Population III star formation in an X-ray background: III. Periodic radiative feedback and luminosity induced by elliptical orbits

ABSTRACT We model Pop III star formation in different FUV and X-ray backgrounds, including radiation feedback from protostars. confirm previous results that a moderate background increases the number of systems per unit cosmological volume, but masses multiplicities system are reduced. The stellar mass function also agrees with results, we outward migration stars within protostellar discs. find nearly all hierarchical, i.e. binaries binaries. Typically, two equal-mass form near centre disc migrate outwards. Around these stars, mini-discs fragment forming Stars may at Lagrange points L4/L5 system. Afterwards, becomes more stochastic due to large multiplicity, zero-metallicity low-mass can when rapidly ejected disc. often have eccentric orbits, leading periodic modulation their accretion rates luminosities. At pericentre, strong accretion, enter red-supergiant phase reaching Eddington luminosity optical bands (mAB ∼ 34 for 100 M⊙ z = 6). During this phase, star, rather than its nebular lines, be observed directly by JWST, if sufficiently magnified gravitational lens. ∼10 000 AU separations high eccentricities many our simulations favourable parameters IMBH mergers – waves emission through orbital excitation field stars.