Granulation in a main-sequence F-type star

The modal approach developed by Nelson and Musman (1977) is used to investigate convection in an F-type main-sequence star (effective temperature of 7300 K, g = 10,000 cm per sec per sec). The convective velocities and intensity contrasts are found to be larger than in the sun. Even though the convective flux is less than 1% of the total flux at a mean optical depth of unity, the spectral-energy distribution is strongly reddened as a result of the fluctuating opacity. This has important implications in the conversion scale from observed colors to effective temperature. The scale of the surface granulation is expected to be in the range 1000-5000 km. Calculations of the combined H-He I and He II convection zones support the prediction of Toomre et al. (1976) that the stable region between the zones is well mixed