Helium in the Galactic Disk B Stars

Abstract

Greenstein and Münch¹, and Sargent and Searle², have recently shown that the atmospheric helium abundance in the halo and globular cluster B stars is low compared with that for normal B stars in the Galaxy. Greenstein, Truran and Cameron³ have suggested that the low abundance may be the result of gravitational diffusion of helium from the atmosphere to a lower layer within the star. They consider that normally mixing currents set up by stellar rotation would counteract such diffusion. In contrast to galactic disk B stars, most of the halo stars appear to be slow rotators. This result is apparently confirmed by Sargent and Strittmatter⁴, who have discussed the weak helium line stars in Orion and conclude that they are intrinsically slow rotators, and that the anomaly is an atmospheric one.