1,651 research outputs found

    Hot molecular hydrogen in the central parsec of the Galaxy through near-infrared 3D fitting

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    Aims. We have investigated neutral gas in the central cavity of the circumnuclear disk (CND) at the Galactic Center, where the ionized minispiral lies, to describe the H2 distribution and properties in this ionized environment. Methods. This study was carried out through a spectro-imaging data cube of the central cavity obtained with SPIFFI on the VLT. The observed field of view is 36"x 29" , with a spectral resolution R = 1 300 in the near-infrared. These observations cover several H2 lines. To preserve the spatial resolution and avoid edge effects, we applied a new line-fitting method that consists of a regularized 3D fitting. We also applied a more classical 1D fitting to compare the relative strength of the H2 lines. Results. We present high spatial and spectral resolution maps of the intensity, velocity, and width of five H2 lines and an extinction map derived from H2. Molecular gas is detected everywhere in the field. In particular, in addition to the known CND features, we detected an emission from the northern arm cloud and from the minicavity. The excitation diagrams allow us to estimate the temperature, mass, and density of these features. Conclusions. We interpret the CND emission as coming from a hot, thermalized, thin layer at the surface of the clouds. The observed H2 corresponds only to a small fraction of the total H2 mass. The emission remains fairly strong in the whole central cavity, but it is not thermalized. A strong deviation from thermal equilibrium is detected near the minicavity. We suggest that this emission is caused by constantly forming H2 that is destroyed again before it reaches ortho/para equilibrium

    Near-infrared mapping of spiral barred galaxies

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    In external galaxies, near-infrared emission originates from stellar populations, hot dust, free-free emission from H+ regions, gaseous emission, non-thermal nucleus if any. Because of the low extinction compared to the visible, infrared wavelengths are useful to probe regions obscured by dust such as central parts where starburst phenomena can occur because of the large quantity of matter. The results presented were obtained with a 32 x 32 InSb charge injection device (CID) array cooled at 4K, at the f/36 cassegrain focus of the 3m60 Canada-France-Hawaii telescope with a spatial resolution of 0.5 inches per pixel. The objects presented are spiral barred galaxies mapped at J(1.25 microns), H(1.65 microns) and K(2.2 microns). The non-axisymetric potential due to the presence of a bar induces dynamical processes leading to the confinement of matter and peculiar morphologies. Infrared imaging is used to study the link between various components. Correlations with other wavelengths ranges and 2-colors diagrams ((J-H), (H-K)) lead to the identification of star forming regions, nucleus. Maps show structures connected to the central core. The question is, are they flowing away or toward the nucleus. Observations of M83 lead to several conclusions. The star forming region, detected in the visible and the infrared cannot be very compact and must extend to the edge of the matter concentration. The general shape of the near-infrared emission and the location of radio and 10 micron peaks suggest the confinement of matter between the inner Linblad resonances localized from CO measurements about 100 and 400 pc. The distribution of color indices in the arc from southern part to the star forming region suggests an increasing amount of gas and a time evolution eventually triggered by supernova explosions. Close to the direction of the bar, a bridge-like structure connects the arc to the nucleus with peculiar color indices. Perhaps, this structure can be linked to a height velocity component seen in UV and we can attribute it to a jet and/or a matter flow along the bar toward the nucleus, fuelling it. NGC 1068 is the nearest Seyfert 2 galaxy. It has been a subject of many studies at all wavelengths. This object was mapped at J, H, K, L and M, and in polaro-imagery. Results are given

    Resonance Paramagnetic Relaxation and Alignment of Small Grains

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    We show that the energy-level splitting arising from grain rotation ensures that paramagnetic dissipation acts at its maximum rate, i.e., the conditions for paramagnetic resonance are automatically fulfilled. We refer to this process as ``resonance relaxation''. The differences between the predictions of classical Davis-Greenstein relaxation and resonance relaxation are most pronounced for grains rotating faster than 1 GHz, i.e., in the domain where classical paramagnetic relaxation is suppressed. This mechanism can partially align even very small grains, resulting in linearly polarized microwave emission which could interfere with efforts to measure the polarization of the cosmic microwave background.Comment: 4 pages emulated ApJ style, submitted ApJ

    Angular motion of a PAH molecule in interstellar environment

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    Polycyclic aromatic hydrocarbon (PAH) molecules have recently been proposed as an important and hitherto undetected component of the Interstellar Medium (ISM). The theory was based on an explanation of the Unidentified IR Emission Bands by Leger et al. It has already led to a verified prediction on extended galactic and extragalactic emissions measured by IRAS, or by a recent balloon borne experiment. The physics that rules the motion of such molecules in the ISM was studied, taking into account their coupling with the ambient gas, the radiation field (absorption and emission) and the static magnetic field. This is important for many implications of the PAH theory such as the radio emission by these molecules or the expected polarization of their IR emission. A reflection nebulae is considered where the situation is rather well known. Every day life of a mean PAH molecule in such a region is as follows: every 3 hrs a UV photon is absorbed heating the molecule to a thousand degs; the temperature decay due to cooling by IR emission follows then within a few seconds. A collision with a molecule of gas occurs typically once a week, while an H atom is ejected or captured at the same rate. A typical cooling cycle after a heat impulse is given. The PAH molecules studied as representative of the family has typically 50 atoms, a radius of 4.5 A, is circular and has a molecular mass of M = 300; its permanent dipole moment is 3 Debye

    Transdet: a matched-filter based algorithm for transit detection - application to simulated COROT light curves

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    We present a matched-filter based algorithm for transit detection and its application to simulated COROT light curves. This algorithm stems from the work by Bord\'e, Rouan & L\'eger (2003). We describe the different steps we intend to take to discriminate between planets and stellar companions using the three photometric bands provided by COROT. These steps include the search for secondary transits, the search for ellipsoidal variability, and the study of transit chromaticity. We also discuss the performance of this approach in the context of blind tests organized inside the COROT exoplanet consortium.Comment: 6 pages, 4 figures, in Transiting Extrasolar Planets Workshop, meeting held in Heidelberg, 25-28 September 200

    Le flou des marques discursives est-il un inconvénient ? Vers la notion de 'leurre discursif'

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    International audienceQuatre phénomènes aussi différents que le guidage discursif explicite, les conduites discursives d'amadouage de la modulation et de l'hypocorrection, ou enfin d'authentiques difficultés de mise en mots peuvent être invoqués pour rendre compte de certaines formes, notamment de particules comme « enfin, bon, quoi, ben »... dont le caractère sémantiquement et fonctionnellement flou a été fréquemment souligné. Le contexte peut n'éclairer en rien la fonction de ces marques, concentrées par définition dans les mêmes situations énonciatives. Les paramètres mimogestuels peuvent aider à discriminer ces fonctions. Mais le caractère flou de certaines particules discursives, oscillant du statut d'instructions précises à celui de phatique ou de temporisateur pourrait, selon notre hypothèse, constituer le mécanisme même d'emplois où le locuteur donne le change, recourant à ces « petits mots » comme à des « leurres discursifs ». Dérivant leur pouvoir de trompe-l'œil de leurs emplois sémantiquement forts, ils serviraient à temporiser en conférant une rigueur illusoire à un discours hésitant ; dans d'autres stratégies interactives, ces mêmes formes serviraient à la mise en scène calculée d'un embarras simulé

    Le flou des marques discursives est-il un inconvénient ? Vers la notion de 'leurre discursif'

    No full text
    International audienceQuatre phénomènes aussi différents que le guidage discursif explicite, les conduites discursives d'amadouage de la modulation et de l'hypocorrection, ou enfin d'authentiques difficultés de mise en mots peuvent être invoqués pour rendre compte de certaines formes, notamment de particules comme « enfin, bon, quoi, ben »... dont le caractère sémantiquement et fonctionnellement flou a été fréquemment souligné. Le contexte peut n'éclairer en rien la fonction de ces marques, concentrées par définition dans les mêmes situations énonciatives. Les paramètres mimogestuels peuvent aider à discriminer ces fonctions. Mais le caractère flou de certaines particules discursives, oscillant du statut d'instructions précises à celui de phatique ou de temporisateur pourrait, selon notre hypothèse, constituer le mécanisme même d'emplois où le locuteur donne le change, recourant à ces « petits mots » comme à des « leurres discursifs ». Dérivant leur pouvoir de trompe-l'œil de leurs emplois sémantiquement forts, ils serviraient à temporiser en conférant une rigueur illusoire à un discours hésitant ; dans d'autres stratégies interactives, ces mêmes formes serviraient à la mise en scène calculée d'un embarras simulé

    Role-Playing Game and Learning for Young People About Sustainable Development Stakes: An Experiment in Transferring and Adapting Interdisciplinary Scientific Knowledge

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    The study refers to the interactions between socio-economic and natural dynamics in an island biosphere reserve by using companion modelling. This approach provides scientific results and involves interdisciplinarity. In the second phase of the study, we transferred knowledge by adapting the main research output, a role-playing game, to young people. Our goal was to introduce interactions between social and ecological systems, coastal dynamics and integrated management. Adapting the game required close collaboration between the scientists and educators in order to transform both its substance and form and to run it with an easy-to-handle ergonomic platform.Children Education, Multi-Agent Environment, Role-Playing Game
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