The assessment of the near infrared identification of carbon stars

Free access article

Issue		A&A Volume 474, Number 1, October IV 2007


Page(s)		35 - 41
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20077760

A&A 474, 35-41 (2007)
DOI: 10.1051/0004-6361:20077760

I. The Local Group galaxies WLM, IC 10 and NGC 6822

P. Battinelli¹, S. Demers², and F. Mannucci³

¹ INAF, Osservatorio Astronomico di Roma, Viale del Parco Mellini 84, 00136 Roma, Italy
    e-mail: battinel@oarhp1.rm.astro.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
³ INAF - Instituto di Radioastronomia, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: filippo@arcetri.astro.it

(Received 30 April 2007 / Accepted 18 July 2007 )

Abstract
Context.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.
Aims.We intend to assess the NIR colour technique to identify C and M stars.
Methods.We compare the NIR colours of several C stars previously identified from spectroscopy or narrow band techniques in WLM, IC 10 and NGC 6822.
Results.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.
Conclusions.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.

Key words: galaxies: individual: IC 10 -- galaxies: individual: WLM -- galaxies: individual: NGC 6822 -- stars: carbon -- stars: AGB and post-AGB -- galaxies: dwarf

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