A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons

The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for very-high-precision spectroscopy at the level of \updelta\lambda/\lambda<10^{-9}. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-P\'erot-based calibration source. On the basis of calibration frames acquired each night since the Fabry-P\'erot etalon was installed on HARPS in 2011, we construct a combined wavelength solution which fits simultaneously the thorium emission lines and the Fabry-P\'erot lines. The combined fit is anchored to the absolute thorium wavelengths, which provide the `zero-point' of the spectrograph, while the Fabry-P\'erot lines are used to improve the (spectrally) local precision. The obtained wavelength solution is verified for auto-consistency and tested against a solution obtained using the HARPS Laser-Frequency Comb (LFC). The combined thorium+Fabry-P\'erot wavelength solution shows significantly better performances compared to the thorium-only calibration. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.Comment: 15 pages, 8 figure

Evaluation of the Shear Modulus in Models for Shallow-Foundation Dynamics within the Elastic Domain

The aim of this presentation is to examine the relationship of the equivalent homogeneous shear moduli used in impedance models with stresses under the footing, through the use of scaled models in the centrifuge and an impact loading. The analysis of time and frequency vertical responses of footings reveals that reflections on the boundaries are negligible. The frequency response of a series of circular and square footings is shown to be rather easily-fitted with Wolf’s models for foundations on an infinite half-space with reasonably consistent parameters for masses, damping and shear moduli. The damping is nearly constant, yet significantly lower than in a prototype scale with real soil. The mass is fitted with a greater level of scatter. The correlation of shear modulus to the square root of the minimum mean stress appears to be better than that to the square root of the uniform stress under the footing

Low-Dimensional Materials for Disruptive Microwave Antennas Design

This chapter is devoted to a complete analysis of remarkable electromagnetic properties of nanomaterials suitable for antenna design miniaturization. After a review of state of the art mesoscopic scale modeling tools and characterization techniques in microwave domain, new approaches based on wideband material parameters identification (complex permittivity and conductivity) will be described from impedance equivalence formulation achievement by de-embedding techniques applicable in integrated technology or in free space. A focus on performances of 1D materials such as vertically aligned multi-wall carbon nanotube (VA-MWCNT) bundles, from theory to technology, will be presented as a disruptive demonstration for defense and civil applications as in radar systems

Consequences of spectrograph illumination for the accuracy of radial-velocimetry

For fiber-fed spectrographs with a stable external wavelength source, scrambling properties of optical fibers and, homogeneity and stability of the instrument illumination are important for the accuracy of radial-velocimetry. Optical cylindric fibers are known to have good azimuthal scrambling. In contrast, the radial one is not perfect. In order to improve the scrambling ability of the fiber and to stabilize the illumination, optical double scrambler are usually coupled to the fibers. Despite that, our experience on SOPHIE and HARPS has lead to identified remaining radial-velocity limitations due to the non-uniform illumination of the spectrograph. We conducted tests on SOPHIE with telescope vignetting, seeing variation and centering errors on the fiber entrance. We simulated the light path through the instrument in order to explain the radial velocity variation obtained with our tests. We then identified the illumination stability and uniformity has a critical point for the extremely high-precision radial velocity instruments (ESPRESSO@VLT, CODEX@E-ELT). Tests on square and octagonal section fibers are now under development and SOPHIE will be used as a bench test to validate these new feed optics.Comment: to appear in the Proceedings conference "New Technologies for Probing the Diversity of Brown Dwarfs and Exoplanets", Shanghai, 200

Stabilising a nulling interferometer using optical path difference dithering

Context. Nulling interferometry has been suggested as the underlying principle for the Darwin and TPF-I exoplanet research missions. Aims. There are constraints both on the mean value of the nulling ratio, and on its stability. Instrument instability noise is most detrimental to the stability of the nulling performance. Methods. We applied a modified version of the classical dithering technique to the optical path difference in the scientific beam. Results. Using only this method, we repeatedly stabilised the dark fringe for several hours. This method alone sufficed to remove the 1/ f component of the noise in our setup for periods of 10 minutes, typically. These results indicate that performance stability may be maintained throughout the long-duration data acquisitions typical of exoplanet spectroscopy. Conclusions. We suggest that further study of possible stabilisation strategies should be an integral part of Darwin/TPF-I research and developmen

Identification of Different Seismic Waves Generated by Foundation Vibration in the Centrifuge: Travel Time, Spectral and Numerical Investigations

For the analysis of footings under dynamic loading scaled modeling in the centrifuge assumes that the soil behaves like at prototype scale. This paper demonstrates that for a container filled with dry sand, wave velocities can be described by a model based on the relation between the shear modulus and the depth dependent stress level proposed by Iwasaki and Tatsuoka. A preliminary estimation of the shear wave velocities and of the Poisson’s ratio confirms by dynamical measurements the currently use value of 0.25. A FEM modeling also helps to strengthen the validity of the model proposed, providing another insight in the propagation of waves in a soil with a velocity gradient

Interaction Site-Ville : Approches expérimentales et numériques

À l’échelle d’une ville, les structures de surface telles que les bâtiments peuvent modifier le mouvement sismique en 'champ libre' et agir comme des sources sismiques secondaires. Des observations ont en particulier été réalisées sur des données réelles. Elles montrent que cet effet peut être significatif. La conséquence directe de cette 'interaction site-ville' est la pollution du mouvement sismique en milieu urbain par un champ d’onde secondaire. Des modélisations en centrifugeuse et numériques tendent à confirmer que ce phénomène n’est pas anecdotique. En particulier, ces résultats montrent qu’entre deux bâtiments proches des interactions existent, modifiant le mouvement du sol mais aussi la réponse des structures impliquées. À l’échelle d’une ville, ce phénomène sera d’autant plus marqué lorsqu’un fort couplage existe entre la réponse du sol et la réponse du milieu urbain

Broadband near-infrared astronomical spectrometer calibration and on-sky validation with an electro-optic laser frequency comb

The quest for extrasolar planets and their characterisation as well as studies of fundamental physics on cosmological scales rely on capabilities of high-resolution astronomical spectroscopy. A central requirement is a precise wavelength calibration of astronomical spectrographs allowing for extraction of subtle wavelength shifts from the spectra of stars and quasars. Here, we present an all-fibre, 400 nm wide near-infrared frequency comb based on electro-optic modulation with 14.5 GHz comb line spacing. Tests on the high-resolution, near-infrared spectrometer GIANO-B show a photon-noise limited calibration precision of <10 cm/s as required for Earth-like planet detection. Moreover, the presented comb provides detailed insight into particularities of the spectrograph such as detector inhomogeneities and differential spectrograph drifts. The system is validated in on-sky observations of a radial velocity standard star (HD221354) and telluric atmospheric absorption features. The advantages of the system include simplicity, robustness and turn-key operation, features that are valuable at the observation sites

Multi-agent system for modelling the restructured energy market

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