TY - JOUR
T1 - Upper stellar mass limit by radiative feedback at low-metallicities
T2 - Metallicity and accretion rate dependence
AU - Fukushima, Hajime
AU - Omukai, Kazuyuki
AU - Hosokawa, Takashi
N1 - Funding Information:
The authors wish to express our cordial thanks to Prof Takahiro Tanaka for his continual interest and advice. We also thank Daisuke Nakauchi, Kazu Sugimura, Sanemichi Takahashi, Hidekazu Tanaka and Hide Yajima for fruitful discussions. This work is supported in part by MEXT/JSPS KAKENHI grants (KO:25287040, 17H01102 and TH:16H05996).
Publisher Copyright:
© 2018 The Author(s).
PY - 2018/2/1
Y1 - 2018/2/1
N2 - 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.
AB - 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.
KW - Accretion
KW - Accretion discs
KW - Stars: Population II
KW - Stars: formation
KW - Stars: massive
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U2 - 10.1093/mnras/stx2620
DO - 10.1093/mnras/stx2620
M3 - Article
AN - SCOPUS:85046094018
VL - 473
SP - 4754
EP - 4772
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -