Chemical abundances of newly discovered old open clusters
Final Report Abstract
The observing run took place in June 12 – 15 2015 at the Calar Alto Observatory (Spain). We used the 3.5m telescope and the TWIN spectrograph to acquire medium resolution, optical spectra of about 10 stars in each of the following Galactic open clusters: MWSC 5371 and MWSC 5366. Unfortunately, some bad weather conditions and some technical problems of the telescope encountered during the observations did not allowed us to acquire spectra for the third cluster in the target list (i.e. MWSC 5367). We selected the stars to be observed in terms of their cluster membership (based on both their proper motion and position on the 2MASS colour-magnitude diagram). We were able to collect high S/N (between 50 and 100 according to the star magnitude) data which are under reduction. Once the spectra are reduced and extracted, they will be analyzed with the chemical code SP_Ace, which operates in the range 5200- 6900 Å for stars with effective temperatures lower than 7000 K, thus optimized for the analysis of stars with spectral types FGKM. This code will measure the radial velocity of each star (which we will use to confirm/discard its cluster membership) and, at the same time, the stellar parameters (effective temperature and gravity), total metallicity and the [α/Fe] ratio. We will then use the chemical compositions determined only for the confirmed cluster member stars to estimate the cluster average metallicity and [α/Fe] ratio, which will be then compared with the chemical radial and vertical gradients of field stars at the cluster position. Since the observations were carried out through a long slit, we happened to observe also a compact galaxy, whose only GALEX (far and near UV) luminosity had been previously measured. We reduced and extracted its spectra, which are characterized by a very low and flat continuum with strong emission lines (indicative of on-going star formation) and no stellar absorption features. This likely qualifies the observed galaxy as a HII galaxy, the only one so far detected at a redshift z ~ 0.07 (the others known being at z ~ 0).
