Near-infrared spectroscopy of AGB star candidates in Fornax, Sculptor and NGC 6822 - Astrophysics > Astrophysics of GalaxiesReport as inadecuate




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Abstract: Context: The Asymptotic Giant Branch AGB phase is characterised bysubstantial mass loss that is accompanied by the formation of dust. In extremecases this will make the star no longer visible in the optical. For a betterunderstanding of AGB evolution it is important to identify and characterisethese very red AGB stars.Aims: The first aim of this article is to improve the census of red AGB starsin three Local Group galaxies, based on near-IR spectroscopic observations ofnew candidates with red 2MASS J-K colours. The opportunity is taken tocompare 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 36targets in Fornax, Sculptor and NGC 6822.Results: Twelve new C-stars are found in Fornax, and one is confirmed inSculptor. All C-stars have J-K > 1.6, and are brighter than -3.55 inbolometric magnitude. Ten new oxygen-rich late-type giant stars are identifiedin Fornax, but none is extremely red or very luminous. Five luminous O-rich AGBstars are identified in NGC 6822, of which 3 show water absorption, indicativeof spectral type M. Again, none is as red as Milky Way OH-IR stars, but in thisgalaxy the list of candidate AGB stars is biased against very red objects. Insome C-stars with J-K>2 an extremely strong 1.53 $\mu$m absorption band isfound. These stars are probably all Mira variables and the feature is relatedto the low temperature, high density chemistry that is a first step towardsdust formation and mass loss.



Author: M.A.T. Groenewegen, A. Lancon, M. Marescaux

Source: https://arxiv.org/







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