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

Authors: Takeda & Takada-Hidai
Link to paper:  http://arxiv.org/abs/1102.3210

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).