The infrared flux method ( IRFM ) has been applied to a sample of 135 dwarf and 36 giant stars covering the following regions of the atmospheric parameters space : 1 ) the metal-rich ( \mathrm { [ Fe / H ] } \gtrsim 0 ) end ( consisting mostly of planet-hosting stars ) , 2 ) the cool ( T _ { \mathrm { eff } } \lesssim 5000 K ) metal-poor ( -1 \lesssim \mathrm { [ Fe / H ] } \lesssim - 3 ) dwarf region , and 3 ) the very metal-poor ( \mathrm { [ Fe / H ] } \lesssim - 2.5 ) end .
These stars were especially selected to cover gaps in previous works on T _ { \mathrm { eff } } vs. color relations , particularly the IRFM T _ { \mathrm { eff } } scale of A. Alonso and collaborators .
Our IRFM implementation was largely based on the Alonso et al .
study ( absolute infrared flux calibration , bolometric flux calibration , etc . )
with the aim of extending the ranges of applicability of their T _ { \mathrm { eff } } vs. color calibrations .
In addition , in order to improve the internal accuracy of the IRFM T _ { \mathrm { eff } } scale , we recomputed the temperatures of almost all stars from the Alonso et al .
work using updated input data .
The updated temperatures do not significantly differ from the original ones , with few exceptions , leaving the T _ { \mathrm { eff } } scale of Alonso et al .
mostly unchanged .
Including the stars with updated temperatures , a large sample of 580 dwarf and 470 giant stars ( in the field and in clusters ) , which cover the ranges : 3600 K \lesssim T _ { \mathrm { eff } } \lesssim 8000 K , -4.0 \lesssim \mathrm { [ Fe / H ] } \lesssim + 0.5 , have T _ { \mathrm { eff } } homogeneously determined with the IRFM .
The mean uncertainty of the temperatures derived is 75 K for dwarfs and 60 K for giants , which is about 1.3 % at solar temperature and 4500 K , respectively .
It is shown that the IRFM temperatures are reliable in an absolute scale given the consistency of the angular diameters resulting from the IRFM with those measured by long-baseline interferometry , lunar occultation and transit observations .
Using the measured angular diameters and bolometric fluxes , a comparison is made between IRFM and direct temperatures , which shows excellent agreement , with the mean difference being less than 10 K for giants and about 20 K for dwarf stars ( the IRFM temperatures being larger in both cases ) .
This result was obtained for giants in the ranges : 3800 K < T _ { \mathrm { eff } } < 5000 K , -0.7 < \mathrm { [ Fe / H ] } < 0.2 ; and dwarfs in the ranges : 4000 K < T _ { \mathrm { eff } } < 6500 K , -0.55 < \mathrm { [ Fe / H ] } < 0.25 ; and thus the zero point of the IRFM T _ { \mathrm { eff } } scale is essentially the absolute one ( that derived from angular diameters and bolometric fluxes ) within these limits .
The influence of the bolometric flux calibration adopted is explored and it is shown that its effect on the T _ { \mathrm { eff } } scale , although systematic , is conservatively no larger than 50 K. Finally , a comparison with temperatures derived with other techniques is made .
Agreement is found with the temperatures from Balmer line-profile fitting and the surface-brightness technique .
The temperatures derived from the spectroscopic equilibrium of Fe i lines are differentially consistent with the IRFM but a systematic difference of about 100 K and 65 K ( the IRFM temperatures being lower ) is observed in the metal-rich dwarf and metal-poor giant T _ { \mathrm { eff } } scales , respectively .