We report discovery of a luminous F-type post-asymptotic-giant-branch ( PAGB ) star in the Galactic globular cluster ( GC ) M79 ( NGC 1904 ) .
At visual apparent and absolute magnitudes of V = 12.20 and M _ { V } = -3.46 , this “ yellow ” PAGB star is by a small margin the visually brightest star known in any GC .
It was identified using CCD observations in the uBVI photometric system , which is optimized to detect stars with large Balmer discontinuities , indicative of very low surface gravities .
Follow-up observations with the SMARTS 1.3- and 1.5-m telescopes show that the star is not variable in light or radial velocity , and that its velocity is consistent with cluster membership .
Near- and mid-infrared observations with 2MASS and WISE show no evidence for circumstellar dust .
We argue that a sharp upper limit to the luminosity function exists for yellow PAGB stars in old populations , making them excellent candidates for Population II standard candles , which are four magnitudes brighter than RR Lyrae variables .
Their luminosities are consistent with the stars being in a PAGB evolutionary phase , with core masses of \sim 0.53 M _ { \odot } .

We also detected four very hot stars lying above the horizontal branch ( “ AGB-manqué ” stars ) ; along with the PAGB star , they are the brightest objects in M79 in the near ultraviolet .
In an Appendix , we give periods and light curves for five variables in M79 : three RR Lyrae stars , a Type II Cepheid , and a semiregular variable .