A New Survey of Stellar Kinematics in the Central Milky Way
We present the results of a photometric and spectroscopic study of 189 stars in a field at (l, b) = (8.4(deg,) -6.0(deg)) . We measure radial velocities and selected indices of line strength from the spectra and derive reddening, metallicity, photometric parallaxes and azimuthal rotation velocities and dispersion. We find an average reddening and extinction to the field of E(V-I) = 0.43 +/- 0.09 and A_V = 1.07+/- 0.22. We use distances derived from photometric parallaxes and find that the distribution of stars along this line-of-sight is not strongly peaked at the tangent point. In an attempt to understand the apparent decrease in line-of-sight velocity dispersion with increasing metallicity, we divide our sample into metal-rich and metal-poor groups. Though we lack enough stars to statistically analyze each group, we find the average distances of the metal-rich and metal-poor groups to be, < R> = 3.1 kpc and < R> = 7.0 kpc. Excluding stars in our sample which are likely to be in the foreground disk, we calculate a rotational velocity for the bulge of Vrot = 97+/- 9 km s(-1) , sigma_ phi = 71+/- 11 km s(-1) . Combining this result with studies at other (l, b), we find a rotation rate for the bulge of 10.6+/- 0.6 km s(-1) deg(-1) or 77+/- 5 km s(-1) kpc(-1) . We conclude that when attempting to understand the properties of stars along lines-of-sight into the bulge it is important to consider the line-of-sight distribution of the stars, especially when more than a few degrees from the galactic center.
The Astronomical Journal
- Pub Date:
- January 1997