Near-infrared spectroscopy of AGB star candidates in Fornax, Sculptor
  and NGC 6822
  Context: The Asymptotic Giant Branch (AGB) phase is characterised by
substantial mass loss that is accompanied by the formation of dust. In extreme
cases this will make the star no longer visible in the optical. For a better
understanding of AGB evolution it is important to identify and characterise
these very red AGB stars.
  Aims: The first aim of this article is to improve the census of red AGB stars
in three Local Group galaxies, based on near-IR spectroscopic observations of
new candidates with red 2MASS (J-K) colours. The opportunity is taken to
compare the near-IR spectra with those of Milky Way stars.
  Methods: We used ISAAC on the ESO VLT to take J and H-band spectra of 36
targets in Fornax, Sculptor and NGC 6822.
  Results: Twelve new C-stars are found in Fornax, and one is confirmed in
Sculptor. All C-stars have (J-K) > 1.6, and are brighter than -3.55 in
bolometric magnitude. Ten new oxygen-rich late-type giant stars are identified
in Fornax, but none is extremely red or very luminous. Five luminous O-rich AGB
stars are identified in NGC 6822, of which 3 show water absorption, indicative
of spectral type M. Again, none is as red as Milky Way OH/IR stars, but in this
galaxy the list of candidate AGB stars is biased against very red objects. In
some C-stars with (J-K)>2 an extremely strong 1.53 $\mu$m absorption band is
found. These stars are probably all Mira variables and the feature is related
to the low temperature, high density chemistry that is a first step towards
dust formation and mass loss.
