Clusters of stars are key objects for the study of the dynamical
and chemical evolution of the Galaxy and its neighbors. In particular chemical
composition is obtained from different kinds of stars (hot main-sequence
stars, cool main-sequence stars, horizontal-branch stars, RGB stars) using different
methodologies. Our aim is to apply these methodologies to the stars
of the Open Cluster NGC 6475. Obtaining a census of the most
important elements we will be able to test their consistence.
We finally want to establish more robust fundamental parameters for this cluster.We selected high S/N high resolution spectra of 7 stars of the Open Cluster NGC 6475 from
the ESO database covering the Teff range 4500-10000 K and of luminosity
class V (dwarf) and III (giants).
We determined the chemical abundances of several elements. For hot stars
(Teff > 9000 K) we applied the Balmer Lines fitting method
to obtained atmospheric parameters. For cool stars (Teff < 6500
K) we used the FeI/II abundance equilibrium method. For the two groups
of stars the use of different line-lists was mandatory. LTE approximation
was used. For elements affected by NLTE deviation (C,N,O,Na,Mg) corrections
were applied. The abundance of many elements were obtained from the
measurement of the equivalent width of spectral lines. For those elements
for which only blended lines were available (O, He) comparison of real
spectrum with synthetic ones was used. Hyperfine structure was taken in
account for V and Ba.First of all we showed that the two methodologies we used give abundances which
are in agreement within the errors. This implies that no appreciable relative
systematic effects are present for the derived chemical content of cool and hot stars.
On the other hand giants stars show clear chemical peculiarities with
respect the dwarf concerning light elements (up to Si) and maybe Ba.
This fact can be explained as an evolutionary effect.
Then, having a new estimation of the metallicity for the cluster
([Fe/H] = +0.03±0.02, [α/Fe] = -0.06±0.02)
we fitted suitable isochrones to the CMD of the cluster obtaining
the basic parameters (E(B-V) = 0.08±0.02, (m-M)0 = 7.65±0.05, Age = 200±50 Myrs).