1.3mm polarized emission in the circumstellar disk of a massive protostar

TL;DR

This study presents the first resolved 1.3mm polarized emission observations of a high-mass protostar's disk, exploring magnetic fields and dust grain properties during early star formation.

Contribution

It provides new high-resolution polarization data of a massive protostar's disk, analyzing potential polarization mechanisms and implications for grain growth.

Findings

Polarization vectors are uniform with a 57-degree position angle.

Both magnetic alignment and scattering can explain the polarization pattern.

Grain sizes may grow to several tens of microns in early high-mass star formation.

Abstract

We present the first resolved observations of the 1.3mm polarized emission from the disk-like structure surrounding the high-mass protostar Cepheus A HW2. These CARMA data partially resolve the dust polarization, suggesting an uniform morphology of polarization vectors with an average position angle of 57 degrees and an average polarization fraction of 2.0%. The distribution of the polarization vectors can be attributed to (1) the direct emission of magnetically aligned grains of dust by a uniform magnetic field, or (2) the pattern produced by the scattering of an inclined disk. We show that both models can explain the observations, and perhaps a combination of the two mechanisms produce the polarized emission. A third model including a toroidal magnetic field does not match the observations. Assuming scattering is the polarization mechanism, these observations suggest that during the first few 10000 years of high-mass star formation, grain sizes can grow from 1 to several 10s micron.