Search for a command to run...
Colors have been obtain~d for 238 stars of all spectral types from 0 to M by measuring intensities six spectral regions from X 3530 to X 10,300 A (Tables 2 and 3). The early-type stars from 0 to B3 sho small dispersion in iniTinsic color, but many are strongly affected by space reddening. A dozen late-tyi giants in low latitudes are likewise affected. The most marked effect of absolute magnitude is near sp~ trum KO, where the colors of dwarfs, ordinary giants, and supergiants are all different (Fig. 1). The observed colors of the stars agree closely with the colors of a black body at suitable temperatur~ (Fig. 2). The derived relative color temperatures are based upon the mean of ten stars of spectrum dG with an assumed temperature of 5500°K. On this scale the values are 23,000° for 0 stars, 11,000° for A~ and 59500 for dGO. An alternative scale, with 6700° and spectrum dG2 for the sun, gives 140,000° ft 0 stars, 16,000° for AO, and 6900° for dGO (Table 7). A definitive zero point for the temperature sca~ has not been determined. The bluest 0 and B stars agree very well with each other, but there is stifi the possibffity that all ai slightly affected by space reddening. A dozen bright stars of the Pleiades seem normal for their type. TI: colors of P Cygni are anomalous, as is the space reddening of the Trapezium cluster of Orion (Fig 3 and 4). Comparisons of the new colors with the International colors arid our previous photoelectric colors C of the North Polar Sequence give the ratios of the scales of color index. These ratios depend upon wheth change of color is caused by change of spectral type or by change of space reddening (Table 11). Goo agreement is found with the Greenwich gradients and especially with the results of the spectrophotometr by John S. Hall (Fig. 5). I. THE OBSERVATION