Cool carbon stars in the halo: a new survey based on 2MASS

21 pages, 12 figs, accepted by Astron. & AstrophysicsWe present the first results of a new survey for finding cool N-type carbon (C) stars in the halo of the Galaxy. Candidates were first selected in the 2MASS Second Incremental Release database with JHKs colours typical of red AGB C stars and Ks < 13, and susequently checked through slit spectroscopy. 27 new halo C stars were discovered, and a detailed study of their properties are given (distance, radial velocity, variablility, proper motion, colors etc). It is found that most probably all these stars are true luminous AGB stars, rather than C dwarfs. It is finally found that about half of these stars belong to the Sgr Stream. (this abstract was shortened