Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Measurement of the Magnitude and Orientation of the Magnetic
  Field in Molecular Clouds   We demonstrate that the combination of Zeeman, polarimetry and ion-to-neutral
molecular line width ratio measurements permits the determination of the
magnitude and orientation of the magnetic field in the weakly ionized parts of
molecular clouds. Zeeman measurements provide the strength of the magnetic
field along the line of sight, polarimetry measurements give the field
orientation in the plane of the sky and the ion-to-neutral molecular line width
ratio determines the angle between the magnetic field and the line of sight. We
apply the technique to the M17 star-forming region using a HERTZ 350 um
polarimetry map and HCO+-to-HCN molecular line width ratios to provide the
first three-dimensional view of the magnetic field in M17.

12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph