Abstract
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%.
Highlights
In its nominal mission the Kepler space telescope [1] provided long-term photometric data for more than 100 000 stars, among which many pulsating red giants were found
We observe a high fraction of red giants in binary systems, for which g-dominated mixed modes are not pronounced
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
Summary
In its nominal mission the Kepler space telescope [1] provided long-term photometric data for more than 100 000 stars, among which many pulsating red giants were found. Red giants are evolved stars showing solar-like oscillations which are stochastically excited and intrinsically damped by the near surface convection. Their oscillation spectrum comprises several overtones of radial order (n) and spherical degree ( ) modes. Tidal interactions can impact upon the oscillation spectra of the individual stars in the form of mode damping or even complete mode suppression [4]. This interplay between binary components is not expected in detached systems, where stars are assumed to evolve separately. We investigate if the lack of pronounced g-dominated mixed modes is mainly observed in red giants that belong to binary or triple-star systems or if it is a common phenomenon among field red giants
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