scholarly journals Ground-based detection of a cloud of methanol from Enceladus: when is a biomarker not a biomarker?

2017 ◽  
Vol 18 (1) ◽  
pp. 25-32 ◽  
Author(s):  
E. Drabek-Maunder ◽  
J. Greaves ◽  
H. J. Fraser ◽  
D. L. Clements ◽  
L.-N. Alconcel
Keyword(s):  
Radiative Transfer ◽  
Reference Frame ◽  
Line Of Sight ◽  
Beam Diameter ◽  
Parent Species ◽  
Secondary Product ◽  
Chemical Interactions ◽  
Liquid Environment ◽  
Surface Ocean ◽  
Gas Cloud

ABSTRACTSaturn's moon Enceladus has vents emerging from a sub-surface ocean, offering unique probes into the liquid environment. These vents drain into the larger neutral torus in orbit around Saturn. We present a methanol (CH3OH) detection observed with IRAM 30-m from 2008 along the line-of-sight through Saturn's E-ring. Additionally, we also present supporting observations from the Herschel public archive of water (ortho-H2O; 1669.9 GHz) from 2012 at a similar elongation and line-of-sight. The CH3OH 5(1,1)-4(1,1) transition was detected at 5.9σ confidence. The line has 0.43 km s−1 width and is offset by +8.1 km s−1 in the moon's reference frame. Radiative transfer models allow for gas cloud dimensions from 1750 km up to the telescope beam diameter ~73 000 km. Taking into account the CH3OH lifetime against solar photodissociation and the redshifted line velocity, there are two possible explanations for the CH3OH emission: methanol is primarily a secondary product of chemical interactions within the neutral torus that: (1) spreads outward throughout the E-ring or (2) originates from a compact, confined gas cloud lagging Enceladus by several km s−1. We find either scenario to be consistent with significant redshifted H2O emission (4σ) measured from the Herschel public archive. The measured CH3OH:H2O abundance (>0.5%) significantly exceeds the observed abundance in the direct vicinity of the vents (~0.01%), suggesting CH3OH is likely chemically processed within the gas cloud with methane (CH4) as its parent species.

Large-scale, high-resolution maps of interseismic strain accumulation from Sentinel-1, and incorporation of along-track measurements

2021 ◽  
Author(s):  
Andy Hooper ◽  
Pawan Piromthong ◽  
Tim Wright ◽  
Jonathan Weiss ◽  
Milan Milan Lazecky ◽  
...  
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Velocity Field ◽  
Reference Frame ◽  
Line Of Sight ◽  
Tectonic Deformation ◽  
Low Resolution ◽  
Gnss Measurements ◽  
Along Track ◽  
East West

<p>High-resolution geodetic measurements of crustal deformation from InSAR have the potential to provide crucial constraints on a region’s tectonics, geodynamics and seismic hazard. Here, we present a high-resolution crustal velocity field for the Alpine-Himalayan Seismic Belt (AHSB) derived from Sentinel-1 InSAR and GNSS. We create time series and average velocities from ~220,000 interferograms covering an area of 15 million km<sup>2</sup>, with an average of 170 acquisitions per measurement point. We tie the velocities to a Eurasian reference frame by jointly inverting the InSAR data with GNSS data to produce a low-resolution model of 3D surface velocities. We then use the referenced InSAR velocities to invert for high-resolution east-west and sub-vertical velocity fields for the entire region. The sub-vertical velocities, which also include a small component of north-south motion, are dominated by non-tectonic deformation, such as subsidence due to water extraction. The east-west velocity field, however, reveals the tectonics of the AHSB with an unprecedented level of detail.</p><p>The approach described above only provides good constraints on horizontal displacement in the east-west direction, with the north-south component provided by low-resolution GNSS measurements. Sentinel-1 does also have the potential to provide measurements that are sensitive to north-south motion, through exploitation of the burst overlap areas produced by the TOPS acquisition mode. These along-track measurements have lower precision than line-of-sight InSAR and are more effected by ionospheric noise, but have the advantage of being almost insensitive to tropospheric noise. We present a time series approach to tease out the subtle along-track signals associated with interseismic strain. Our approach includes improvements to the mitigation of ionospheric noise and we also investigate different filtering approaches to optimize the reduction of decorrelation noise. In contrast to the relative measurements of line-of-sight InSAR, these along-track measurements are automatically provided in a global reference frame. We present results from five years of data for the West-Lut Fault in eastern Iran and the Chaman Fault in Pakistan and Afghanistan. Our results agree well with independent GNSS measurements; however, the denser coverage of the technique allows us to also detect the variation in slip rate along the faults.</p><p>Finally, we demonstrate the improvement in the resolution of horizontal strain rates when including these along-track measurements, in addition to the conventional line-of-sight InSAR measurements.</p>

scholarly journals First clear detection of the CCS Zeeman splitting toward the pre-stellar core, Taurus Molecular Cloud 1

2019 ◽  
Author(s):  
Fumitaka Nakamura ◽  
Seiji Kameno ◽  
Takayoshi Kusune ◽  
Izumi Mizuno ◽  
Kazuhito Dobashi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radiative Transfer ◽  
Field Strength ◽  
Magnetic Flux ◽  
Molecular Cloud ◽  
Sound Speed ◽  
Flux Ratio ◽  
Zeeman Splitting ◽  
Line Of Sight ◽  
Taurus Molecular Cloud

Abstract We report the first clear detection of the Zeeman splitting of a CCS emission line at 45 GHz toward the nearby pre-stellar dense filament, Taurus Molecular Cloud 1 (TMC-1). We observed HC$_3$N non-Zeeman lines simultaneously with the CCS line, and did not detect any significant splitting of the HC$_3$N lines. Thus, we conclude that our detection of CCS Zeeman splitting is robust. The derived line-of-sight magnetic field strength is about $117 \pm 21 \, \mu$G, which corresponds to a normalized mass-to-magnetic flux ratio of 2.2 if we adopt an inclination angle of 45$^\circ$. Thus, we conclude that the TMC-1 filament is magnetically supercritical. Recent radiative transfer calculations of the CCS and HC$_3$N lines along the line of sight suggest that the filament is collapsing with a speed of $\sim$0.6 km s$^{-1}$, which is comparable to three times the isothermal sound speed. This infall velocity appears to be consistent with the evolution of a gravitationally infalling core.

scholarly journals Modeling of the Be Stars

2011 ◽  
Vol 7 (S282) ◽  
pp. 261-262 ◽  
Author(s):  
K. Šejnová ◽  
V. Votruba ◽  
P. Koubský
Keyword(s):  
Radiative Transfer ◽  
Parameter Space ◽  
Three Dimensional ◽  
Line Of Sight ◽  
Circumstellar Disk ◽  
Physical Parameters ◽  
Be Stars ◽  
Star Program ◽  
Be Star ◽  
Moving Media

AbstractThe Be stars are still a big unknown in respect to the origin and geometry of the circumstellar disk around the star. Program shellspec is designed to solve the simple radiative transfer along the line of sight in three-dimensional moving media. Our goal was to develop an effective method to search in parameter space, which can allow us to find a good estimate of the physical parameters of the disk. We also present here our results for Be star 60 Cyg using the modified code.

scholarly journals Py4CAtS—PYthon for Computational ATmospheric Spectroscopy

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 262 ◽  
Author(s):  
Franz Schreier ◽  
Sebastián Gimeno García ◽  
Philipp Hochstaffl ◽  
Steffen Städt
Keyword(s):  
Radiative Transfer ◽  
Cross Sections ◽  
Large Range ◽  
Line Of Sight ◽  
Atmospheric Spectroscopy ◽  
Computational Aspects ◽  
Line Cross ◽  
Computationally Intensive ◽  
The Individual ◽  
Radiative Transfer Modeling

Radiation is a key process in the atmosphere. Numerous radiative transfer codes have been developed spanning a large range of wavelengths, complexities, speeds, and accuracies. In the infrared and microwave, line-by-line codes are crucial esp. for modeling and analyzing high-resolution spectroscopic observations. Here we present Py4CAtS—PYthon scripts for Computational ATmospheric Spectroscopy, a Python re-implemen-tation of the Fortran Generic Atmospheric Radiation Line-by-line Code GARLIC, where computationally-intensive code sections use the Numeric/Scientific Python modules for highly optimized array processing. The individual steps of an infrared or microwave radiative transfer computation are implemented in separate scripts (and corresponding functions) to extract lines of relevant molecules in the spectral range of interest, to compute line-by-line cross sections for given pressure(s) and temperature(s), to combine cross sections to absorption coefficients and optical depths, and to integrate along the line-of-sight to transmission and radiance/intensity. Py4CAtS can be used in three ways: in the (Unix/Windows/Mac) console/terminal, inside the (I)Python interpreter, or Jupyter notebook. The basic design of the package, numerical and computational aspects relevant for optimization, and a sketch of the typical workflow are presented. In conclusion, Py4CAtS provides a versatile environment for “interactive” (and batch) line-by-line radiative transfer modeling.

Study on a New Nonlinear H∞ Guidance Law for Autonomous Underwater Vehicle

2011 ◽  
Vol 219-220 ◽  
pp. 362-365
Author(s):  
Hao Ding ◽  
Kui Ping Liu ◽  
Wen Li You
Keyword(s):  
Reference Frame ◽  
Relative Motion ◽  
High Performance ◽  
Autonomous Underwater Vehicle ◽  
Normal Load ◽  
Underwater Vehicle ◽  
Target Line ◽  
Line Of Sight ◽  
Guidance Law ◽  
Target Pursuit

The key for Autonomous Underwater Vehicle (AUV) to implement target pursuit is to design high performance guidance law. The globose reference frame is adopted, and equations for 3-D relative motion between AUV and the target are built. Then the H∞ theory is used, and a new AUV nonlinear H∞ guidance law is obtained by solving Hamilton-Jacobi inequation. Simulation is taken on to verify the performance of H∞ guidance law. And the results show that the H∞ guidance law can help AUV overtake the target in less time, and the azimuth and pitching angle of the target line of sight are always staying at the initial numerical values. Furthermore, the normal load decreases to zero gradually. So the guidance law is effective for AUV to pursuit target.

scholarly journals Effects of Dust Extinction in Galactic Discs

1996 ◽  
Vol 171 ◽  
pp. 363-363
Author(s):  
A. Di Bartolomeo ◽  
G. Barbaro ◽  
M. Perinotto
Keyword(s):  
Radiative Transfer ◽  
Interstellar Medium ◽  
Spectral Range ◽  
Transfer Equation ◽  
Spiral Galaxies ◽  
Radiative Transfer Equation ◽  
Line Of Sight ◽  
Dust Extinction

We have solved the radiative transfer equation taking into account both absorption and scattering into the line of sight to the observer to model the disc of spiral galaxies.A dust model has been adopted, suitable for the diffuse interstellar medium of our Galaxy, to obtain, in aU the considered spectral range (1000 ÷ 10000 Å), consistent quantities to describe both the absorption and the scattering properties of the dust.

scholarly journals Investigation of dust attenuation and star formation activity in galaxies hosting GRBs

2018 ◽  
Vol 617 ◽  
pp. A141 ◽  
Author(s):  
D. Corre ◽  
V. Buat ◽  
S. Basa ◽  
S. Boissier ◽  
J. Japelj ◽  
...  
Keyword(s):  
Star Formation ◽  
Radiative Transfer ◽  
Rest Frame ◽  
Spectral Energy Distribution ◽  
Extinction Curve ◽  
Line Of Sight ◽  
Host Galaxy ◽  
Attenuation Curve ◽  
Dust Extinction ◽  
Dust Attenuation

Context. The gamma-ray bursts hosts (GRBHs) are excellent targets to study the extinction properties of dust and its effects on the global emission of distant galaxies. The dust extinction curve is measured along the GRB afterglow line of sight and the analysis of the spectral energy distribution (SED) of the host galaxy gives access to the global dust attenuation of the stellar light. Aims. In this pilot study we gather information on dust extinction in GRBHs to compare the properties of the extinction curve to those of the dust obscuration affecting the total stellar light of the host galaxy. Assuming the extinction curve to be representative of the dust properties, we aim to investigate which dust-stars geometries and local dust distribution in the inter stellar medium (ISM) can reproduce the observed attenuation curve. Methods. We selected a sample of 30 GRBs for which the extinction curve along the GRB afterglow line-of-sight (l.o.s.) is measured in the rest-frame ultraviolet (UV) up to optical and we analysed the properties of the extinction curve as a function of the host galaxy properties. From these 30 GRBs, we selected seven GRBHs with a good rest-frame UV to near-infrared (NIR) spectral coverage for the host. The attenuation curve was derived by fitting the SEDs of the GRBH sample with the CIGALE SED fitting code. Different star formation histories (SFH) were studied to recover the star formation rates (SFR) derived using Hα luminosities. Implications for the dust-stars geometries in the ISM are inferred by a comparison with radiative transfer simulations. Results. The most extinguished GRBs are preferentially found in the more massive hosts and the UV bump is preferentially found in the most extinguished GRB l.o.s. Five out of seven hosts are best fitted with a recent burst of star formation, leading to lower stellar mass estimates than previously found. The average attenuation in the host galaxies is about 70% of the amount of extinction along the GRB l.o.s. We find a great variety in the derived attenuation curves of GRBHs, the UV slope can be similar, flatter or even steeper than the extinction curve slope. Half of the attenuation curves are consistent with the Calzetti attenuation law and there is evidence of a UV bump in only one GRBH. We find that the flatter (steeper) attenuation curves are found in galaxies with the highest (lowest) SFR and stellar masses. The comparison of our results with radiative transfer simulations leads to a uniform distribution of dust and stars in a very clumpy ISM for half the GRBHs and various dust-stars geometries for the second half of the sample.

scholarly journals Cosmological radiative transfer for the line-of-sight proximity effect

2010 ◽  
Vol 524 ◽  
pp. A85 ◽  
Author(s):  
A. M. Partl ◽  
A. Dall’Aglio ◽  
V. Müller ◽  
G. Hensler
Keyword(s):  
Radiative Transfer ◽  
Proximity Effect ◽  
Line Of Sight

scholarly journals Is multiphase gas cloudy or misty?

2020 ◽  
Vol 494 (1) ◽  
pp. L27-L31 ◽  
Author(s):  
Max Gronke ◽  
S Peng Oh
Keyword(s):  
Radiative Transfer ◽  
Thermal Instability ◽  
Weak Dependence ◽  
Multistage Process ◽  
Pressure Balance ◽  
Hydrodynamic Simulations ◽  
Contraction Phase ◽  
Gas Cloud ◽  
Resolution Requirements ◽  
Cold Gas

ABSTRACT Cold T ∼ 104 K gas morphology could span a spectrum ranging from large discrete clouds to a fine ‘mist’ in a hot medium. This has myriad implications, including dynamics and survival, radiative transfer, and resolution requirements for cosmological simulations. Here, we use 3D hydrodynamic simulations to study the pressure-driven fragmentation of cooling gas. This is a complex, multistage process, with an initial Rayleigh–Taylor unstable contraction phase that seeds perturbations, followed by a rapid, violent expansion leading to the dispersion of small cold gas ‘droplets’ in the vicinity of the gas cloud. Finally, due to turbulent motions, and cooling, these droplets may coagulate. Our results show that a gas cloud ‘shatters’ if it is sufficiently perturbed out of pressure balance (δP/P ∼ 1) and has a large final overdensity χf ≳ 300, with only a weak dependence on the cloud size. Otherwise, the droplets reassemble back into larger pieces. We discuss our results in the context of thermal instability and clouds embedded in a shock-heated environment.

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