Morgan Lopez

AMBER, the near-infrared spectro-interferometric three-telescope VLTI instrument

Context: Optical long-baseline interferometry is moving a crucial step forward with the advent of general-user scientific instruments that equip large aperture and hectometric baseline facilities, such as the Very Large Telescope Interferometer (VLTI). Aims: AMBER is one of the VLTI instruments that combines up to three beams with low, moderate and high spectral resolutions in order to provide milli-arcsecond spatial resolution for compact astrophysical sources in the near-infrared wavelength domain. Its main specifications are based on three key programs on young stellar objects, active galactic nuclei central regions, masses, and spectra of hot extra-solar planets. Methods: These key science goals led to scientific specifications, which were used to propose and then validate the instrument concept. AMBER uses single-mode fibers to filter the entrance signal and to reach highly accurate, multiaxial three-beam combination, yielding three baselines and a closure phase, three spectral dispersive elements, and specific self-calibration procedures. Results: The AMBER measurements yield spectrally dispersed calibrated visibilities, color-differential complex visibilities, and a closure phase allows astronomers to contemplate rudimentary imaging and highly accurate visibility and phase differential measurements. AMBER was installed in 2004 at the Paranal Observatory. We describe here the present implementation of the instrument in the configuration with which the astronomical community can access it. Conclusions: .After two years of commissioning tests and preliminary observations, AMBER has produced its first refereed publications, allowing assessment of its scientific potential.

Interferometric data reduction with AMBER/VLTI. Principle, estimators, and illustration

Aims. In this paper, we present an innovative data reduction method for single-mode interferometry. It has been specifically developed for the AMBER instrument, the three-beam combiner of the Very Large Telescope Interferometer, but it can be derived for any single-mode interferometer. Methods. The algorithm is based on a direct modelling of the fringes in the detector plane. As such, it requires a preliminary calibration of the instrument in order to obtain the calibration matrix that builds the linear relationship between the interferogram and the interferometric observable, which is the complex visibility. Once the calibration procedure has been performed, the signal processing appears to be a classical least-square determination of a linear inverse problem. From the estimated complex visibility, we derive the squared visibility, the closure phase, and the spectral differential phase. Results. The data reduction procedures have been gathered into the so-called amdlib software, now available for the community, and are presented in this paper. Furthermore, each step in this original algorithm is illustrated and discussed from various on-sky observations conducted with the VLTI, with a focus on the control of the data quality and the effective execution of the data reduction procedures. We point out the present limited performances of the instrument due to VLTI instrumental vibrations which are difficult to calibrate.

Constraining the wind launching region in Herbig Ae stars: AMBER/VLTI spectroscopy of HD 104237

This work has been partly supported by the nMIUR COFIN grant 2003/027003-001 and 025227/2004 to the INAFOsservatorio nAstrofisico di Arcetri. This project has benefited from nfunding from the French Centre National de la Recherche Scientifique n(CNRS) through the Institut National des Sciences de l’Univers n(INSU) and its Programmes Nationaux (ASHRA, PNPS). The authors nfrom the French laboratories would like to thank the successive ndirectors of the INSU/CNRS directors. C. Gil work was supported nin part by the Fundac¸˜ao para a Ciˆencia e a Tecnologia through nproject POCTI/CTE-AST/55691/2004 from POCTI,with funds from nthe European program FEDER.

Seasonal variation of N2O emissions in France inferred from atmospheric N2O and 222Rn measurements

[1]xa0Nitrous oxide (N2O) concentrations and 222Rn activities are measured semi-continuously at three stations in France: Gif-sur-Yvette (a semi-urban station near Paris), Trainou tower (a rural station) and Puy-de-Dome (a mountain site). From 2002 to 2011, we have found a mean rate of N2O increase of 0.7 pbb a−1. The analysis of the mean diurnal N2O and 222Rn cycles shows maximum variabilities at the semi-urban site of Gif-sur-Yvette (0.96 ppb for N2O and 2 Bq m−3 for 222Rn) compared to the rural site of Trainou tower (0.32 ppb for N2O and 1.3 Bq m−3 for 222Rn). The use of 222Rn as a tracer for vertical mixing and atmospheric transport, combined with the semi-continuous N2O measurements, allows estimation of N2O emissions by applying the Radon-Tracer-Method. Mean N2O emissions values between 0.34 ± 0.12 and 0.51 ± 0.18 g(N2O) m−2 a−1 and 0.52 ± 0.18 g(N2O) m−2 a−1were estimated in the catchment area of Gif-sur-Yvette and Trainou, respectively. The mean annual N2O fluxes at Gif-sur-Yvette station correlate well with annual precipitation. A 25% increase in precipitation corresponds to a 32% increase in N2O flux. The N2O fluxes calculated with the Radon-Tracer-Method show a seasonal cycle, which indicates a strong contribution from the agricultural source, with the application of fertilizers in the early spring inducing a strong increase in N2O emissions. Finally, the results of the Radon-Tracer-Method agree well with the national and global emission inventories, accounting for the uncertainties of both methods.

Optical configuration and analysis of the AMBER/VLTI instrument

Aims. This paper describes the design goals and engineering efforts that led to the realization of AMBER (Astronomical Multi BEam combineR) and to the achievement of its present performance. Methods. On the basis of the general instrumental concept, AMBER was decomposed into modules whose functions and detailed characteristics are given. Emphasis is put on the spatial filtering system, a key element of the instrument. We established a budget for transmission and contrast degradation through the different modules, and made the detailed optical design. The latter confirmed the overall performance of the instrument and defined the exact implementation of the AMBER optics. Results. The performance was assessed with laboratory measurements and commissionings at the VLTI, in terms of spectral coverage and resolution, instrumental contrast higher than 0.80, minimum magnitude of 11 in K, absolute visibility accuracy of 1%. and differential phase stability of 10 -3 . I rad over one minute.