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We investigate the effect of helium abundance and $\alpha$-elementenhancement on the properties of convection in envelopes of solar-likemain-sequence stars stars using a grid of 3D radiation hydrodynamicsimulations. Helium abundance increases the mean molecular weight of the gas,and alters opacity by displacing hydrogen. Since the scale of the effect ofhelium may depend on the metallicity, the grid consists of simulations withthree 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 generallyaffects structure and convective dynamics in a way opposite to that ofmetallicity. Furthermore, the effect is considerably smaller than that ofmetallicity. The signature of helium differs from that of metallicity in themanner in which the photospheric velocity distribution is affected. \rev{Wealso find that helium abundance and surface gravity behave largely in similarways, but differ in the way they affect the mean molecular weight}. A simplemodel for spectral line formation suggests that the bisectors and absoluteDoppler shifts of spectral lines depends on the helium abundance. We look atthe effect of $\alpha$-element enhancement and find that it has a considerablysmaller effect on the convective dynamics in the SAL compared to that of heliumabundance.

Helium-Abundance and Other Composition Effects on the Properties of Stellar Surface Convection in Solar-like Main-sequence Stars