On the Origin of the Ultraviolet upturn in elliptical galaxies. II. Test of the horizontal-branch hypothesis

摘要

Whether or not metal-rich HB stars are the dominant UV source in giant elliptical galaxies(Ges) is an important question in current astronomical research. We follow up our previous evolutionary popu- lation synthesis study with quantitative tests to answer this question affirmatively under the following three conditions: (1) Reimers's empirical mass-loss formula is proper, (2) the mass-loss efficiency param- eter η in metal-rich stars is somewhat larger than the value estimated from the metal-poor star studies, and (3) the true value of the helium-enrichment parameter(△Y/△Z) is positive.