We present the B-fields mapped in IRDC G34.43+0.24 using 850 µm polarized dust emission observed with the POL-2 instrument at JCMT. We examine the magnetic field geometries and strengths in the northern, central, and southern regions of the filament. The overall field geometry is ordered and aligned closely perpendicular to the filament's main axis, particularly in regions containing the central clumps MM1 and MM2, whereas MM3 in the north has field orientations aligned with its major axis. The overall field orientations are uniform at large (POL-2 at 14 ′′ and SHARP at 10 ′′ ) to small scales (TADPOL at 2.5 ′′ and SMA at 1.5 ′′ ) in the MM1 and MM2 regions. SHARP/CSO observations in MM3 at 350 µm from Tang et al. show a similar trend as seen in our POL-2 observations. TADPOL observations demonstrate a well-defined field geometry in MM1/MM2 consistent with MHD simulations of accreting filaments. We obtained a plane-of-sky magnetic field strength of 470±190 µG, 100±40 µG, and 60±34 µG in the central, northern and southern regions of G34, respectively, using the updated Davis-Chandrasekhar-Fermi relation. The estimated value of field strength, combined with column density and velocity dispersion values available in the literature, suggests G34 to be marginally critical with criticality parameter λ values 0.8±0.4, 1.1±0.8, and 0.9±0.5 in the central, northern, and southern regions, respectively. The turbulent motions in G34 are sub-Alfvénic with Alfvénic Mach numbers of 0.34±0.13, 0.53±0.30, and 0.49±0.26 in the three regions. The observed aligned B-fields in G34.43+0.24 are consistent with theoretical models suggesting that B-fields play an important role in guiding the contraction of the cloud driven by gravity.

Oxygen-rich Asymptotic Giant Branch (AGB) stars can be intense emitters of SiO (v=1 and 2, J=1→0) and H 2 O maser lines at 43 and 22 GHz, respectively. VLBI observations of the maser emission provide a unique tool to probe the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned H 2 O and v=1 and v=2 SiO maser maps have traditionally limited the physical constraints that can be placed on the SiO maser pumping mechanism. We present phase referenced simultaneous spectral-line VLBI images for the SiO v=1 and v=2, J=1→0, and H 2 O maser emission around the AGB star R LMi, obtained from the Korean VLBI Network (KVN). The simultaneous multi-channel receivers of the KVN offer great possibilities for astrometry in the frequency domain. With this facility we have produced images with bona-fide absolute astrometric registration between high frequency maser transitions of different species to provide the positions of the H 2 O maser emission, and the centre of the SiO maser emission, and hence reducing the uncertainty in the proper motion for R LMi by an order of magnitude over that from Hipparcos. This is the first successful demonstration of source frequency phase referencing for mm-VLBI spectral-line observations and also where the ratio between the frequencies is not an integer.

We present 850 μm polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where N H 2 < 0.93 × 10 22 cm−2 (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at N H 2 ≈ 4.6 × 10 22 cm−2. This can be interpreted as a signature of core formation. At N H 2 ≈ 16 × 10 22 cm−2, magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments (B POS = 60–300 μG)) using the Davis–Chandrasekhar–Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.