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It is common to attribute a flat rotation curve to our Galaxy. However Galazutdinov et al. (2015) in a recent paper have obtained a Keplerian rotation curve for interstellar clouds in outer parts of the Galaxy. They have calculated the distances from equivalent widths of interstellar CaII lines. The radial velocity was also measured on the interstellar CaII absorption line. We verify the result by Galazutdinov et al. (2015) basing on observations of old open clusters. We propose, that the observations of flat and Keplerian rotation curves may be caused by the assumption of circular orbits. The application of formulas derived with the assumption of circular orbits to elliptical ones may mimics the flat rotation curve. The interstellar clouds with cross-sections larger than stars may have almost circular orbits, and the derived rotation curve will be Keplerian.

Keplerian Rotation of Our Galaxy?