685 research outputs found
Gain Stabilization of a Submillimeter SIS Heterodyne Receiver
We have designed a system to stabilize the gain of a submillimeter heterodyne
receiver against thermal fluctuations of the mixing element. In the most
sensitive heterodyne receivers, the mixer is usually cooled to 4 K using a
closed-cycle cryocooler, which can introduce ~1% fluctuations in the physical
temperature of the receiver components. We compensate for the resulting mixer
conversion gain fluctuations by monitoring the physical temperature of the
mixer and adjusting the gain of the intermediate frequency (IF) amplifier that
immediately follows the mixer. This IF power stabilization scheme, developed
for use at the Submillimeter Array (SMA), a submillimeter interferometer
telescope on Mauna Kea in Hawaii, routinely achieves a receiver gain stability
of 1 part in 6,000 (rms to mean). This is an order of magnitude improvement
over the typical uncorrected stability of 1 part in a few hundred. Our gain
stabilization scheme is a useful addition to SIS heterodyne receivers that are
cooled using closed-cycle cryocoolers in which the 4 K temperature fluctuations
tend to be the leading cause of IF power fluctuations.Comment: 7 pages, 6 figures accepted to IEEE Transactions on Microwave Theory
and Technique
Synergy of multifrequency studies from observations of NGC6334I
We combine multifrequency observations from the millimeter to near infrared
wavelengths that demonstrate the spatial distributions of H2, CO, and NH3
emission, which are all manifestations of various shocks driven by outflows of
deeply embedded sources in NGC6334I. In addition to the well-known
northeast-southwest outflow we detect at least one more outflow in the region
by combining observations from APEX, ATCA, SMA, Spitzer and VLT/ISAAC.
Potential driving sources will be discussed. NGC6334I exhibits several signs of
active star formation and will be a major target for future observatories such
as Herschel and ALMA.Comment: 6 pages, 6 figures, appeared in the proceedings of the workshop 'The
Universe Under The Microscope - Astrophysics At High Angular Resolution', see
http://www.iop.org/EJ/toc/1742-6596/131/
High Spatial Resolution Observations of Two Young Protostars in the R Corona Australis Region
We present multi-wavelength, high spatial resolution imaging of the IRS 7
region in the R Corona Australis molecular cloud. Our observations include 1.1
mm continuum and HCO^+ J = images from the SMA, ^{12}CO J =
outflow maps from the DesertStar heterodyne array receiver on the HHT, 450
m and 850 m continuum images from SCUBA, and archival Spitzer IRAC
and MIPS 24 \micron images. The accurate astrometry of the IRAC images allow us
to identify IRS 7 with the cm source VLA 10W (IRS 7A) and the X-ray source X_W.
The SMA 1.1 mm image reveals two compact continuum sources which are also
distinguishable at 450 m. SMA 1 coincides with X-ray source CXOU
J190156.4-365728 and VLA cm source 10E (IRS 7B) and is seen in the IRAC and
MIPS images. SMA 2 has no infrared counterpart but coincides with cm source VLA
9. Spectral energy distributions constructed from SMA, SCUBA and Spitzer data
yield bolometric temperatures of 83 K for SMA 1 and 70 K for SMA 2. These
temperatures along with the submillimeter to total luminosity ratios indicate
that SMA 2 is a Class 0 protostar, while SMA 1 is a Class 0/Class I
transitional object (L= \Lsun). The ^{12}CO J = outflow map
shows one major and possibly several smaller outflows centered on the IRS 7
region, with masses and energetics consistent with previous work. We identify
the Class 0 source SMA 2/VLA 9 as the main driver of this outflow. The complex
and clumpy spatial and velocity distribution of the HCO^+ J =
emission is not consistent with either bulk rotation, or any known molecular
outflow activity.Comment: 31 pages, 8 figures, Accepted to Ap
A Photonic mm-Wave Local Oscillator
A photonic millimeter wave local oscillator capable of producing two
microwatts of radiated power at 224 GHz has been developed. The device was
tested in one antenna of Smithsonian Institution's Submillimeter Array (SMA)
and was found to produce stable phase on multiple baselines. Graphical data is
presented of correlator output phase and amplitude stability. A description of
the system is given in both open and closed loop modes. A model is given which
is used to predict the operational behavior. A novel method is presented to
determine the safe operating point of the automated system.Comment: 4 pages, 7 figures, to appear in the Proceedings of the 17th
International Symposium on Space Terahertz Technology, held 10-12 May 2006 in
Pari
Canadian and U.S. Antitrust Law--Areas of Overlap between Anitrust and Import Relief Laws
Competition and Dispute Resolution in the North American Context and antitrust and free trade zone
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