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 neutronrich relativistic QN ejecta leads to spallation of 56 Ni 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 56 Ni 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 56 Ni (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 6 Li plateau with 6 Li/ 7 Li < 0.3.

A resolution of the cosmic Lithium problem

“…< 40M ⊙ range (e.g. Ouyed et al 2009a;Ouyed et al 2009b;Leahy&Ouyed 2009;Ouyed&Leahy 2013;Ouyed 2013). Thus, primordial QNe are expected to occur in the wake of these Pop.…”

“…These iron-poor clouds form into low metallicity Pop. II stars (Ouyed 2013). A key parameter is the time delay between the first SN explosion and the subsequent QN explosion.…”

“…If the time t delay between SN and QN explosions is too lengthy (of the order of months), the SN ejecta will have dissipated such that the QN erupts in isolation. However, when t delay is on the order of days to weeks the neutron-rich QN ejecta interacts with the preceding SN ejecta leading to spallation products that are unique to dsQNe (Ouyed et al 2011;Ouyed 2013).…”

“…To produce a realistic distribution of product nuclei from this sub-layer, we draw the number of hits from a Poisson distribution. The interested reader is referred to Ouyed et al (2011; see eqs 3, 4 and 5 in that paper) and Ouyed (2013) for more details on the spallation process, numerical procedure, and relevant references.…”

Hints of a second explosion (a quark nova) in Cassiopeia A supernova

“…We predict about ∼ 10 −4 M ⊙ of light nuclei adjacent to 44 Ti in the inner ejecta of Cas A, particularly in the SE direction. A wide range of stable isotopes produced by spallation includes 45 Sc and 9 F (see Figure 2 in Ouyed 2013). -The spallation (multi-generation) neutrons add up to a total mass of ∼ 0.1M ⊙ M QN,−3 (see Ouyed et al 2011) 9 .…”