Forming spectroscopic massive protobinaries by disc fragmentation

Abstract

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.

Core fragmentation and Toomre stability analysis of W3(H2O)

“…The median β value is 1.8 × 10 −4 , and the maximum value found in the outskirts is on the order of 10 −2 , which is much lower than the critical value of 1-5. This finding is consistent with that of Klassen et al (2016) and Meyer et al (2018) who also find β 1 in their simulation of collapsing protostellar cores with a mass of 100 M at later times. The rotating bodies within W3(H 2 O) are therefore able to cool rapidly and any local collapse induced by the gravitational instabilities in the disks will lead to fragmentation.…”

“…However, they find that the Toomre conditions combined with the cooling of the disk (Gammie 2001) would potentially yield the formation of a binary companion. Similarly, simulations by Kuiper et al (2011) see such spiral arms in a massive disk, and simulations by Krumholz et al (2009) and more recently Meyer et al (2017Meyer et al ( , 2018) see disk fragmentation on even smaller spatial scales, on the order of hundreds of AU. Therefore, disk fragmentation scenarios in the high-mass regime are valid from a theoretical stand point.…”

“…Are close binary/multiple systems an outcome of disk fragmentation (as suggested by e.g. Meyer et al 2018)? If so, stability analyses of these high-mass rotating cores and disks are needed to shed light on fragmentation at disk scales.…”

Formation and Evolution of Disks Around Young Stellar Objects

“…Usually, increasing the resolution promotes fragmentation. While Kuiper et al (2011) only yields to the formation of spiral arms, these spiral arms fragment in the higher resolution versions (Meyer et al 2017(Meyer et al , 2018. Often, due to limited resolution (e.g., 10-20 au in high mass simulations), sink particles are used to follow the evolution of individual stellar components.…”

From clump to disc scales in W3 IRS4

“…In a previous study of part of W3 including W3 IRS4, Wang et al (2012b) were able to separate the principle structures in the W3 IRS4 region and identify some chemical differences with SMA observations at 1.4 mm. However, they only had shortspacing information from IRAM 30 m observations for 12 CO and 13 CO, so could not explore the variation of temperature and abundance in the region, and their limited velocity and spatial resolution (1.2 km s −1 and 2.2 × 1.7 in the lines, corresponding to 2000 AU scales, respectively) meant they were not really able to probe the 1000 AU scales where discs are expected around high-mass protostars (for example Krumholz et al 2009;Peters et al 2010a;Kuiper et al 2011;Klassen et al 2016;Meyer et al 2017Meyer et al , 2018Kölligan & Kuiper 2018).…”