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| EPoS Contribution |
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Modeling disk fragmentation and multiplicity in massive star formation
Rolf Kuiper ZAH/ITA, U Heidelberg, Heidelberg, DE | |
| Context: There is growing evidence that massive stars grow by disk accretion in a similar way to their low-mass counterparts. Early in evolution, these disks can achieve masses that are comparable to the current stellar mass, and therefore the forming disks are highly susceptible to gravitational fragmentation. Aims: We investigate the formation and early evolution of an accretion disk around a forming massive protostar, focussing on its fragmentation physics. To this end, we follow the collapse of a molecular cloud of gas and dust, the formation of a massive protostar, the formation of its circumstellar disk, and the formation and evolution of the disk fragments. Methods: We used a grid-based, self-gravity radiation hydrodynamics code including a sub-grid module for stellar evolution and dust evolution. We purposely do not use a sub-grid module for fragmentation such as sink particles to allow for all paths of fragment formation and destruction, but instead we keep the spatial grid resolution high enough to properly resolve the physical length scales of the problem, namely the pressure scale height and Jeans length of the disk. Simulations are performed on a grid in spherical coordinates with a logarithmic spacing of the grid cells in the radial direction and a cosine distribution of the grid cells in the polar direction, focusing the spatial resolution on the disk midplane. As a consequence, roughly 25% of the total number of grid cells, corresponding to ~26 million grid cells, are used to model the forming disk alone. These constitute the highest resolution simulations performed up to now on disk fragmentation around a forming massive star with the physics considered here. For a better understanding of the effects of spatial resolution and to compare our high-resolution results with previous lower resolution studies in the literature, we perform the same simulation at five different resolutions, each run differing in resolution from its predecessor by a factor of two. Results: The cloud collapses and a massive (proto)star is formed in its center surrounded by a fragmenting Keplerian-like accretion disk with spiral arms. The fragments have masses of ~1 Msun, and their continuous interactions with the disk, spiral arms, and other fragments result in eccentric orbits. Fragments form hydrostatic cores surrounded by secondary disks with spiral arms that also produce new fragments. We identified several mechanisms of fragment formation, interaction, and destruction. Central temperatures of the fragments can reach the hydrogen dissociation limit, form second Larson cores, and evolve into companion stars. Based on this, we study the multiplicity predicted by the simulations and find approximately six companions at different distances from the primary: from possible spectroscopic multiples, to companions at distances between 1000 and 2000 au. | |
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| Caption: Convergence test with respect to spatial resolution. Upper panel: Midplane cut through the disk's gas mass density. Data were taken at t = 7.5 kyr for all the maps in the row. Lower panel: Comparison of spatial resolution of the disk's pressure scale height and Jeans length in our spherical coordinate grid code and other studies that use Cartesian adaptive mesh refinement (AMR). The different relevant scales of the system are shown as dashed lines; these were calculated as averages for the time period [6,8] kyr, and the corresponding disk radius is shown in the gray box. The number following the label for the AMR curves indicates the minimum cell size in astronomical units. | |
| Collaborators: A. Oliva, U Tuebingen |
Key publication
Suggested Session: High Mass |