A new visual – near-infrared diagnostic to estimate the metallicity of cluster and field dwarf stars

¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
e-mail: annalisa.calamida@oa-roma.inaf.it
² IAC – Instituto de Astrofisica de Canarias, Calle via Lactea, 38200 La Laguna, Tenerife, Spain
e-mail: monelli@iac.es; milone@iac.es
³ Department of Astrophysics, University of La Laguna, 38200 La Laguna, Tenerife, Spain
⁴ Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Rome, Italy
e-mail: Giuseppe.Bono@roma2.infn.it; eplagioia@roma2.infn.it
⁵ INAF – Osservatorio Astronomico di Collurania, via M. Maggini, 64100 Teramo, Italy
e-mail: adriano@oa-teramo.inaf.it

Received: 30 May 2012
Accepted: 14 July 2012

Abstract

We present a theoretical calibration of a new metallicity diagnostic based on the Strömgren index m₁ and on visual – near-infrared (NIR) colors to estimate the global metal abundance of cluster and field dwarf stars. To perform the metallicity calibration we adopt α-enhanced evolutionary models transformed into the observational plane by using atmosphere models computed adopting the same chemical mixture. We apply the new visual-NIR metallicity-index-color (MIC) relations to two different samples of field dwarfs and we find that the difference between photometric estimates and spectroscopic measurements is on average smaller than 0.1 dex, with a dispersion smaller than σ = 0.3 dex. We apply the same MIC relations to a metal-poor (M 92) and a metal-rich (47 Tuc) globular cluster. We find a peak of  −2.01 ± 0.08 (σ = 0.30 dex) and  −0.47 ± 0.01 (σ = 0.42 dex), respectively.