Colors of seven Cepheid variable stars in Cygnus.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Colors of seven Cepheid variable stars in Cygnus. Heyden, Francis J. Abstract Light curves of seven Cepheid variables in Cygnus, namely, V 386, MW, VY, BZ, TX, SZ and CD Cygni, have been determined in blue- photographic, photovisual and photored light from photometric plates taken at the Harvard Oak Ridge Station. The mean light-curves were derived from observations taken during the summers of 1944 and 1945. Two telescopes were used so that each yellow or red plate was taken simultaneously with a blue one. Color curves showing the variation of the blue- yellow and the blue-red color indices have been derived from the mean light-curves for each of the seven stars. These color curves show a definite correlation with the spectral curves which have been prdvided for this program by Dr. Struve of Yerkes Observatory. Color excesses from the blue-yellow color indices are based on the difference between the observed color index at minimum light and provisional normal color indices for stars of luminosity class Ib in the Morgan, Keenan and Kellman system. These normal colors were prepared by Miss Hagopian at Harvard Observatory. The color index at minimum light was selected because Struve has found1 the spectra nearest to normal at that part of the light curve. Total photographic absorptions have been computed by multiplying the color excesses b the factor 5. This factor is perhaps too large. The distance of the stars have been computed from the median absolute magnitude taken from Dr. Shapley `S photographic period-luminosity curve, from the median apparent magnitude of the blue light-curves and from the total photographic absorption. The formula used was: 5 log r = m - M - A $ 5. The following table contains a summarN' of the results. Variable m Sp. M c.E. A Distance (Cygni) (pg) (MKK) (pg) (mag) (pg) (parsecs) V386 11.00 GI -1.53 0.91 4.55 395 MW 10.60 GI -1.64 0.61 3.05 689 VY 10.60 GI -1.85 0.71 3.55 603 BZ 11.75 G -2.02 o.8o 4.00 900 TX 11.25 G6 -2.32 0.93 4.65 6o8 SZ 10.75 Ko -2.33 0.50 2.50 1308 CD 10.00 Ko -2.42 0.10 0.50 2421 The total absorptions found for these seven stars agree very well with those estimated by F. Miller2 from star counts in the obscured regions near the North American nebula, and by Oort and Oosterhoff3 from the colors of fotir Cepheids in the Cygnus star cloud. I.Observamry, 65, 257, 1944. 2.Ann. Harv. Colt. Obs. 105, 316, 1936. 3.B. A. N. 9, 325, 1942. Georgetown College Observatory, Washington, D. C. Publication: The Astronomical Journal Pub Date: July 1946 DOI: 10.1086/105900 Bibcode: 1946AJ.....52...44H full text sources ADS |