CCD photometric search for peculiar stars in open clusters VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120

Context. We continue our survey of magnetic chemically peculiar (CP2) stars in galactic open clusters to shed more light on their origin and evolution. Aims. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at a wide range of evolutionary stages. The knowledge of open cluster ages and metallicities can help for finding a correlation between these parameters and the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Methods. The intermediate band Δa photometric system samples the depth of the 5200 Å flux depression by comparing the flux at the centre with the adjacent regions with bandwidths of 110 A to 230 A. It is capable of detecting magnetic CP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) λBootis and classical Be/shell stars can be successfully investigated. In addition, it allows the age, reddening, and distance modulus to be determined with appropriate accuracy by fitting isochrones. Results. From the 1677 observed members of the eight open clusters, one Ae and twenty-five CP2 stars were identified. Furthermore nineteen deviating stars are designated as questionable for several reasons. The estimated age, reddening, and distance for the programme clusters were compared with published values of the literature and discussed in this context. Conclusions. The current paper shows that CP2 stars are continuously present in very young (7 Myr) to intermediate age (500 Myr) open clusters at distances greater than 2 kpc from the Sun. © ESO 2007.Fil: Netopil, M.. Universidad de Viena; AustriaFil: Paunzen, E.. Universidad de Viena; AustriaFil: Maitzen, H.M.. Universidad de Viena; AustriaFil: Pintado, Olga Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Claret, A.. Instituto de Astrofísica de Andalucía - Csic;Fil: Miranda, L.F.. Instituto de Astrofísica de Andalucía - Csic;Fil: Hiev, I.Kh.. National Astronomical Observatory Rozhen; BulgariaFil: Casanova, V.. Instituto de Astrofísica de Andalucía - Csic

Photoelectric search for peculiar stars in open clusters XV. Feinstein 1, NGC 2168, NGC 2323, NGC 2437, NGC 2547, NGC 4103, NGC 6025, NGC 6633, Stock 2, and Trumpler 2

The chemically peculiar (CP) stars of the upper main sequence are mainly characterized by strong overabundances of heavy elements. Two subgroups (CP2 and CP4) have strong local magnetic fields which make them interesting targets for astrophysical studies. This star group, in general, is often used for the analysis of stellar formation and evolution in the context of diffusion as well as meridional circulation. In continuation of a long term study of CP stars (initiated in the 1980s), we present new results based on photoelectric measurements for ten open clusters that are, with one exception, younger than 235 Myr. Observations in star clusters are favourable because they represent samples of stars of constant age and homogeneous chemical composition. The very efficient tool of Δa photometry was applied. It samples the flux depression at 5200 Å typically for CP stars. In addition, it is able to trace emission line Be/Ae and lambda Bootis stars. Virtually all CP2 and CP4 stars can be detected via this tool, and it has been successfully applied even in the Large Magellanic Cloud. For all targets in the cluster areas, we performed a kinematic membership analysis. We obtained new photoelectric Δa photometry of 304 stars from which 207 objects have a membership probability higher than 50%. Our search for chemically peculiar objects results in fifteen detections. The stars have masses between 1.7 Msun and 7.7 Msun and are between the zero- and terminal-age-main-sequence. We discuss the published spectral classifications in the light of our delta-a photometry and identify several misclassified CP stars. We are also able to establish and support the nature of known bona fide CP candidates. It is vital to use kinematic data for the membership determination and also to compare published spectral types with other data, such as Δa photometry. There are no doubts about the accuracy of photoelectric measurements, especially for stars brighter than 10th magnitude. The new and confirmed CP stars are interesting targets for spectroscopic follow-up observations to put constraints on the formation and evolution of CP stars