Unpredictable Stars

Not all stars twinkle steadily night after night. Some regularly fade away, then suddenly flare up again with undiminished brilliance. Others grow dim quickly, unpredictably, then gradually regain their former radiance. The latter type of variable star has long puzzled astronomers, since its spectrum at its dullest shows little change, indicates that no fundamental alteration has occurred. Prime example is R Coronae Borealis. Reappearance is slow, sometimes taking many months. Last week John O'Keefe of the Harvard Observatory published an explanation for the behavior of R Coronae Borealis in The Telescope.

The R Coronae group of stars is composed chiefly of carbon, least volatile of the elements. Carbon evaporates more slowly than any of the other elements, condenses more rapidly. The sun frequently ejects matter from its atmosphere and R Coronae Borealis may very well do likewise. This cast-off material, reasons Astronomer O'Keefe, condenses rapidly, since it is carbon, and forms a sooty cloud which obscures the light of the stars. One per cent of the total amount of carbon in the atmosphere of R Coronae Borealis could cut out 99% of its light. Astronomer O'Keefe supposes that as the cloud dissipates the stars appear bright again.

Another unusual star was described to the American Astronomical Society meeting at Ann Arbor last week, by young Dr. Ralph B. Baldwin of the University of Pennsylvania. Gamma, of the constellation Cassiopeia (visible in the Northern hemisphere), is 400 times brighter than the sun, nearly five times as hot. Year ago Gamma began to grow brighter, like a nova, or exploding star. Astronomers were sure that the increased brilliance would be accompanied by generation of additional heat, but they were mistaken. For the temperature of Gamma dropped from 28,800DEG F. to 15,660DEG. Last May the star attained its greatest brilliance, suddenly "took a nose dive," said Dr. Baldwin, as its light ebbed. Paradoxically its heat increased. It is now at normal temperature again. At present it is racked by tremendous disturbances and is "blowing away its atmosphere." Most logical explanation, said Dr. Baldwin, was that Gamma's compressed atmosphere expanded so rapidly that its gasses were cooled. Thus the star grew brighter and cooler at the same time.

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