Extended Data Figure 2 : Models with helium versus hydrogen diffusion.

From: Rapidly rotating second-generation progenitors for the ‘blue hook’ stars of ω Centauri

Extended Data Figure 2

a and b show a comparison of blue hook tracks from Xenv-in = 0.007 to Xenv-in = 0.41, from left to right, for Mturb = 10−6M (full lines) and 10−7M (dashed lines). The bolometric luminosity (b) and the F225W magnitude (a) are shown as function of Teff. The hot side of the zero-age horizontal branch for Y = 0.37 is shown (solid black line with dots). c, Evolution with time of the surface N(He)/N(H) due to diffusion. The solar ratio is shown as a horizontal grey dotted line. The observations of blue hook stars show that the slower diffusion is a better description (Fig. 2).