Colors of elliptical and spiral nebulae in the Corona Borealis cluster.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Colors of elliptical and spiral nebulae in the Corona Borealis cluster. Whitford, A. E. Abstract Colors of four elliptical and seven spiral nebulae in the Corona Borealis cluster have been measured photoelectrically at Mount Wilson. The previous colors in clusters of nebulae reported by Stebbins and Whitford1 showed an unexplained color excess, but the objects measured were all elliptical nebulae, and therefore represented pure population II. The spiral objects in the Corona Borealis cluster were selected as the most remote examples of population I with a known distance; spirals have not been resolved in the Bootes cluster. For the four ellipticals the international color excess is O.28 mag., of which 0.15 mag. is not accounted for by the red shift. Intermediate type spirals also show a residual excess, but the interpretation is clouded by uncertainty about the classification. The four spirals classified as type Sc, with the largest proportion of population I, show a mean excess of O.09 mag., which with a calculated red-shift effect of o.15 mag., leaves a residual of -o.o6 mag. The negative residual is probably not significant, on account of the intrinsic color dispersion of the objects and the observational difficulties in measuring faint diffuse spirals. But the difference between ellipticals and late spirals favors the hypothesis that the unexplained excess is a time effect in population II, as suggested by Schwarzschild, and not a space-reddening effect caused by intergalactic material. The red super- giant stars which have burned themselves out and faded in nearby ellipticals, but which were present 130 million years ago in the Corona nebulae, would add only slightly to the mass and to the photographic luminosity. In evaluating nebular counts to the faintest magnitude limits, however, a very appreciable luminosity correction would be necessary, particularly on red plates. I. A. J. 53, 206, 1942; Ap. J. io8, 413, 1948. Washburn Observatory, Madison, Wis. Publication: The Astronomical Journal Pub Date: 1949 DOI: 10.1086/106311 Bibcode: 1949AJ.....54S.138W full text sources ADS |