Tables 786 and 787 

 TABLE 786.— Stellar Spectra and Related Characteristics 



617 



The spectra of almost all the stars can be arranged in a continuous sequence, the various 

 types connected in a series of imperceptible gradations. With one unimportant exception, 

 the sequence is linear. According to the now generally adopted Harvard system of classifica- 

 tion, certain principal types of spectrum are designated by letters — O, B, A, F, G, K, M, R, 

 S, N, P, and Q — and the intermediate types by suffixed numbers. A spectrum halfway 

 between classes B and A is denoted B5, while those differing slightly from Class A in the 

 direction of Class B are called B8 or B9. In Classes M and O the notation Ma, Mb, Mc, 

 etc., is employed. Classes R and N apparently form a side chain branching from the main 

 series near Class K. 



The colors of the stars, the degree to which they are concentrated into the region of the 

 sky, including the Milky Way, and the average magnitudes of their peculiar velocities in 

 space, referred to the center of gravity of the naked-eye stars as a whole, all show important 

 correlations with the spectral type. In the case of colors, the correlation is so close as to 

 indicate that both spectrum and color depend almost entirely on the surface temperature 

 of the stars. The correlation in the other two cases, though statistically important, is by 

 no means as close. 



Examples of all classes from O to M are found among the bright stars. The brightest 

 star of Class N is of magnitude 5.3; the brightest of Class R, 7.0. About 1% show bright 

 lines. 



TABLE 787.— The Harvard Spectrum Classification 



Class 



M 

 R 



N 

 P 



Q 



Principal spectral lines 



(dark unless otherwise 



stated) 



Bright H lines, bright 

 spark lines of He, 

 N, O, C. 



H, He, spark lines of 

 N and O, a few spark 

 lines of metals 



H series very strong, 

 spark lines of metals 



H lines fainter. Spark 

 and arc linesof metals 



Arc lines of metals, 

 spark lines very 

 faint 



Arc lines of metals, 

 spectrum faint in 

 violet 



Bands of Ti0 2 , flame 

 and arc linesof metals 



Bands of carbon, flame 

 and arc lines of 

 metals 



Bands Zr0 2 , metal 

 flame and arc lines; 

 in S e , bright H and 

 metallic linesof high 

 excitation. Latter 

 are always long 

 period variables . . . 



Bands of carbon, 

 bright lines, very 

 little violet light. . . 



Isolated bright lines, 

 gaseous nebulae . . . 



Novae (see Russell, 

 Dugan and Stewart, 

 Astronomy, p. 780) 



Effective 

 surface 

 tempera- 

 ture, K. 



20,000 

 1 1 ,000° 



7,500 c 



5-ooo° 



4,200° 

 3,100° 



3,000° 



3,000° ? 

 2,300° 



Mean 

 peculiar 

 velocity, 

 km/sec. 



6 

 10 

 14 



15 



17 

 17 



15 



13 



Compiled mainly from the Harvard Annals. Temperatures based on the work of Wilsing and Scheiner 

 (see also pp. 632-3). Radial velocities from Campbell. Data for classes R and N from Curtis and Rufus. The 

 peculiar velocities are in the radial direction (towards or from the sun). The average velocities in space should 

 be twice as great. The "galactic reeion" here means the zone between galactic latitudes ± 30 , and including 

 half the area of the heavens. 96 % of the stars of known spectra belong to classes A, F, G, K, 09.7 % including B 

 and M (Innes. 1919)- Henry Draper Catalogue, 9 vols., 1918-24, with later volumes give positions, magnitudes 

 and spectra of more than 225,000 stars. See also Catalogue of Bright Stars. Schlesinger, Yale Univ. Obs., 1930. 



Smithsonian Tables 



