761 



TABLE 870.— VARIABLE STARS, GENERAL CHARACTERISTICS (concluded) 



minima, irrespective of principal and secondary) range from 16 d .5 (SX Centauri) to 73* 

 (R Scuti). Galactic distribution suggests Population I. Only 60 stars can be safely 

 assigned to this group. 



Explosive stars. — U Geminorum stars. Typical variable : U Geminorum (8 m .8 — 

 14 m .O; average cycle 97 d ). Characterized by long permanence at minimum light, interrupted 

 by brief, sudden explosions which bring the star almost always to the same maximum mag- 

 nitude ; the time between explosions might vary as from 1 to 4 for an individual star, but 

 the average length of cycles over long periods of time are constant for each star. Average 

 cycle length ranges from 13 d (AB Draconis) to 340 d (AW Geminorum). A few stars 

 undergo temporary spells of continuous, irregular fluctuations. The amplitude increases 

 from 3 magnitudes for short-cycle stars to 5 magnitudes for long-cycle stars. Spectra are 

 of early type and peculiar ; hydrogen lines in emission at minimum in absorption at maxi- 

 mum galactic concentration low for short-cycle variables, greater for long-cycle ones. 

 Group numbers about 70 stars. 



Z Camel opardalis stars. Typical variable: Z Camelopardalis (10'".5 — 13 m .3 ; average 

 cycle 22 d .l). Similar to the preceding, but with shorter minima and smaller amplitudes; 

 erratic variation is the rule rather than the exception : Less than a dozen stars are known 

 of this type. 



Novae, repeating novae, and novaelike stars. Novae are stars that suddenly blaze up 

 with startling rapidity and then gradually fade out again. For data on bright or well- 

 observed novae see Table 866. A repeating (or recurrent) nova, such as T Pyx, has 

 several outbursts, any one of which would have identified it as a nova. A novalike star, 

 e.g., Z Andromeda, from time to time shows novalike characteristics with the formation 

 of a shell spectrum and displaced absorption lines and later emission lines. Nebular lines 

 are often associated with these objects. 



Erratic variables. — R Coronae Borcalis stars. Supergiants with G and R spectra and 

 an abnormal abundance of carbon in their atmospheres. For long periods of time (often 

 years) the light remains constant at maximum. At entirely irregular intervals the light 

 is dimmed, probably by a carbon veil, with resulting fluctuations which may reach 9 or 10 

 magnitudes. Typical stars: R Coronae Borealis (variable from 5 m .8 to 15 m .0), RY Sagit- 

 tarii (variable from 5 m .9 to 15"' .0 and probably fainter). Only 23 stars are known to 

 belong to this type. 



Variables associated unth nebulosities. Stars in gaseous nebulae of the diffuse or of the 

 cometary type, or even in dark nebulae, often show erratic variations with various ampli- 

 tudes and speeds. At least three subtypes are indicated, typified by the following stars : 

 T Ononis (9 m .6 — ll m .9; rapid; often constant at maximum) ; R Monocerotis (10'" — 14 m ; 

 slow) ; RW Aurigae (9"'.0 — 13'". 5 ; very rapid, no constant light at any time). About 200 

 stars can be attributed to one or the other of these groups. 



P Cygni and Be Stars. These early-type giants are normally quiescent, but occasionally 

 some of them undergo slow fluctuations of moderate amplitude (l m — 4 m ) which last over 

 a series of years. Typical : P Cygni (3'" — 6 m ), active in the 17th century; 7 Cassiopeiae 

 (l m .6 — 3 m .0), active after 1936. 



TABLE 871.— VISUAL BINARY STARS* 



A. Visual binary stars are cataloged as follows : 



1. "New General Catalog of Double Stars within 120° of the North Pole" (abbre- 



viated : ADS = Aitken Double Stars), by R. G. Aitken, Carnegie Inst. Wash- 

 ington Publ. 417, 1932 (2 vols.) ; contains 17,180 objects. 



2. ADS is the successor to BDS = "A General Catalog of Double Stars within 



121° of the North Pole," by S. W. Burnham, Carnegie Inst. Washington Publ. 

 5, 1906 (2 vols.) ; this catalog contains 13,665 pairs. About one-third of these 

 (mostly wide objects) are not repeated in ADS. 



3. SDS or "Southern Double Star Catalog," from —19° to —90° declination, by 



R. T. A. Innes, B. H. Dawson, and W. H. van den Bos, Union Observatory, 

 Johannesburg, South Africa, 1927 (4 vols.). 



4. Many ividc double stars of interest are contained in "Measures of Proper Motion 



Stars," by S. W. Burnham, Carnegie Inst. Washington Publ. 168, 1913. 



B. A full discussion of mass determinations of visual binary stars is found in "The 



Masses of the Stars with a General Catalog of Dynamical Parallaxes," by H. N. 

 Russell and C. E. Moore, Univ. Chicago Press, 1940. 



C. Orbits of visual binaries are listed in W. H. Finsen, "Second Catalog of Orbits of 



Visual Binary Stars," Union Obs. Circ. 100, 1938. Supplementary orbits are found 

 in later Union Observatory Circulars and in the Astronomical Journal. 



* Prepared by G. P. Kuiper, Yerkes Observatory. 

 SMITHSONIAN PHYSICAL TABLES 



