This paper presents speckle observations of Mira (o Cet) and late-type stars with the PISCO speckle camera of Pic du Midi during the period 1995-1998. A survey for binarity among a sample of ...late-type stars was performed, which led to 7 positive detections out of 36 objects. Photometric and color variations of the companion of Mira were searched for, but no significant brightness variations could be found over a time scale of ∼5–10 minutes. The position and photometry measurements, the restored images with high angular resolution of the binary system Mira A-B (ADS 1778) are in full agreement with HST data obtained atthe same epoch. A new orbit has been derived for Mira A-B.
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.
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.
ABSTRACT We present observations made in 2006 with the single-star SCIDAR (SSS) at Dome C in Antarctica, allowing us to determine optical turbulence C N 2 ( h ) and velocity V(h) profiles from ice ...levels up to about 25 km above sea level (a.s.l.). SSS is a 16 inch telescope placed on an equatorial mount that continuously tracks the Canopus star. About 90,000 individual profiles are analyzed from March to September, where surface-layer contribution to seeing can be separated from the rest of the atmosphere. Medians of high angular resolution parameters relevant to astronomy are statistically studied, such as seeing (1.0′′), isoplanatic angle (6.9′′), and wavefront coherence time (3.4 ms). For a telescope placed above the turbulent surface layer, superb conditions are encountered (medians of seeing better than 0.3′′, isoplanatic angle better than 6.9′′, and coherence time larger than 10 ms). Astronomical conditions are twice as good at the beginning of the night, with ε0 ≈ 0.5′′, θ0 ≈ 11.5′′, and τ0 ≈ 15 ms. SSS wind-velocity profiles are consistent with National Oceanic and Atmospheric Administration analysis up to 17 km (a.s.l.), within a ± 2 m s - 1 error bar. Coherence étendue (which is a combination of ε0, θ0, and τ0), well adapted to adaptive optics performances, is likely 4 times better at Dome C than at the already-known observatories such as Mauna Kea or ORM.
The HAR observing methods such as Adaptive Optics and Interferometery, require a better understanding of the behavior of the perturbed wavefronts, more exactly a better knowledge of the atmospheric ...turbulence model in addition to the associate parameters. This is very crucial for modeling the HAR techniques and particularly for the evaluation of their performance. Indeed, it is well-known that the performance of an AO system depends upon the seeing conditions, the outer scale, the isoplanatic angle and the coherence time. A review of the site-testing instruments deployed at Dome C will be given, their pertinence and their implications on HAR techniques will be discussed comparatively to the Paranal site.
The optical turbulence above Dome C in winter is mainly concentrated in the first tens of meters above the ground. The properties of this so-called surface layer were investigated during the last two ...winterover by a set of sonics anemometers placed on a 45 m high tower. These anemometers provide measurements of the temperature and the wind speed vector. The sampling rate of 10 Hz allows to derivate the refractive index structure constant Cn2. We report here the first analysis of these data.
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