The assessment of the near infrared identification of Carbon stars. I. The Local Group galaxies WLM, IC 10 and NGC 6822

Abstract

{The selection of AGB C and M stars from NIR colours has been done in recent years using adjustable criteria that are in needs of standardization if one wants to compare, in a coherent manner, properties of various populations.} We intend to assess the NIR colour technique to identify C and M stars. We compare the NIR colours of several C stars previously identified from spectroscopy or narrow band techniques in WLM, IC 10 and NGC 6822. We demonstrate that very few M stars have $(J-K{)}_0>1.4$ but a non negligible number of C stars are bluer than this limit. Thus, counts of M and C stars based on such limit do not produce pure samples. C/M ratios determined from NIR colours must be regarded as underestimates mainly because the M numbers include many warm C stars and also K stars if no blue limit is considered.

arXiv commentA&A accepted 18.07.2007

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• Astrophysical Distance Scale II. Application of the JAGB Method: A Nearby Galaxy Sample
• SAO-6m Telescope Spectroscopic Observations of Globular Clusters in Nearby Galaxies
• The AGB population in IC 1613 using JHK photometry
• Carbon Stars in the Satellites and Halo of M31
• The Stellar Disk of M81
• Asymptotic Giant Branch Stars in the Nearby Dwarf Galaxy Leo P
• Near-infrared properties of asymptotic giant branch stars in nearby dwarf elliptical Galaxy NGC 205