Tables 835, 836A and 836B 639 



TABLE 835.— Classification of Nebulae 



(Hubble, Astrophys. Journ., 64, 321, 1926; Contr. Mt. Wilson Obs., no. 324.) 



Symbol e. g. 



I Galactic nebulae — A Planetaries P N.G.C. 7662 



B Diffuse D 



(1) Predominantly luminous DL N.G.C. 6618 



(2) obscure DO Barnard 92 



(3) Conspicuously mixed. . . DLO N.G.C. 7023 

 II Extra-galactic nebulae— A Regular 



(N.G.C. 3379 Eo 



(1) Elliptical EN I " 221 E2 



1 to 7 shows ellipticity " 461 1 E5 



I " 2117 E7 



(2) Spirals 



(a) Normal spirals S 



(1 ) Early Sa N.G.C. 4594 



(2) Intermediate.... Sb " 2841 



(3) Late.. Sc " 5457 



(b) Barred spirals SB 



(1 ) Early SBa N.G.C. 2859 



(2) Intermediate SBc " 3351 



(3) Late SBc " 7479 



B Irregular Irr N.G.C. 4449 



Extra-galactic nebulae too faint to be classified, "Q" 



TABLE 836a.— Galactic Nebulae 



(Russell, Dugan, and Stewart, Astronomy, 1927; Russell, Atkinson, Nature, 127, 661, 1931.) 



Dark nebulae: Detected by obscuration of stars. 



Diffuse Irregular of outline and shape — probably owing their detection to 



reflected light from nearby stars. 

 Planetary " Roundish, sharply defined, almost always with a central star; less 

 than 150 known. Gerasimovic (1929) gives mean distance about 790 

 parsecs. The largest parallax is for N.G.C. 7283 in Aquarius, 12' in 

 diameter. Russell gives mean parallax 0.008", mean diameter 54". 

 Nuclear star absolute mag. -f- 7 to + 8 (Russell, Menzel), + 5 

 (Gerasimovic). Classes O, Oe (ordinary isolated O type stars abs. 

 mag. —4). Proper motion, mean of 9, 0.022"; av. radial veloc. ±37 

 km/sec; 6 > 100 km/sec. 



Zanstra gives temperatures 30,000 to 100,000° K. for 20 of these 

 objects; radius perhaps 1/43 our sun's; density 100,000 g/cm 2 , pos- 

 sibly, io 6 or io 7 g/cm 2 . Apparently upper end of a white dwarf 

 sequence probably parallel to main dwarf sequence, viz. : 



Planetary nuclei. . .M v 4 Sp. = O Sirius B M v 10 A5 



o Ceti B 6 BSe Van Maanen's 14.5 F 



02 Eridani B n AO Wolf 489 13 G 



Observed velocity of rotation 1.4 to 18, av. value 5.3 km/sec. at an apparent distance 

 of 5.7" from center. Period of rotation must be large, 4,000 to 15,000 years. 



TABLE 836b.— Data on Six Planetary Nebulae 



Smithsonian Tables 



