The star Beta Lyræ shows variations quite different in their nature
from those of Algol, yet having a certain analogy to them. Anyone
who looks at the constellation Lyræ a few nights in succession and
compares Beta with Gamma, a star of nearly the same brightness in its
neighborhood, will see that while on some evenings the stars are of
equal brightness, on others Beta will be fainter by perhaps an entire
magnitude.
A careful examination of these variations shows us a very remarkable
feature. On a preliminary study, the period will seem to be six and
one-half days. But, comparing the alternate minima, we shall find them
unequal. Hence the actual period is thirteen days. In this period there
are two unequal minima, separated by equal maxima. That is to say, the
partial eclipses at intervals of six and one-half days are not equal.
At the alternate minima the star is half as bright again as at the
intermediate minima.
It is impossible to explain such a change as this merely by the
interposition of a dark body, and this for two reasons. Instead of
remaining invariable between the minima, the variation is continuous
during the whole period, like the rising and falling of a tide.
Moreever, the inequality of the alternating minima is against the
theory.
Pickering, however, found from the doubling of the spectral lines that
there were two stars revolving round each other. Then Prof. G. W.
Myers, of Indiana, worked out a very elaborate mathematical theory to
explain the variations, which is not less remarkable for its ingenuity
than for the curious nature of the system it brings to light. His
conclusions are these:
Beta Lyræ consists of two bodies, gaseous in their nature, which
revolve round each other, so near as to be almost touching. They are
of unequal size. Both are self-luminous. By their mutual attraction
they are drawn out into ellipsoids. The smaller body is somewhat darker
than the other. When we see the two bodies laterally, they are at their
brightest. As they revolve, however, we see them more and more end
on, and thus the light diminishes. At a certain point one begins to
cover the other and hide its light. Thus the combined light continues
to diminish until the two bodies move across our line of sight. Then
we have a minimum. At one minimum, however, the smaller and darker of
the two bodies is projected upon the brighter one, and thus diminishes
its light. At the other minimum, it is hiding behind the other, and
therefore we see the light of the larger one alone.
This theory receives additional confirmation from the fact, shown
by the spectroscope, that these stars are either wholly gaseous, or
at least have self-luminous atmospheres. Some of Professor Myers’s
conclusions respecting the magnitudes are summarized as follows:
The larger body is about 0.4 as bright as the smaller.
The flattening of the ellipsoidal masses is about 0.17.
The distance of centers is about 1-7/8 the semi-major axis of the
larger star, or about 50,000,000 kilometers (say 30,000,000 miles).
The mass of the larger body is about twice that of the smaller, and 9½
times the mass of the sun.