The UV satellite GALEX is obtaining a valuable UV spectral evolution data for numerous bright cluster galaxies. The apparent trend in redshift vs FUV - V colour seems consistent with the prediction from the single stellar population models. This is comforting while observers feel obliged to build up their database much more substantially in order to make it statistically robust.
Two new issues are notable. Firstly, binary population synthesis community feels odd to find that the simplistic single-star population models are found to be good enough. The in-principle more advanced binary population models are obliged to reproduce the observed CMDs of simple populations (globular clusters) before attempting to model galaxies. For example, I am very eager to see their models reproduce the ordinary HB first, before explaining the EHB.
Secondly, the enhanced helium hypothesis based on the globular clusters in Milky Way and M87 is a very exciting possibility. The deduced value of the helium abundance seems unphysical to be a global property for the galaxy but may be possible for small systems that are vulnerable to a chemical fluctuation in the proto-galaxy cloud. While a more detailed investigation is called for it may be difficult to be influential to the entire stellar population of a galaxy. For instance, adding all spectral energy distributions of the Milky Way globular clusters would not yield anything close to the spectrum of a UV upturn galaxy. Of course, a metallicity difference may act as an added complication.
The secret will be revealed through time and hard work, perhaps very soon.
Acknowledgements
I thank Uli Heber the Bamberg meeting organiser for the great workshop. Special thanks go to Chang H. Ree for providing slides for my review presentation at the meeting. I thank Chul Chung for generating Figure 3 specifically for this article. This article is based on many insightful discussions with Chang H. Ree, Young-Wook Lee, Mike Rich, Jean-Michel Deharveng, Suk-Jin Yoon, Tony Sohn, Sugata Kaviraj, Andres Jordan, Kevin Schawinski, and David Brown. I acknowledge many helps from the GALEX science operation and data analysis team. This trip and review was possible with the support from the KOSEF fund.