485 research outputs found
Millimeter polarisation of the protoplanetary nebula OH 231.8+4.2: A follow-up study with CARMA
In order to investigate the characteristics and influence of the magnetic
field in evolved stars, we performed a follow-up investigation of our previous
submillimeter analysis of the proto-planetary nebula (PPN) OH 231.8+4.2 (Sabin
et al. 2014), this time at 1.3mm with the CARMA facility in polarisation mode
for the purpose of a multi-scale analysis. OH 231.8+4.2 was observed at ~2.5"
resolution and we detected polarised emission above the 3-sigma threshold (with
a mean polarisation fraction of 3.5 %). The polarisation map indicates an
overall organised magnetic field within the nebula. The main finding in this
paper is the presence of a structure mostly compatible with an ordered toroidal
component that is aligned with the PPN's dark lane. We also present some
alternative magnetic field configuration to explain the structure observed.
These data complete our previous SMA submillimeter data for a better
investigation and understanding of the magnetic field structure in OH
231.8+4.2.Comment: 7 pages, 5 figures, 2 tables. Accepted for publication in MNRA
Dispersion of Magnetic Fields in Molecular Clouds. IV - Analysis of Interferometry Data
We expand on the dispersion analysis of polarimetry maps toward applications to interferometry data. We show how the filtering of low spatial frequencies can be accounted for within the idealized Gaussian turbulence model, initially introduced for single-dish data analysis, to recover reliable estimates for correlation lengths of magnetized turbulence, as well as magnetic field strengths (plane-of-the-sky component) using the Davis–Chandrasekhar–Fermi method. We apply our updated technique to TADPOL/CARMA data obtained on W3(OH), W3 Main, and DR21(OH). For W3(OH), our analysis yields a turbulence correlation length δ ≃ 19 mpc, a ratio of turbulent-to-total magnetic energy 〈B〉_^2_t/〈B^2〉 ≃ 0.58, and a magnetic field strength B_0 ~ 1.1 mG for W3 Main δ ≃ 22mpc, 〈B_t^2〉/〈B^2〉 ≃ 0.74, and B_0 ~ 0.7 mG while for DR21(OH) δ ≃ 12 mpc, 〈B_t^2〉/〈B^2〉 ≃ 0.70, and B_0 ~ 1.2 mG
High Resolution Millimeter-Wave Mapping of Linearly Polarized Dust Emission: Magnetic Field Structure in Orion
We present 1.3 and 3.3 mm polarization maps of Orion-KL obtained with the
BIMA array at approximately 4 arcsec resolution. Thermal emission from
magnetically aligned dust grains produces the polarization. Along the Orion
``ridge'' the polarization position angle varies smoothly from about 10 degrees
to 40 degrees, in agreement with previous lower resolution maps. In a small
region south of the Orion ``hot core,'' however, the position angle changes by
90 degrees. This abrupt change in polarization direction is not necessarily the
signpost of a twisted magnetic field. Rather, in this localized region
processes other than the usual Davis-Greenstein mechanism might align the dust
grains with their long axes parallel with the field, orthogonal to their normal
orientation.Comment: AAS preprint:14 pages, 2 figures (3mm.eps and 1mm.eps); requires
aaspp4.sty To be published in Astrophysical Journal Letter
An extremely high velocity molecular jet surrounded by an ionized cavity in the protostellar source Serpens SMM1
We report ALMA observations of a one-sided, high-velocity (80 km
s) CO() jet powered by the intermediate-mass
protostellar source Serpens SMM1-a. The highly collimated molecular jet is
flanked at the base by a wide-angle cavity; the walls of the cavity can be seen
in both 4 cm free-free emission detected by the VLA and 1.3 mm thermal dust
emission detected by ALMA. This is the first time that ionization of an outflow
cavity has been directly detected via free-free emission in a very young,
embedded Class 0 protostellar source that is still powering a molecular jet.
The cavity walls are ionized either by UV photons escaping from the accreting
protostellar source, or by the precessing molecular jet impacting the walls.
These observations suggest that ionized outflow cavities may be common in Class
0 protostellar sources, shedding further light on the radiation, outflow, and
jet environments in the youngest, most embedded forming stars.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letter
ALMA observations of dust polarization and molecular line emission from the Class 0 protostellar source Serpens SMM1
We present high angular resolution dust polarization and molecular line
observations carried out with the Atacama Large Millimeter/submillimeter Array
(ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these
observations with new polarization observations from the Submillimeter Array
(SMA) and archival data from the Combined Array for Research in Millimeter-wave
Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare
the magnetic field orientations at different spatial scales. We find major
changes in the magnetic field orientation between large (~0.1 pc) scales --
where the magnetic field is oriented E-W, perpendicular to the major axis of
the dusty filament where SMM1 is embedded -- and the intermediate and small
scales probed by CARMA (~1000 AU resolution), the SMA (~350 AU resolution), and
ALMA (~140 AU resolution). The ALMA maps reveal that the redshifted lobe of the
bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of
the source; however, on the northwestern side and elsewhere in the source, low
velocity shocks may be causing the observed chaotic magnetic field pattern.
High-spatial-resolution continuum and spectral-line observations also reveal a
tight (~130 AU) protobinary system in SMM1-b, the eastern component of which is
launching an extremely high-velocity, one-sided jet visible in both CO(2-1) and
SiO(5-4); however, that jet does not appear to be shaping the magnetic field.
These observations show that with the sensitivity and resolution of ALMA, we
can now begin to understand the role that feedback (e.g., from protostellar
outflows) plays in shaping the magnetic field in very young, star-forming
sources like SMM1.Comment: 15 pages, 6 figures, 4 tables, 1 appendix. Accepted for publication
in the Astrophysical Journal. Materials accessible in the online version of
the (open-access) ApJ article include the FITS files used to make the ALMA
image in Figure 1(d), and a full, machine-readable version of Table
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