The Orbit of the Classical Cepheid SU Cygni

Abstract

New radial velocity data are presented for the classical Cepheid SU Cyg. An orbit has been derived from the new data, CORAVEL data by Imbert (1985) and data from 1906, and is presented in the paper. The pulsation radial velocity curves are compared from the plate material from David Dunlap Observatory (DDO) and several radial velocity spectrophotometers. For radial velocity spectrophotometers with reciprocal dispersion of 8 A/mm or higher, no differences from the DDO velocities are seen over the range of velocity, temperature, or line width. Two analytic representations of the pulsation curve are compared with the data; both are accurate for a simple curve.