In a few years, the VLTI will be able to combine light from 4 to 8telescopes equipped with adaptive optics. In order to exploit thefull VLTI infrastructure, a second generation instrument, based onthe densified pupil concept (VIDA), has been proposed for veryhigh resolution direct imaging and coronagraphy. This paperpresents some possible coronagraphic devices providing a totalstar extinction on the VLTI when there are no phase errors.Lastly, the expected performances considering cophasing andadaptive optics residual errors are also presented.

We present a project on study of groups composed of dwarf galaxies only. We selected such structures using HyperLEDA and NED databases with visual inspection on SDSS images and on digital copy of POSS. The groups are characterized by size of few tens of kpc and line-of-sight velocity dispersion about 18 km s−1. Our groups similar to associations of nearby dwarfs from Tully et al. (2006). This specific population of multiple dwarf galaxies such as I Zw 18 may contain significant amount of dark matter. It is very likely that we see them at the stage just before merging of its components.

The dynamics of a massive binary System in a galactic nucleus are presented.These are the first results from simulations applying a hybrid "self consistent field"(SCF) 1 and direct Aarseth N body integrator (NBODY6) 2, which synthesisesthe advantages of the direct force calculation with the efficiency of the field method.The code is aimed for use on parallel architectures and is therefore applicablefor collisional N-body integrations with extraordinarily large particle numbers(> 105). It opens the perspective to simulate the dynamics of globular clusters withrealistic collisional relaxation, as well as stellar Systems surrounding a supermassiveblack hole in galactic nuclei.

Up-conversion, or hybrid, detectors have been investigated in quantum communication experiments to replace Indium-Gallium-Arsenide avalanche photodiodes (InGaAs-APD) for the detection of infrared and telecom single photons. Those detectors are based on the supposedly noise-free process of frequency up-conversion, also called sum-frequency generation (SFG), using a second order (χ2) non-linear crystal. Powered by an intense pump laser, this process permits transposing with a certain probability the single photons at telecom wavelengths to the visible range where silicon APDs (Si-APD) operate with a much better performance than InGaAs detectors. To date, the literature reports up-conversion detectors having efficiency and noise figures comparable to that of the best commercially available IngaAs-APDs. However, in all of these previous realizations, a pump-induced noise is always observed which was initially expected to be as low as the dark count level of the Si-APDs. Although this additional noise represents a problem for the detection, up-conversion detectors have advantageously replaced InGaAs-APDs in various long-distance quantum cryptography schemes since they offer a continuous regime operation mode instead of a gated mode necessary for InGaAs-APDs, and the possibility of much higher counting rates. Despite attempted explanations, no detailed nor conclusive study of this noise has been reported.

The aim of this paper is to offer a definitive explanation for this noise.We first give a review of the state of the art by describing already demonstrated up-conversion detectors. We discuss these realizations especially regarding the choices made for the material, in bulk or guided configurations, the single photon wavelengths, and the pump scheme. Then we describe an original device made of waveguides integrated on periodically poled lithium niobate (PPLN)or on single-domain lithium niobate aimed at investigating the origin of the additional pump-induced noise. The poled waveguides are designed to up-convert single photons at 1550 nm to 600 nm when a 980 nm diode laser is used as pump. We obtain an overall efficiency of about 0.6% for a noise level of about 8 × 103 counts/s. This overall efficiency includes both insertion and propagation losses, and internal up-conversion and quantum detection (Si-APD) efficiencies. Despite a low efficiency value compared to what has been obtained so far by other groups, the efficiency/noise ratio is still comparable which still allows us investigating the noise issue.

From the spectrum obtained in both poled and non-poled waveguides we conclude that the noise comes from an alternative phase-matching scheme which permits creating paired photons at 1550 and 2700 nm wavelength by down-conversion of the 980 nm pump laser. Knowing that 1550 nm corresponds to the input signal wavelength, up-conversion of actual signal or pump-induced photons at this particular wavelength cannot be discriminated, therefore contributing to the noise at the final wavelength of 600 nm. We believe that this process of down-conversion of the pump laser to the signal wavelength (plus complementary wavelength) is responsible for the unexpected noise level reported in all the up-conversion detector realizations.

In a first part of the paper we give a simple introduction to the free space propagation of light at the level of a Master degree in Physics. The presentation promotes linear filtering aspects at the expense of fundamental physics. Following the Huygens-Fresnel approach, the propagation of the wave writes as a convolution relationship, the impulse response being a quadratic phase factor. We give the corresponding filter in the Fourier plane. As an illustration, we describe the propagation of wave with a spatial sinusoidal amplitude, introduce lenses as quadratic phase transmissions, discuss their Fourier transform properties and give some properties of Soret screens. Classical diffractions of rectangular diaphragms are also given here. In a second part of the paper, the presentation turns into the use of external occulters in coronagraphy for the detection of exoplanets and the study of the solar corona. Making use of Lommel series expansions, we obtain the analytical expression for the diffraction of a circular opaque screen, giving thereby the complete formalism for the Arago-Poisson spot. We include there shaped occulters. The paper ends up with a brief application to incoherent imaging in astronomy.

We present results of daytime site testing at Dome C in summer2003–2004. Daytime seeing has been monitored during 2$\frac{1}{2}$months using a DIMM on the bright star Canopus, giving median value of0.54 arcsec. An every-day best seeing period has been observed around5 pm with seeing around 0.3 arcsec. First isoplanatic anglemeasurements, based on stellar scintillation, were also performedduring the month of January 2004, and have given median value of 6.8 arcsec.


Antarctica offers probably the best ground-based conditions for observing in the 1–3 μm region, and may thus be considered as an alternative to Space for this domain. We examine the potential of integral-field spectro-photometry over wide areas of the sky in this wavelength range for the study of carbon stars, that seems promising. On the other hand,the conditions of transparency, background, and their short-time stability from Antarctic sites still need to be evaluated.

We present the basic theory of nuclear reactions in stars and sketchthe general rules of stellar evolution. Then we shortly review thesubject of supernova explosions both by core collapse in massivestars (type II) and carbon-deflagration in binary systems when oneof the components is a White Dwarf accreting mass from the companion(type Ia). We also present elementary notions of s- and r-processnucleo-synthesis. Finally, we shortly review the topic of galacticchemical evolution and highlight some simple solutions aimed atunderstanding the main observational data on abundances andabundance ratios.

An active carbon chemistry is observed at the border of photo-dissociation regions(PDRs), involving small hydrocarbons, polycyclic aromatic hydrocarbon (PAH) macromoleculesand evaporating very small grains (VSGs). In this context, we aim at quantifying thephysical and chemical evolution of PAHs (hydrogenation and charge states, aggregation, andcomplexation with heavy atoms) as a function of the local physical conditions (radiationfield, temperature, density, abundances of atomic and molecular hydrogen, electrons andheavy atoms). We have developed a numerical model that follows the time dependency of theabundance and internal energy of each species. In this paper, we use this model tocalculate the hydrogenation and charge states of coronene C24H12 asan interstellar PAH prototype. We take advantage of recent results on photodissociationand reaction rates and provide guidelines for future laboratory studies. Reaction rates ofcoronene-derived radical cations with H and H2 are found to be sufficientlyconstrained by experiments, whereas the absence of experimental data for neutral speciesis critical.

Radio astronomy is a subject full of serendipity and coincidence. This paper recounts the strange sequence of incidental events and oversights that led to the establishment of Jodrell Bank as one of radio astronomy's founding institutions. Particular emphasis is given to the purpose for which it was originally intended; the study of high-energy cosmic rays.

We present the results of the analysis of our recent interferometric observations of Betelgeuse, using the AMBER instrument of the VLTI. Using the medium spectral resolution mode (R ~ 1500) we detected the presence of the water vapour and carbon monoxide (CO) molecules in the H and K bands. We also derived the photospheric angular diameter in the continuum. By analysing the depth of the molecular lines and the interferometric visibilities, we derived the column densities of the molecules, as well as the temperature and the size of the corresponding regions in the atmosphere of Betelgeuse (the MOLsphere) using a single shell model around the photosphere. Our results confirm the findings by Perrin et al. (2004) and Ohnaka et al. (2011) that the H2O and CO molecules are distributed around Betelgeuse in a MOLsphere extending to approximately 1.3 times the star’s photospheric radius.

Recent systematic surveys providing massive datasets of white dwarf stars show that there is still a deficit of a factor of 2.5 in the ratio of white dwarfs showing helium absorption lines to those with hydrogen absorption lines in the temperature range 30 000 K < Teff < 45 000 K. Since all white dwarfs have to evolve through this temperature range along similar sequences in the color-magnitude diagram, this implies that most of the helium atmosphere white dwarfs evolve into hydrogen atmosphere hot DA stars in that temperature range and then back again to helium atmosphere white dwarfs. I describe possible scenarios for this chameleon-like disguises of white dwarfs with helium dominant atmospheres and a new kind of pulsating white dwarfs predicted to appear near the lower end of the temperature range 45 000–30 000 K from these scenarios. Recently searches have discovered a pulsating DA white dwarf, WD1017−138, in the predicted temperature range. This discovery opens the possibility of a direct test of the explanation for the deficit of helium atmosphere white dwarfs at these temperatures by asteroseismic probing of the atmospheric layers of the hot DAV stars.


We describe in this communication the principle of imaging withdiluted apertures from the theoretical point of view of Fourieroptics, for a noiseless experiment using perfect telescopes inspace. Two extreme cases are considered, corresponding to denseand sparse arrays. Dense arrays make it possible to obtain acomplete spatial frequency coverage; after signal processing, theimages are comparable to those obtained with a very largemonolithic aperture. Such a perfect frequency coverage cannot beobtained with parse arrays for which the distances betweentelescopes are very large compared to their size. These arrays canonly sample the Fourier plane at point-like individualfrequencies, with the drawback of a field limitation. Sparsearrays have however the most promising perspectives for imagery ofstars and exoplanets surfaces.

The standard model of cosmology considers the existence of two components of unknown nature, “dark matter” and “dark energy”, which determine the cosmological evolution. Their nature remains unknown, and other models can also be considered. In particular, it may be possible to reinterpret the recent cosmological observations so that the Universe does not contain two fluids of unknown natures, but only one fluid with particular properties. After a brief review of constraints on this unifying “dark fluid”, we will discuss a specific model of dark fluid based on a complex scalar fluid.

The serendipitous discovery of a gravitational lens system formedby an elliptical galaxy at z ~ 1 and a post-starburstgalaxy at z ~ 3.8 brings a unique opportunity to study indetail the mass profile of a massive and relaxed object at a lookback time of half the age of the universe. We sketch here a comparisonof different methods to reconstruct the mass of the lens, both parametricallyand non-parametrically, highlighting their advantanges and limitations.

Directional detection is a promising search strategy to discover galactic Dark Matter. We present a Bayesian analysis framework dedicated to data from upcoming directional detectors. The interest of directional detection as a powerful tool to set exclusion limits, to authentify a Dark Matter detection or to constrain the Dark Matter properties, both from particle physics and galactic halo physics, will be demonstrated.

Gamma-ray bursts (GRB) are extremely energetic events and produce highly diverse lightcurves. Light curves are believed to be resulting from internal shocks reflecting theactivities of the GRB central engine. Hence their temporal studies can potentially lead tothe understanding of the GRB central engine and its evolution. The light curve variabilitytime scale is an interesting parameter which most models attribute to a physical origine.g., central engine activity, clumpy circum-burst medium, orrelativistic turbulence. We develop a statistical method to estimate the GRB minimumvariability time scale (MVT) for long and short GRBs detected by GBM. We find that the MVTof short bursts is distinctly shorter than that for long GRBs supporting the possibilityof a more compact central engine of the former. We find that MVT estimated by this methodis consistent with the shortest rise time of the fitted pulses. Hence we use the fittedpulse rise times to study the evolution of burst variability time scale. Variability timeis in turn related to the minimum bulk Lorentz factor. Using this we relate the GRBspectral evolution to the evolution of the variability time scale.

"Densified-pupil multi-aperture imaging interferometers" also called "hypertelescopes" can provide direct images at their focal plane. Coronagraphic masking is applicable for nulling a star's image and searching associated planets. The scheme is applicable at the infra-red wavelengths where a planet has its best contrast, but also potentially at visible wavelengths where chlorophyll-like spectral features are to be searched. In the infra-red, where zodiacal and exo-zodiacal clouds tend to contaminate the image, the scheme provides a better rejection of this contamination than schemes using a beam-splitter and flat interference. For a typical Earth-like exo-planet the detection time is reduced 10 to 100 times. In the visible, planets are often resolved from their star by an interferometer's sub-aperture. Visible coronagraphy is then achievable in each sub-aperture before combining the beams and producing the high-resolution image. This relaxes the piston tolerances. Whether for sub-apertures or a densified pupil, or even a conventional telescope, multiple stages ofcoronagraphy are of interest, if equipped with as many deformable mirrors or transmissive plates. Located in the successive image planes, such adaptive correctors can phase the residual stellar speckles without affecting the planet peak. This generates a central peak of starlight, which can be masked without much obstructing the planet's wavefront. A design concept studied for an "Exo-Earth Discoverer", a hypertelescope variant proposed to NASA for its Terrestrial Planet Finder, involves 37 mirror elements of 1 m, driven by small solar sails and arranged to form a 40-300 m diluted spherical mirror. One or several focal combiners move along the focal surface. Optical solutions have been explored in preliminary detail.

Finite Difference and Finite Element algorithms for the solution of the radiative transfer equationas required for the modeling of modern high quality observations are briefly describedand discussed. It is emphasized that in the Finite Element approach there is the possibility to obtain an a-posteriori error estimator, which allows to locally refine the grid and in this way to obtain numerical solutions that do not differfrom the (unknown) analytical solutions by more than a prescribed tolerance.

The relevance of organometallic complexes in the chemistry of the interstellar medium(ISM) was first suggested in the early 90s. This initial proposal has recently beenre-considered in the light of new astronomical data, benefiting from pioneeringexperimental techniques and theoretical methods. In this article, a review of recenttheoretical and experimental results obtained for PAHs coordinated to Fe atoms ispresented, focusing on: -(i)- the IR spectra of [FePAH]+ and[Fe(PAH)2]+ complexes, found to be in line with the AIBs, withadditional specific features in the far-IR range and -(ii)- the photo-evaporation of[FexPAHy]+ clustersas possible candidates for very small grains releasing PAHs in photodissociation regions.These results call for new astronomical data at high spatial resolution. Studies on largerclusters will require further experimental and theoretical developments.