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Membership and binarity of solar-type dwarfs in the nearby open cluster Alpha Persei (Mel 20)
Context: The Alpha Persei open cluster (Melotte 20) is one of the nearbyclusters (d < 500 pc) for which a long-term systematicradial-velocity monitoring of the solar-type stars has not beenpublished so far. Aims: We undertook an observing program in 1982 tostudy the membership, duplicity, and rotation of the main-sequence starsand to compare the results with those of the other nearby clusters. Methods: Radial-velocity observations of 60 solar-type stars in Mel 20were obtained with CORAVEL, and of 44 fainter stars with ELODIEspectrographs, in the magnitude range 9.5 < V < 13.85 Results:The membership of 37 stars from the list compiled by Heckmann isconfirmed according to their proper motions, radial velocities, andphotometry. We discovered twelve spectroscopic binaries (3 double-lined,8 single-lined, 1 suspected) among the members and determined an orbitfor the double-lined binary He 848. The observed frequency ofspectroscopic binaries is therefore 32% (12/37). Four stars arephotometric binaries. In addition, the membership of 33 stars with APnumbers is supported by the present radial velocities. Two single-linedand three double-lined binaries were detected in this sample. Thecluster mean radial velocity is -1.39 ± 0.17 km s-1based on 18 stars within 2σ. We found a systematic difference of3.67 ± 1.48 km s-1 between observed- and astrometricradial velocities. Conclusions: The Alpha Persei cluster members definea tight main sequence in the colour-magnitude diagrams. The remainingscatter observed in the colour-magnitude diagrams and in radialvelocities may be due to the difficulty of separating the core AlphaPersei stars from the extended comoving stream.based on observations collected at the Haute-Provence Observatory(France). Table 5 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/488/409
| 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.
| 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
| Eigenbewegungen in der Umgebung von α Persei
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