Long-slit medium-resolution spectra of the Galactic globular clusters ( GCs ) NGC 6229 and NGC 6779 , obtained with the CARELEC spectrograph at the 1.93-m telescope of the Haute-Provence observatory , have been used to determine the age , helium abundance ( Y ) , and metallicity [ Fe/H ] as well as the first estimate of the abundances of C , N , O , Mg , Ca , Ti , and Cr for these objects .
We solved this task by comparing the observed spectra and the integrated synthetic spectra , calculated with the use of the stellar atmosphere models with the parameters preset for the stars from these clusters .
The model mass estimates , T _ { eff } , and \log~ { } g were derived by comparing the observed “ color–magnitude ” diagrams and the theoretical isochrones .
The summing-up of the synthetic blanketed stellar spectra was conducted according to the Chabrier mass function .
To test the accuracy of the results , we estimated the chemical abundances , [ Fe/H ] , \log~ { } t , and Y for the NGC 5904 and NGC 6254 clusters , which , according to the literature , are considered to be the closest analogues of the two GCs of our study .
Using the medium-resolution spectra from the library of Schiavon et al. , we obtained for these two clusters a satisfactory agreement with the reported estimates for all the parameters within the errors .
We derived the following cluster parameters .
NGC 6229 : [ Fe / H ] = -1.65 dex , t = 12.6 Gyr , Y = 0.26 , [ \alpha / Fe ] = 0.28 dex ; NGC 6779 : [ Fe / H ] = -1.9 dex , t = 12.6 Gyr , Y = 0.23 , [ \alpha / Fe ] = 0.08 dex ; NGC 5904 : [ Fe / H ] = -1.6 dex , t = 12.6 Gyr , Y = 0.30 , [ \alpha / Fe ] = 0.35 dex ; NGC 6254 : [ Fe / H ] = -1.52 dex , t = 11.2 Gyr , Y = 0.30 , [ \alpha / Fe ] = 0.025 dex .
The value [ \alpha / Fe ] denotes the average of the Ca and Mg abundances .