uvby–β photometry and kinematics of metal–poor stars: A search for moving groups in the Galactic stellar halo

 

J. S. Silva,^1,2 W. J. Schuster,¹ and M. E. Contreras¹

 

¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, 22800 Ensenada, B.C., México. (mcontreras@astrosen.unam.mx, schuster@astrosen.unam.mx, jsilva@astrosen.unam.mx).

² Observatório Nacional/MCT. Rua Gal. Jose Cristino 77, São Cristóvão, CEP20291–400 Rio de Janeiro RJ, Brazil. (jsergio@on.br).

 

Received 2011 October 20.
Accepted 2012 January 10.

 

RESUMEN

Se ha examinado la posible presencia de grupos en movimiento en el Halo galáctico en base a la nueva fotometría uvby — β de 143 estrellas pobres en metales, unida a la fotometría de las 1533 estrellas de los catálogos previos de Schuster & Nissen (1988), Schuster et al. (1993) y Schuster et al. (2006). Este nuevo conjunto de datos fotometricos junto con la velocidad radial y los movimientos propios tomados de la literatura permitiá obtener las componentes de velocidad galáctica U', V', y W' para casi toda la muestra. Con esta información cinemática se obtuvieron tres diagramas: [Fe/H] vs V_rot, Bottlinger (V' vs U') y Toomre (V' vs (U'² + W'²)^1/2), usados para identificar grupos de estrellas comunes a cada uno de ellos. Una vez identificados, se compararon con grupos en movimiento reportados en la literatura. En particular, se identificaron posibles miembros de los grupos Kapteyn y ω Cen.

 

ABSTRACT

The possible presence of moving groups in the local Galactic stellar halo has been examined based on new uvby — β photometry for a sample of 143 metal–poor stars joined to the photometry of 1553 stars from the previous catalogues of Schuster & Nissen (1988), Schuster et al. (1993), and Schuster et al. (2006). This new set of photometric data, together with radial velocities and proper motions taken from the literature, have allowed us to obtain Galactic space velocities U' , V' , and W' for nearly the entire sample. With this kinematic information, three diagrams: the [Fe/H] vs V_rot, the Bottlinger (V' vs U') and the Toomre (V' vs (U'² + W'²)^1/2) have been obtained and used to identify probable groups of stars in common between them. Once identified, these groups were compared to moving groups reported in the literature. In particular, probable members of the Kapteyn group and ω Cen were identified.

Key Words: Galaxy: halo — Galaxy: kinematics and dynamics — Galaxy: structure — stars: kinematics and dynamics — stars: Population II — techniques: photometric.

 

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ACKNOWLEDGMENTS

This work was supported by the Conacyt projects CB-2005-01-49434 and CB-2005-49002, and we are very appreciative of this funding which helped considerably with the data reductions and analyses. We thank very much the support and technical staff at the San Pedro Mártir Observatory for their considerable help during the taking of the uvby — β photometric data. As always, B. Hernández has helped expertly with the computer systems and software. We also thank Sean Ryan and Bruce Carney for sharing their lists of metal-poor and subgiant stars.

 

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