Seismic evidence for non-synchronization in two close sdB+dM binaries from Kepler photometry

TL;DR

This study uses Kepler photometry to demonstrate that two close sdB+dM binary stars are not synchronized in rotation, revealing insights into tidal interactions and companion masses through pulsation analysis.

Contribution

The paper provides the first evidence of non-synchronous rotation in close sdB+dM binaries using pulsation frequency analysis and tidal interaction theory.

Findings

Both stars rotate much slower than their orbital periods.

Companion masses are constrained to be below 0.26 solar masses.

Pulsation spectra show high-overtone g-mode signatures.

Abstract

We report on extended photometry of two pulsating sdB stars in close binaries. For both cases, we use rotational splitting of the pulsation frequencies to show that the sdB component rotates much too slowly to be in synchronous rotation. We use a theory of tidal interaction in binary stars to place limits on the mass ratios that are independent of estimates based on the radial velocity curves. The companions have masses below 0.26 M\odot. The pulsation spectra show the signature of high-overtone g-mode pulsation. One star, KIC 11179657, has a clear sequence of g-modes with equal period spacings as well as several periodicities that depart from that trend. KIC 02991403 shows a similar sequence, but has many more modes that do not fit the simple pattern.