EDP Sciences
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Volume 436, Number 1, June II 2005
Page(s) 91 - 99
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20042536

A&A 436, 91-99 (2005)
DOI: 10.1051/0004-6361:20042536

The C star outer disk population of M 31 seen with the SLOAN filters

S. Demers1 and P. Battinelli2

1  Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
    e-mail: demers@astro.umontreal.ca
2  INAF - Osservatorio Astronomico di Roma, Viale del Parco Mellini 84, 00136 Roma, Italia
    e-mail: battinel@oarhp1.rm.astro.it

(Received 14 December 2004 / Accepted 17 February 2005 )

We employ the CFHT Megacam camera to survey ~one deg2 of the southern outer disc of M 31, a region which includes the area where Battinelli et al. (2003, AJ, 125, 1298) have identified nearly one thousand C stars. In the outer M 31 region not previously surveyed, we identify 361 new C star candidates, having similar photometric properties to the known ones, and confirm the slight decrease in the luminosity of C stars with galactocentric distances. We show that the Sloan g', r', i' filters are a viable approach, comparable to (CN - TiO), to identify C stars. We find that the (g' - r') colours of cool C stars can be so red that prohibitively long g' exposures are needed to acquire faint extragalactic C stars. This makes the Sloan filters a less promising approach to extend a C star survey to several Mpc. Our uniform large field survey detects the edge of M 31 disk at ~35 kpc. The intermediate-age population, represented by C stars, extends further to ~40 kpc.

Key words: galaxies: individual: M 31 -- stars: carbon

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