  The frequencies of oscillation modes in stars contain valuable information
about the stellar properties. In red giants the frequency spectrum also
contains mixed modes, with both pressure (p) and gravity (g) as restoring
force, which are key to understanding the physical conditions in the stellar
core. We observe a high fraction of red giants in binary systems, for which
g-dominated mixed modes are not pronounced. This trend leads us to investigate
whether this is specific for binary systems or a more general feature. We do so
by comparing the fraction of stars with only p-dominated mixed modes in
binaries and in a larger set of stars from the APOKASC sample. We find only
p-dominated mixed modes in about 50% of red giants in detached eclipsing
binaries compared to about 4% in the large sample. This could indicate that
this phenomenon is tightly related to binarity and that the binary fraction in
the APOKASC sample is about 8%.
