Passage: The unusually low metallicity of Vega makes it a weak Lambda Boötis star. However, the reason for the existence of such chemically peculiar, spectral class A0-F0 stars remains unclear. One possibility is that the chemical peculiarity may be the result of diffusion or mass loss, although stellar models show that this would normally only occur near the end of a star's hydrogen-burning lifespan. Another possibility is that the star formed from an interstellar medium of gas and dust that was unusually metal-poor.The observed helium to hydrogen ratio in Vega is 0.030 ± 0.005, which is about 40% lower than the Sun. This may be caused by the disappearance of a helium convection zone near the surface. Energy transfer is instead performed by the radiative process, which may be causing an abundance anomaly through diffusion.

Question: Vega is what kind of Manda Bootis star?
weak