in the cluster is approximately 25%.As in the Pleiades cluster, the main-sequence variables may be slowerrotators than the nonvariables in the instability strip. The exclusionof pulsation among main-sequence Am stars in the cluster is alsoconfirmed.
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Multicolor photometry of metallic-line stars. III. A photometric catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974RMxAA...1..175M&db_key=AST
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Four-color and H beta photometry for open clusters. 10. The alf Per cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..687C&db_key=AST
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Thirty-five new peculiar stars.
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Metallicism in Border Regions of the AM Domain. I. Extremely Young AM Stars in the Orion 1c Association
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...175..765S&db_key=AST
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The H-R diagram of the alf Per cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..242M&db_key=AST
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The radial velocities., luminosities of 77 stars in the field of the alf Per cluster.
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Studies of Stellar Rotation.IV. a Comparison of Rotational Velocities in the Alpha Persei Cluster and the Pleiades
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...148..129K&db_key=AST
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Photometry of the α Persei Cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960ApJ...132...68M&db_key=AST
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Eigenbewegungen in der Umgebung von α Persei
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