We present a method estimating the atmospheric parameters T _ { \mathrm { eff } } , \log g , [ Fe/H ] for stars observed , even at low signal to noise ratio , with the echelle spectrograph ELODIE on the 193cm telescope at Observatoire de Haute-Provence .
The method relies on the least-square comparison of the spectrum of a target star to a library of 211 spectra of reference stars for which the atmospheric parameters are well known and which were observed with the same instrument .
In order to obtain a meaningful comparison between target and reference spectra , all features which are not intrinsic to the objects must be removed .
This treatment involves the correction of the blaze efficiency for each order , cosmic rays hits and telluric line removal , convolution of the spectra to a common spectral resolution , wavelength scale and flux level adjustment .
The library available at the present time covers the effective temperature range [ 4000K , 6300K ] , the metallicity range [ - 2.9 , +0.35 ] and the gravities of both unevolved and evolved stars existing at these temperatures and metallicities .
Tests performed with the actual library allow us to estimate the internal accuracy to be 86 K , 0.28 dex and 0.16 dex for T _ { \mathrm { eff } } , \log g , [ Fe/H ] for a target star with S/N = 100 and 102 K , 0.29 dex and 0.17 dex at S/N = 10 .
This accuracy will improve in the future as the number of reference stars in the library will increase .
The software ( named TGMET ) has been installed at Observatoire de Haute-Provence for the on-line analysis of the high-resolution spectra of ELODIE , which was originaly conceived for accurate radial velocity measurements .