Photometric membership and metallicities of red giant candidates in selected open clusters

CLARIA OLMEDO, JUAN JOSÉ; PIATTI, ANDRÉS E.; MERMILLIOD, J.C.; PALMA, T.

Astron. Nachrichten

Año: 2008 vol. 329 p. 609 - 618

As part of a long-term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high-precision $DDO$ photoelectric observations for a sample of 33 red giant candidatesprojected in the fields of nine Galactic open clusters. These data are supplemented with $UBV$ photoelectricphotometry of 24 of these stars as well as with CORAVEL radial-velocity observations for 13 red giant candidatesin four of the clusters. We also present Washington photoelectric photometry of a small sample of red giantcandidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with $UBV$ and $DDO$ data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While $E(B-V)$ colour excesses were determined from combined $B-V$ and $DDO$ colours, calibrations of the $DDO$ system were used to derive MK spectral types, effective temperatures and metallicities.The derived $DDO$ metallicities range between values typical of moderately metal-poor clusters ([Fe/H] = -0.19) to moderately metal-rich ([Fe/H] = 0.25) ones.