New age-metallicity diagnostic diagram for the Washington photometric system

• Autores: Piatti, Andrés E.; Perren, Gabriel Ignacio
• Año de publicación: 2015
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Astronómicas; Techniques: photometric
• Institución: Universidad Nacional de La Plata

The age calibration of the Washington δT₁ index is mainly used to estimate ages of star clusters older than 1 Gyr and no age-metallicity degeneracy effect is considered. We have profusely exploited synthetic T₁ versus C - T₁ colour magnitude diagrams to explore the intrinsic behaviour of the δT₁ index. The analysis shows that δT₁ varies with age and metal content as well. In general, the dependence on age weakens for ages greater than ~6 Gyr, and is even less sensitive to age as the metallicity decreases. For ages younger than ~5 Gyr, δT₁ shows a strong correlation with both age and metallicity. The δC index - defined as δT₁ for the C passband - is also a combined measurement of age and metallicity. We introduce a new age-metallicity diagnostic diagram, δT₁ versus δC - δT₁, which can unambiguously provide age and metallicity estimates, simultaneously. The new procedure can be used to derive ages from 1 up to 13 Gyr and metallicities [Fe/H] from -2.0 up to +0.5 dex, and is independent of the cluster reddening and distance modulus. It solves the constraints found in the δT₁ index and surpasses the performance of the standard giant branch metallicity method. All these features make the diagnostic diagram a powerful tool for estimating accurate ages as well as metallicities.
Facultad de Ciencias Astronómicas y Geofísicas