This is the astro-ph blog of the Theoretical Modelling of Cosmic Structures group (TMoX) at the Max-Planck-Institute for Extraterrestrial Physics. We are an independent Max-Planck Research Group focusing on the various aspects in the formation and evolution of galaxies. Part of our focus is on the formation and evolution of early-type galaxies, super-massive black holes, the formation of the first structures in the universe and the enrichment history of the Universe. We are theoreticians using analytic modelling as well as numerical simulations in our work.

The CosmologyCake blog is dedicated to the discussion of research papers and current developments. We will regularly post interesting papers and comment on them. Feel free to leave your comments as well. We encourage authors of discussed papers to post replies if they wish to. Our aim is to provide a platform to discuss recent astro-ph papers within a wider audience. Please feel free to send papers you would like to be discussed to us at

17 February 2011

Chromospheres in Metal-Poor Stars Evidenced from the He I 10830 Angstrom Line

Authors: Takeda & Takada-Hidai
Link to paper:

Observations are presented which reveal the presence of hot chromospheres in extremely metal-poor stars.  This raises a challenge to the conventional view that old low-mass stars should have little chromospheric activity as a result of magnetic braking (which slows the rotation of the star, and hence could shut off the dynamo process that produces the magnetic activity which, in turn, powers the chromosphere).  Interestingly, this result also strongly suggests that old metal-free (Pop III) stars may also exhibit substantial chromospheric activity.  If this is the case, then these stars should launch a weak solar-like wind, which we have found (Johnson & Khochfar 2011) would likely prevent the pollution of their surfaces by ISM material.  This provides reason for optimism about the possibility of detecting, unequivocally, Pop III stars in the Galaxy today, if such low-mass primordial stars formed (as suggested by recent high-resolution cosmological simulations; Clark et al. 2011, Greif et al. 2011).

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