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Loison J.C.,CNRS Institute of Molecular Sciences | Dobrijevic M.,French National Center for Scientific Research | Dobrijevic M.,Laboratoire Dastrophysique Of Bordeaux | Hickson K.M.,CNRS Institute of Molecular Sciences | Heays A.N.,Leiden University
Icarus | Year: 2017

The origin of CO and the external source of H2O in the atmosphere of Titan is still a matter of debate. We investigated the chemical fractionation of oxygen isotopologues in order to give new constraints on the origin of oxygen species. We created a new chemical scheme and we developed a 1-D time-dependent photochemical model to compute the mole fraction profiles of various oxygen isotopologues. We show that the photochemical fractionation of oxygen isotopologues is quite low. Observations of C18O and CO18O are compatible with both an external origin or an internal origin of CO considering that the various sources of oxygen have a cometary 16O/18O ratio (16O/18O ≈ 500). Improvement of the measurements of the 16O/18O ratio in both Enceladus’ plumes and atmospheric CO2 could give a valuable constraint on the origin of oxygen in Titan's atmosphere. © 2017 Elsevier Inc.

Lelli F.,Case Western Reserve University | Duc P.-A.,University Paris Diderot | Brinks E.,University of Hertfordshire | Bournaud F.,University Paris Diderot | And 10 more authors.
Astronomy and Astrophysics | Year: 2015

Tidal dwarf galaxies (TDGs) are recycled objects that form within the collisional debris of interacting and merging galaxies. They are expected to be devoid of non-baryonic dark matter, since they can only form from dissipative material ejected from the discs of the progenitor galaxies. We investigate the gas dynamics in a sample of six bona fide TDGs around three interacting and post-interacting systems: NGC 4694, NGC 5291, and NGC 7252 ("Atoms for Peace"). For NGC 4694 and NGC 5291, we analyse existing HI data from the Very Large Array (VLA),while for NGC 7252 we present new HI observations from the Jansky VLA, together with long-slit and integral-field optical spectroscopy. For all six TDGs, the HI emission can be described by rotating disc models. These HI discs, however, have undergone less than a full rotation since the time of the interaction/merger event, raising the question of whether they are in dynamical equilibrium. Assuming that these discs are in equilibrium, the inferred dynamical masses are consistent with the observed baryonic masses, implying that TDGs are devoid of dark matter. This puts constraints on putative "dark discs" (either baryonic or non-baryonic) in the progenitor galaxies. Moreover, TDGs seem to systematically deviate from the baryonic Tully-Fisher relation. These results provide a challenging test for alternative theories like MOND. © 2015 ESO.

Lammer H.,Austrian Academy of Sciences | Blanc M.,French National Center for Scientific Research | Benz W.,University of Bern | Fridlund M.,European Space Agency | And 20 more authors.
Astrobiology | Year: 2013

A scientific forum on The Future Science of Exoplanets and Their Systems, sponsored by Europlanet* and the International Space Science Institute (ISSI)† and co-organized by the Center for Space and Habitability (CSH)‡ of the University of Bern, was held during December 5 and 6, 2012, in Bern, Switzerland. It gathered 24 well-known specialists in exoplanetary, Solar System, and stellar science to discuss the future of the fast-expanding field of exoplanetary research, which now has nearly 1000 objects to analyze and compare and will develop even more quickly over the coming years. The forum discussions included a review of current observational knowledge, efforts for exoplanetary atmosphere characterization and their formation, water formation, atmospheric evolution, habitability aspects, and our understanding of how exoplanets interact with their stellar and galactic environment throughout their history. Several important and timely research areas of focus for further research efforts in the field were identified by the forum participants. These scientific topics are related to the origin and formation of water and its delivery to planetary bodies and the role of the disk in relation to planet formation, including constraints from observations as well as star-planet interaction processes and their consequences for atmosphere-magnetosphere environments, evolution, and habitability. The relevance of these research areas is outlined in this report, and possible themes for future ISSI workshops are identified that may be proposed by the international research community over the coming 2-3 years. © Copyright 2013, Mary Ann Liebert, Inc. 2013.

Kramer C.,Instituto Radioastronomia Milimetrica IRAM | Abreu-Vicente J.,Instituto Radioastronomia Milimetrica IRAM | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Relano M.,University of Granada | And 11 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. We aim to better understand the heating of gas by observing the prominent gas cooling line [C ii] at 158 μm in the low-metallicity environment of the Local Group spiral galaxy M 33 on scales of 280 pc. In particular, we describe the variation of the photoelectric heating efficiency with the galactic environment. Methods. In this study, we present [C ii] observations along the major axis of M 33 using the Infrared Space Observatory in combination with Herschel continuum maps, IRAM 30 m CO 2-1, and VLA H i data to study the variation in velocity integrated intensities. The ratio of [C ii] emission over the far-infrared continuum is used as a proxy for the heating efficiency, and models of photon-dominated regions are used to study the local physical densities, far-ultraviolet radiation fields, and average column densities of the molecular clouds. Results. The heating efficiency stays constant at 0.8% in the inner 4.5 kpc radius of the galaxy, where it increases to reach values of ~3% in the outskirts at about a 6 kpc radial distance. The rise of efficiency is explained in the framework of PDR models by lowered volume densities and FUV fields for optical extinctions of only a few magnitudes at constant metallicity. For the significant fraction of H i emission stemming from PDRs and for typical pressures found in the Galactic cold neutral medium (CNM) traced by H i emission, the CNM contributes ~15% to the observed [C ii] emission in the inner 2 kpc radius of M 33. The CNM contribution remains largely undetermined in the south, while positions between radial distances of 2 and 7.3 kpc in the north of M 33 show a contribution of ~40% ± 20%. © ESO, 2013.

Von Paris P.,German Aerospace Center | Von Paris P.,Laboratoire Dastrophysique Of Bordeaux | Von Paris P.,University of Bordeaux Segalen | Cabrera J.,German Aerospace Center | And 8 more authors.
Astronomy and Astrophysics | Year: 2011

Context. Were a potentially habitable planet to be discovered, the next step would be the search for an atmosphere and its characterization. Eventually, surface conditions, hence habitability, and biomarkers as indicators for life would be assessed. Aims. The super-Earth candidate Gliese (GL) 581 d is the first potentially habitable extrasolar planet so far discovered. Therefore, GL 581 d is used to illustrate a hypothetical detailed spectroscopic characterization of such planets. Methods. Atmospheric profiles for a wide range of possible one-dimensional (1D) radiative-convective model scenarios of GL 581 d were used to calculate high-resolution synthetic emission and transmission spectra. Atmospheres were assumed to be composed of N2, CO 2, and H2O. From the spectra, signal-to-noise ratios (SNRs) were calculated for a telescope such as the planned James Webb Space Telescope (JWST). Exposure times were set to be equal to the duration of one transit. Results. The presence of the model atmospheres can be clearly inferred from the calculated synthetic spectra thanks to strong water and carbon-dioxide absorption bands. Surface temperatures can be inferred for model scenarios with optically thin spectral windows. Dense, CO2-rich (potentially habitable) scenarios do not enable us to determine the surface temperatures nor assess habitability. Degeneracies between CO2 concentration and surface pressure complicate the interpretation of the calculated spectra, hence the determination of atmospheric conditions. Still, inferring approximative CO2 concentrations and surface pressures is possible. In practice, detecting atmospheric signals is challenging because the calculated SNR values are well below unity in most of the cases. The SNR for a single transit was only barely larger than unity in some near-IR bands for transmission spectroscopy. Most interestingly, the false-positive detection of biomarker candidates such as methane and ozone might be possible in low resolution spectra because CO 2 absorption bands overlap biomarker spectral bands. This can be avoided, however, by observing all main CO2 IR bands instead of concentrating on, e.g., the 4.3 or 15 μm bands only. Furthermore, a masking of ozone signatures by CO2 absorption bands is shown to be possible. Simulations imply that such a false-negative detection of ozone would be possible even for rather high ozone concentrations of up to 10-5. © 2011 ESO.

Chavarria L.,University of Chile | Chavarria L.,Harvard - Smithsonian Center for Astrophysics | Chavarria L.,Laboratoire Dastrophysique Of Bordeaux | Chavarria L.,CSIC - National Institute of Aerospace Technology | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538. Spitzer data is combined with NIR observations to identify and classify the young population while 12CO and 13CO observations are used to examine the parental molecular cloud.We detect in total 3021 young stellar objects (YSOs). Of those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material. We identify in total 41 embedded clusters containing between 52 and 73 per cent of the YSOs. Clusters are in general non-virialized, turbulent and have star formation efficiencies between 5 and 50 per cent.We compare the physical properties of embedded clusters harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc. © 2014 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Timpe M.,University of Washington | Timpe M.,United Virtual | Barnes R.,University of Washington | Barnes R.,United Virtual | And 6 more authors.
Astronomical Journal | Year: 2013

If mutual gravitational scattering among exoplanets occurs, then it may produce unique orbital properties. For example, two-planet systems that lie near the boundary between circulation and libration of their periapses could result if planet-planet scattering ejected a former third planet quickly, leaving one planet on an eccentric orbit and the other on a circular orbit. We first improve upon previous work that examined the apsidal behavior of known multiplanet systems by doubling the sample size and including observational uncertainties. This analysis recovers previous results that demonstrated that many systems lay on the apsidal boundary between libration and circulation. We then performed over 12,000 three-dimensional N-body simulations of hypothetical three-body systems that are unstable, but stabilize to two-body systems after an ejection. Using these synthetic two-planet systems, we test the planet-planet scattering hypothesis by comparing their apsidal behavior, over a range of viewing angles, to that of the observed systems and find that they are statistically consistent regardless of the multiplicity of the observed systems. Finally, we combine our results with previous studies to show that, from the sampled cases, the most likely planetary mass function prior to planet-planet scattering follows a power law with index -1.1. We find that this pre-scattering mass function predicts a mutual inclination frequency distribution that follows an exponential function with an index between -0.06 and -0.1. © 2013. The American Astronomical Society. All rights reserved.

Pierens A.,University of Bordeaux 1 | Pierens A.,Laboratoire Dastrophysique Of Bordeaux | Baruteau C.,University of Cambridge | Hersant F.,University of Bordeaux 1 | Hersant F.,Laboratoire Dastrophysique Of Bordeaux
Monthly Notices of the Royal Astronomical Society | Year: 2012

Low-mass objects embedded in isothermal protoplanetary discs are known to suffer rapid inwards Type I migration. In non-isothermal discs, recent work has shown that a decreasing radial profile of the disc entropy can lead to a strong positive corotation torque which can significantly slow down or reverse Type I migration in laminar viscous disc models, depending on the amount of viscous and thermal diffusion operating in the planet's horseshoe region. Since the latter is a fraction of the pressure scale height of the disc, it is not clear, however, how this picture changes in turbulent disc models. The aim of this study is to examine the impact of turbulence on the torque experienced by a low-mass planet embedded in a non-isothermal protoplanetary disc. We particularly focus on the role of turbulence on the corotation torque whose amplitude depends on the efficiency of diffusion processes in the planet's horseshoe region. The main issues we want to address are whether the part of the corotation torque scaling with the entropy gradient can remain unsaturated in the presence of turbulence and whether the saturation process in non-isothermal discs can be satisfactorily modelled using laminar disc models. We performed 2D numerical simulations using a grid-based hydrodynamical code in which turbulence is modelled as stochastic forcing. In order to provide estimations for the viscous and thermal diffusion coefficients as a function of the amplitude of turbulence, we first set up non-isothermal disc models for different values of the amplitude of the turbulent forcing. We then include a low-mass planet and determine the evolution of its running time-averaged torque. We show that in non-isothermal discs, the entropy-related corotation torque can indeed remain unsaturated in the presence of turbulence. For turbulence amplitudes that do not strongly affect the disc temperature profile, we find that the running time-averaged torque experienced by an embedded protoplanet is in fairly good agreement with laminar disc models with appropriate values for the thermal and viscous diffusion coefficients and with the formulae of Paardekooper, Baruteau & Kley for the total torque in non-isothermal discs. In discs with turbulence driven by stochastic forcing, the corotation torque therefore behaves similarly as in laminar viscous discs and can be responsible for significantly slowing down or reversing Type I migration. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Jofre P.,Max Planck Institute for Astrophysics | Jofre P.,Laboratoire Dastrophysique Of Bordeaux
EPJ Web of Conferences | Year: 2012

A study of stellar ages for a sample from the Sloan Digital Sky Survey (SDSS) is presented. The results are consolidated with a set of globular clusters (GCs) and show that this stellar sample is composed by one dominant population of 10-12 Gyr. This supports the Eggen's scenario, which claims that the inner halo of the Milky Way formed rapidly, probably during the collapse of the proto-Galactic cloud. © Owned by the authors, published by EDP Sciences, 2012.

Jofre P.,Max Planck Institute for Astrophysics | Jofre P.,Laboratoire Dastrophysique Of Bordeaux | Weiss A.,Max Planck Institute for Astrophysics
Astronomy and Astrophysics | Year: 2011

We determined the age of the stellar content of the Galactic halo by considering main-sequence turn-off stars. From the large number of halo stars provided by Sloan Digital Sky Survey, we could accurately detect the turn-off as a function of metallicity of the youngest dominant population, which was done by looking at the hottest (bluest) stars of a population. Using the turn-off temperature of a population of a given metallicity, we looked for the isochrones with that turn-off temperature and metallicity and found no age gradient as a function of metallicity. This would mean that this dominating population of the Galactic halo formed rapidly, probably during the collapse of the proto-Galactic gas. Moreover, we could find a significant number of stars with hotter temperatures than the turn-off, which might be blue horizontal branch (BHB) stars, blue stragglers, or main sequence stars that are younger than the dominant population and were probably formed in external galaxies and accreted later on to our Milky Way. Motivated by the current debate about the efficiency of gravitational settling (atomic diffusion) in the interior of old solar-type stars, we used isochrones with and without settling to determine the ages. When ignoring diffusion in the isochrones we obtained ages of 14-16 Gyr. This result is a strong argument against inhibited diffusion in old halo field stars, since it results in a serious conflict with the age of the Universe of 13.7 Gyr. The age obtained including diffusion in the isochrones was 10-12 Gyr, which agrees with the absolute age of the old globular clusters in the inner halo. © 2011 ESO.

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