BD+14$^circ$3061: A Luminous Yellow Post-AGB Star in the Galactic Halo

I report the discovery that the 9th-magnitude Galactic-halo star BD+14$^circ$3061 is a member of the rare class of luminous metal-poor yellow post-AGB stars. Its Gaia DR2 parallax implies an absolute magnitude of $M_V=-3.44pm0.27$, and it is a very high-velocity star moving in a retrograde Galactic orbit. BD+14$^circ$3061 is a field analog of the half-dozen yellow PAGB stars known in Galactic globular clusters, which have closely similar absolute magnitudes. These objects are the visually brightest members of old stellar populations; their apparently narrow luminosity function makes them potentially useful as Population II standard candles. The spectral-energy distribution of BD+14$^circ$3061 out to $22,mu$m shows no evidence for circumstellar dust. The star is a low-amplitude semi-regular pulsating variable, with typical periods of 30-32 days. A radial-velocity study suggests that it is a spectroscopic binary with a period of 429.6 days, making it similar to known binary yellow PAGB stars such as HD 46703 and BD+39$^circ$4926.