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Lagadec E.,European Southern Observatory | Verhoelst T.,Catholic University of Leuven | Mekarnia D.,Laboratoire Fizeau | Suarez O.,Laboratoire Fizeau | And 11 more authors.
Proceedings of the International Astronomical Union | Year: 2011

Post-AGB stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the Asymptotic Giant Branch (AGB) towards the planetary nebula stage. There is growing evidences that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VISIR/VLT, T-Recs/Gemini South and Michelle/Gemini North. We found that all the the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non resolved. The resolved targets can be divided in two categories. The nebulae with a dense central core, that are either bipolar and multipolar. The nebulae with no central core have an elliptical morphology. The dense central torus observed likely host binary systems which triggered fast outflows that shaped the nebulae. © 2012 International Astronomical Union. Source


Lagadec E.,European Southern Observatory | Verhoelst T.,Catholic University of Leuven | Mekarnia D.,French National Center for Scientific Research | Suarez O.,French National Center for Scientific Research | And 11 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

Post-asymptotic giant branch (post-AGB) stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the AGB towards the planetary nebula stage. There is growing evidence that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VLT spectrometer and imager for the mid-infrared (VISIR)/VLT, T-Recs/Gemini-South and Michelle/Gemini-North. We found that all the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non-resolved. The resolved targets can be divided into two categories. (i) The nebulae with a dense central core, that are either bipolar and multipolar and (ii) the nebulae with no central core, with an elliptical morphology. The dense central torus observed likely hosts binary systems which triggered fast outflows that shaped the nebulae. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Lennon D.J.,STS Inc | Evans C.J.,ATC | Bastian N.,University of Exeter | Beletsky Y.,ESO | And 25 more authors.
Proceedings of the International Astronomical Union | Year: 2010

The Tarantula Survey is an ESO Large Programme which has obtained multi-epoch spectroscopy of over 1,000 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The assembled consortium will exploit these data to address a range of fundamental questions in both stellar and cluster evolution. © International Astronomical Union 2011. Source


Gonzalez-Galindo F.,Institute Astrofsica Of Andaluca | Gonzalez-Galindo F.,University Paris - Sud | Bougher S.W.,University of Michigan | Lopez-Valverde M.A.,Institute Astrofsica Of Andaluca | And 2 more authors.
Planetary and Space Science | Year: 2010

We have used two different General Circulation Models to study the thermal and wind structure of the Martian upper atmosphere (mesosphere and thermosphere). Both models take into account the effects of waves propagating from the lower atmosphere, although they use different methods for this purpose. We present the results of three simulations that allow us to take into account the seasonal variability of the Martian atmosphere. Simplified dust scenarios and a common set of input parameters are used. The temperatures and winds predicted by both models show an overall good agreement. However, some differences have been identified, generally of a local nature. The magnitude of these differences tends to increase with the amount of dust in the lower atmosphere. The different heating terms of the upper atmosphere predicted by both models are in good agreement, which suggests that the differences between the models have their origin in the propagation of waves from the lower atmosphere. This study has allowed us to confirm the important role of the redistribution of the energy by the winds in producing the longitudelatitude structure of the temperatures. Both models predict also a thermospheric polar warming during the Southern summer solstice, although its intensity seems to be model-dependent and connected to lower atmosphere dust loading. © 2010 Elsevier Ltd. All rights reserved. All rights reserved. Source


Molina-Cuberos G.J.,University of the Basque Country | Molina-Cuberos G.J.,Institute Astrofsica Of Andaluca | Godard R.,Royal Military College of Canada | Lopez-Moreno J.J.,Institute Astrofsica Of Andaluca | And 15 more authors.
Planetary and Space Science | Year: 2010

The Huygens Probe measured the electrical conductivity of Titan atmosphere from about 140 km down to the surface, employing relaxation and mutual impedance techniques. Previous analyses have shown some differences on the conductivity measurements obtained with two independent sensorsrelaxation probe (RP) and mutual impedance probe (MIP). A 20-fold maximum discrepancy occurred around the conductivity peak at 6070 km. To understand the nature of such discrepancy, we reassess the RP data by taking into account a geometrical factor related to the electrode finite size and the Debye length of the ionized medium. The present analysis implies replacing the standard Laplace field distribution by a more elaborated model considering the Poisson equation and the resistance between the RP electrodes and the medium. Although a complete understanding of the conductivity profile is still missing, this work brings RP and MIP data to a much better agreement. The conductivity maximum difference derived from the two sensors is now lower a factor of 2. This reassessment is also useful for future instruments and missions. © 2010 Elsevier Ltd. All rights reserved. All rights reserved. Source

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