Extreme coronagraphy with an adaptive hologram

We present a solution to improve the performances of coronagraphs in general for the detection of exo-planets. We simulate several kinds of coronagraphic systems using an IDL software, with the aim of evaluating the gain obtained using an adaptive hologram. The detection limit in flux ratio between a star and a planet observed with an apodized Lyot coronagraph characterized by wavefront bumpiness imperfections of lambda/20 (resp. lambda /100) turns out to be increased by a factor 1`000 (resp. 1`000`000) when equipped with an hologram. This technique could provide a direct imaging of an exo-earth at a distance of 11 parsec with a space telescope with a mirror quality analog to the HST, and with a diameter analog to the JWST

The Optimal Gravitational Lens Telescope

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster,...), it is possible via numerical lens inversion to retrieve the real source image, taking full advantage of the magnifying power of the cosmic lens. This has been achieved in the past for several remarkable gravitational lens systems. Instead, we propose here to invert an observed multiply imaged source directly at the telescope using an ad-hoc optical instrument which is described in the present paper. Compared to the previous method, this should allow one to detect fainter source features as well as to use such an optimal gravitational lens telescope to explore even fainter objects located behind and near the lens. Laboratory and numerical experiments illustrate this new approach

Tests with a Carlina-type diluted telescope; Primary coherencing

Studies are under way to propose a new generation of post-VLTI interferometers. The Carlina concept studied at the Haute- Provence Observatory is one of the proposed solutions. It consists in an optical interferometer configured like a diluted version of the Arecibo radio telescope: above the diluted primary mirror made of fixed cospherical segments, a helium balloon (or cables suspended between two mountains), carries a gondola containing the focal optics. Since 2003, we have been building a technical demonstrator of this diluted telescope. First fringes were obtained in May 2004 with two closely-spaced primary segments and a CCD on the focal gondola. We have been testing the whole optical train with three primary mirrors. The main aim of this article is to describe the metrology that we have conceived, and tested under the helium balloon to align the primary mirrors separate by 5-10 m on the ground with an accuracy of a few microns. The servo loop stabilizes the mirror of metrology under the helium balloon with an accuracy better than 5 mm while it moves horizontally by 30 cm in open loop by 10-20 km/h of wind. We have obtained the white fringes of metrology; i.e., the three mirrors are aligned (cospherized) with an accuracy of {\approx} 1 micron. We show data proving the stability of fringes over 15 minutes, therefore providing evidence that the mechanical parts are stabilized within a few microns. This is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or under a balloon. Carlina, like the MMT or LBT, could be one of the first members of a new class of telescopes named diluted telescopes.Comment: 18 pages, 17 figures, A&A, accepte

Measuring differential rotation of the K-giant ζ\zeta\,And

We investigate the temporal spot evolution of the K-giant component in the RS CVn-type binary system $\zeta$\,Andromedae to establish its surface differential rotation. Doppler imaging is used to study three slightly overlapping spectroscopic datasets, obtained independently at three different observing sites. Each dataset covers one full stellar rotation with good phase coverage, and in total, results in a continuous coverage of almost three stellar rotations ($P_{\rm rot}=$17.8\,d). Therefore, these data are well suited for reconstructing surface temperature maps and studying temporal evolution in spot configurations. Surface differential rotation is measured by the means of cross-correlation of all the possible image pairs. The individual Doppler reconstructions well agree in the revealed spot pattern, recovering numerous low latitude spots with temperature contrasts of up to $\approx$1000\,K with respect to the unspotted photosphere, and also an asymmetric polar cap which is diminishing with time. Our detailed cross-correlation study consistently indicate solar-type differential rotation with an average surface shear $\alpha\approx0.055$, in agreement with former results.Comment: accepted for publication in A&A, 4 pages, 3 figure

The Structure of Radiative Shock Waves. IV. Effects of Electron Thermal Conduction

We considered the structure of steady-state radiative shock waves propagating in the partially ionized hydrogen gas with density rho1 = 1e-10 gm/cm^3 and temperature 3000K <= T1 <= 8000K. The radiative shock wave models with electron thermal conduction in the vicinity of the viscous jump are compared with pure radiative models. The threshold shock wave velocity above of which effects of electron thermal conduction become perceptible is of U1=70 km/s and corresponds to the upstream Mach numbers from M1= 6 at T1=8000K to M1=11 at T1=3000K. In shocks with efficient electron heat conduction more than a half of hydrogen atoms are ionized in the radiative precursor, whereas behind the viscous jump the hydrogen gas undergoes the full ionization. The existence of the electron conductive precursor leads to the enhancement of the Lyman continuum flux trapped in the surroundings of the discontinuous jump. For upstream velocities ranged within 70 km/s <= U1 <= 85 km/s the partially ionized hydrogen gas of the radiative precursor undergoes the additional ionization (<= 5%), whereas the total radiave flux emerging from the shock wave increases by 10% <= delta(FRad) <= 25% .Comment: 6 pages, 5 figures, LaTeX, accepted for publication in A

Planet Formation Imager (PFI): Introduction and Technical Considerations

Complex non-linear and dynamic processes lie at the heart of the planet formation process. Through numerical simulation and basic observational constraints, the basics of planet formation are now coming into focus. High resolution imaging at a range of wavelengths will give us a glimpse into the past of our own solar system and enable a robust theoretical framework for predicting planetary system architectures around a range of stars surrounded by disks with a diversity of initial conditions. Only long-baseline interferometry can provide the needed angular resolution and wavelength coverage to reach these goals and from here we launch our planning efforts. The aim of the "Planet Formation Imager" (PFI) project is to develop the roadmap for the construction of a new near-/mid-infrared interferometric facility that will be optimized to unmask all the major stages of planet formation, from initial dust coagulation, gap formation, evolution of transition disks, mass accretion onto planetary embryos, and eventual disk dispersal. PFI will be able to detect the emission of the cooling, newly-formed planets themselves over the first 100 Myrs, opening up both spectral investigations and also providing a vibrant look into the early dynamical histories of planetary architectures. Here we introduce the Planet Formation Imager (PFI) Project (www.planetformationimager.org) and give initial thoughts on possible facility architectures and technical advances that will be needed to meet the challenging top-level science requirements.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2014, Paper ID 9146-35, 10 pages, 2 Figure

The SPHERE data center: a reference for high contrast imaging processing

The objective of the SPHERE Data Center is to optimize the scientific return of SPHERE at the VLT, by providing optimized reduction procedures, services to users and publicly available reduced data. This paper describes our motivation, the implementation of the service (partners, infrastructure and developments), services, description of the on-line data, and future developments. The SPHERE Data Center is operational and has already provided reduced data with a good reactivity to many observers. The first public reduced data have been made available in 2017. The SPHERE Data Center is gathering a strong expertise on SPHERE data and is in a very good position to propose new reduced data in the future, as well as improved reduction procedures.Comment: SF2A proceeding

The Carlina-type diluted telescope: Stellar fringes on Deneb

Context. The performance of interferometers has largely been increased over the last ten years. But the number of observable objects is still limited due to the low sensitivity and imaging capability of the current facilities. Studies have been done to propose a new generation of interferometers. Aims. The Carlina concept studied at the Haute-Provence Observatory consists in an optical interferometer configured as a diluted version of the Arecibo radio telescope: above the diluted primary mirror made of fixed co-spherical segments, a helium balloon or cables suspended between two mountains and/or pylons, carries a gondola containing the focal optics. This concept does not require delay lines. Methods. Since 2003, we have been building a technical demonstrator of this diluted telescope. The main goals of this project were to find the opto-mechanical solutions to stabilize the optics attached under cables at several tens of meters above the ground, and to characterize this diluted telescope under real conditions. In 2012, we have obtained metrology fringes, and co-spherized the primary mirrors within one micron accuracy. In 2013, we have tested the whole optical train: servo loop, metrology, and the focal gondola. Results. We obtained stellar fringes on Deneb in September 2013. In this paper, we present the characteristics of these observations: quality of the guiding, S /N reached, and possible improvements for a future system. Conclusions. It is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or pylons. Carlina, like the MMT or LBT, could be one of the first members of a new class of telescopes named Large Diluted Telescopes. Its optical architecture has many advantages for future projects: Planet Formation Imager, Post-ELTs, Interferometer in space.Comment: 8 pages, 7 figures, Astronomy & Astrophysic

The Pulsation of Chi Cygni Imaged by Optical Interferometry; a Novel Technique to Derive Distance and Mass of Mira Stars

We present infrared interferometric imaging of the S-type Mira star Chi Cygni. The object was observed at four different epochs in 2005-2006 with the IOTA optical interferometer (H band). Images show up to 40% variation in the stellar diameter, as well as significant changes in the limb darkening and stellar inhomogeneities. Model fitting gave precise time-dependent values of the stellar diameter, and reveals presence and displacement of a warm molecular layer. The star radius, corrected for limb darkening, has a mean value of 12.1 mas and shows a 5.1mas amplitude pulsation. Minimum diameter was observed at phase 0.94+/-0.01. Maximum temperature was observed several days later at phase 1.02+/-0.02. We also show that combining the angular acceleration of the molecular layer with CO (Delta v = 3) radial velocity measurements yields a 5.9+/-1.5 mas parallax. The constant acceleration of the CO molecules -- during 80% of the pulsation cycle -- lead us to argument for a free-falling layer. The acceleration is compatible with a gravitational field produced by a 2.1(+1.5/-0.7) solar mass star. This last value is in agreement with fundamental mode pulsator models. We foresee increased development of techniques consisting in combining radial velocity with interferometric angular measurements, ultimately allowing total mapping of the speed, density, and position of the diverse species in pulsation driven atmospheres.Comment: 36 pages, accepted in Ap