642 Tables 841 and 842 



TABLE 841. — Extra-Galactic Nebulae, High Velocities 



(Hubble, Humason, Astrophys. Journ., 74, 43, 1931.) 



Velocity ( km/sec. ) = ( Distance in parsecs)/i790 



Extra-galactic nebulae. — (Analysis of 900 plates with 60- and 100-in. Mt. Wilson 

 reflectors, Hubble, Science, 75, 24, 1931.) (1) None found in low galactic latitudes; 

 avoidance zone irregular, io° to 40 width — apparently due to known obscuring clouds 

 in Taurus, Cassiopeia, Ophiuchus, etc. Inclined belt of bright B stars and diffuse nebulosity 

 reaches highest latitude in Taurus and Ophiuchus. (2) Avoidance zone bordered by partial 

 obscuration to — 40 in general direction of center of galactic system (long. 330 to 340°) ; 

 very limited in opposite direction (except in Taurus) long. 140 , lat. — 35 to — 40 . 

 (3) Lat. > 40 (and in lower lat. towards anti-center) nebulae approx. uniform distribu- 

 tion log number per sq., degree = 2.375. Variation with exposure time indicates uniform 

 distribution also in depth. (4) Appreciable absorption of light in extra-galactic space 

 appears inadmissible. (5) Mean abs. phtg. mag. — 13.8. Density one neb. A3 X io~ 31 

 parsec 3 . Mean mass 5 X io 8 sun's. Mean density in observable space 5 X io~ 31 g/cm 3 . (6) 

 It may be hazarded that clustered nebulae (in 1 hr. plates) may be expected one per square 

 degree. 



TABLE 842. — Rotation of Stars 



Values derived for the components, in the line of sight, of the equatorial velocities of 

 rotation for single stars, to 250 km/sec. Assuming that the axes of the stars having the 

 largest rotational velocities are at right angles to the line of sight, it appears that these 

 stars are still stable. " Our analysis of the spectra of giants and dwarfs shows that all 

 single stars belonging to the later spectrum classes show little rotation. On the other 

 hand, a number of spectroscopic binaries of late type, such as W Urs. Maj. have a very 

 rapid rotation. In fact, Adams and Joy have in a number of cases successfully predicted 

 that stars of spectrum classes F or G showing diffuse lines are close spectroscopic 

 binaries. It is probable that we have here a real difference in behavior : in the early 

 spectrum types rapid axial rotation is observed in single stars about as frequently as in 

 spectroscopic binaries ; while in the later types rapid rotation occurs only in close binaries. 

 This may have a bearing on the problem of the origin of double stars. (Struve-Elrey, 

 M. N. 26, 91, 663, 1931.) 



Smithsonian Tables 



