Dust grain growth and the formation of the extremely primitive star SDSS J102915+172927

Gen Chiaki, Raffaella Schneider, Takaya Nozawa, Kazuyuki Omukai, Marco Limongi, Naoki Yoshida, Alessandro Chieffi

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

Dust grains in low-metallicity star-forming regions may be responsible for the formation of the first low-mass stars. The minimal conditions to activate dust-induced fragmentation require the gas to be pre-enriched above a critical dust-to-gas mass ratio Dcr = [2.6-6.3] × 10-9. The recently discovered Galactic halo star SDSS J102915+172927 has a stellar mass of 0.8M⊙ and a metallicity of Z ̃ 4.5 × 10-5 Z⊙ and represents an optimal candidate for the dust-induced low-mass star formation. Indeed, the critical dust-to-gas mass ratio can be overcome provided that at least 0.4M⊙ of dust condenses in Pop III supernova ejecta, allowing for moderate destruction by the reverse shock. Here, we show that grain growth during the collapse of the parent gas cloud is sufficiently rapid to activate dust cooling and fragmentation into low-mass stars, even if dust formation in the first supernovae is less efficient or strong dust destruction does occur. We find that carbon grains do not experience grain growth because at densities below nH ̃ 106 cm-3 carbon atoms are locked into CO molecules. Silicates and magnetite grains accrete gas-phase species in the density range 109 ≤ nH ≤ 1012 cm-3, until their gasphase abundance drops to zero, reaching condensation efficiencies ̃1. The corresponding increase in the dust-to-gas mass ratio allows dust-induced cooling and fragmentation to be activated at 1012 < nH ≤ 1014 cm-3, before the collapsing cloud becomes optically thick to continuum radiation.

Original languageEnglish
Pages (from-to)3121-3127
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume439
Issue number3
DOIs
Publication statusPublished - 2014 Apr

Keywords

  • Abundances-dust
  • Evolution
  • Extinction-galaxies
  • Formation-stars
  • Low-mass-stars
  • Population II-ISM
  • Stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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