ja_mageia

A. Katherina Vivas Centro de Investigaciones de Astronomía, Apdo. Postal 264, Mérida 5101-A, Venezuela; Esta dirección electrónica esta protegida contra spam bots. Necesita activar JavaScript para visualizarla
Robert Zinn Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520; Esta dirección electrónica esta protegida contra spam bots. Necesita activar JavaScript para visualizarla
and Carme Gallart Instituto de Astrofı´sica de Canarias, Calle Vía Láctea, E-38200 La Laguna, Tenerife, Spain; Esta dirección electrónica esta protegida contra spam bots. Necesita activar JavaScript para visualizarla

Sixteen RR Lyrae variables from the QUEST survey that lie in the leading arm of the tidal stream from the Sagittarius dSph galaxy have been observed spectroscopically to measure their radial velocities and metal abundances. The systemic velocities of 14 stars, which were determined by fitting a standard velocity curve to the individual measurements, have a sharply peaked distribution with a mean of 33 km s
1 and a standard deviation of only 25 km s
1. The [Fe=H] distribution of these stars has a mean of
1.76 and a standard deviation of 0.22. These measurements are in good agreement with previous ones from smaller samples of stars. The mean metallicity is consistent with the age-metallicity relation that is observed in the main body of the Sgr dSph galaxy. The radial velocities and the distances from the Sun of these stars are compared with recent numerical simulations of the Sgr streams that assume different shapes for the dark matter halo. Models that assume a oblate halo do not fit the data as well as ones that assume a spherical or a prolate distribution. However, none of the fits are completely satisfactory. Every model fails to reproduce the long extent of the stream in right ascension (36) that is seen in the region covered by the QUESTsurvey. Further modeling is required to see if this and the other mismatches between theory and observation can be removed by judicial choices for the model parameters or instead rule out a class of

Key words: galaxies: individual (Sagittarius) — stars: abundances — stars: kinematics — stars: variables: other

ver archivo pdf