Discussions of Color Index and Spectral Type.

Abstract

view Abstract Citations (9) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discussions of Color Index and Spectral Type. Seares, Frederick H. ; Joyner, Mary C. Abstract Color indices from the Mt. W. Polar Catalogue and numerous observations of spectral types made at Upsala, Harvard, Bergedorf, Yerkes, and Mount Wilson give the following results: 1. Information on the consistency of the color indices-For stars brighter than m = 9.0 and types earlier than GO the colors require a correction depending on the magnitude (Fig. 3). 2. A determination of the spectrum-color relation (Table 7, Fig. 4; international system for color, HD for spectra).-Freed from the effects of space absorption, C for A0 is -0.15 mag., in agreement with results from stars in unobscured regions. 3. A determination of the mean color excess E as afunction of distance (Table 11, Fig. 5).-To 400 parsecs (distance corrected for absorption) E increases at the rate of about 0.06 mag. per 100 parsecs. From 450 to about 700 parsecs it has an approximately constant value of 0.27 mag., as though the obscuring cloud ended a little beyond 400 parsecs. The corresponding absorptions for photographic and photovisual light (X' law) are 1.3 and 1.0 mag., respectively. The foregoing results leave for each star a residual (about 1350 in all) which includes the influence of deviations from the mean absorption E, of dispersion in color for stars of the same spectrum, and of ob- servational errors in color and in spectrum. The statistical relationships are such that these influences can be partially separated and estimated. Local zero-point errors (ME) in C for the Mt. W. Polar Catalogue are about ± 0.015 mag. (Table 12, relation [19]). Deviations from the mean E are appreciable but apparently local; the obscuring cloud extends over the polar cap north of +80° with little evidence of progressive change from side to side (Table 12, Figs. 6, 7). Except for types later than about K2, the dispersion in color for the same spectrum averages less than ± 0.035 mag. (Table 13, relation [25]). For late K and M giants it seems to be 0.1 mag. or more. Spectral-classification errors (Tables 14-14b) for early A's and for gK stars are generally smaller than for intermediate fypes. Slit spectrograms naturally show a higher precision than objective-prism plates; the errors for MW (only 53 stars available) average from 0.6 to 0.8 those for the HD in the polar re- gion, which for most types seem to be less than the average for the HD as a whole Publication: The Astrophysical Journal Pub Date: November 1943 DOI: 10.1086/144572 Bibcode: 1943ApJ....98..261S full text sources ADS | Related Materials (1) Reprint: 1943CMWCI.684....1S