169 research outputs found
The Alignment of the Magnetic Field and Collimated Outflows in Star-forming Regions: the Case of NGC 2071
The magnetic field is believed to play a crucial role in the process of star
formation. From the support it provides during the initial collapse of
molecular clouds to the creation of strong collimated jets responsible for
large mass losses, current theories predict its importance in many different
stages during the formation of stars. Here we report on observational evidence
which tests one aspect that can be inferred from these theories: the alignment
between the local magnetic field and collimated bipolar outflows in such
environments. There is good evidence of an alignment in the case of NGC 2071.Comment: 11 pages, 4 figure
The eSMA: description and first results
The eSMA ("extended SMA") combines the SMA, JCMT and CSO into a single
facility, providing enhanced sensitivity and spatial resolution owing to the
increased collecting area at the longest baselines. Until ALMA early science
observing (2011), the eSMA will be the facility capable of the highest angular
resolution observations at 345 GHz. The gain in sensitivity and resolution will
bring new insights in a variety of fields, such as protoplanetary/transition
disks, high-mass star formation, solar system bodies, nearby and high-z
galaxies. Therefore the eSMA is an important facility to prepare the grounds
for ALMA and train scientists in the techniques.
Over the last two years, and especially since November 2006, there has been
substantial progress toward making the eSMA into a working interferometer. In
particular, (i) new 345-GHz receivers, that match the capabilities of the SMA
system, were installed at the JCMT and CSO; (ii) numerous tests have been
performed for receiver, correlator and baseline calibrations in order to
determine and take into account the effects arising from the differences
between the three types of antennas; (iii) first fringes at 345 GHz were
obtained on August 30 2007, and the array has entered the science-verification
stage.
We report on the characteristics of the eSMA and its measured performance at
230 GHz and that expected at 345 GHz. We also present the results of the
commissioning and some initial science-verification observations, including the
first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located
along the line of sight to the lensed quasar PKS1830-211, and on the imaging of
the vibrationally excited HCN line towards IRC+10216.Comment: 12 pages, 7 figures, paper number 7012-12, to appear in Proceedings
of SPIE vol. 7012: "Ground-based and Airborne Telescopes II", SPIE conference
on Astronomical Instrumentation, Marseille, 23-28 June 200
Detection of CI in absorption towards PKS 1830-211 with the eSMA
We report the first science observations and results obtained with the
"extended" SMA (eSMA), which is composed of the SMA (Submillimeter Array), JCMT
(James Clerk Maxwell Telescope) and CSO (Caltech Submillimeter Observatory).
Redshifted absorptions at z=0.886 of CI (^3P_1 - ^3P_0) were observed with the
eSMA with an angular resolution of 0.55"x0.22" at 1.1 mm toward the
southwestern image of the remarkable lensed quasar PKS 1830-211, but not toward
the northeastern component at a separation of ~1". Additionally, SMA
observations of CO, 13CO and C18O (all J=4-3) were obtained toward this object:
CO was also detected toward the SW component, but none of the isotopologues
were. This is the first time [CI] is detected in this object, allowing the
first direct determination of relative abundances of neutral atomic carbon to
CO in the molecular clouds of a spiral galaxy at z>0.1. The [CI] and CO
profiles can be decomposed into two and three velocity components respectively.
We derive C/CO column density ratios ranging from <0.5 (representative of dense
cores) to ~2.5 (close to translucent clouds values). This could indicate that
we are seeing environments with different physical conditions or that we are
witnessing chemical evolution of regions where C has not completely been
converted into CO.Comment: 6 pages using emulateapj, 3 tables, 2 figures ; accepted for
publication in ApJ
1.6:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310  GHz atmospheric window
Although high-resistivity, low-loss silicon is an excellent material for terahertz transmission optics, its high refractive index necessitates an antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive-ion etching (DRIE). A wafer with this treatment on both sides has <−20  dB (<1%) reflectance over 187–317 GHz at a 15° angle of incidence in TE polarization. We also demonstrated that bonding wafers introduce no reflection features above the −20  dB level (also in TE at 15°), reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment
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.Comment: 37 pages, 12 figures, 3 table
1.6:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310  GHz atmospheric window
Although high-resistivity, low-loss silicon is an excellent material for terahertz transmission optics, its high refractive index necessitates an antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive-ion etching (DRIE). A wafer with this treatment on both sides has <−20  dB (<1%) reflectance over 187–317 GHz at a 15° angle of incidence in TE polarization. We also demonstrated that bonding wafers introduce no reflection features above the −20  dB level (also in TE at 15°), reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment
pi+ + d --> p + p reaction between 18 and 44 MeV
A study of the reaction pi+ + d --> p + p has been performed in the energy
range of 18 - 44 MeV. Total cross sections and differential cross sections at
six angles have been measured at 15 energies with an energy increment of 1 - 2
MeV. This is the most systematic data set in this energy range. No structure in
the energy dependence of the cross section has been observed within the
accuracy of this experiment.Comment: 20 pages, 7 Postscript figure
Serum albumin level adjusted with C-reactive protein predicts hemodialysis patient survival
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