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(b)
Figure 13-7
Light curves
only and (b) the reflection
of close eclipsing
effect only.
binaries
showing
(0) the ellipticity
effect
This effect, called the refiection effect, is recognized by a slight
rise in the light curve just before and after the secondary minimum
(Figure 13-7b).
The effect is seen only when the smaller star
eclipses the larger because the higher temperature
exists on the
inner faces.
Since both the effect of ellipticity and the reflection effect result
from the closeness of two stars it is difficult to separate one effect
from the other.
The proximity gives rise to other effects, too, for not only does
one star cause tidal forces that distort the shape of the other but
also gases often appear to stream from one star to the other. These
gaseous streams can be detected in several ways. A few spectral
lines, usually of hydrogen or helium, or both, show an increased
intensity during certain phases of the period, indicating an uneven
distribution of these gases about the system.
Or these lines may
show a Doppler shift that does not conform to the velocity curve of
the system, indicating that these gases are moving with respect to
the stars. Streaming gases may also be revealed by irregularities
in the light curve.
The most famous star of this type is Beta Lyrae, an eclipsing.