Accretion phase of star formation in clouds with different metallicities

Machida, Masahiro N.; Nakamura, Teppei

doi:10.1093/mnras/stu2633

Cited by 49 publications

(48 citation statements)

References 108 publications

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“…This was expected from comparison with disc fragmentation studies in the low-mass star formation regime where the irradiation is negligible, see e.g. Lichtenberg & Schleicher (2015), but also from models in the context of primordial star formation, in which stellar feedback is efficiently at work, see Greif et al (2011);; Machida & Nakamura (2015) and the Fig. 3 of Hosokawa et al (2016) for a resolution study.…”

Section: Effects Of Protostellar Irradiationmentioning

confidence: 66%

Forming spectroscopic massive protobinaries by disc fragmentation

Meyer

Kuiper

Kley

et al. 2017

Monthly Notices of the Royal Astronomical Society

168

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The surroundings of massive protostars constitute an accretion disc which has numerically been shown to be subject to fragmentation and responsible for luminous accretion-driven outbursts. Moreover, it is suspected to produce close binary companions which will later strongly influence the star's future evolution in the Hertzsprung-Russel diagram. We present threedimensional gravitation-radiation-hydrodynamic numerical simulations of 100 M pre-stellar cores. We find that accretion discs of young massive stars violently fragment without preventing the (highly variable) accretion of gaseous clumps onto the protostars. While acquiring the characteristics of a nascent low-mass companion, some disc fragments migrate onto the central massive protostar with dynamical properties showing that its final Keplerian orbit is close enough to constitute a close massive proto-binary system, having a young high-mass and a low-mass component. We conclude on the viability of the disc fragmentation channel for the formation of such short-period binaries, and that both processes -close massive binary formation and accretion bursts-may happen at the same time. FU-Orionis-type bursts, such as observed in the young high-mass star S255IR-NIRS3, may not only indicate ongoing disc fragmentation, but also be considered as a tracer for the formation of close massive binaries -progenitors of the subsequent massive spectroscopic binaries -once the high-mass component of the system will enter the main-sequence phase of its evolution. Finally, we investigate the ALMA-observability of the disc fragments.

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Section: Effects Of Protostellar Irradiationmentioning

confidence: 66%

Forming spectroscopic massive protobinaries by disc fragmentation

Meyer

Kuiper

Kley

et al. 2017

Monthly Notices of the Royal Astronomical Society

168

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“…Greif et al (2012) no approx. 10 19 cm −3 Cosmological, 4 halos, averaged Stacy et al (2012) sink 10 12 cm −3 Cosmological, 1 halo, RF/NF Susa (2013) sink 3 × 10 13 cm −3 BE-sphere, 1 cloud, RF/NF Vorobyov et al (2013) 1 sink + stiff EOS 10 14 cm −3 Cosmological, 1 halo, 2D, time averaged Susa et al (2014) sink 3 × 10 13 cm −3 Cosmological, 59 halos, RF, averaged Machida & Nakamura (2015) stiff EOS 10 19 cm −3 BE-sphere, 1 cloud, time averaged Hartwig et al (2015b) sink 10 17 cm −3 Cosmological, 4 halos Hosokawa et al (2016) cut cooling 10 10 − 10 12 cm −3 Cosmological, 5 halos, RF/NF, polar coord. Stacy et al (2016) sink 10 15 cm −3 Cosmological, 1 halo, RF Hirano & Bromm (2017) cut cooling 10 10 , 10 13 , 10 15 cm −3 Cosmological, 1 halo Note.…”

Section: Comparison With Previous Simulations In the Literaturementioning

confidence: 99%

Merge or Survive: Number of Population III Stars per Minihalo

Susa

2019

ApJ

104

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The formation process of Population III (PopIII) stars in the mass accretion phase is investigated by numerical experiments. The barotropic relation of primordial gas and artificial stiffening of the equation of state in very dense regions (> 10 15 cm −3 ) enables us to follow the fragmentation of PopIII circumstellar disks and the merging processes of the fragments. The disk becomes gravitationally unstable to fragmentation , followed by a rapid merger process typically within 100 yrs, which roughly corresponds to one orbital time of the circumstellar disk. We also find that the fragmentation of the gas disk around a multiple system, a circumbinary disk, is rare; however, it is frequent in the disk around an individual protostar. We also perform a simulation with standard sink particles, where the number and total mass of sink particles are in rough agreement with those of the stiff equation of state runs. Based on the results of these numerical results, we model the evolution of the number of fragments with a simple phenomenological equation. We find that the average number of fragments is roughly proportional to t 0.3 , where t is the elapsed time since the formation of the first protostar. Next, we compare this trend with a number of published numerical studies by scaling the elapsed time according to the scale-free nature of the system. As a result, we find most of the results in the literature agree well with the relation. Present results combined with the previous studies in the literature imply that the PopIII stars tend to be born not as single stars, but in multiple systems.

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“…For example, the magnetic field rarely dissipates in primordial mini-halos and starburst galaxies with a relatively high ionization degree (or small magnetic diffusivity), while it significantly dissipates in our galaxy and more evolved galaxies with a lower ionization degree (or large magnetic diffusivity). Although using three-dimensional simulations, some studies focused on star formation in different environments with different metallicities (Jappsen et al 2007(Jappsen et al , 2009aDopcke et al 2011Dopcke et al , 2013Bate 2014;Chiaki et al 2016), in addition to our previous studies (Machida 2008b;Machida et al 2009,b;Machida & Nakamura 2015), such studies ignored the effect and dissipation of magnetic field. This is because the diffusion rate for the magnetic field, which is derived from the ionization degree of the star forming cloud, in different environments or different metallicities had not been investigated until they were estimated by Susa et al (2015).…”

Section: Introductionmentioning

confidence: 93%

Evolution of magnetic fields in collapsing star-forming clouds under different environments

Higuchi

Machida

Susa

2018

Monthly Notices of the Royal Astronomical Society

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In nearby star-forming clouds, amplification and dissipation of the magnetic field are known to play crucial roles in the star-formation process. The star-forming environment varies from place to place and era to era in galaxies. In the present study, amplification and dissipation of magnetic fields in star-forming clouds are investigated under different environments using magnetohydrodynamics (MHD) simulations. We consider various star-forming environments in combination with the metallicity and the ionization strength, and prepare prestellar clouds having two different mass-to-flux ratios. We calculate the cloud collapse until protostar formation using ideal and nonideal (inclusion and exclusion of Ohmic dissipation and ambipolar diffusion) MHD calculations to investigate the evolution of the magnetic field. We perform 288 runs in total and show the diversity of the density range within which the magnetic field effectively dissipates, depending on the environment. In addition, the dominant dissipation process (Ohmic dissipation or ambipolar diffusion) is shown to strongly depend on the star-forming environment. Especially, for the primordial case, magnetic field rarely dissipates without ionization source, while it efficiently dissipates when very weak ionization sources exist in the surrounding environment. The results of the present study help to clarify star formation in various environments.

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Accretion phase of star formation in clouds with different metallicities

Cited by 49 publications

References 108 publications

Forming spectroscopic massive protobinaries by disc fragmentation

Forming spectroscopic massive protobinaries by disc fragmentation

Merge or Survive: Number of Population III Stars per Minihalo

Evolution of magnetic fields in collapsing star-forming clouds under different environments

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