TABLE 883.— ROTATION OF STARS* 



771 



The maximum component {z> sin i) along the line of sight of the equatorial velocity v 

 of rotation is found from the distortion of an absorption line produced by differential 

 Doppler effect across the observed hemisphere. For stars in the following groups, v > 

 50 km/sec very rarely, and v << 50 km/sec usually: supergiants, giants; main-sequence 

 stars later than F 5 and not close spectroscopic binaries. For main-sequence stars of early 

 type, and not spectroscopic binaries or cluster members, the distribution function / (v) is 

 found to be well represented by the formula 



/ (v) = (// V^r) { exp [— P (v - zh) 2 ] + exp [-/ (v + »)•] }, 



where the parameters j~ x , V\, and v have the following values : 



Spectral type 



j' 1 (km/sec) 

 Vi (km/sec) 

 v (km/sec) 



Be 

 70 



350 

 348 



O-B 



63 

 95 

 94 



A 



107 

 107 

 112 



F0-F2 



90 







51 



In an idealized Roche model, rotational instability sets in at v = 560 km/sec. The Be 

 stars are surmised to be rotationally unstable fl's. Number of B 8's per B 9>e = 123 ; num- 

 ber of (B 0-B 5)'s per (B Oc-B 5e) = 15. In the Pleiades and in h and x Persei, v for 5's 

 is ~ 2 X v for noncluster B's. For 13 Pleiades earlier than B 9, number of 5's per Be = 

 3. In many close spectroscopic binaries of both late and early types, the components rotate 

 with the orbital period. In some eclipsing systems, the sense of rotation is found from the 

 Doppler shift of an absorption line at partial phrase. The sense is always that of the 

 orbital motion. For the sun, 7' = 2.1 km/sec. 



* Prepared by A. J. Deutsch, Harvard University. 



TABLE 884.— TRANSMISSION OF LIGHT THROUGH SPACE* 



The obscuring matter in space is too irregularly distributed to be described by a mean 

 extinction coefficient for the galaxy. For bright Milky Way regions a minimum value of 

 0.2 m/kpc has been found. 21 ' 



Photoelectric measurements by Stebbins and Whitford *" indicate that the wavelength 

 dependence of the interstellar extinction is essentially the same throughout the galaxy. 

 Their results are given with the table. See references to Oort WH and Strohmeier ^ for 

 possibility of variations in bright and obscured regions. 



X (A) 



^(M" 1 ) 



m (mag) 



An unknown constant must be added to these values to give the actual extinction. The 

 scale has been adjusted arbitrarily to give 1 mag differential extinction between \ 4200 

 and 10,300. 



A value of 4 for the ratio of total photographic absorption to international color excess 

 [R = Aum/(Aum — A Mm )] is obtained by extrapolation of the above table to l/\ = 0. 

 Most observational determinations are between 3 and 5. 300 



Light from distant stars shows polarization up to 5 percent, approximately proportional 

 to reddening. Plane of polarization variable but generally perpendicular to galactic plane. 801 



* Prepared by B. Donn, Harvard University. t Preliminary values, currently under investigation 



by Whitford. 



208 Stebbins, Huffer, and Whitford, Astrophys. Journ., vol. 96, p. 209, 1939; Bok, Pop. Astron., vol. 

 52. p. 261, 1944. 



287 Stebbins and Whitford, Astrophys. Journ., vol. 98, p. 323, 1943; Whitford, Astrophys. Journ., 

 vol. 107, p. 102, 1948. 



298 Oort, Ann. d'Astrophys., vol. 1, p. 91, 1938. 



289 Strohmeier, Zeitschr. Astrophys., vol. 17, p. 83, 1939. 



300 Greenstein, Astrophys. Journ., vol. 87, p. 151, 1938; Oort, Bull. Astron. Inst. Netherlands, vol. 8, 

 p. 308, 1938; Stebbins, Astrophys. Journ., vol. 90, p. 209, 1939; van Rhijn, Groningen Publ. 51, 1946; 

 Weaver, Astrophys. Journ., vol. 110, p. 190, 1949. 



301 Hall, Science, vol. 109, p. 166, 1949; Hiltner, Science, vol. 109, p. 165, 1949, Astrophys. Journ., 

 1949. 



SMITHSONIAN PHYSICAL TABLES 



