論文

査読有り
2018年2月

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

Monthly Notices of the Royal Astronomical Society

DOI
10.1093/mnras/stx2620

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<SUP>-3</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP>, both direct and diffuse light jointly operate to prevent mass accretion at Z ≳ 10<SUP>-1</SUP> Z<SUB>☉</SUB>. At Z ≲ 10<SUP>-1</SUP> Z<SUB>☉</SUB>, the diffuse light is no longer effective and the direct light solely limits the mass accretion. At Z ≲ 10<SUP>-3</SUP> Z<SUB>☉</SUB>, formation of the H II region plays an important role in terminating the accretion. The resultant upper mass limit increases with decreasing metallicity, from a few × 10 M<SUB>☉</SUB> to ∼10<SUP>3</SUP> M<SUB>☉</SUB> over Z = 1 Z<SUB>☉</SUB>-10<SUP>-4</SUP> Z<SUB>☉</SUB>. 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 1 Z<SUB>☉</SUB>, shifts to < 3 μm at Z ≲ 0.1 Z<SUB>☉</SUB>. Secondly, a characteristic feature at 10 μm due to the amorphous silicate band appears as a dip at 1 Z<SUB>☉</SUB>, but changes to a bump at Z ≲ 0.1 Z<SUB>☉</SUB>. Using these spectral signatures, we can search massive accreting protostars in nearby low-metallicity environments with upcoming observations....

リンク情報
DOI
https://doi.org/10.1093/mnras/stx2620
URL
http://orcid.org/0000-0003-3127-5982