38 research outputs found

    Scanamorphos: a map-making software for Herschel and similar scanning bolometer arrays

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    Scanamorphos is one of the public softwares available to post-process scan observations performed with the Herschel photometer arrays. This post-processing mainly consists in subtracting the total low-frequency noise (both its thermal and non-thermal components), masking high-frequency artefacts such as cosmic ray hits, and projecting the data onto a map. Although it was developed for Herschel, it is also applicable with minimal adjustment to scan observations made with some other imaging arrays subjected to low-frequency noise, provided they entail sufficient redundancy; it was successfully applied to P-Artemis, an instrument operating on the APEX telescope. Contrary to matrix-inversion softwares and high-pass filters, Scanamorphos does not assume any particular noise model, and does not apply any Fourier-space filtering to the data, but is an empirical tool using purely the redundancy built in the observations -- taking advantage of the fact that each portion of the sky is sampled at multiple times by multiple bolometers. It is an interactive software in the sense that the user is allowed to optionally visualize and control results at each intermediate step, but the processing is fully automated. This paper describes the principles and algorithm of Scanamorphos and presents several examples of application.Comment: This is the final version as accepted by PASP (on July 27, 2013). A copy with much better-quality figures is available on http://www2.iap.fr/users/roussel/herschel

    Recent Development of MESSINE, a 3D Eddy Current Model

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    In the 1996 QNDE Conference, we presented a parametric forward model [1], which has been recently named MESSINE (Model for Electromagnetic Simplified Simulation In Nondestructive Evaluation), to predict eddy current signal. The proposed model first discretizes the eddy current distribution into current loops. A parametric description of the shape of these loops is given according to the observation of the results obtained with a three-dimensional finite element code which provides a realistic distribution of the induced currents. The loops’ inductances and resistances are then calculated. By considering the system constituted of the coil and the current loops as a « multi-transformer», their current intensity is determined. The impedance change, which is the component of the eddy current signal, can then be deduced. The model was validated in the case of axisymmetric configurations. Comparisons with both analytical (Dodd and Deeds [2]) and numerical models showed very good agreements. Then the proposed model was applied to three-dimensional configurations. Impedance changes of a coil along rectangular through-wall slot were calculated. Comparisons with experimental results show a fairly good agreement for the impedance change phases, but a poorer one for the impedance change amplitudes. Investigations were made to improve the parametric description of the current loop deformation. One of the solutions to improve the parametric description is presented here

    Evidence of triggered star formation in G327.3-0.6. Dust-continuum mapping of an infrared dark cloud with P-ArT\'eMiS

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    Aims. Expanding HII regions and propagating shocks are common in the environment of young high-mass star-forming complexes. They can compress a pre-existing molecular cloud and trigger the formation of dense cores. We investigate whether these phenomena can explain the formation of high-mass protostars within an infrared dark cloud located at the position of G327.3-0.6 in the Galactic plane, in between two large infrared bubbles and two HII regions. Methods: The region of G327.3-0.6 was imaged at 450 ? m with the CEA P-ArT\'eMiS bolometer array on the Atacama Pathfinder EXperiment telescope in Chile. APEX/LABOCA and APEX-2A, and Spitzer/IRAC and MIPS archives data were used in this study. Results: Ten massive cores were detected in the P-ArT\'eMiS image, embedded within the infrared dark cloud seen in absorption at both 8 and 24 ?m. Their luminosities and masses indicate that they form high-mass stars. The kinematical study of the region suggests that the infrared bubbles expand toward the infrared dark cloud. Conclusions: Under the influence of expanding bubbles, star formation occurs in the infrared dark areas at the border of HII regions and infrared bubbles.Comment: 4 page

    Characterizing filaments in regions of high-mass star formation: High-resolution submilimeter imaging of the massive star-forming complex NGC 6334 with ArTeMiS

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    Context. Herschel observations of nearby molecular clouds suggest that interstellar filaments and prestellar cores represent two fundamental steps in the star formation process. The observations support a picture of low-mass star formation according to which filaments of ~0.1 pc width form first in the cold interstellar medium, probably as a result of large-scale compression of interstellar matter by supersonic turbulent flows, and then prestellar cores arise from gravitational fragmentation of the densest filaments. Whether this scenario also applies to regions of high-mass star formation is an open question, in part because the resolution of Herschel is insufficient to resolve the inner width of filaments in the nearest regions of massive star formation. Aims. In an effort to characterize the inner width of filaments in high-mass star-forming regions, we imaged the central part of the NGC 6334 complex at a resolution higher by a factor of >3 than Herschel at 350 μm. Methods. We used the large-format bolometer camera ArTéMiS on the APEX telescope and combined the high-resolution ArTéMiS data at 350 μm with Herschel/HOBYS data at 70–500 μm to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the structure of the main narrow filament of the complex with a resolution of 8″ or <0.07 pc at d ~ 1.7 kpc. Results. Our study confirms that this filament is a very dense, massive linear structure with a line mass ranging from ~500 M⊙/pc to ~2000 M⊙/pc over nearly 10 pc. It also demonstrates for the first time that its inner width remains as narrow as W ~ 0.15 ± 0.05 pc all along the filament length, within a factor of <2 of the characteristic 0.1 pc value found with Herschel for lower-mass filaments in the Gould Belt. Conclusions. While it is not completely clear whether the NGC 6334 filament will form massive stars in the future, it is two to three orders of magnitude denser than the majority of filaments observed in Gould Belt clouds, and has a very similar inner width. This points to a common physical mechanism for setting the filament width and suggests that some important structural properties of nearby clouds also hold in high-mass star-forming regions

    CAMISTIC: THz/submm astronomy at Dome C in Antarctica

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    Measurements of the Suprathermal Electron Density Profile by Electron Cyclotron Emission at the Upper Cut-Off Layer in Tore Supra

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    The possibility of measuring the radial profile of fast-electron distributions from ECE spectra is discussed. The most usual ECE diagnostic set-up, i.e. the second-harmonic X-mode, observed by low-held side antennae in the equatorial plane, can be used by exploiting the reflection of spontaneously emitted radiation by the upper cut-off layer and the length of the sightline between the reflecting surface and the receiving antenna. The emitted intensity depends on this length, which introduces an element of spatial resolution in the suprathermal ECE spectra. Two methods are proposed. First, a dynamic method is described in which the length of the sightline is varied by density perturbations. Second, a spectral method is discussed that uses the length variation of the sightline with the observation frequency. A proof of the principle behind both methods is given for a lower hybrid current driven discharge in Tore Supra in which a pellet was injected
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