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Nice, France

Millour F.,University Cote dAzur
EAS Publications Series | Year: 2015

Olivier Chesneau challenged several fields of observational stellar astrophysics with bright ideas and an impressive amount of work to make them real in the span of his career, from his first paper on P Cygni in 2000, up to his last one on V838 Mon in 2014. He was using all the so-called high-angular resolution techniques since it helped his science to be made, namely study in details the inner structure of the environments around stars, be it small mass (AGBs), more massive (supergiant stars), or explosives (Novae). I will focus here on his work on massive stars. © 2015 EAS, EDP Sciences. Source

Izidoro A.,University of Bordeaux 1 | Izidoro A.,University Cote dAzur | Morbidelli A.,University Cote dAzur | Raymond S.N.,French National Center for Scientific Research | And 2 more authors.
Astronomy and Astrophysics | Year: 2015

Reproducing Uranus and Neptune remains a challenge for simulations of solar system formation. The ice giants' peculiar obliquities suggest that they both suffered giant collisions during their formation. Thus, there must have been an epoch of accretion dominated by collisions among large planetary embryos in the primordial outer solar system. We test this idea using N-body numerical simulations including the effects of a gaseous protoplanetary disk. One strong constraint is that the masses of the ice giants are very similar-the Neptune and Uranus mass ratio is ~1.18. We show that similar-sized ice giants do indeed form by collisions between planetary embryos beyond Saturn. The fraction of successful simulations varies depending on the initial number of planetary embryos in the system, their individual and total masses. Similar-sized ice giants are consistently reproduced in simulations starting with five to ten planetary embryos with initial masses of ~3-6 M⊕. We conclude that accretion from a population of planetary embryos is a plausible scenario for the origin of Uranus and Neptune. © 2015 ESO. Source

Millour F.,University Cote dAzur | Lagadec E.,University Cote dAzur
EAS Publications Series | Year: 2015

Olivier Chesneau founded a brand new field of observational astrophysics with his attempts to resolve the novae expanding fireball from the very first days of the explosion. With the images he could get, he showed that novae do indeed explode in an aspherical way, leading to a change of paradigm for the physics of these yet-poorly understood catastrophic systems. He also set the stage for a new way of estimating novae distances, by directly measuring the sky-size of the fireball and comparing it with spectroscopic scales, taking into account the tremendous effects of the fireball geometry. © 2015 EAS, EDP Sciences. Source

Salabert D.,University Paris Diderot | Salabert D.,University Cote dAzur | Regulo C.,Institute of Astrophysics of Canarias | Regulo C.,University of La Laguna | And 20 more authors.
Astronomy and Astrophysics | Year: 2016

The continuous photometric observations collected by the Kepler satellite over 4 yr provide a wealth of data with an unequalled quantity and quality for the study of stellar evolution of more than 200 000 stars. Moreover, the length of the dataset provides a unique source of information for detecting magnetic activity and associated temporal variability in the acoustic oscillations. In this regards, the Kepler mission was awaited with great expectations. The search for the signature of magnetic activity variability in solar-like pulsations still remained unfruitful more than 2 yr after the end of the nominal mission. Here, however, we report the discovery of temporal variability in the low-degree acoustic frequencies of the young (1 Gyr-old) solar analog KIC 10644253 with a modulation of about 1.5 yr with significant temporal variations for the duration of the Kepler observations. The variations agree with the derived photometric activity. The frequency shifts extracted for KIC 10644253 are shown to result from the same physical mechanisms involved in the inner subsurface layers as in the Sun. In parallel, a detailed spectroscopic analysis of KIC 10644253 is performed based on complementary ground-based, high-resolution observations collected by the HERMES instrument mounted on the Mercator telescope. Its lithium abundance and chromospheric activity S index confirm that KIC 10644253 is a young and more active star than the Sun. © ESO, 2016. Source

Adam R.,CNRS Laboratory of Subatomic Physics & Cosmology | Adam R.,University Cote dAzur | Comis B.,CNRS Laboratory of Subatomic Physics & Cosmology | Bartalucci I.,University Paris Diderot | And 45 more authors.
Astronomy and Astrophysics | Year: 2016

The prototype of the NIKA2 camera, NIKA, is a dual-band instrument operating at the IRAM 30-m telescope, which can observe the sky simultaneously at 150 and 260 GHz. One of the main goals of NIKA (and NIKA2) is to measure the pressure distribution in galaxy clusters at high angular resolution using the thermal Sunyaev-Zel'dovich (tSZ) effect. Such observations have already proved to be an excellent probe of cluster pressure distributions even at intermediate and high redshifts. However, an important fraction of clusters host sub-millimeter and/or radio point sources, which can significantly affect the reconstructed signal. Here we report on <20 arcsec angular resolution observations at 150 and 260 GHz of the cluster MACS J1423.8+2404, which hosts both radio and sub-millimeter point sources. We examine the morphological distribution of the tSZ signal and compare it to other datasets. The NIKA data are combined with Herschel satellite data to study the spectral energy distribution (SED) of the sub-millimeter point source contaminants. We then perform a joint reconstruction of the intracluster medium (ICM) electronic pressure and density by combining NIKA, Planck, XMM-Newton, and Chandra data, focusing on the impact of the radio and sub-millimeter sources on the reconstructed pressureprofile. We find that large-scale pressure distribution is unaffected by the point sources because of the resolved nature of the NIKA observations. The reconstructed pressure in the inner region is slightly higher when the contribution of point sources are removed. We show that it is not possible to set strong constraints on the central pressure distribution without accurately removing these contaminants. The comparison with X-ray only data shows good agreement for the pressure, temperature, and entropy profiles, which all indicate that MACS J1423.8+2404 is a dynamically relaxed cool core system. The present observations illustrate the possibility of measuring these quantities with a relatively small integration time, even at high redshift and without X-ray spectroscopy. This work is part of a pilot study aiming at optimizing tSZ observations with the future NIKA2 camera. © 2016 ESO. Source

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