2009AJ....137.4149F -
Astron. J., 137, 4149-4159 (2009/May-0)
The kinematics of late-type stars in the solar cylinder studied with SDSS data.
FUCHS B., DETTBARN C., RIX H.-W., BEERS T.C., BIZYAEV D., BREWINGTON H., JAHREISS H., KLEMENT R., MALANUSHENKO E., MALANUSHENKO V., ORAVETZ D., PAN K., SIMMONS A. and SNEDDEN S.
Abstract (from CDS):
We study the velocity distribution of Milky Way disk stars in a kiloparsec-sized region around the Sun, based on ∼2 million M-type stars from DR7 of SDSS, which have newly re-calibrated absolute proper motions from combining SDSS positions with the USNO-B catalogue. We estimate photometric distances to all stars, accurate to ∼20%, and combine them with the proper motions to derive tangential velocities for this kinematically unbiased sample of stars. Based on a statistical deprojection method we then derive the vertical profiles (to heights of Z = 800 pc above the disk plane) for the first and second moments of the three-dimensional stellar velocity distribution. We find that <W≥-7±1km/s and <U≥-9±1 km/s, independent of height above the mid-plane, reflecting the Sun's motion with respect to the local standard of rest. In contrast, <V> changes distinctly from -20±2 km/s in the mid-plane to <V≥-32km/s at Z=800 pc, reflecting an asymmetric drift of the stellar mean velocity that increases with height. All three components of the M-star velocity dispersion show a strong linear rise away from the mid-plane, most notably σZZ, which grows from 18 km/s (Z = 0) to 40 km/s (at Z = 800 pc). We determine the orientation of the velocity ellipsoid, and find a significant vertex deviation of 20°-25°, which decreases only slightly to heights of Z = 800 pc. Away from the mid-plane, our sample exhibits a remarkably large tilt of the velocity ellipsoid toward the Galactic plane, which reaches 20° at Z = 800 pc and which is not easily explained. Finally, we determine the ratio σ2 φφ/σ2RR near the mid-plane, which in the epicyclic approximation implies an almost perfectly flat rotation curve at the solar radius.
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Journal keyword(s):
Galaxy: kinematics and dynamics - solar neighborhood
Simbad objects:
2
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