1,151 research outputs found

    "Advanced" data reduction for the AMBER instrument

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    The amdlib AMBER data reduction software is meant to produce AMBER data products from the raw data files that are sent to the PIs of different proposals or that can be found in the ESO data archive. The way defined by ESO to calibrate the data is to calibrate one science data file with a calibration one, observed as close in time as possible. Therefore, this scheme does not take into account instrumental drifts, atmospheric variations or visibility-loss corrections, in the current AMBER data processing software, amdlib. In this article, we present our approach to complement this default calibration scheme, to perform the final steps of data reduction, and to produce fully calibrated AMBER data products. These additional steps include: an overnight view of the data structure and data quality, the production of night transfer functions from the calibration stars observed during the night, the correction of additional effects not taken into account in the standard AMBER data reduction software such as the so-called "jitter" effect and the visibility spectral coherence loss, and finally, the production of fully calibrated data products. All these new features are beeing implemented in the modular pipeline script amdlibPipeline, written to complement the amdlib software.Comment: 10 pages, will be published in the proceeding of the SPIE conference "astronomical Telescopes and Instrumentation: Optical and Infrared Interferometry", held in Marseille from 23 to 27 june 200

    AMBER closure and differential phases: accuracy and calibration with a Beam Commutation

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    The first astrophysical results of the VLTI focal instrument AMBER have shown the importance of the differential and closure phase measures, which are supposed to be much less sensitive to atmospheric and instrumental biases than the absolute visibility. However there are artifacts limiting the accuracy of these measures which can be substantially overcome by a specific calibration technique called Beam Commutation. This paper reports the observed accuracies on AMBER/VLTI phases in different modes, discusses some of the instrumental biases and shows the accuracy gain provided by Beam Commutation on the Differential Phase as well as on the Closure Phase.Comment: This paper will be published in the proceeding of SPIE ``astronomical Telescopes and Instrumentation: Optical and Infrared Interferometry'

    Differential interferometry of QSO broad line regions I: improving the reverberation mapping model fits and black hole mass estimates

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    Reverberation mapping estimates the size and kinematics of broad line regions (BLR) in Quasars and type I AGNs. It yields size-luminosity relation, to make QSOs standard cosmological candles, and mass-luminosity relation to study the evolution of black holes and galaxies. The accuracy of these relations is limited by the unknown geometry of the BLR clouds distribution and velocities. We analyze the independent BLR structure constraints given by super-resolving differential interferometry. We developed a three-dimensional BLR model to compute all differential interferometry and reverberation mapping signals. We extrapolate realistic noises from our successful observations of the QSO 3C273 with AMBER on the VLTI. These signals and noises quantify the differential interferometry capacity to discriminate and measure BLR parameters including angular size, thickness, spatial distribution of clouds, local-to-global and radial-to-rotation velocity ratios, and finally central black hole mass and BLR distance. A Markov Chain Monte Carlo model-fit, of data simulated for various VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be compared to 0.44 dex for reverberation mapping mass-luminosity fits. We evaluate the number of QSOs accessible to measures with current (AMBER), upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers) VLTI instruments. With available technology, the VLTI could resolve more than 60 BLRs, with a luminosity range larger than four decades, sufficient for a good calibration of RM mass-luminosity laws, from an analysis of the variation of BLR parameters with luminosity.Comment: 19 pages, 14 figures, accepted by MNRAS on December 5, 201

    Statistical characterization of polychromatic absolute and differential squared visibilities obtained from AMBER/VLTI instrument

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    In optical interferometry, the visibility squared modulus are generally assumed to follow a Gaussian distribution and to be independent of each other. A quantitative analysis of the relevance of such assumptions is important to help improving the exploitation of existing and upcoming multi-wavelength interferometric instruments. Analyze the statistical behaviour of both the absolute and the colour-differential squared visibilities: distribution laws, correlations and cross-correlations between different baselines. We use observations of stellar calibrators obtained with AMBER instrument on VLTI in different instrumental and observing configurations, from which we extract the frame-by-frame transfer function. Statistical hypotheses tests and diagnostics are then systematically applied. For both absolute and differential squared visibilities and under all instrumental and observing conditions, we find a better fit for the Student distribution than for the Gaussian, log-normal and Cauchy distributions. We find and analyze clear correlation effects caused by atmospheric perturbations. The differential squared visibilities allow to keep a larger fraction of data with respect to selected absolute squared visibilities and thus benefit from reduced temporal dispersion, while their distribution is more clearly characterized. The frame selection based on the criterion of a fixed SNR value might result in either a biased sample of frames or in a too severe selection.Comment: A&A, 13 pages and 9 figure

    DISCO: a Spatio-Spectral Recombiner for Pupil Remapping Interferometry

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    Pupil-remapping is a new high-dynamic range imaging technique that has recently demonstrated feasibility on sky. The current prototypes present however deceiving limiting magnitude, restricting the current use to the brightest stars in the sky. We propose to combine pupil-remapping with spatio-spectral encoding, a technique first applied to the VEGA/CHARA interferometer. The result is an instrument proposal, called "Dividing Interferometer for Stars Characterizations and Observations" (DISCO). The idea is to take profit of wavelength multiplexing when using a spectrograph in order to pack as much as possible the available information, yet providing a potential boost of 1.5 magnitude if used in existing prototypes. We detail in this paper the potential of such a concept.Comment: Improving the performances of current optical interferometers \& future designs, France (2013

    Wolf-Rayet stars probed by AMBER/VLTI

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    Massive stars deeply influence their surroundings by their luminosity and the injection of kinetic energy. So far, they have mostly been studied with spatially unresolved observations, although evidence of geometrical complexity of their wind are numerous. Interferometry can provide spatially resolved observations of massive stars and their immediate vicinity. Specific geometries (disks, jets, latitude-dependent winds) can be probed by this technique. The first observation of a Wolf-Rayet (WR) star (\gamma^2 Vel) with the AMBER/VLTI instrument yielded to a re-evaluation of its distance and an improved characterization of the stellar components, from a very limited data-set. This motivated our team to increase the number of WR targets observed with AMBER. We present here new preliminary results that encompass several spectral types, ranging from early WN to evolved dusty WC. We present unpublished data on WR79a, a massive star probably at the boundary between the O and Wolf- Rayet type, evidencing some Wolf-Rayet broad emission lines from an optically thin wind. We also present new data obtained on \gamma^2 Vel that can be compared to the up-to-date interferometry-based orbital parameters from North et al. (2007). We discuss the presence of a wind-wind collision zone in the system and provide preliminary analysis suggesting the presence of such a structure in the data. Then, we present data obtained on 2 dusty Wolf-Rayet stars: WR48a-b and WR118, the latter exhibiting some clues of a pinwheel-like structure from the visibility variations.Comment: This paper will be published in the proceeding of SPIE ``astronomical Telescopes and Instrumentation: Optical and Infrared Interferometry'

    High spectral resolution imaging of the dynamical atmosphere of the red supergiant Antares in the CO first overtone lines with VLTI/AMBER

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    We present high spectral resolution aperture-synthesis imaging of the red supergiant Antares (alpha Sco) in individual CO first overtone lines with VLTI/AMBER. The reconstructed images reveal that the star appears differently in the blue wing, line center, and red wing and shows an asymmetrically extended component. The appearance of the star within the CO lines changes drastically within one year, implying a significant change in the velocity field in the atmosphere. Our modeling suggests an outer atmosphere (MOLsphere) extending to 1.2--1.4 stellar radii with CO column densities of (0.5--1)x10^{20} cm^{-2} and a temperature of ~2000 K. While the velocity field in 2009 is characterized by strong upwelling motions at 20--30 km/s, it changed to strong downdrafts in 2010. On the other hand, the AMBER data in the continuum show only a slight deviation from limb-darkened disks and only marginal time variations. We derive a limb-darkened disk diameter of 37.38+/-0.06 mas and a power-law-type limb-darkening parameter of (8.7+/-1.6)x10^{-2} (2009) and 37.31+/-0.09 mas and (1.5+/-0.2)x10^{-1} (2010). We also obtain Teff = 3660+/-120 K and log L/Lsun = 4.88+/-0.23, which suggests a mass of 15+/-5 Msun with an age of 11-15 Myr. This age is consistent with the recently estimated age for the Upper Scorpius OB association. The properties of the outer atmosphere of Antares are similar to those of another well-studied red supergiant, Betelgeuse. The density of the extended outer atmosphere of Antares and Betelgeuse is higher than predicted by the current 3-D convection simulations by at least six orders of magnitude, implying that convection alone cannot explain the formation of the extended outer atmosphere.Comment: 18 pages, 16 figures, accepted for publication in Astronomy and Astrophysics, short discussion on the age of Antares and the Upper Scorpius OB association added, movies of the reconstructed images available at http://www.mpifr-bonn.mpg.de/staff/kohnaka
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