This paper presents orbits and masses for 22 visual double stars, partly derived using their last observations made with the speckle camera PISCO. For 13 of them we have determined their first-time ...orbits. Masses were calculated from Hipparcos and Gaia parallaxes when available, and from dynamical parallaxes otherwise. They are compared with masses deduced from spectral types. Other physical and orbital properties are also considered.
This paper analyses 3$\frac{1}{2}$ years of site testing data obtained at Dome C, Antarctica, based on measurements obtained with three DIMMs located at three different elevations. Basic statistics ...of the seeing and the isoplanatic angle are given, as well as the characteristic time of temporal fluctuations of these two parameters, which we found to around 30 min at 8 m. The 3 DIMMs are exploited as a profiler of the surface layer, and provide a robust estimation of its statistical properties. It appears to have a very sharp upper limit (less than 1 m). The fraction of time spent by each telescope above the top of the surface layer permits us to deduce a median height of between 23 m and 27 m. The comparison of the different data sets led us to infer the statistical properties of the free atmosphere seeing, with a median value of 0.36 arcsec. The $C_n^2$ profile inside the surface layer is also deduced from the seeing data obtained during the fraction of time spent by the 3 telescopes inside this turbulence. Statistically, the surface layer, except during the 3-month summer season, contributes to 95 percent of the total turbulence from the surface level, thus confirming the exceptional quality of the site above it.
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Aims. An experiment was set up at the Concordia station in Antarctica during the winter-over period in 2012 to determine the behaviour of atmospheric optical turbulence in the lower part of the ...atmospheric boundary layer. The aim of the experiment was to study the influence of turbulence and weather conditions on the quality of astronomical observations. The Concordia station is characterised by the high quality of astronomical images thanks to very low seeing values. The surface layer in the interior of Antarctica during the winter is very stably stratified with the differences of temperature between the surface and the top of the inversion, which reach 20−35°C. In spite of this strong static stability, considerable thermal optically active turbulence sometimes occurs and extends to several tens of metres above the surface, depending on weather conditions. It is important to know the meteorological characteristics that favour good astronomical observations. Methods. The optical measurements of the seeing made by differential image motion monitors installed at two levels of 8 and 20 m were accompanied by observations of turbulence in the lowest one hundred meters. Turbulence was detected and evaluated using a high-resolution sodar developed specially for this purpose. The statistics of some relevant meteorological variables including the long-wave downward radiation, which indicates cloudiness, were determined. Results. Typical patterns of the vertical and temporal structure of turbulence shown by sodar echograms were identified, analysed, and classified. The statistics of the depth of the surface-based turbulent layer and the turbulent optical factor for different height layers are presented together with the seeing statistics. We analysed the dependence of both seeing and integral turbulence intensity within the first 100 m on temperature and wind speed. Conclusions. Seeing and turbulence intensity in the atmospheric boundary layer appear to be correlated. The best values of the seeing (<1 arcsec) are observed when the sodar shows very low turbulence intensity. The main contribution to the image distortion is due to turbulence generated within the lowest 30−50 m near the surface. The presented statistics of the vertical distribution of the atmospheric optical turbulence can be used to determine the optimal location for astronomical instruments.
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The optical turbulence above Dome C in winter is mainly concentrated in the first tens of metres above the ground. Properties of this so-called surface layer (SL) were investigated during the period ...2007–2012 by a set of sonic anemometers placed on a 45 m high tower. We present the results of this long-term monitoring of the refractive index structure constant
$C_n^2$
within the SL, and confirm its thickness of 35 m. We give statistics of the contribution of the SL to the seeing and coherence time. We also investigate properties of large-scale structure functions of the temperature and show evidence of a second inertial zone at kilometric spatial scales.
Aims. Future extremely large telescopes will certainly be equipped with wide-field adaptive optics systems. The optimization of the performances of these techniques requires a precise specification ...of the different components of these AO systems. Most of these technical specifications are related to the atmospheric turbulence parameters, particularly the profile of the refractive index structure constant CN2(h). A new monitor called Profiler of Moon Limb (PML) for the extraction of the CN2(h) profile with high vertical resolution and its first results are presented. Methods. The PML instrument uses an optical method based on the observation of the Moon limb through two subapertures. The use of the lunar limb leads to a continuum of double stars allowing a scan of the whole atmosphere with high resolution in altitude. Results. The first prototype of the PML has been installed at Dome C in Antarctica and the first results of the PML are presented and compared to radio-sounding balloon profiles. In addition to the CN2(h) profile obtained with high vertical resolution, PML is also able to provide other atmospheric turbulence parameters such as the outer scale profile, the total seeing, and the isoplanatic and isopistonic angles.
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Abstract
We analyze, in the framework of high angular resolution imaging, a novel image reconstruction method denoted as PSE (which stands for power spectrum extended). It works in the Fourier space, ...combining the information from both the average power spectrum of the images and a phase estimation from an ad-hoc shift-and-add process. PSE allows to perform image reconstruction up to the diffraction limit of the telescope from a series of short-exposure frames, with a refined lucky-imaging selection process. The method is well adapted to partially corrected adaptive-optics images, in particular in case of low Strehl corrections, and/or small diameter telescopes. In this paper we analyze the PSE technique by means of Monte-Carlo simulations and compare it with the ISFAS lucky-imaging method. Comparative performances were investigated using three metrics: Strehl ratio for reconstructed point-like sources, intensity ratio for binary stars, and least-square distance between images for a simulated artificial satellite. We found that PSE provides an improvement of a factor ∼2 over ISFAS on the Strehl ratio in the case of faint point sources. It seems also to give better images reconstruction on some kinds of extended objects (planets or binary stars with small magnitude difference). PSE has also the advantage to be very fast and well adapted to real-time image reconstruction.
ABSTRACT We used the large photometric database of the ASTEP program, whose primary goal was to detect exoplanets in the southern hemisphere from Antarctica, to search for eclipsing binaries (EcBs) ...and variable stars. 673 EcBs and 1166 variable stars were detected, including 31 previously known stars. The resulting online catalogs give the identification, the classification, the period, and the depth or semi-amplitude of each star. Data and light curves for each object are available at http://astep-vo.oca.eu.
We present relative astrometric measurements of visual binaries, made in 2015, with the speckle camera PISCO of the 102‐cm Zeiss telescope of Brera Astronomical Observatory, Merate, Italy. Our ...observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 196 new measurements of 173 visual binary stars, with angular separations in the range 0″.27–11″.3, and an average accuracy of 0″.019. The mean error on the position angles is 0°.6. Most of the position angles were determined without the usual 180° ambiguity with the application of triple‐correlation techniques and/or by inspection of the long integration files. We present new revised orbits for DUN 5, ADS 5958, 6276, 7294, 8211, and 13169, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. We also computed new rectilinear elements for ADS 4841 for which the physical connection is doubtful from our (and other recent) observations.
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We report site‐testing results obtained in the nighttime during the polar autumn and winter at Dome C. These results were collected during the first Concordia winterover by A. Agabi. They are based ...on seeing and isoplanatic angle monitoring, as well as in situ balloon measurements of the refractive index structure constant profiles
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. Atmosphere is divided into two regions: (1) a 36 m high surface layer responsible for 87% of the turbulence, and (2) a very stable free atmosphere above, with a median seeing of 0
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36 ± 0
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19 at an elevation of
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m. The median seeing measured with a differential image motion monitor placed on top of an 8.5 m high tower is 1
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3 ± 0
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8.
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A good astronomical site must fulfill several criteria including low atmospheric turbulence and low wind speeds. It is therefore important to have a detailed knowledge of the temperature and wind ...conditions of a location considered for future astronomical research. Antarctica has unique atmospheric conditions that have already been exploited at the South Pole station. Dome C, a site located on a local maximum of the Antarctic plateau, is likely to have even better conditions. In this paper we present the analysis of two decades of wind speed measurements taken at Dome C by an automated weather station (AWS). We also present temperature and wind speed profiles taken over four Antarctic summers using balloon-borne weather sondes. We will show that as well as having one of the lowest average wind speed ever recorded at an existing or potential observatory, Dome C also has an extremely stable upper atmosphere and a very low inversion layer.
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