Upper stellar mass limit by radiative feedback at low-metallicities: Metallicity and accretion rate dependence

Hajime Fukushima, Kazuyuki Omukai, Takashi Hosokawa

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15 Citations (Scopus)


We investigate the upper stellar mass limit set by radiative feedback for a forming star with various accretion rates and metallicities. Thus, we numerically solve the structures of both a protostar and its surrounding accretion envelope assuming a spherical symmetric and steady flow. The optical depth of the dust cocoon, a dusty part of the accretion envelope, differs for direct light from the stellar photosphere and diffuse light re-emitted as dust thermal emission. As a result, varying the metallicity qualitatively changes the way that the radiative feedback suppresses the accretion flow. With a fixed accretion rate of 10-3M yr-1, both direct and diffuse light jointly operate to prevent mass accretion at Z 10-1 Z. At Z ≲ 10-1 Z, the diffuse light is no longer effective and the direct light solely limits the mass accretion. At Z ≲ 10-3 Z, formation of the HII region plays an important role in terminating the accretion. The resultant upper mass limit increases with decreasing metallicity, from a few × 10M to ~103M over Z = 1Z-10-4 Z. We also illustrate how the radiation spectrum of massive star-forming cores changes with decreasing metallicity. First, the peak wavelength of the spectrum, which is located around 30 μm at 1Z, shifts to < 3 μm at Z ≲ 0.1 Z. Secondly, a characteristic feature at 10 μm due to the amorphous silicate band appears as a dip at 1 Z, but changes to a bump at Z ≲ 0.1 Z. Using these spectral signatures, we can search massive accreting protostars in nearby low-metallicity environments with upcoming observations.

Original languageEnglish
Pages (from-to)4754-4772
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2018 Feb 1


  • Accretion
  • Accretion discs
  • Stars: Population II
  • Stars: formation
  • Stars: massive

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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