The Milky Way spiral structure parameters from data on masers and selected open clusters

Abstract

To estimate the parameters of the Galactic spiral structure - namely, the\npitch angle i and the number of spiral arms,- data on Galactic masers with\nknown trigonometric parallaxes were used. We applied the well-known method\nbased on analysis of the "position angle - distance logarithm" diagram.\nEstimates of the pitch angle i obtained from four segments of different arms\nbelonging to the global Galactic structure are self-consistent and close to\ni=-13+/-1 degrees. The segment which is most interesting is that of the Outer\narm. It contains only three masers. Hence, in order to obtain correct\nestimates, we also used the data on 12 very young star clusters with distances\ndetermined by Camargo et al. from infrared photometry. The estimates obtained\nallow us to conclude in favor of the four-armed model of the Galactic spiral\nstructure.\n