We investigate the effect of helium abundance and \alpha -element enhancement on the properties of convection in envelopes of solar-like main-sequence stars stars using a grid of 3D radiation hydrodynamic simulations .
Helium abundance increases the mean molecular weight of the gas , and alters opacity by displacing hydrogen .
Since the scale of the effect of helium may depend on the metallicity , the grid consists of simulations with three helium abundances ( Y = 0.1 , 0.2 , 0.3 ) , each with two metallicities ( Z = 0.001 , 0.020 ) .
We find that changing the helium mass fraction generally affects structure and convective dynamics in a way opposite to that of metallicity .
Furthermore , the effect is considerably smaller than that of metallicity .
The signature of helium differs from that of metallicity in the manner in which the photospheric velocity distribution is affected .
We also find that helium abundance and surface gravity behave largely in similar ways , but differ in the way they affect the mean molecular weight .
A simple model for spectral line formation suggests that the bisectors and absolute Doppler shifts of spectral lines depends on the helium abundance .
We look at the effect of \alpha -element enhancement and find that it has a considerably smaller effect on the convective dynamics in the SAL compared to that of helium abundance .