Hot subdwarfs ( sdO/Bs ) are the helium-burning cores of red giants , which lost almost all of their hydrogen envelopes .
This mass loss is often triggered by common envelope interactions with close stellar or even substellar companions .
Cool companions like late-type stars or brown dwarfs are detectable via characteristic light curve variations like reflection effects and often also eclipses .
To search for such objects we obtained multi-band light curves of 26 close sdO/B binary candidates from the MUCHFUSS project with the BUSCA instrument .
We discovered a new eclipsing reflection effect system ( P = 0.168938 d ) with a low-mass M dwarf companion ( 0.116 M _ { \odot } ) .
Three more reflection effect binaries found in the course of the campaign were already published , two of them are eclipsing systems , in one system only showing the reflection effect but no eclipses the sdB primary is found to be pulsating .
Amongst the targets without reflection effect a new long-period sdB pulsator was discovered and irregular light variations were found in two sdO stars .
The found light variations allowed us to constrain the fraction of reflection effect binaries and the substellar companion fraction around sdB stars .
The minimum fraction of reflection effect systems amongst the close sdB binaries might be greater than 15 % and the fraction of close substellar companions in sdB binaries might be as high as 8.0 \% .
This would result in a close substellar companion fraction to sdB stars of about 3 % .
This fraction is much higher than the fraction of brown dwarfs around possible progenitor systems , which are solar-type stars with substellar companions around 1 AU , as well as close binary white dwarfs with brown dwarf companions .
This might be a hint that common envelope interactions with substellar objects are preferentially followed by a hot subdwarf phase .