A new model for the origin of very metal poor stars and their chemical composition

Abstract

The genesis and chemical patterns of the metal poor stars in the galactic halo remains an open question. Current models do not seem to give a satisfactory explanation for the observed abundances of Lithium in the galactic metal-poor stars and the existence of carbon-enhanced metal-poor (CEMP) and Nitrogen-enhanced metal-poor (NEMP) stars. In order to deal with some of these theoretical issues, we suggest an alternative explanation, where some of the Pop. III SNe are followed by the detonation of their neutron stars (Quark-Novae; QNe). In QNe occurring a few days to a few weeks following the preceding SN explosion, the neutron-rich relativistic QN ejecta leads to spallation of 56Ni processed in the ejecta of the preceding SN explosion and thus to "iron/metal impoverishment" of the primordial gas swept by the combined SN+QN ejecta. We show that the generation of stars formed from fragmentation of pristine clouds swept-up by the combined SN+QN ejecta acquire a metallicity with -7.5 < Fe/H] < -1.5 for dual explosions with 2 < t_delay (days) < 30. Spallation leads to the depletion of 56Ni and formation of sub-Ni elements such as Ti, V, Cr, and Mn providing a reasonable account of the trends observed in galactic halo metal-poor stars. CEMP stars form in dual explosions with short delays (t_delay < 5 days). These lead to important destruction of 56Ni (and thus to a drastic reduction of the amount of Fe in the swept up cloud) while preserving the carbon processed in the outer layers of the SN ejecta. Lithium is produced from the interaction of the neutron-rich QN ejecta with the outer (oxygen-rich) layers of the SN ejecta. A Lithium plateau with 2 < A(Li) < 2.4 can be produced in our model as well as a corresponding 6Li plateau with 6Li/7Li < 0.3.