ar X iv : a st ro - p h / 04 07 28 2 v 1 1 4 Ju l 2 00 4 1 AGB stars in the Local Group , and beyond

1.1 Introduction Carbon stars are tracers of the intermediate age population in galaxies. Either they are currently undergoing third dredge-up on the (Thermal-Pulsing) Asymp-totic Giant Branch (TP-AGB) – the cool and luminous N-type carbon stars (or the " infrared carbon stars " , when they are significantly reddened by circumstel-lar dust through mass-loss) –, or have been enriched with carbon-rich material in a binary system when the present-day white dwarf was on the AGB (the carbon dwarfs and CH-stars. The R-stars may be the result of a coalescing binary [McClure 1997]). Similarly, there are " intrinsic " and " extrinsic " S-stars which represent, respectively , the stars currently on the AGB, and the stars polluted by a present-day white dwarf (e.g. Jorissen 2003). Next to the classical oxygen-rich giants (of spectral type M and MS), there are the OH/IR stars (which are obscured by circumstellar dust) and the Barium-dwarfs and Barium-giants which are polluted by a present-day WD (e.g. Jorissen 2003). Since their spectral signature is very different from oxygen-rich and S-type stars, it is relatively easy to identify carbon stars even at large distances. In Sect. 1.2 the main technique to identify carbon stars is briefly discussed, and various recent surveys for carbon stars in external galaxies are summarised. That section is an update of reviews I gave at IAU Symposium 191 (Groenewegen 1999; hereafter G99), and a Ringberg conference (Groenewegen 2002; hereafter G02), and here I will only refer to new results published since then. Please refer to G99, G02 and the similar review by Azzopardi (1999) for the full story. Sections 1.3 and 1.4 discuss aspects related to NIR work and variability properties of AGB stars in LG galaxies. This has been discussed in some detail in G99. Briefly, the most effective method for large scale surveys of late-type M-and C-stars uses typically two broad-band filters from the set V, R, I, and two narrow-band filters near 7800 and 8100Å, which are centred on a CN-band in carbon stars, and a TiO band in oxygen-rich stars, respectively.