Effective temperatures and surface gravities for the hot UV -bright stars in globular clusters. For stars hotter than 40 000 K, we show the results obtained with model spectra with [M/H] = +1. Stars from the literature without helium abundance are assumed to have solar abundance. The panels show the metallicity bins −2.3 (top left), −2 (top right), −1.5 (bottom left), and −1.0 (bottom right). The symbols along the tracks mark constant time steps. The cyan symbols mark time steps of 50 000 years along the white dwarf merger track from Zhang & Jeffery (2012).