Richard L. Branham, Jr.
Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, C.C. 330, 5500 Mendoza, Argentina (rlb@lanet.com.ar)
Received 2006 December 6
Accepted 2007 October 2
RESUMEN
]]> Para estudiar la cinemática de las estrellas M gigante (clase de luminosidad III se usaron 1,532 estrellas con movimientos propios incluidos en el catálogo Hipparcos, de las cuales 480 poseen velocidades radiales. Se excluyeron estrellas más lejanas que 700 pc porque inducen una notable inclinación en la distribución de las estrellas. Se calcularon varias soluciones de las cuales se tomó la solución dada por la robusta norma L1 como la mejor. Se calcula simultáneamente una solución para los parámetros cinemáticos y para los coeficientes del elipsoide de velocidades. Los resultados obtenidos son razonables: velocidad solar de 24.20 ± 0.70km s–1; constantes de Oort, en unidades de km s–1 kpc–1, A = 16.86 ± 2.78 y B = –6.34 ± 2.56, las cuales indican una velocidad rotacional de 197.27 ± 26.80 km s–1. El elipsoide de velocidades está inclinado marcadamente respecto al plano Galáctico en la dirección y.
ABSTRACT
To study the kinematics of M giant stars (luminosity class III) use is made of 1,532 stars with proper motions taken from the Hipparcos catalog, of which 480 have radial velocities. Stars farther off than 700 pc were excluded because they induce a noticeable tilt in the distribution of the stars. Various solutions were performed, and the one calculated by the robust L1 norm was taken as the best. Kinematical parameters and the coefficients of the velocity ellipsoid are solved for simultaneously. The results obtained are reasonable: solar velocity of 24.20 ± 0.70 km s –1; Oort's constant's, in units of km s–1 kpc–1, A = 16.86 ± 2.78 and B = –6.34 ± 2.56, implying a rotational velocity of 197.27 ± 26.80 km s–1. The velocity ellipsoid is tilted considerably with respect to the Galactic plane in the y direction.
Key Words: Galaxy: kinematics and dynamics — methods: numerical
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