434 research outputs found
Higher Order Nyquist Zone Sampling with RFSoC Data Converters for Astronomical and High Energy Physics Readout Systems
From generation to generation, the maximum RF frequency and sampling rate of
the integrated data converters in RF system-on-chip (RFSoC) family devices from
Xilinx increases significantly. With the integrated digital mixers and up and
down conversion blocks in the datapaths of the data converters, those RFSoC
devices offer the capability for implementing a full readout system of ground
and space-based telescopes and detectors across the electromagnetic spectrum
within the devices with minimum or no analog mixing circuit. In this paper, we
present the characterization results for the the data converters sampling at
higher orders of Nyquist zones to extend the frequency range covered for our
targeted readout systems of microwave-frequency resonator-based cryogenic
detector and multiplexer systems and other astronomical and high-energy physics
instrumentation applications, such as, axion search and dark matter detection.
The initial evaluation of the data converters operating higher order Nyquist
zones covers two-tones and comb of tones tests to address the concerns in the
RF inter-modulation distortion, which is the key performance index for our
targeted applications. The characterization of the data converters is performed
in the bandwidth of 4-6 GHz and results meet our requirements. The settings and
operating strategies of the data converters for our targeted applications will
be summarised
Molecular cloud abundances and anomalous diffusion
The chemistry of molecular clouds has been studied for decades, with an
increasingly general and sophisticated treatment of the reactions involved. Yet
the treatment of turbulent diffusion has remained extremely sketchy, assuming
simple Fickian diffusion with a scalar diffusivity D. However, turbulent flows
similar to those in the interstellar medium are known to give rise to anomalous
diffusion phenomena, more specifically superdiffusion (increase of the
diffusivity with the spatial scales involved). This paper considers to what
extent and in what sense superdiffusion modifies molecular abundances in
interstellar clouds. For this first exploration of the subject we employ a very
rough treatment of the chemistry and the effect of non-unifom cloud density on
the diffusion equation is also treated in a simplified way. The results
nevertheless clearly demonstrate that the effect of superdiffusion is quite
significant, abundance values at a given radius being modified by order of
unity factors. The sense and character of this influence is highly nontrivial.Comment: 4 pages, 8 figure
CSO and CARMA Observations of L1157. II. Chemical Complexity in the Shocked Outflow
L1157, a molecular dark cloud with an embedded Class 0 protostar possessing a
bipolar outflow, is an excellent source for studying shock chemistry, including
grain-surface chemistry prior to shocks, and post-shock, gas-phase processing.
The L1157-B1 and B2 positions experienced shocks at an estimated ~2000 and 4000
years ago, respectively. Prior to these shock events, temperatures were too low
for most complex organic molecules to undergo thermal desorption. Thus, the
shocks should have liberated these molecules from the ice grain-surfaces en
masse, evidenced by prior observations of SiO and multiple grain mantle species
commonly associated with shocks. Grain species, such as OCS, CH3OH, and HNCO,
all peak at different positions relative to species that are preferably formed
in higher velocity shocks or repeatedly-shocked material, such as SiO and HCN.
Here, we present high spatial resolution (~3") maps of CH3OH, HNCO, HCN, and
HCO+ in the southern portion of the outflow containing B1 and B2, as observed
with CARMA. The HNCO maps are the first interferometric observations of this
species in L1157. The maps show distinct differences in the chemistry within
the various shocked regions in L1157B. This is further supported through
constraints of the molecular abundances using the non-LTE code RADEX (Van der
Tak et al. 2007). We find the east/west chemical differentiation in C2 may be
explained by the contrast of the shock's interaction with either cold, pristine
material or warm, previously-shocked gas, as seen in enhanced HCN abundances.
In addition, the enhancement of the HNCO abundance toward the the older shock,
B2, suggests the importance of high-temperature O-chemistry in shocked regions.Comment: Accepted for publication in the Astrophysical Journa
The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core
We present the first mid-infrared (MIR) detections of HNC and H13CN in the interstellar medium, and numerous, resolved HCN rovibrational transitions. Our observations span 12.8 to 22.9 micron towards the hot core Orion IRc2, obtained with the Echelon-Cross-Echelle Spectrograph aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Exceptional, ~5 km/s, resolution distinguishes individual rovibrational transitions of the HNC and HCN P, Q, and R branches; and the H13CN R branch. This allows direct measurement of the species' excitation temperatures, column densities, and relative abundances. HNC and H13CN exhibit a local standard rest velocity of -7 km/s that may be associated with an outflow from nearby radio source I and an excitation temperature of about 100 K. We resolve two velocity components for HCN, the primary component also being at -7 km/s with temperature 165 K. The hottest component, which had never before been observed, is at 1 km/s with temperature 309 K. This is the closest component to the hot core's centre measured to date. The derived 12C/13C=13 is below expectation for Orion's Galactocentric distance, but the derived HCN/HNC=72 is expected for this extreme environment. Compared to previous sub-mm and mm observations, our SOFIA line survey of this region shows that the resolved MIR molecular transitions are probing a distinct physical component and isolating the chemistry closest to the hot core
Detection of Interstellar HCNC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions
We report an astronomical detection of HCNC for the first time in the
interstellar medium with the Green Bank Telescope toward the TMC-1 molecular
cloud with a minimum significance of . The total column density
and excitation temperature of HCNC are determined to be
cm and K,
respectively, using the MCMC analysis. In addition to HCNC, HCCNC is
distinctly detected whereas no clear detection of HCNC is made. We propose
that the dissociative recombination of the protonated cyanopolyyne,
HCNH, and the protonated isocyanopolyyne, HCNCH, are the main
formation mechanisms for HCNC while its destruction is dominated by
reactions with simple ions and atomic carbon. With the proposed chemical
networks, the observed abundances of HCNC and HCCNC are reproduced
satisfactorily.Comment: Accepted in the Astrophysical Journal Letter
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