Chemical abundance analysis of the open clusters Cr 110, NGC 2099 (M 37), NGC 2420, NGC 7789, and M 67 (NGC 2682)
Context. The present number of Galactic open clusters that have high resolution abundance determinations, not only of [Fe/H], but also of other key elements, is largely insufficient to enable a clear modeling of the Galactic disk chemical evolution.
Aims: To increase the number of Galactic open clusters with high quality measurements.
Methods: We obtained high resolution (R ~ 30 000), high quality (S/N ~ 50-100 per pixel), echelle spectra with the fiber spectrograph FOCES, at Calar Alto, Spain, for three red clump stars in each of five Open Clusters. We used the classical equivalent width analysis method to obtain accurate abundances of sixteen elements: Al, Ba, Ca, Co, Cr, Fe, La, Mg, Na, Nd, Ni, Sc, Si, Ti, V, and Y. We also derived the oxygen abundance using spectral synthesis of the 6300 Å forbidden line.
Results: Three of the clusters were never studied previously with high resolution spectroscopy: we found [Fe/H] = +0.03±0.02 (±0.10) dex for Cr 110; [Fe/H] = +0.01±0.05 (±0.10) dex for NGC 2099 (M 37), and [Fe/H] = -0.05±0.03 (±0.10) dex for NGC 2420. This last finding is higher than typical literature estimates by 0.2-0.3 dex approximately and in closer agreement with Galactic trends. For the remaining clusters, we find that [Fe/H] = +0.05±0.02 (±0.10) dex for M 67 and [Fe/H] = +0.04±0.07 (±0.10) dex for NGC 7789. Accurate (to ~0.5 km s-1) radial velocities were measured for all targets, and we provide the first velocity estimate derived from high resolution data for Cr 110, < V_r> = 41.0±3.8 km s-1.
Conclusions: With our analysis of the new clusters Cr 110, NGC 2099, and NGC 2420, we increase the sample of clusters with high-resolution-based abundances by 5%. All our program stars show abundance patterns which are typical of open clusters, very close to solar with few exceptions. This is true for all the iron-peak and s-process elements considered, and no significant α-enhancement is found. No significant (anti-)correlations for Na, Al, Mg, and O abundances are found. If anticorrelations are present, the involved spreads must be <0.2 dex. We then compile high resolution data of 57 OC from the literature and find a gradient of [Fe/H] with Galactocentric radius of -0.06±0.02 dex kpc-1, in agreement with past work and with results for Cepheids and B stars in the same range. A change of slope is seen outside RGC = 12 kpc and [α/Fe] shows a tendency to increase with RGC. We also confirm the absence of a significant age-metallicity relation, finding slopes of -2.6±1.1 × 10-11 dex Gyr-1 and 1.1±5.0 × 10-11 dex Gyr-1 for [Fe/H] and [α/Fe] respectively.
Astronomy and Astrophysics
- Pub Date:
- February 2010
- stars: abundances;
- Galaxy: disk;
- open clusters and;
- associations: general;
- Astrophysics - Astrophysics of Galaxies
- 20 pages, 10 figures, accepted for publication by A&