Next-generation phase-mask coronagraphy for extrasolar planetary system imaging

Conference (2006, March 16)

The Butcher-Oemler effect at z similar to 0.35: a change in perspective

in Monthly Notices of the Royal Astronomical Society (2006), 365(3), 915-928

In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven groups ... [more ▼]

In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven groups/clusters at z similar to 0.35, we have measured the blue fraction from the cluster core to the cluster outskirts and the field mainly using wide-field Cerro Tololo Inter-American Observatory images. This sample represents a random selection of a volume complete X-ray selected cluster sample, selected so that there is no physical connection with the studied quantity (blue fraction), to minimize observational biases. In order to statistically assess the significance of the Butcher-Oemler effect, we introduce the tools of Bayesian inference. Furthermore, we have modified the blue fraction definition in order to take into account the reduced age of the Universe at higher redshifts, because we should no longer attempt to reject an unphysical universe in which the age of the Universe does depend on redshift, whereas the age of its content does not. We have measured the blue fraction from the cluster centre to the field and we find that the cluster affects the properties of the galaxies up to two virial radii at z similar to 0.35. Data suggest that during the last 3 Gyr no evolution of the blue fraction, from the cluster core to the field value, is seen beyond that needed to account for the varying age with the redshift of the Universe and of its content. The agreement of the radial profiles of the blue fraction at z= 0 and z similar to 0.35 implies that the pattern infall did not change over the last 3 Gyr, or, at least, its variation has no observational effect on the studied quantity. [less ▲]

SEE-COAST: The Super-Earth Explorer

in Barret, D.; Casoli, F.; Lagache, G. (Eds.) et al SF2A-2006: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics (2006)

The Super-Earth Explorer Coronagraphic Off Axis Space Telescope (SEE-COAST) is a space mission concept to be submitted to ESA call for proposals. It is devoted to the direct imaging, in the visible, of ... [more ▼]

The Super-Earth Explorer Coronagraphic Off Axis Space Telescope (SEE-COAST) is a space mission concept to be submitted to ESA call for proposals. It is devoted to the direct imaging, in the visible, of the stellar light reflected by its planetary companion. Here we present the type of planetary characterization we may accomplish with SEE-COAST, and we include a brief description of the spacecraft and mission strategy. [less ▲]

Current generation arrays: current status, getting the most out of them and future development

in “Future Directions for Interferometry” (2006)

New generation phase coronagraphy

Poster (2006)

Subwavelength surface-relief gratings for stellar coronagraphy

in Applied Optics (2005), 44 Issue 34

We present a new design of a phase mask coronagraph implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. Phase mask coronagraphy is a recent ... [more ▼]

We present a new design of a phase mask coronagraph implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. Phase mask coronagraphy is a recent technique that seeks to accommodate both high dynamic and high angular resolution imaging of faint sources around bright astrophysical objects such as exoplanets orbiting their host stars. The original design we propose is a new, integrated, and flexible solution to the pi phase-shift chromaticity of the phase mask coronagraphs. It will allow broadband observations, i.e., shorter integration times and object characterizations, by means of spectroscopic analysis. The feasibility of the component manufacturing is also considered through a tolerance study. [less ▲]

The XMM large-scale structure survey: an initial sample of galaxy groups and clusters to a redshift z < 0.6

in Monthly Notices of the Royal Astronomical Society (2005), 363(2), 675-691

We present X-ray and optical spectroscopic observations of 12 galaxy groups and clusters identified within the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey. Groups and clusters are selected ... [more ▼]

We present X-ray and optical spectroscopic observations of 12 galaxy groups and clusters identified within the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey. Groups and clusters are selected as extended X-ray sources from a 3.5 deg(2) XMM image mosaic above a flux limit 8 x 10(-15) erg s(-1) cm(-2) in the [0.5-2] keV energy band. Deep BVRI images and multi-object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29 < z < 0.56. We combine line-of-sight velocity dispersions with the X-ray properties of each structure computed from a two-dimensional surface brightness model and a single temperature fit to the XMM spectral data. The resulting distribution of X-ray luminosity, temperature and velocity dispersion indicate that the XMM-LSS survey is detecting low-mass clusters and galaxy groups to redshifts z < 0.6. Confirmed systems display little or no evidence for X-ray luminosity evolution at a given X-ray temperature compared to lower-redshift X-ray group and cluster samples. A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM-LSS survey. [less ▲]

Use of subwavelength gratings in TIR incidence as achromatic phase shifters

in Optics Express (2005), 13(22), 8686-8692

Nulling interferometry constitutes a very promising technique in observational astrophysics. This method consists in attenuating the signal of a bright astrophysical object in order to detect much fainter ... [more ▼]

Nulling interferometry constitutes a very promising technique in observational astrophysics. This method consists in attenuating the signal of a bright astrophysical object in order to detect much fainter nearby features, e.g. exoplanets around their host star. An on-axis destructive interference is created by adjusting the phases of the beams coming from various telescopes. The huge flux ratio between the parent star and the planet (106 in the thermal infrared) requires unprecedented high performance broadband phase shifters. We present a new design for these key components called Achromatic Phase Shifters (APS). We propose to use subwavelength diffractive optical elements under total internal reflection (TIR) incidence. Our component can be seen as an evolution of the Fresnel Rhomb technology. [less ▲]

The XMM-LSS survey - The XMDS/VVDS 4 sigma catalogue

in Astronomy and Astrophysics (2005), 439(1), 413-425

We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed and ... [more ▼]

We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed and used to derive a well defined catalogue of X-ray sources. The present catalogue is limited to a sub-sample of 286 sources detected at 4 sigma in the 1 deg(2) area covered by the photometric VVDS (VIRMOS VLT Deep Survey), which allows us to provide optical and radio identifications. We also discuss the X-ray properties of a larger X-ray sample of 536 sources detected at > 4 sigma in the full 3 deg(2) area of the XMM Medium Deep Survey (XMDS) independently of the optical identification. We also derive the log N - log S relationship for a sample of more than one thousand sources that we discuss in the context of other surveys at similar fluxes. [less ▲]

Accurate photometric light curves of the lensed components of Q2237+0305 derived with an optimal image subtraction technique: Evidence for microlensing in image A

in Astronomy and Astrophysics (2005), 436(2), 479-492

Using an optimal image subtraction technique, we have derived the V and R light curves of the four lensed QSO components of Q2237+0305 from the monitoring CCD frames obtained by the GLITP collaboration ... [more ▼]

Using an optimal image subtraction technique, we have derived the V and R light curves of the four lensed QSO components of Q2237+0305 from the monitoring CCD frames obtained by the GLITP collaboration with the 2.6m NOT telescope in 1999/2000 (Alcalde et al. 2002). We give here a detailed account of the data reduction and analysis and of the error estimates. In agreement with Wozniak et al. (2000a,b), the good derived photometric accuracy of the GLITP data allows to discuss the possible interpretation of the light curve of component A as due to a microlensing event taking place in the deflecting galaxy. This interpretation is strengthened by the colour dependence of the early rise of the light curve of component A, as it probably corresponds to a caustics crossing by the QSO source. [less ▲]