343 research outputs found
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
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
End-to-End Modeling of the TDM Readout System for CMB-S4
The CMB-S4 experiment is developing next-generation ground-based microwave
telescopes to observe the Cosmic Microwave Background with unprecedented
sensitivity. This will require an order of magnitude increase in the 100 mK
detector count, which in turn increases the demands on the readout system. The
CMB-S4 readout will use time division multiplexing (TDM), taking advantage of
faster switches and amplifiers in order to achieve an increased multiplexing
factor. To facilitate the design of the new readout system, we have developed a
model that predicts the bandwidth and noise performance of this circuity and
its interconnections. This is then used to set requirements on individual
components in order to meet the performance necessary for the full system. We
present an overview of this model and compare the model results to the
performance of both legacy and prototype readout hardware.Comment: This manuscript was submitted to the Journal of Low Temperature
Physics as part of the special issue "LTD20", supporting the conference
contribution RP-00
Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
Ubiquitous unidentified infrared emission bands are seen in many astronomical
sources. Although these bands are widely, if not unanimously, attributed to the
collective emission from polycyclic aromatic hydrocarbons, no single species
from this class has been detected in space. We present the discovery of two -CN
functionalized polycyclic aromatic hydrocarbons, 1- and 2-cyanonaphthalene, in
the interstellar medium aided by spectral matched filtering. Using radio
observations with the Green Bank Telescope, we observe both bi-cyclic ring
molecules in the molecular cloud TMC-1. We discuss potential in situ gas-phase
formation pathways from smaller organic precursor molecules
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