Abstract
In the inner Galaxy, we statistically find the mean pitch angle of the recently mapped Norma arm in two galactic quadrants (observed tangentially at galactic longitudes near \(l=328^{\circ}\) and near \(l=20^{\circ}\)), using the twin-tangent method, and obtain \(-13.7^{\circ}\pm 1.4^{\circ}\). We compared with other measurements in the literature. Also, using the latest published data on pitch angle and the latest published data on the radial starting point of the four arms (\(R_{\mathrm{Gal}} = 2.2~\mbox{kpc}\)) in each galactic quadrant, a revised velocity plot of the Norma spiral arm is made, along with other spiral arms in the Milky Way, in each Galactic quadrant.
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Acknowledgements
The figure production made use of the PGPLOT software at NRC Canada in Victoria. I thank an anonymous referee for useful, careful, and historical suggestions.
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Vallée, J.P. The Norma spiral arm: large-scale pitch angle. Astrophys Space Sci 362, 173 (2017). https://doi.org/10.1007/s10509-017-3145-5
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DOI: https://doi.org/10.1007/s10509-017-3145-5