2017ApJ...835...28J

We present a revised Tip of the Red Giant Branch (TRGB) calibration, accurate to 2.7% of distance. A modified TRGB magnitude corrected for its color dependence, the QT magnitude, is introduced for better measurement of the TRGB. We determine the color-magnitude relation of the TRGB from photometry of deep images of HST/ACS fields around eight nearby galaxies. The zero-point of the TRGB at the fiducial metallicity ([Fe/H] = -1.6 ((V-I)_0,TRGB=1.5)) is obtained from photometry of two distance anchors, NGC 4258 (M106) and the Large Magellanic Cloud (LMC), to which precise geometric distances are known: M_QT,TRGB = -4.023 ± 0.073 mag from NGC 4258 and M_QT,TRGB = -4.004 ± 0.096 mag from the LMC. A weighted mean of the two zero-points is M_QT,TRGB = -4.016 ± 0.058 mag. Quoted uncertainty is ∼2x smaller than those of previous calibrations. We compare the empirical TRGB calibration derived in this study with theoretical stellar models, finding that there are significant discrepancies, especially for red color ((F606W-F814W)₀ 2.5). We provide the revised TRGB calibration in several magnitude systems for future studies.