New high-dispersion radial-velocity curves of W Sagittarii.

Radial-velocity curves of W Sgr for 1969 and 1973 have been constructed from the author's definitive measurements of 20 high-dispersion spectrograms taken by Wallerstein with the coude' spectrographs at Mount Wilson, Kitt Peak, and Cerro Tololo. The curves were compared with the author's high-dispersion curves constructed from his Mills three-prism spectrograms of 1923 and 1925. From an intercomparison of the various curves the following results emerge: (1) To a first approximation the systemic velocity varies in an estimated period of 80 years in a manner well described by Keplerian orbital elements. (2) The shape of the curve representing the short-period pulsation of 7.59+ days is definitely variable with time. There is definite evidence of a 51-year separation between two similar shapes. A comparison with curves of lower dispersion by Curtiss, Stibbs, and Evans suggest the possibility of a 17-year periodicity in the changing shapes. (3) The average spectroscopic pulsation period between 1923 and 1973 is derived. Comparison of this value with the four best-determined photometric periods reveals an increase in period between 1872 and about 1917 at the average rate of 1.364s per year, and a linearly decreasing period at the rate of 0.1345 per year after about 1917. The apparent spectroscopic pulsation period for y = -27.58 km 1 should be given by 7.594875 - 0.00000155(t - 1938.6) mean solar days. (4) The spectra show interstellar D-lines of Na I at a constant velocity of -4.20km 5- Subject headings: binaries - Cepheids and W Virginis stars - stars, individual