MORE MISSING STELLAR OPACITY

Observational data for Population I stars have shown that blue loops on the H-R diagram form for stellar masses as low as similar to 4 M.. However, current state-of-the-art stellar models, unlike the older ones that were based on smaller opacities, fail to loop out of the red-giant region during core helium burning for masses less than 7 M.. A possible explanation is that the currently used Livermore opacities need to be further increased, by at least 70%, at temperatures characteristic of the base of the outer convection zone, around 1x10(6) K. Indeed, no other suggested remedy seems to yield a blue loop at the lowest observed loop luminosities.