The tip of the red giant branch (TRGB) marks the onset of core helium flash in low--mass stars. In the I-band, the TRGB stars first appear at MI ~-4.0 pm 0.1 and this luminosity has been shown both theoretically and observationally to be an excellent distance indicator, being insensitive to both metallicity and age for low-metallicity systems. Another major advantage of the TRGB method over some other distance indicators, such as the Cepheid PL relation, is that since it is a Population II method, it can be applied to any morphological type of galaxy. It has also been shown that distances derived by two independent methods (TRGB and Cepheids) are in agreement with each other at 0.1 mag level. Some recent observations and applications are reviewed during this talk. We will also review how the TRGB method can be used to test for a metallicity dependence of the Cepheid PL relation.
Cosmological Parameters and the Evolution of the Universe
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