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Making Bright Giants Invisible At The Galactic Centre



ABSTRACT

Current observations of the Galactic Centre (GC) seem to display a core-like distribution of bright stars from ̃5 arcsec inwards. On the other hand, we observe young, massive stars at the GC, with roughly 20-50 per cent of them in a disc, mostly in the region where the bright giants appear to be lacking. In a previous publication we put the idea forward that the missing stars are deeply connected to the presence of this disc. The progenitor of the stellar disc is very likely to have been a gaseous disc that at some point fragmented and triggered star formation. This caused the appearance of overdensity regions in the disc that had high enough densities to ensure stripping large giants of their atmospheres and thus rendering them very faint. In this paper, we use a stellar evolution code to derive the properties that a red giant would display in a colour-magnitude diagram, as well as a non-linearity factor required for a correct estimate of the mass loss. We find that in a very short time-scale, the red giants leave their standard evolutionary track. The non-linearity factor has values that not only depend on the properties of the clumps, but also on the physical conditions of the giant stars, as we predicted analytically. According to our results, envelope stripping works, moving stars on a short time-scale from the giant branch to the white dwarf stage, thus rendering them invisible to observations.