Selective Absorption Near the North Pole and the Spectrum-Colour Relation

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Author: Seares, Federick H.
• Format: Text
• Language: English
• Published: Oxford University Press 1944
• Subjects: Articles; North Pole; Mount Wilson
• Online Access: http://mnras.oxfordjournals.org/cgi/content/short/103/6/281; https://doi.org/10.1093/mnras/103.6.281

Discussion of spectral types and colour indices (Mount Wilson Polar Catalogue ) for about iooo stars north of +80° declination gives (1) the magnitude error in C , (2) a revised spectrum-colour relation, (3) the mean colour excess as a function of distance. The magnitude error, which affects stars brighter than Pυ m 9.2 of types earlier than Go, accounts for the contradictions in the selective absorption and in the colour of Ao stars found by E. G. Martin. For Ao the absorption-free value is C = −0.15 mag. The obscuring cloud, which apparently extends to about 450 parsecs, produces a maximum colour excess of 0.27 mag. (international system).