An Observational Approach to the Problem of Spiral Structure

Abstract

view Abstract Citations (29) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Observational Approach to the Problem of Spiral Structure Dixon, M. E. Abstract This paper describes a method by which the mechanism that produces spiral structure may be investigated. The method is based on (B, V) photometry of individual stars and is illustrated by reference to stars in the outer (R > 3 kpc) pai ts of the southern spiral arm of M33. Present results indicate that outside R = 3 kpc there is an age progression across the southern spiral arm and that the older stars are at the inner edge of the arm, The results are interpreted in terms of the spiral-wave picture of spiral structure. An alternative interpretation, involving a spatial separation of recently formed stars and the gases in which they were born, does not fit the observations. Present observational data permit a rough estimate of pattern speeds. They indicate that, at R = 3.4 kpc, (Vp - Vp) + 12 km , where V is the tangential component of velocity, the subscript p refers to the pattern, and the subscript g refers to the gas. If this result is correct, if the pattern rotates "rigidly," and if Brandt's rotation curve for the interstellar gas is correct, then Vp = Vp at R = 2.8 kpc and Vp < V5 at R < 2.8 kpc. Publication: The Astrophysical Journal Pub Date: March 1971 DOI: 10.1086/150856 Bibcode: 1971ApJ...164..411D full text sources ADS | data products NED (1)