THE MILKY WAYS SPIRAL ARMS TRACED BY MAGNETIC-FIELDS, DUST, GAS, AND STARS

What is the proper pitch angle (p) of the spiral arms? How many spiral arms (m) are there? Is the fragmented arm (flocculent) model better o r worse than the logarithmic arm model, with two arms (grand-design) o r four arms (multiple-arm), in our Galaxy? New analyses of the observa tional data are presented here, namely, a statistical analysis is brou ght to bear on the wide range of pitch angle values derived from eight observational methods, comparisons are made between the Milky Way and other spiral galaxies that look like the Milky Way, and a comparison is made with two spiral models (a logarithmic-type model and a floccul ent type model). For the first time, magnetic field data are used in a statistical study of spiral arm characteristics. Here the available e vidence of the last 15 years indicates that p approximate to - 12 degr ees +/- 1 degrees (radially inward), that m = 4, and that the best of the two models above is the logarithmic spiral (not the flocculent typ e).