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It is well established that stellar effective temperatures determined fromphotometry and spectroscopy yield systematically different results. We describea new, simple method to correct spectroscopically derived temperatures("excitation temperatures") of metal-poor stars based on a literature samplewith -3.3<[Fe/H]<-2.5. Excitation temperatures were determined from FeI lineabundances in high-resolution optical spectra in the wavelength range of ~3700to ~7000A, although shorter wavelength ranges, up to 4750 to 6800A, can also beemployed, and compared with photometric literature temperatures. Our adjustmentscheme increases the temperatures up to several hundred degrees for cool redgiants, while leaving the near-main-sequence stars mostly unchanged. Hence, itbrings the excitation temperatures in good agreement with photometricallyderived values. The modified temperature also influences other stellarparameters, as the FeI-FeII ionization balance is simultaneously used todetermine the surface gravity, while also forcing no abundance trend on theabsorption line strengths to obtain the microturbulent velocity. As a result ofincreasing the temperature, the often too low gravities and too highmicroturbulent velocities in red giants become higher and lower, respectively.Our adjustment scheme thus continues to build on the advantage of derivingtemperatures from spectroscopy alone, independent of reddening, while at thesame time producing stellar chemical abundances that are more straightforwardlycomparable to studies based on photometrically derived temperatures. Hence, ourmethod may prove beneficial for comparing different studies in the literatureas well as the many high-resolution stellar spectroscopic surveys that are orwill be carried out in the next few years.

Deriving Stellar Effective Temperatures of Metal-Poor Stars with the Excitation Potential Method