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The MPIA conference series
at Ringberg Castle
The MPIA conference series
at Ringberg Castle
EPoS 2020 Suggested Contribution
Linking zoom-in models of embedded protostar formation to observations of polarized dust

Michael Kueffmeier
ZAH, Heidelberg, DE
ALMA provides maps of polarized dust around embedded protostars that help to constrain the magnetic field structure during star formation. However, interpreting the observations is challenging without models that can consistently account for the turbulent protostellar birth environment. Using zoom-in simulations, we are able to model the formation of low-mass stars embedded in a filamentary Giant Molecular Cloud without the restriction of initial and boundary conditions associated with the "spherical cow" approach of collapsing prestellar cores. For the less common case of isolated prestellar cores, the formation process is similar to what is expected from spherical collapse models. However, the majority of stars are deeply embedded along filaments in the Giant Molecular Cloud, and their formation process deviates significantly from classical models. In particular, we find sequential formation in systems of protostellar multiples during which bridge-like structures occur. The characteristic density in the most prominent bridge of our sample is about 10-16g/cm3, and the magnetic field strength in the bridge is about 1 to 2 mG. Producing synthetic maps of dust polarization through emission and self-scattering, we can directly compare our results to ALMA observations. While the density is in good agreement with estimates for observations of e.g. IRAS 16293-2422, the preliminary polarization patterns suggests differences in the field morphology and the field strength is estimated to be approximately 10 times lower compared to observations. This suggests that the magnetic field is non-critical for the formation of bridge structures though the magnetic field is crucial for magnetic braking and the launching of outflows in the vicinity of the protostars. Finally, consistent with gas observations of young disks, our models predict the presence of filamentary accretion arms feeding the young disk. In this contribution, we will show synthetic maps of dust polarization and discuss the observational implications for these "streamers".
Caption: Left: Magnetic field strength in a bridge associated with a forming protostellar triple. The bridge connects a binary system with ~100 au separation (located in the yellow region at the bottom of the image) to a third protostar at 2100 au (forming at the upper end). The color displays the magnetic field strength displayed on an isosurface of density 10-16g/cm3. Right: Synthetic observations of the bridge-structure from the RAMSES simulations with the radiative transfer code POLARIS. The plots show the intensity of dust polarization (Stokes I) in the synthetic bridge. The upper panel shows the polarization due to dust emission, the lower one due to scattering. The brighter region corresponds to the forming third companion.
S. Reissl, ZAH, DE
C.P. Dullemond, ZAH, DE
S. Sadavoy, Queens, CA
T. Haugbolle, NBI, DK
Å. Nordlund, NBI, DK
L.E. Kristensen, NBI, DK
H. Calcutt, Chalmers, SE
Key publication

Suggested Session: Magnetic Fields