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We report the discovery of a luminous "yellow" post-asymptotic-giant-branch(PAGB) star in the globular cluster (GC) M19 (NGC 6273), identified during ouruBVI survey of Galactic GCs. The uBVI photometric system is optimized to detectstars with large Balmer discontinuities, indicating very low surface gravitiesand high luminosities. The spectral-energy distribution (SED) of the star isconsistent with an effective temperature of about 6250 K and a surface gravityof $\log g=0.5$. We use Gaia data to show that the star's proper motion andradial velocity are consistent with cluster membership. One aim of our programis to test yellow PAGB stars as candidate Population II standard candles fordetermining extragalactic distances. We derive a visual absolute magnitude of$M_V=-3.39\pm0.09$ for the M19 star. This is in close agreement with the $M_V$values found for yellow PAGB stars in the GCs omega Cen, NGC 5986, and M79,indicating a very narrow luminosity function. These objects are four magnitudesbrighter than RR Lyrae variables, and they can largely avoid the issues ofinterstellar extinction that are a problem for Population I distanceindicators. We also identified a second luminous PAGB object in M19, this one ahotter "UV-bright" star. Its SED is consistent with an effective temperature ofabout 11,750 K and $\log g=2.0$. The two objects have nearly identicalbolometric luminosities, $\log L/L_\odot=3.24$ and 3.22, respectively.

Two Luminous Post-AGB Stars in the Galactic Globular Cluster M19