Planetary influences on photometric variations of the extreme helium subdwarf KIC 10449976

We propose that the unstable 3.9 d photometric periodicity of the hot subdwarf (sdO) KIC 10449976 results from a tidally locked planet that is heated to ~5000K by the UV radiation from the hot sdO star. Although the bolometric radiation from the planet is very small relative to that of the star, in the visible band the planet contributes~0.07 per cent of the light, sufficient to explain the observed periodic behaviour. In our proposed scenario, the stochastic variations in period and light amplitude are attributed to weather on the planet. Namely streams on the surface and thermal variations in the planet's atmosphere that are driven by the heating and by the planet rotation lead to stochastic changes in the amount of radiation emitted by the planets. We predict that a careful monitoring will reveal a gas giant planet at an orbital separation of 8.3 R⊙ from KIC 10449976.