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Paper: Asymmetries in the Disk of the Milky Way
Volume: 275, Disks of Galaxies: Kinematics, Dynamics and Perturbations
Page: 134
Authors: Drimmel, R.; Bucciarelli, B.; Lattanzi, M.; Morbidelli, R.; Smart, R.; Spagna, A.
Abstract: Asymmetries in the stellar disk of the Milky Way, manifested by the Galactic warp and spiral arms, are investigated using Galactic diffuse NIR emission, as measured by COBE, and optical star counts from the recently released Guide Star Catalogue II. Star counts for approximately 80 lines-of-sight within 25 degrees of the North Galactic Pole, covering nearly 2000 square degrees of sky, are analyzed using a model-independent method to assess the amplitude of a local tilt in the stellar disk. An estimated local tilt of 0.33 degrees is found from starcounts to 18th magnitude in the photometric F band (red), consistent with a Galactic warp starting within the Solar Circle, as seen in the diffuse NIR emission measured by COBE (Drimmel & Spergel 2001; Freudenreich 1998). Finally, various spiral arm geometries, including one based on the dynamical model of Amaral & Lepine (1997), are incorporated in a model of the Galactic diffuse NIR emission that is then fit to observations made by the COBE satellite. The favored models have two dominating spiral arms with a pitch angle of about 16 degrees. One of these corresponds to the Scutum arm while the Sagittarius-Carina arm is weak or not evident in the NIR.
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