3,602 research outputs found
Submillimeter Spectrum of Formic Acid
We have measured new submillimeter-wave data around 600 GHz and around 1.1
THz for the 13C isotopologue of formic acid and for the two deuterium
isotopomers; in each case for both the trans and cis rotamer. For cis-DCOOH and
cis-HCOOD in particular only data up to 50 GHz was previously available. For
all species the quality and quantity of molecular parameters has been increased
providing new measured frequencies and more precise and reliable frequencies in
the range of existing and near-future submillimeter and far-infrared
astronomical spectroscopy instruments such as Herschel, SOFIA and ALMA
A tunable cavity-locked diode laser source for terahertz photomixing
An all solid-state approach to the precise frequency synthesis and control of widely tunable terahertz radiation by differencing continuous-wave diode lasers at 850 nm is reported in this paper. The difference frequency is synthesized by three fiber-coupled external-cavity laser diodes. Two of the lasers are Pound-Drever-Hall locked to different orders of a Fabry-Perot (FP) cavity, and the third is offset-frequency locked to the second of the cavity-locked lasers using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produce the difference frequency, whose value is accurately determined by the sum of an integer multiple of the free spectral range of the FP cavity and the offset frequency. The dual-frequency 850-nm output of the three laser system is amplified to 500 mW through two-frequency injection seeding of a single semiconductor tapered optical amplifier. As proof of precision frequency synthesis and control of tunability, the difference frequency is converted into a terahertz wave by optical-heterodyne photomixing in low-temperature-grown GaAs and used for the spectroscopy of simple molecules. The 3-dB spectral power bandwidth of the terahertz radiation is routinely observed to be ≾1 MHz. A simple, but highly accurate, method of obtaining an absolute frequency calibration is proposed and an absolute calibration of 10^(-7) demonstrated using the known frequencies of carbon monoxide lines between 0.23-1.27 THz
Polarization Observations with the Cosmic Background Imager
We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13 element interferometer which operates in the 26-36 GHz band from Llano de Chajnantour in northern Chile. The array consists of 90-cm Cassegrain antennas mounted on a steerable platform which can be rotated about the optical axis to facilitate polarization observations. The CBI employs single mode circularly polarized receivers which sample multipoles from ℓ~400
to ℓ~4250. The instrumental polarization of the CBI was calibrated with 3C279, a bright polarized point source
which was monitored with the VLA
Laboratory Spectroscopy of CH(+) and Isotopic CH
The A1II - X1(Epsilon) electronic band of the CH(+) ion has been used as a probe of the physical and dynamical conditions of the ISM for 65 years. In spite of being one of the first molecular species observed in the ISM and the very large number of subsequent observations with large derived column densities, the pure rotational spectra of CH+ has remained elusive in both the laboratory and in the ISM as well. We report the first laboratory measurement of the pure rotation of the CH(+) ion and discuss the detection of CH-13(+) in the ISM. Also reported are the somewhat unexpected chemical conditions that resulted in laboratory production
The Microbial Community of a Terrestrial Anoxic Inter-Tidal Zone: A Model for Laboratory-Based Studies of Potentially Habitable Ancient Lacustrine Systems on Mars
Evidence indicates that Gale crater on Mars harboured a fluvio-lacustrine environment that was subjected to physio-chemical variations such as changes in redox conditions and evaporation with salinity changes, over time. Microbial communities from terrestrial environmental analogues sites are important for studying such potential habitability environments on early Mars, especially in laboratory-based simulation experiments. Traditionally, such studies have predominantly focused on microorganisms from extreme terrestrial environments. These are applicable to a range of Martian environments; however, they lack relevance to the lacustrine systems. In this study, we characterise an anoxic inter-tidal zone as a terrestrial analogue for the Gale crater lake system according to its chemical and physical properties, and its microbiological community. The sub-surface inter-tidal environment of the River Dee estuary, United Kingdom (53°21'015.40" N, 3°10'024.95" W) was selected and compared with available data from Early Hesperian-time Gale crater, and temperature, redox, and pH were similar. Compared to subsurface ‘groundwater’-type fluids invoked for the Gale subsurface, salinity was higher at the River Dee site, which are more comparable to increases in salinity that likely occurred as the Gale crater lake evolved. Similarities in clay abundance indicated similar access to, specifically, the bio-essential elements Mg, Fe and K. The River Dee microbial community consisted of taxa that were known to have members that could utilise chemolithoautotrophic and chemoorganoheterotrophic metabolism and such a mixed metabolic capability would potentially have been feasible on Mars. Microorganisms isolated from the site were able to grow under environment conditions that, based on mineralogical data, were similar to that of the Gale crater’s aqueous environment at Yellowknife Bay. Thus, the results from this study suggest that the microbial community from an anoxic inter-tidal zone is a plausible terrestrial analogue for studying habitability
of fluvio-lacustrine systems on early Mars, using laboratory-based simulation experiments
Dynamic Density Functional Theory for Sedimentation Processes on Complex Domains: Modelling, Spectral Elements, and Control Problems
Herschel/HIFI Spectral Mapping of C, CH, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH Formation
The CH ion is a key species in the initial steps of interstellar carbon
chemistry. Its formation in diverse environments where it is observed is not
well understood, however, because the main production pathway is so endothermic
(4280 K) that it is unlikely to proceed at the typical temperatures of
molecular clouds. We investigation CH formation with the first
velocity-resolved spectral mapping of the CH rotational
transitions, three sets of CH -doubled triplet lines, C and
C, and CHOH 835~GHz E-symmetry Q branch transitions, obtained
with Herschel/HIFI over 12 arcmin centered on the Orion BN/KL
source. We present the spatial morphologies and kinematics, cloud boundary
conditions, excitation temperatures, column densities, and C optical
depths. Emission from C, CH, and CH is indicated to arise in the
diluted gas, outside of the explosive, dense BN/KL outflow. Our models show
that UV-irradiation provides favorable conditions for steady-state production
of CH in this environment. Surprisingly, no spatial or kinematic
correspondences of these species are found with H S(1) emission tracing
shocked gas in the outflow. We propose that C is being consumed by rapid
production of CO to explain the lack of C and CH in the outflow, and
that fluorescence provides the reservoir of H excited to higher
ro-vibrational and rotational levels. Hence, in star-forming environments
containing sources of shocks and strong UV radiation, a description of CH
formation and excitation conditions is incomplete without including the
important --- possibly dominant --- role of UV irradiation.Comment: Accepted for publication in The Astrophysical Journa
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