Multicolour photometry and Coravel observations of stars in the southern open cluster IC 2488

We preseent new UBV photoelectric observations of 119 stars in the field of the southern open cluster IC 2488, supplemented by DDO and Washington photometry and Coravel radial velocities for a sample of red giant candidates. Nearly 50% of the stars sampled - including three red giants and one blue straggler - are found to be probable cluster members. Photometric membership probabilities of the red giant candidates show good agreement with those obtained from Coravel data. A mean radial velocity of (-2.63 +/- 0.06) km/s is derived for the cluster giants. The reddening across the cluster is found to be E(B-V) = 0.24 +/- 0.04. IC 2488, located at a distance of (1250 +/- 120) pc from the Sun and 96 below the Galactic plane, is most probably not related to the planetary nebulae ESO 166-PN21. A metal abundance 0.10 +/- 0.06 relative to the Sun is determined from DDO data of the red giant members, in good agreement with the metallicity values derived from five independent Washington abundance indices. An age of 180 Myr is determined from the fitting of isochrones computed with convective overshooting for Z = 0.019. The isochrone for log t = 8.25 reproduces remarkably well not only the morphology of the upper main sequence but also the observed red giant pattern.Fil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Lapasset Gomar, Emilio. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mermilliod, J. C.. Universite de Lausanne; Suiz

Mergers of close primordial binaries

We study the production of main sequence mergers of tidally-synchronized primordial short-period binaries. The principal ingredients of our calculation are the angular momentum loss rates inferred from the spindown of open cluster stars and the distribution of binary properties in young open clusters. We compare our results with the expected number of systems that experience mass transfer in post-main sequence phases of evolution and compute the uncertainties in the theoretical predictions. We estimate that main-sequence mergers can account for the observed number of single blue stragglers in M67. Applied to the blue straggler population, this implies that such mergers are responsible for about one quarter of the population of halo blue metal poor stars, and at least one third of the blue stragglers in open clusters for systems older than 1 Gyr. The observed trends as a function of age are consistent with a saturated angular momentum loss rate for rapidly rotating tidally synchronized systems. The predicted number of blue stragglers from main sequence mergers alone is comparable to the number observed in globular clusters, indicating that the net effect of dynamical interactions in dense stellar environments is to reduce rather than increase the blue straggler population. A population of subturnoff mergers of order 3-4% of the upper main sequence population is also predicted for stars older than 4 Gyr, which is roughly comparable to the small population of highly Li-depleted halo dwarfs. Other observational tests are discussed.Comment: number of pages depends on font, margins, columns etc (58 with given format), 14 figures, submitted to the Astrophysical Journa

Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters

We present metallicity estimates for seven open clusters based on spectrophotometric indices from moderate-resolution spectroscopy. Observations of field giants of known metallicity provide a correlation between the spectroscopic indices and the metallicity of open cluster giants. We use \chi^2 analysis to fit the relation of spectrophotometric indices to metallicity in field giants. The resulting function allows an estimate of the target-cluster giants' metallicities with an error in the method of \pm0.08 dex. We derive the following metallicities for the seven open clusters: NGC 1245, [m/H]=-0.14\pm0.04; NGC 2099, [m/H]=+0.05\pm0.05; NGC 2324, [m/H]=-0.06\pm0.04; NGC 2539, [m/H]=-0.04\pm0.03; NGC 2682 (M67), [m/H]=-0.05\pm0.02; NGC 6705, [m/H]=+0.14\pm0.08; NGC 6819, [m/H]=-0.07\pm0.12. These metallicity estimates will be useful in planning future extra-solar planet transit searches since planets may form more readily in metal-rich environments.Comment: 38 pages, including 12 figures. Accepted for publication in A

Estudio preliminar de las binarias eclipsantes RT Hydri y V594 Centauri

Se presentan las primeras observaciones fotoeléctricas UBV de dos sistemas binarios eclipsantes de corto período orbital: RT Hydri y V594 Centauri. Se determinan nuevos tiempos de mínimo y se actualizan las efemérides, incluyendo posibles variaciones del período. Las curvas de luz derivadas de las presentes observaciones exhiben las características típicas de las binarias tipo W UMa, con apreciables profundidades en los mínimos. Un análisis preliminar de las curvas en magnitud V permite clasificar a los dos sistemas estudiados dentro del gtupo de las binarias cerradas de contacto marginal.Asociación Argentina de Astronomí

Photometric variability of stars belonging to the trapezium-type systems

We report the variability of 21 stars belonging to 17 systems considered to be Trapezium-type systems by Allenet al. (1977a). In order to avoid serious problems due to possible light contamination by neighbouring stars, we have only considered systems with angular separations between components equal or greater than five seconds of arc. Among the new variables here reported there are five having ΔV variations greater than 0m.3. For six systems we have spectrograms of the individual components. Three of the six systems are probably optical configurations and only two of the variables in the remaining three systems may be physical companions.Universidad Nacional de La Plat

Extensión del catálogo de blue stragglers en cúmulos abiertos

Se presenta un estudio estadístico de las características observacionales de blue stragglers en cúmulos abiertos del hemisferio norte, basado en la inspección visual de los diagramas color-magnitud de mas del 90 % de los cúmulos con fotometría realizada hasta diciembre de 1992. Este trabajo completa el relevamiento de blue stragglers en cúmulos abiertos, habiéndose examinado un total de 420 cúmulos de todo el cielo. Los blue stragglers se han clasificado en 3 categorías de acuerdo a la probabilidad estimada de pertenencia a los cúmulos y a la calidad de las observaciones. Con los nuevos datos se han actualizado las estadísticas, mostrándose las relaciones entre el número de blue stragglers y las edades de los cúmulos, entre el número de blue stragglers y el número de estrellas normales en los cúmulos, y también el grado de concentración de los blue stragglers, en varios intervalos de edad de los cúmulos.Asociación Argentina de Astronomí

New catalogue of blue stragglers in open clusters

We present a catalogue of blue-straggler candidates in galactic open clusters. It is based on the inspection of the colour–magnitude diagrams of the clusters, and it updates and supersedes the first version (Ahumada & Lapasset 1995). A new bibliographical search was made for each cluster, and the resulting information is organised into two tables. Some methodological aspects have been revised, in particular those concerning the delimitation of the area in the diagrams where the stragglers are selected. A total of 1887 blue-straggler candidates have been found in 427 open clusters of all ages, doubling the original number. The catalogued stars are classified into two categories mainly according to membership information

Spectroscopic orbits of two short-period early-type binaries using two-dimensional cross-correlations

We apply the two-dimensional cross-correlation technique TODCOR to derive spectroscopic orbits for the two B-type double-lined spectroscopic binaries HD 66066