Assessment of the near infrared identification of carbon stars^*,**

II. The local group galaxies IC 1613 and NGC 3109

¹ INAF, Osservatorio Astronomico di Roma Viale del Parco Mellini 84, 00136 Roma, Italy e-mail: battinel@inaf.it
² Département de Physique, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Qc, H3C 3J7, Canada e-mail: demers@astro.umontreal.ca

Received: 16 July 2008
Accepted: 3 October 2008

Abstract

Context. Thousands of C stars have been identified in Local Group galaxies using narrow band photometry. To survey C stars at larger distances and alternative to the narrow-band approach is needed.

Aims. We obtain, from ESO Archive data, NIR magnitudes and colours of previously known C stars in two dwarf irregular Local Group galaxies, namely IC 1613 and NGC 3109.

Methods. We compare the NIR magnitudes and colours of the C star populations, previously identified from narrow band techniques to estimate the star formation history of their intermediate-age populations.

Results. We demonstrate that the photometric properties of C stars show a wider range in the NIR than in the optical. As confirmed by models we see, among the four galaxies investigated with a 0.7 dex metallicity range, little if any metallicity effect in the C star colour distribution.