117 research outputs found
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 DavisâChandrasekharâFermi 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 ÎŽ â 19 mpc, a ratio of turbulent-to-total magnetic energy â©BâȘ_^2_t/â©B^2âȘ â 0.58, and a magnetic field strength B_0 ~ 1.1 mG for W3 Main ÎŽ â 22mpc, â©B_t^2âȘ/â©B^2âȘ â 0.74, and B_0 ~ 0.7 mG while for DR21(OH) ÎŽ â 12 mpc, â©B_t^2âȘ/â©B^2âȘ â 0.70, and B_0 ~ 1.2 mG
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
A Parallactic Distance of 389 +24/-21 parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations
We determine the parallax and proper motion of the flaring, non-thermal radio
star GMR A, a member of the Orion Nebula Cluster, using Very Long Baseline
Array observations. Based on the parallax, we measure a distance of 389 +24/-21
parsecs to the source. Our measurement places the Orion Nebula Cluster
considerably closer than the canonical distance of 480 +/- 80 parsecs
determined by Genzel et al. (1981). A change of this magnitude in distance
lowers the luminosities of the stars in the cluster by a factor of ~ 1.5. We
briefly discuss two effects of this change--an increase in the age spread of
the pre-main sequence stars and better agreement between the zero-age
main-sequence and the temperatures and luminosities of massive stars.Comment: 10 pages, 4 figures, emulateapj, accepted to Ap
A Giant Outburst at Millimeter Wavelengths in the Orion Nebula
BIMA observations of the Orion nebula discovered a giant flare from a young
star previously undetected at millimeter wavelengths. The star briefly became
the brightest compact object in the nebula at 86 GHz. Its flux density
increased by more than a factor of 5 on a timescale of hours, to a peak of 160
mJy. This is one of the most luminous stellar radio flares ever observed.
Remarkably, the Chandra X-ray observatory was in the midst of a deep
integration of the Orion nebula at the time of the BIMA discovery; the source's
X-ray flux increased by a factor of 10 approximately 2 days before the radio
detection. Follow-up radio observations with the VLA and BIMA showed that the
source decayed on a timescale of days, then flared again several times over the
next 70 days, although never as brightly as during the discovery. Circular
polarization was detected at 15, 22, and 43 GHz, indicating that the emission
mechanism was cyclotron. VLBA observations 9 days after the initial flare yield
a brightness temperature Tb > 5 x 10^7 K at 15 GHz. Infrared spectroscopy
indicates the source is a K5V star with faint Br gamma emission, suggesting
that it is a weak-line T Tauri object. Zeeman splitting measurements in the
infrared spectrum find B ~ 2.6 +/- 1.0 kG. The flare is an extreme example of
magnetic activity associated with a young stellar object. These data suggest
that short observations obtained with ALMA will uncover hundreds of flaring
young stellar objects in the Orion region.Comment: 29 pages, 7 figures, accepted for publication in Ap
A Resolved Ring of Debris Dust around the Solar Analog HD 107146
We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at λ = 1.3 mm and the CSO at λ = 350 Ό. Both images show that the dust emission extends over an approximately 10" diameter region. The high-resolution (3") CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in a flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by ~140° in the position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of ~45-75 AU
THE MAGNETIC FIELD MORPHOLOGY OF THE CLASS 0 PROTOSTAR L1157-mm
We present the first detection of polarization around the Class 0 low-mass protostar L1157-mm at two different wavelengths. We show polarimetric maps at large scales (10 '' resolution at 350 mu m) from the SHARC-II Polarimeter and at smaller scales (1.'' 2-4.'' 5 at 1.3 mm) from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The observations are consistent with each other and show inferred magnetic field lines aligned with the outflow. The CARMA observations suggest a full hourglass magnetic field morphology centered about the core; this is only the second well-defined hourglass detected around a low-mass protostar to date. We apply two different methods to CARMA polarimetric observations to estimate the plane-of-sky magnetic field magnitude, finding values of 1.4 and 3.4 mG.</p
Misalignment of magnetic fields and outflows in protostellar cores
We present results of λ1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with âŒ2.âł5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of âŒ1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they forme
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