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Search Results: 1 - 10 of 1257 matches for " Hervé Bouy "
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Protoplanetary disk lifetimes vs stellar mass and possible implications for giant planet populations
álvaro Ribas,Hervé Bouy,Bruno Merín
Physics , 2015, DOI: 10.1051/0004-6361/201424846
Abstract: We study the dependence of protoplanetary disk evolution on stellar mass using a large sample of young stellar objects in nearby young star-forming regions. We update the protoplanetary disk fractions presented in our recent work (paper I of this series) derived for 22 nearby (< 500 pc) associations between 1 and 100 Myr. We use a subsample of 1 428 spectroscopically confirmed members to study the impact of stellar mass on protoplanetary disk evolution. We divide this sample into two stellar mass bins (2 M$_{\odot}$ boundary) and two age bins (3 Myr boundary), and use infrared excesses over the photospheric emission to classify objects in three groups: protoplanetary disks, evolved disks, and diskless. The homogeneous analysis and bias corrections allow for a statistically significant inter-comparison of the obtained results. We find robust statistical evidence of disk evolution dependence with stellar mass. Our results, combined with previous studies on disk evolution, confirm that protoplanetary disks evolve faster and/or earlier around high-mass (> 2 M$_{\odot}$) stars. We also find a roughly constant level of evolved disks throughout the whole age and stellar mass spectra. We conclude that protoplanetary disk evolution depends on stellar mass. Such a dependence could have important implications for gas giant planet formation and migration, and could contribute to explaining the apparent paucity of hot Jupiters around high-mass stars.
Disk evolution in the solar neighborhood. I Disk frequencies from 1 to 100 Myr
álvaro Ribas,Bruno Merín,Hervé Bouy,Luke T. Maud
Physics , 2013, DOI: 10.1051/0004-6361/201322597
Abstract: We study the evolution of circumstellar disks in 22 young (1 to 100 Myr) nearby (within 500 pc) associations over the entire mass spectrum using photometry covering from the optical to the mid-infrared. We compiled a catalog of 2340 spectroscopically-confirmed members of these nearby associations. We analyzed their spectral energy distributions and searched for excess related to the presence of protoplanetary disks in a homogeneous way. Sensitivity limits and spatial completeness were also considered. We derive disk fractions as probed by mid-infrared excess in these regions. The unprecedented size of our sample allows us to confirm the timescale of disk decay reported in the literature and to find new trends. The fraction of excess sources increases systematically if measured at longer wavelengths. Disk percentages derived using different wavelength ranges should therefore be compared with caution. The dust probed at 22-24 um evolves slower than that probed at shorter wavelengths (3.4-12 um). Assuming an exponential decay, we derive a timescale tau=4.2-5.8 Myr at 22-24 um for primordial disks, compared to 2-3 Myr at shorter wavelength (3.4-12 um). Primordial disks disappear around 10 Myr, matching in time a brief increase of the number of 'evolved' disks. The increase in timescale of excess decay at longer wavelength is compatible with inside-out disk clearing scenarios. The increased timescale of decay and larger dispersion in the distribution of disk fractions at 22-24 um suggest that the inner and outer zones evolve differently, the latter potentially following a variety of evolutionary paths. The drop of primordial disks and the coincident rise of evolved disks at 10 Myr are compatible with planet formation theories suggesting that the disappearance of the gas is immediately followed by the dynamical stirring of the disk.
Warm Debris Disks Candidates in Transiting Planets Systems
álvaro Ribas,Bruno Merín,David R. Ardila,Hervé Bouy
Physics , 2012, DOI: 10.1051/0004-6361/201118306
Abstract: We have bandmerged candidate transiting planetary systems (from the Kepler satellite) and confirmed transiting planetary systems (from the literature) with the recent Wide-field Infrared Survey Explorer (WISE) preliminary release catalog. We have found 13 stars showing infrared excesses at either 12 and/or 22 microns. Without longer wavelength observations it is not possible to conclusively determine the nature of the excesses, although we argue that they are likely due to debris disks around the stars. If confirmed, our sample ~ doubles the number of currently known warm excess disks around old main sequence stars. The ratios between the measured fluxes and the stellar photospheres are generally larger than expected for Gyr-old stars, such as these planetary hosts. Assuming temperature limits for the dust and emission from large dust particles, we derive estimates for the disk radii. These values are comparable to the planet's semi-major axis, suggesting that the planets may be stirring the planetesimals in the system.
Herschel/PACS photometry of transiting-planet host stars with candidate warm debris disks
Bruno Merín,David R. Ardila,álvaro Ribas,Hervé Bouy,Geoffrey Bryden,Karl Stapelfeldt,Deborah Padgett
Physics , 2014, DOI: 10.1051/0004-6361/201322956
Abstract: Dust in debris disks is produced by colliding or evaporating planetesimals, remnants of the planet formation process. Warm dust disks, known by their emission at < 24 micron, are rare (4% of FGK main sequence stars) and especially interesting because they trace material in the region likely to host terrestrial planets, where the dust has a very short dynamical lifetime. Statistical analyses of the source counts of excesses as found with the mid-IR Wide Field Infrared Survey Explorer (WISE) suggest that warm-dust candidates found for the Kepler transiting-planet host-star candidates can be explained by extragalactic or galactic background emission aligned by chance with the target stars. These statistical analyses do not exclude the possibility that a given WISE excess could be due to a transient dust population associated with the target. Here we report Herschel/PACS 100 and 160 micron follow-up observations of a sample of Kepler and non-Kepler transiting-planet candidates' host stars, with candidate WISE warm debris disks, aimed at detecting a possible cold debris disk in any of them. No clear detections were found in any one of the objects at either wavelength. Our upper limits confirm that most objects in the sample do not have a massive debris disk like that in beta Pic. We also show that the planet-hosting star WASP-33 does not have a debris disk comparable to the one around eta Crv. Although the data cannot be used to rule out rare warm disks around the Kepler planet-hosting candidates, the lack of detections and the characteristics of neighboring emission found at far-IR wavelengths support an earlier result suggesting that most of the WISE-selected IR excesses around Kepler candidate host stars are likely due to either chance alignment with background IR-bright galaxies and/or to interstellar emission.
Gravitational fragmentation caught in the act: the filamentary Musca molecular cloud
Jouni Kainulainen,Alvaro Hacar,Jo?o Alves,Henrik Beuther,Hervé Bouy,Mario Tafalla
Physics , 2015,
Abstract: Filamentary structures are common in molecular clouds. Explaining how they fragment to dense cores is a missing step in understanding their role in star formation. We perform a case study of whether low-mass filaments are close-to hydrostatic prior to their fragmentation, and whether their fragmentation agrees with gravitational fragmentation models. For this, we study the 6.5 pc long Musca molecular cloud that is an ideal candidate for a filament at an early stage of fragmentation. We employ dust extinction mapping in conjunction with near-infrared data from the NEWFIRM instrument, and 870 um dust continuum emission data from the LABOCA instrument, to estimate column densities. We use the data to identify fragments from the cloud and to determine the radial density distribution of its filamentary part. We compare the cloud's morphology with 13CO and C18O line emission observed with the APEX/SHeFI instrument. The Musca cloud is pronouncedly fragmented at its ends, but harbours a remarkably well-defined, 1.6 pc long filament in its Center region. The line mass of the filament is 21-31 Ms pc^-1 and FWHM 0.07 pc. Its radial profile can be fitted with a Plummer profile that has the power-index of 2.6 \pm 11%, flatter than that of an infinite hydrostatic filament. The profile can also be fitted with a hydrostatic cylinder truncated by external pressure. These models imply a central density of 5-10 x 10^4 cm^-3. The fragments in the cloud have a mean separation of 0.4 pc, in agreement with gravitational fragmentation. These properties, together with the subsonic and velocity-coherent nature of the cloud, suggest a scenario in which an initially hydrostatic cloud is currently gravitationally fragmenting. The fragmentation has started a few tenths of a Myr ago from the cloud ends, leaving its center yet relatively non-fragmented, possibly because of gravitational focusing in a finite geometry.
Proper motions of young stars in Chamaeleon. II. New kinematical candidate members of Chamaeleon I and II
Belén López Martí,Francisco Jiménez Esteban,Amelia Bayo,David Barrado,Enrique Solano,Hervé Bouy,Carlos Rodrigo
Physics , 2013, DOI: 10.1051/0004-6361/201321217
Abstract: The Chamaeleon star-forming region has been extensively studied in the last decades. However, most studies have been confined to the densest parts of the clouds. In a previous paper, we analysed the kinematical properties of the spectroscopically confirmed population of the Chamaeleon I and II clouds. We now report on a search for new kinematical candidate members to the Chamaeleon I and II moving groups using available information from public databases and catalogues. Our candidates were initially selected in an area of 3 deg around each cloud on the basis of proper motions and colours from the UCAC4 Catalog. The SEDs of the objects were constructed using photometry retrieved from the Virtual Observatory and other resources, and fitted to models of stellar photospheres to derive effective temperatures, gravity values, and luminosities. Masses and ages were estimated by comparison with theoretical evolutionary tracks in a Hertzprung-Russell diagram. We have identified 51 and 14 candidate members to the Chamaeleon I and II moving groups, respectively, of which 17 and 1, respectively, are classified as probable young stars (ages < 20 Myr) according to our analysis. Another object in Chamaeleon I located slightly above the 1 Myr isochrone is classified as a possible young star. All these objects are diskless stars with masses in the range 0.3M-1.4MSun, and ages consistent with those reported for the corresponding confirmed members. They tend to be located at the boundaries of or outside the dark clouds, preferably to the north-east and south-east in the case of Chamaeleon I, and to the north-east in the case of Chamaeleon II. We conclude that the kinematical population of Chamaeleon I and II could be larger and spread over a larger area of the sky than suggested by previous studies.
The low-mass diskless population of Corona Australis
Belén López Martí,Loredana Spezzi,Bruno Merín,María Morales-Calderón,Hervé Bouy,David Barrado,Jochen Eisl?ffel
Physics , 2010, DOI: 10.1051/0004-6361/200913718
Abstract: We combine published optical and near-infrared photometry to identify new low-mass candidate members in an area of about 0.64 deg^2 in Corona Australis, using the S-parameter method. Five new candidate members of the region are selected, with estimated ages between 3 and 15 Myr, and masses between 0.05 and 0.15 M_Sun. Using Spitzer photometry, we confirm that these objects are not surrounded by optically thick disks. However, one of them is found to display excess at 24 micron, thus suggesting it harbours a disk with an inner hole. With an estimated mass of 0.07 M_Sun according to the SED fitting, this is one of the lowest-mass objects reported to possess a transitional disk. Including these new members, the fraction of disks is about 50% among the total Corona Australis population selected by the same criteria, lower than the 70% fraction reported earlier for this region. Even so, we find a ratio of transitional to primordial disks (45%) very similar to the value derived by other authors. This ratio is higher than for solar-type stars (5-10%), suggesting that disk evolution is faster in the latter, and/or that the "transitional disk" stage is not such a short-lived step in the case of very low-mass objects. However, this impression needs to be confirmed with better statistics.
Infrared study of transitional disks in Ophiuchus with Herschel
Isabel Rebollido,Bruno Merín,álvaro Ribas,Ignacio Bustamante,Hervé Bouy,Pablo Riviere-Marichalar,Timo Prusti,G?ran L. Pilbratt,Philippe André,Péter ábrahám
Physics , 2015, DOI: 10.1051/0004-6361/201425556
Abstract: Context. Observations of nearby star-forming regions with the Herschel Space Observatory complement our view of the protoplanetary disks in Ophiuchus with information about the outer disks. Aims. The main goal of this project is to provide new far-infrared fluxes for the known disks in the core region of Ophiuchus and to identify potential transitional disks using data from Herschel. Methods. We obtained PACS and SPIRE photometry of previously spectroscopically confirmed young stellar objects (YSO) in the region and analysed their spectral energy distributions. Results. From an initial sample of 261 objects with spectral types in Ophiuchus, we detect 49 disks in at least one Herschel band. We provide new far-infrared fluxes for these objects. One of them is clearly a new transitional disk candidate. Conclusions. The data from Herschel Space Observatory provides fluxes that complement previous infrared data and that we use to identify a new transitional disk candidate.
Molecular gastronomy is a scientific discipline, and note by note cuisine is the next culinary trend
Hervé This
Flavour , 2013, DOI: 10.1186/2044-7248-2-1
Abstract: In 1988, a new scientific discipline, molecular gastronomy, was defined as ‘looking for the mechanisms of phenomena occurring during dish preparation and consumption’ [1,2]. This new definition presented the opportunity to discuss the precise content of molecular gastronomy and its relationship with other existing fields of science.There has always been much confusion between science and technology when it comes to food, including over exactly what food is. Dictionaries give the definition: ‘any substance that can give to living beings the elements necessary for their growth or for their preservation’ [3]. However, one has to recognize that human beings very seldom eat non-transformed tissues or natural products; raw materials are transformed so that chemical and physical changes determine the final composition of all food as well as its ‘bioactivity’, a term which we propose to describe the sensory effects, nutritional value, eventual toxic effects, and so on, of the various compounds released by food systems [4].During food preparation, plant or animal tissues are at least washed and cut, and most food are thermally processed. For example, even for a simple carrot salad, which requires no thermal processing, there is a big difference between the raw product in the field and what is consumed - that is, grated carrots on a plate: this is because cutting the tissue triggers enzymatic reactions [5] and because compounds get transferred between the dressing and the plant tissue [6]. This analysis leads to the conclusion that reagents and products of ‘culinary transformations’ (transformations performed in the kitchen) should not both be called food. The specific transformation occurring from the raw materials to the final prepared dish is worth studying, both for scientific and technological reasons.Making the difference between science and technology clear is particularly important for molecular gastronomy because of the confusion between science and cooking (see, for
Orion Revisited - I. The massive cluster in front of the Orion Nebula Cluster
J. Alves,H. Bouy
Physics , 2012, DOI: 10.1051/0004-6361/201220119
Abstract: The aim of this work is to characterize the stellar population between Earth and the Orion A molecular cloud where the well known star formation benchmark Orion Nebula Cluster (ONC) is embedded. We use the denser regions the Orion A cloud to block optical background light, effectively isolating the stellar population in front of it. We then use a multi-wavelength observational approach to characterize the cloud's foreground stellar population. We find that there is a rich stellar population in front of the Orion A cloud, from B-stars to M-stars, with a distinct 1) spatial distribution, 2) luminosity function, and 3) velocity dispersion from the reddened population inside the Orion A cloud. The spatial distribution of this population peaks strongly around NGC 1980 (iota Ori) and is, in all likelihood, the extended stellar content of this poorly studied cluster. We infer an age of ~4-5 Myr for NGC 1980 and estimate a cluster population of the order of 2000 stars, which makes it one of the most massive clusters in the entire Orion complex. What is currently taken in the literature as the ONC is then a mix of several intrinsically different populations, namely: 1) the youngest population, including the Trapezium cluster and ongoing star formation in the dense gas inside the nebula, 2) the foreground population, dominated by the NGC 1980 cluster, and 3) the poorly constrained population of foreground and background Galactic field stars. Our results support a scenario where the ONC and L1641N are not directly associated with NGC 1980, i.e., they are not the same population emerging from its parental cloud, but are instead distinct overlapping populations. This result calls for a revision of most of the observables in the benchmark ONC region (e.g., ages, age spread, cluster size, mass function, disk frequency, etc.). (abridged)
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