The Temperature Scale of G and K Subgiants

This investigation of nearby Population I stars was motivated by our need for accurate effective temperatures in order to be able to obtain reliable N abundances from lines belonging to the CN red system. These determinations are based on narrowband photometry calibrated by means of synthetic spectra. It is believed that the temperatures are accurate to within 100 K. The results show that recent calculations of evolutionary tracks of G and K subgiants predict the observations quite well. However, a value for the mixing length parameter 1/Hpclose to 1.6 is required.