216 research outputs found
Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A
The first polarimetric images of the OMC-3 region of the Orion A filamentary
molecular cloud are presented. Using the JCMT, we have detected polarized
thermal emission at 850 microns from dust along a 6' length of the dense
filament. The polarization pattern is highly ordered and is aligned with the
filament throughout most of the region. The plane-of-sky magnetic field
direction is perpendicular to the measured polarization. The mean percentage
polarization is 4.2% with a 1 sigma dispersion of 1%. This region is part of
the integral-shaped filament, and active star formation is ongoing along its
length. The protostellar outflow directions do not appear to be consistently
correlated with the direction of the plane-of-sky field or the filament
structure itself. Depolarization toward the filament center, previously
detected in many other star-forming cores and protostars, is also evident in
our data. (abstract abridged)Comment: 9 pages plus 2 figures (1 colour); accepted for publication in the
March 10, 2000 issue (vol. 531 #2) of The Astrophysical Journa
Interferometric Mapping of Magnetic fields: NGC2071IR
We present polarization maps of NGC2071IR from thermal dust emission at 1.3
mm and from CO J= line emission. The observations were obtained using
the Berkeley-Illinois-Maryland Association array in the period 2002-2004. We
detected dust and line polarized emission from NGC2071IR that we used to
constrain the morphology of the magnetic field. From CO J= polarized
emission we found evidence for a magnetic field in the powerful bipolar outflow
present in this region. We calculated a visual extinction mag from our dust observations. This result, when compared with early
single dish work, seems to show that dust grains emit polarized radiation
efficiently at higher densities than previously thought. Mechanical alignment
by the outflow is proposed to explain the polarization pattern observed in
NGC2071IR, which is consistent with the observed flattening in this source.Comment: 17 pages, 4 Figures, Accepted for publication in Ap
Resolved Imaging of the HR 8799 Debris Disk with Herschel
We present Herschel far-infrared and submillimeter maps of the debris disk
associated with the HR 8799 planetary system. We resolve the outer disk
emission at 70, 100, 160 and 250 um and detect the disk at 350 and 500 um. A
smooth model explains the observed disk emission well. We observe no obvious
clumps or asymmetries associated with the trapping of planetesimals that is a
potential consequence of planetary migration in the system. We estimate that
the disk eccentricity must be <0.1. As in previous work by Su et al. (2009), we
find a disk with three components: a warm inner component and two outer
components, a planetesimal belt extending from 100 - 310 AU, with some
flexibility (+/- 10 AU) on the inner edge, and the external halo which extends
to ~2000 AU. We measure the disk inclination to be 26 +/- 3 deg from face-on at
a position angle of 64 deg E of N, establishing that the disk is coplanar with
the star and planets. The SED of the disk is well fit by blackbody grains whose
semi-major axes lie within the planetesimal belt, suggesting an absence of
small grains. The wavelength at which the spectrum steepens from blackbody, 47
+/- 30 um, however, is short compared to other A star debris disks, suggesting
that there are atypically small grains likely populating the halo. The PACS
longer wavelength data yield a lower disk color temperature than do MIPS data
(24 and 70 um), implying two distinct halo dust grain populations.Comment: 13 pages, 8 figures (6 color), accepted for publication in the
Astrophysical Journa
Far-infrared and sub-millimetre imaging of HD 76582's circumstellar disc
Debris discs, the tenuous rocky and icy remnants of planet formation, are believed to be
evidence for planetary systems around other stars. The JCMT/SCUBA-2 debris disc legacy
survey ‘SCUBA-2 Observations of Nearby Stars’ (SONS) observed 100 nearby stars, amongst
them HD 76582, for evidence of such material. Here, we present imaging observations by
JCMT/SCUBA-2 and Herschel/PACS at sub-millimetre and far-infrared wavelengths, respectively.
We simultaneously model the ensemble of photometric and imaging data, spanning
optical to sub-millimetre wavelengths, in a self-consistent manner. At far-infrared wavelengths,
we find extended emission from the circumstellar disc providing a strong constraint
on the dust spatial location in the outer system, although the angular resolution is too poor
to constrain the interior of the system. In the sub-millimetre, photometry at 450 and 850 µm
reveals a steep fall-off that we interpret as a disc dominated by moderately sized dust grains
(amin = 36 µm), perhaps indicative of a non-steady-state collisional cascade within the disc.
A disc architecture of three distinct annuli, comprising an unresolved component at 20 au and
outer components at 80 and 270 au, along with a very steep particle size distribution (γ = 5),
is proposed to match the observations
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