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Trigonometric Parallaxes of Star-forming Regions beyond the Tangent Point of the Sagittarius Spiral Arm

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Abstract

  • As part of the BeSSeL Survey, we report trigonometric parallaxes and proper motions of molecular maser sources associated with 13 distant high-mass star-forming regions in the Sagittarius spiral arm of the Milky Way. In particular, we obtain improved parallax distance estimates for three well-studied regions: {1.9}-0.1+0.1 {kpc} for M17, {5.3}-0.9+1.3 {kpc} for W51, and {7.9}-0.7+0.9 {kpc} for GAL 045.5+00.0. Peculiar motions for all but one source are less than 20 km s-1. We fit a log-periodic spiral to the locations and estimate an average pitch angle of 7.°2 ± 1.°9. We find that the section of the arm beyond the tangent point in the first quadrant of the Milky Way appears 15 pc below the IAU-defined Galactic plane.

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  • 2019

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