The recently discovered subdwarf B ( sdB ) pulsator KIC 11558725 is one of the 16 pulsating sdB stars detected in the Kepler field .
It features a rich g -mode frequency spectrum , with a few low-amplitude p -modes at short periods .
This makes it a promising target for a seismic study aiming to constrain the internal structure of this star , and of sdB stars in general .

We have obtained ground-based spectroscopic radial-velocity measurements of KIC 11558725 based on low-resolution spectra in the Balmer-line region , spanning the 2010 and 2011 observing seasons .
From these data we have discovered that KIC 11558725 is a binary with period P =10.05 d , and that the radial-velocity amplitude of the sdB star is 58 km s ^ { -1 } .
Consequently the companion of the sdB star has a minimum mass of 0.63 M _ { \sun } , and is therefore most likely an unseen white dwarf .

We analyse the near-continuous 2010–2011 Kepler light curve to reveal the orbital Doppler-beaming effect , giving rise to light variations at the 238 ppm level , which is consistent with the observed spectroscopic orbital radial-velocity amplitude of the subdwarf .

We use the strongest 70 pulsation frequencies in the Kepler light curve of the subdwarf as clocks to derive a third consistent measurement of the orbital radial-velocity amplitude , from the orbital light-travel delay .
The orbital radius a _ { sdB } \sin i = 11.5 R _ { \sun } gives rise to a light-travel time delay of 53.6 s , which causes aliasing and lowers the amplitudes of the shortest pulsation frequencies , unless the effect is corrected for .

We use our high signal-to-noise average spectra to study the atmospheric parameters of the sdB star , deriving T _ { eff } = 27 910 K and \log g = 5.41 dex , and find that carbon , nitrogen and oxygen are underabundant relative to the solar mixture .

Furthermore , we analyse the Kepler light curve for its pulsational content and extract more than 160 significant frequencies .
We investigate the pulsation frequencies for expected period spacings and rotational splittings .
We find period-spacing sequences of spherical-harmonic degrees \ell =1 and \ell =2 , and we associate a large fraction of the g -modes in KIC 11558725 with these sequences .

From frequency splittings we conclude that the subdwarf is rotating subsynchronously with respect to the orbit .