The Kinematics And Velocity Ellipsoid Of The G III Stars

 

Richard L. Branham, Jr.

 

Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, C.C. 330, 5500 Mendoza, Argentina (richardbranham_1943@yahoo.com).

 

Received 2010 October 27
Accepted 2011 March 10

 

RESUMEN

Para estudiar la cinemática de las estrellas G gigante (clase de luminosidad III) se usan movimientos propios y paralajes de 3,075 estrellas, de las cuales 658 tienen velocidades radiales. Estas estrellas provienen de la reducción nueva hecha por van Leeuwen del catálogo Hipparcos. La solución da para la velocidad solar 16.72 ± 0.41 km s^–1; para las constantes de Oort, en unidades de km s^–1 kpc^–1, A = 14.05 ± 3.28 y B = –9.30 ± 2.87, valores que representan una velocidad local de rotación de 198.48 ± 26.95 km s^–1 si suponemos una distancia al centro Galáctico de 8.2 ± 1.1 kpc. Para las dispersiones de velocidades obtenemos, en unidades de km s^–1: σ_x = 51.78 ± 0.55, σ_y = 42.81 ± 0.32, σ_z = 28.45 ± 0.22 con una desviación del vertice de 3.°88 ± 6.°62. Una comparacion de esta dispercion con las obtenidas de otras clases espectrales indica que la discontinuidad de Parengo existe también para las estrellas gigantes.

 

ABSTRACT

To study the kinematics of the G giant stars (luminosity class III) use is made of proper motions and parallaxes taken from van Leeuwen's new reduction of the Hipparcos catalog. 3,075 stars, of which 658 have radial velocities, were used in the final study. The solution gives: solar velocity of 16.72 ± 0.41 km s^–1; Oort's constant's, in units of km s^–1 kpc^–1, A = 14.05 ± 3.28 and B = –9.30 ± 2.87, implying a rotational velocity of 198.48 ± 26.95 km s^–1 if we take the distance to the Galactic center as 8.2 ± 1.1 kpc; velocity dispersions, in units of km s ¹, of: σ_x = 51.78 ± 0.55, σ_y = 42.81 ± 0.32, σ_z = 28.45 ± 0.22 with a vertex deviation of 3.°88 ± 6.°62. A comparison of the velocity dispersions with those given by other spectral types shows that Parenago's discontinuity also exists for the giant stars.

Key Words: Galaxy: kinematics and dynamics — methods: numerical.

 

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