Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21724110h&link_type=abstract
American Astronomical Society, AAS Meeting #217, #241.10; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
The Thick Disk and Inner Halo stars in Quadrant I (Q1) have a significant over-density or star count excess compared to similar stars in the complementary fields in Quadrant 4 which extend to 5 kpc along the line of sight. The Thick Disk stars in Q1 have a much slower effective rotation rate compared to the corresponding Q4 stars (Parker et al 2004). We have greatly expanded the kinematic data with radial velocities and derived metallicity parameters for over 4000 stars. We confirm the corresponding kinematic asymmetry, extended to greater distances and with more spatial coverage. The Thick Disk stars in Q1 have a rotational lag of 60 -- 70 km/s relative to circular rotation, and the Metal-Weak Thick Disk stars have an even greater lag of 100 km s. Both lag their corresponding populations in Q4 by approximately 30 km/s. Interestingly, the Disk stars in Q1 also appear to participate in the rotational lag by about 30 km/s. The enhanced rotational lag for the Thick Disk in Q1 extends to 4 kpc or more from the Sun. At 3 to 4 kpc, our sight lines extend above the density contours on the near side of the bar, and as our lines of sight pass directly over the bar the rotational lag appears to decrease. This is consistent with a ``gravitational wake''induced by the rotating bar in the Disk which would trap and pile up stars behind it. We conclude that a dynamical interaction with the stellar bar is the most probable explanation for the observed kinematic and spatial asymmetries. This work was supported by the National Science Foundation.
Beers Timothy C.
Cabanela Juan E.
Grammer Skyler
Humphreys Roberta M.
Larsen Jeffrey A.
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