Spectral Morphology and Rotation in The Open Cluster NGC 6025
Mónica Grosso and Hugo Levato
Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE) Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET Universidad Nacional de San Juan, Argentina, (mgrosso, hlevato@icate–conicet.gob.ar).
Received 2011 January 19
Accepted 2011 April 19
]]> RESUMEN
Hemos clasificado espectralmente a los probables miembros más brillantes del cúmulo abierto NGC 6025 y hemos calculado sus velocidades de rotación. Encontramos un módulo de distancia de 9.80±0.06 (error probable) y derivamos una edad de 84 millones de años para este cúmulo. La estrella más brillante de NGC 6025, HD 143448 fue clasificada como B1Ve y es una estrella azul desubicada (blue straggler) tal como fue propuesto por otros autores (ver Mermilliod 1982). Hemos encontrado tres estrellas peculiares (dos de Si y una de Hg–Mn?) y dos binarias de dos espectros, una de ellas previamente estudiada pero probablemente no miembro del cúmulo. Otra estrella del campo tiene emisión, pero probablemente tampoco es miembro del cúmulo. El promedio de la rotación axial para los miembros de este cúmulo es 73% del promedio de rotación de las estrellas de campo de igual temperatura.
ABSTRACT
We have performed spectral classification and measurements of the axial rotation velocity for the brightest stars in the region of the open cluster NGC 6025. A distance modulus of 9.80 ± 0.06 (pe) and an age of 84 million years were derived. The brightest star of the cluster, HD 143448 was classified as B1Ve and it is a blue straggler as proposed by other authors (see Mermilliod 1982). We found three peculiar stars (two Si and one Hg–Mn?). Another star in the field shows emission but is probably a non–member. We also found two SB2 binaries. The average axial rotation for the cluster members seems to be 73% of the average rotation of the field stars with the same temperature.
Key Words: Hertzsprung–Russell and C–M diagrams — open clusters and associations: individual (NGC 6025) — stars: rotation.
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ACKNOWLEDGMENTS
]]> The CCD and data acquisition system at CASLEO has been partly financed by R. M. Rich through U.S. NSF grant AST–90–15827. This research was partially supported by a grant PIP1113 from the National Research Council (CONICET). We thank Richard Gray who provided the WINMK version 2.4 code. Our appreciation also to W. van Altena for making available to us the SPM4 Catalogue before publication. This research has made use of the WEBDA database, operated at the Institute for Astronomy of the University of Vienna. We appreciate very much the support of CASLEO personnel in the observing process.
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