The direct method applying the near-infrared surface brightness technique along with bolometric flux measurements has been implemented to determine individual temperatures as accurate as 1 % for a sample of 537 A-F-G-K dwarfs and giants selected as ISO standard stars. The investigation shows that the required target accuracy is within the reach of the carefully calibrated photometric correlations as a function of the Johnson broadband colour notably using the high-precision near-infrared K magnitudes obtained for this purpose and Hipparcos parallaxes for interstellar reddening corrections. These improvements enable so tight correlations for bolometric flux parameters that gravity effects become now detectable in the field of giants, whereas the much tighter correlations of dwarfs do not show any signature of metallicity up to the intrinsic scatter set by the observational photometry despite the wide range in metal content for these stars.
The small residual coupling with model-atmosphere calculations required to evaluate systematic corrections in measurements of calibrating angular diameters (limb-darkening) and bolometric fluxes (energy in gaps between observed wavelenghts) makes the actual empirical approach as the best available approximation to fundamental stellar parameters over the sampled temperature range. Hence, these data can be exploited as suitable references to assess random and systematic errors affecting semiempirical methods closely related to model-atmosphere predictions as well as to calibrate different photometric relationships.
© European Southern Observatory (ESO) 1998
Online publication: October 22, 1998