Induced formation of primordial low-mass stars

We show that the explosion of the first supernovae can trigger low-mass star formation via gravitational fragmentation of the supernova-driven gas shell. If the shell mass does not exceed the host galaxy gas mass, all explosions with energies E-SN greater than or equal to 1051 erg can lead to shell fragmentation. However, the minimum ambient density required to induce such fragmentation is much larger, n(0) > 300 cm(-3), for Type II supernovae than for pair-instability ones, which can induce star formation even at lower ambient densities. The typical mass of the unstable fragments is similar to-10(4-7)M(circle dot); their density is in the range 110-6 x 10(7) cm(-3). Fragments have a metallicity strictly lower than 10(-2.6)Z(circle dot) and large values of the gravitational-to-pressure force ratio f similar or equal to 8. Based on these findings, we conclude that the second generation of stars produced by such self-propagating star formation is predominantly constituted by low-mass, long-living, extremely metal-poor (or even metal-free, if mixing is suppressed) stars. We discuss the implications of such results for Pop III star formation scenarios and for the most iron-poor halo star HE0107-5240. (C) 2004 Elsevier B.V. All rights reserved.