Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...459..579m&link_type=abstract
Astrophysical Journal v.459, p.579
Astronomy and Astrophysics
Astronomy
32
Galaxy: Kinematics And Dynamics, Galaxy: Stellar Content, Techniques: Radial Velocities
Scientific paper
Radial velocities for 331 stars in the F588 bulge field at 1, b = (80, 70) are obtained. The mean Galactocentric velocity for 319 stars with R < 12.3 is V = 54.4 + 4.7 km S 1, and the velocity dispersion is Cr = 84.4 + 3.3 km 5-1 These stars have metal abundances based on a set of spectral indices calibrated against a grid of 400 standard stars. Dividing the sample according to metallicity, the halo and bulge components are kinematically distinct. The 65 K giants with [Fe/H] < -1 (mostly halo giants) have = -7.0 + 13.6 km 1 and Cr = 109.4 + 9.6 km s 1 The 31 "pure" halo giants (with [Fe/ H] < -1.5) have V = -5.8 + 20.4 km 5-1 and Cr = 113.5 + 14.4 km 5-1 The mean Galactocentric velocity and velocity dispersion for 194 bulge K giants (stars with [Fe/H] > - 1.0) are = 65.9 + 5.1 km s 1 and q = 71.9 + 3.6 km 1 The difference between halo and bulge kinematics is of very high statistical significance. The Galactic bulge and halo are distinct components, defined by consistency among [Fe/H], V , and Cr. Bulge giants are also found to have their kinematics correlated with their metallicities. After discussing other possible causes, including disk and halo contamination, it is argued that this effect is real. The kinematics of 26 M giants in our sample are compared with those of other evolved bulge tracers (Mira variables, OH/IR stars, SiO masers, etc.). These M giants observed in the field have kinematics consistent with their being bulge members. The dependence of velocity dispersion on distance from the Galactic center is determined by combining the data with existing data from Baade's window. While the line-of-sight velocity dispersion of the bulge giants decreases steeply with distance from the Galactic center, that of halo giants decreases very slowly if at - all. The mass in the inner 1.5 kpc is determined to be M_{1 5 }= (1.38 + 0.26) x 1010 M_{0 }and M_{1 5 }= (1.74 + 0.28) x 1010 M_{0 }for the cases of isotropic and anisotropic inner halo, respectively. On the basis of kinematics and metallicities, we conclude that the bulge is a distinct galactic component and not the inner extension of the halo, thin disk, or thick disk.
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