No compelling evidence of distributed production of CO in comet C/1995 O1 (Hale-Bopp) from millimeter interferometric data and a reanalysis of near-IR lines

Based on long-slit infrared spectroscopic observations, it has been suggested that half of the carbon monoxide present in the atmosphere of comet C/1995 O1 (Hale-Bopp) close to perihelion was released by a distributed source in the coma, whose nature (dust or gas) remains unidentified. We re-assess the origin of CO in Hale-Bopp's coma from millimeter interferometric data and a re-analysis of the IR lines. Simultaneous observations of the CO J(1-0) (115 GHz) and J(2-1) (230 GHz) lines were undertaken with the IRAM interferometer in single-dish and interferometric modes. The diversity of angular resolutions (from 1700 to 42000 km diameter at the comet) is suitable to study the radial distribution of CO and detect the extended source observed in the infrared. We used excitation and radiative transfer models to simulate the observations. Various CO density distributions were considered, including 3D time-dependent hydrodynamical simulations which reproduce a CO rotating jet. The CO J(1-0) and J(2-1) observations can be consistently explained by a nuclear production of CO. Composite 50:50 nuclear/extended productions with characteristic scale lengths of CO parent L_p > 1500 km are rejected. Based on similar radiation transfer calculations, we show that the CO v = 1-0 ro-vibrational lines observed in comet Hale-Bopp at heliocentric distances less than 1.5 AU are severely optically thick. The broad extent of the CO brightness distribution in the infrared is mainly due to optical depth effects. Additional factors can be found in the complex structure of the CO coma, and non-ideal slit positioning caused by the anisotropy of dust IR emission. We conclude that both CO millimeter and infrared lines do not provide compelling evidence for a distributed source of CO in Hale-Bopp's atmosphere.Comment: Accepted for publication in Icarus (55 pages, 13 figures

The properties of Low Surface Brightness galaxies

A description is given of the samples of Low Surface Brightness galaxies (LSBs) used for comparison with models of their chemical and spectro-photometric evolution (Boissier et al., this Volume). These samples show the large variation and scatter in observed global properties of LSBs, some of which cannot be modeled without adding starbursts or truncations to their star formation history.Comment: To appear in the Proceedings of the Euroconference on The Evolution of Galaxies: III. From simple approaches to self-consistent models (Kluwer). 4 page

Star formation history of galaxies from z=0 to z=0.7 A backward approach to the evolution of star-forming galaxies

We investigate whether the mean star formation activity of star-forming galaxies from z=0 to z=0.7 in the GOODS-S field can be reproduced by simple evolution models of these systems. In this case, such models might be used as first order references for studies at higher z to decipher when and to what extent a secular evolution is sufficient to explain the star formation history in galaxies. We selected star-forming galaxies at z=0 and at z=0.7 in IR and in UV to have access to all the recent star formation. We focused on galaxies with a stellar mass ranging between 10^{10} and 10^{11} M_sun for which the results are not biased by the selections. We compared the data to chemical evolution models developed for spiral galaxies and originally built to reproduce the main characteristics of the Milky Way and nearby spirals without fine-tuning them for the present analysis. We find a shallow decrease in the specific star formation rate (SSFR) when the stellar mass increases. The evolution of the SSFR characterizing both UV and IR selected galaxies from z=0 to z=0.7 is consistent with the models built to reproduce the present spiral galaxies. There is no need to strongly modify of the physical conditions in galaxies to explain the average evolution of their star formation from z=0 to z=0.7. We use the models to predict the evolution of the star formation rate and the metallicity on a wider range of redshift and we compare these predictions with the results of semi-analytical models.Comment: 14 pages, 10 figures. accepted for publication in Astronomy & Astrophysic

A stable, single-photon emitter in a thin organic crystal for application to quantum-photonic devices

Single organic molecules offer great promise as bright, reliable sources of identical single photons on demand, capable of integration into solid-state devices. It has been proposed that such molecules in a crystalline organic matrix might be placed close to an optical waveguide for this purpose, but so far there have been no demonstrations of sufficiently thin crystals, with a controlled concentration of suitable dopant molecules. Here we present a method for growing very thin anthracene crystals from super-saturated vapour, which produces crystals of extreme flatness and controlled thickness. We show how this crystal can be doped with a widely adjustable concentration of dibenzoterrylene (DBT) molecules and we examine the optical properties of these molecules to demonstrate their suitability as quantum emitters in nanophotonic devices. Our measurements show that the molecules are available in the crystal as single quantum emitters, with a well-defined polarisation relative to the crystal axes, making them amenable to alignment with optical nanostructures. We find that the radiative lifetime and saturation intensity vary little within the crystal and are not in any way compromised by the unusual matrix environment. We show that a large fraction of these emitters are able to deliver more than $10^{12}$ photons without photo-bleaching, making them suitable for real applications.Comment: 12 pages, 10 figures, comments welcom

Interferometric mapping of the 3.3-mm continuum emission of comet 17P/Holmes after its 2007 outburst

Comet 17P/Holmes underwent a dramatic outburst in October 2007, caused by the sudden fragmentation of its nucleus and the production of a large quantity of grains scattering sunlight. We report on 90 GHz continuum observations carried out with the IRAM Plateau de Bure interferometer on 27.1 and 28.2 October 2007 UT, i.e., 4-5 days after the outburst. These observations probed the thermal radiation of large dust particles, and therefore provide the best constraints on the mass in the ejecta debris. The thermal emission of the debris was modelled and coupled to a time-dependent description of their expansion after the outburst. The analysis was performed in the Fourier plane. Visibilities were computed for the two observing dates and compared to the data to measure their velocity and mass. Optical data and 250-GHz continuum measurements published in the literature were used to further constrain the dust kinematics and size distribution. Two distinct dust components in terms of kinematic properties are identified in the data. The large-velocity component, with typical velocities V0 of 50-100 m/s for 1 mm particles, displays a steep size distribution with a size index estimated to q = -3.7 (\pm0.1), assuming a minimum grain size of 0.1 \mum. It corresponds to the fast expanding shell observed in optical images. The slowly-moving "core" component (V0 = 7-9 m/s) detected near the nucleus has a size index |q| < 3.4 and contains a higher proportion of large particles than the shell. The dust mass in the core is in the range 0.1-1 that of the shell. Using optical constants pertaining to porous grains (50% porosity) made of astronomical silicates mixed with water ice (48% in mass), the total dust mass Mdust injected by the outburst is estimated to 4-14 x 10**11 kg, corresponding to 3-9% the nucleus mass.Comment: 15 pages with 11 figures and 7 tables. Accepted for publication in Astronomy & Astrophysic

From Spirals to Low Surface Brightness galaxies

We show that simple models of the chemical and spectrophotometric evolution of galaxies can be used to explore the properties of present-day galaxies and especially the causes of the observed variety among disc galaxies. We focus on the link between ``classical'' spirals and Low Surface Brightness galaxies.Comment: 4 pages, To appear in the Proceedings of the Euroconference The Evolution of Galaxies: III. From simple approaches to self-consistent models (Kluwer

Ultraviolet to infrared emission of z>1 galaxies: Can we derive reliable star formation rates and stellar masses?

We seek to derive star formation rates (SFR) and stellar masses (M_star) in distant galaxies and to quantify the main uncertainties affecting their measurement. We explore the impact of the assumptions made in their derivation with standard calibrations or through a fitting process, as well as the impact of the available data, focusing on the role of IR emission originating from dust. We build a sample of galaxies with z>1, all observed from the UV to the IR (rest frame). The data are fitted with the code CIGALE, which is also used to build and analyse a catalogue of mock galaxies. Models with different SFHs are introduced. We define different set of data, with or without a good sampling of the UV range, NIR, and thermal IR data. The impact of these different cases on the determination of M_star and SFR are analysed. Exponentially decreasing models with a redshift formation of the stellar population z ~8 cannot fit the data correctly. The other models fit the data correctly at the price of unrealistically young ages when the age of the single stellar population is taken to be a free parameter. The best fits are obtained with two stellar populations. As long as one measurement of the dust emission continuum is available, SFR are robustly estimated whatever the chosen model is, including standard recipes. M_star measurement is more subject to uncertainty, depending on the chosen model and the presence of NIR data, with an impact on the SFR-M_star scatter plot. Conversely, when thermal IR data from dust emission are missing, the uncertainty on SFR measurements largely exceeds that of stellar mass. Among all physical properties investigated here, the stellar ages are found to be the most difficult to constrain and this uncertainty acts as a second parameter in SFR measurements and as the most important parameter for M_star measurements.Comment: 14 pages, 14 figures, accepted for publication A&

Aide à la décision pour l'expertise des barrages

National audienceUn modèle d'évaluation des performances des barrages vis-à-vis de leurs principaux modes de rupture et de dégradation a été développé (Curt, 2008). Les données d'entrée (indicateurs) et de sortie (performance du barrage) de ce modèle sont des distributions de possibilité. Cette communication est axée sur la problématique de la prise de décision associée à ce résultat possibiliste : comment prioriser les actions de maintenance à entreprendre sur le barrage et comment transmettre l'information aux gestionnaires ? Nous proposons une analyse comparative des méthodes de défuzzification afin de sélectionner les méthodes répondant le mieux à cette problématique d'aide à l'expertise des barrages. / An assessment model of dam performances as regards their main failure modes and degradation modes was developed (Curt, 2008). The input data (indicators) and the ouput data (dam performance) of this model are possibility distributions. This paper focuses on the problematic of decision making associated to this possibility result: how to classify maintenance actions that have to be made on that dam and how to convey this result to dam managers? A comparative analysis of defuzzyfication methods is provided; those methods allow to best answer to this problematic of dam expertise

The fate of spiral galaxies in clusters: The star formation history of the anemic Virgo cluster galaxy NGC 4569

We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (Hα) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the Hα rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in cluster