REPORT OF COMMISSION V GV-43 
in the advancing knowledge and understanding of the stellar population. 
A knowledge of stellar distance is a necessary prerequisite in the determina- 
tion of stellar masses. Binary stars are numerous, and they provide virtually 
the only means for measuring stellar masses. The required data are the space- 
time dimensions of the orbital motion of the two stars around each other; to 
ascertain the linear size of these orbits the parallax of the system must be 
known. Accurate orbital data and distances are known for several dozen binary 
stars, and have yielded important information. There appears to be a well- 
established general relation between mass and luminosity for (main-sequence) 
stars. The higher the mass, the higher the luminosity; however, the range in 
mass is small compared with the range in luminosity; the luminosities vary 
approximately as the third power of the mass. Again, there are exceptions for 
certain types of stars—some striking, some very subtle, but all of them helping 
us to better understand the structure and evolution of stars. 
11. PERTURBATIONS 
Another useful application of the methods of long-focus astrometry is the 
study of minute perturbations in "single" stars, caused by the presence of un- 
seen companion stars. A number of stars reveal periodic variations in their 
paths, indicating the presence of companion objects, too faint to be seen by any 
telescope, yet massive enough to influence visibly the motion of the visible, 
primary star. The amplitude and period of these perturbations permit a calcula- 
tion of the masses of the unseen objects. 
Of particular interest is the recent visual discovery of one of these objects. 
For over two decades a perturbation had been observed in the path of the rather 
inconspicuous eleventh-magnitude, red star Ross 614. By 1950 it was firmly 
established that the unseen companion of Ross 614 revolves around the primary 
star in 16.5 years, and that the extent of the perturbation would be greatest in 
1955. The companion was then actually seen and photographed with the 200- 
inch Hale telescope, and proved to be a very faint star, 1/63,000 as luminous 
as the sun, and only 8 per cent as massive as the sun. This makes the companion 
of Ross 614 at present the star of smallest known mass. However it is still 80 
times as massive as Jupiter, the heaviest planet. 
A star is a self-luminous object; a planet, a non-luminous object shining by 
reflected light. A conventional distinction, on the basis of mass, is that an 
object with a mass of 1/20 times that of the sun would be a borderline case. 
Objects with masses over this limit are stars; those below are planets. A simple 
calculation shows that planetary companions of stars other than our sun must 
be very elusive; they could not be seen with any observational means now avail- 
able. The situation would not be quite so hopeless if the planet would reveal 
itself by a perturbation of the primary star. So far, however, there is no conclu- 
sive evidence for companions of planetary mass, though a few cases are sus- 
pected and are being investigated. 
REFERENCES: (Sproul reprints)* 
, 
No. 73. van de Kamp, Peter. “Long-focus Photographic Astrometry.” Popular Astronomy, 59, 
65, 129, 176, 243, 1951. 
No. 86. van de Kamp, Peter. “The Nearest Stars." American Scientist, Vol. 42, No. 4, 572, 1954. 
No. 89. Lippincott, Sarah Lee, “Ross 614 B, The Star of Smallest Known Mass." Sky and. Tele- 
scope, Vol. 14, No. 9, 364, 1955. 
* Copies of these articles may be obtained on request by writing to the Sproul Observatory, 
Swarthmore College, Swarthmore, Pennsylvania.