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تسجيل مستخدم جديدProgress on VLBI Ecliptic Plane Survey
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We launched the VLBI Ecliptic Plane Survey program in 2015. The goal of this program is to find all compact sources within 7.5 degrees of the ecliptic plane which are suitable as phase calibrators for anticipated phase referencing observations of spacecrafts. We planned to observe a complete sample of the sources brighter than 50 mJy at 5 GHz listed in the PMN and GB6 catalogues that have not yet been observed with VLBI. By April 2016, eight 24-hour sessions have been performed and processed. Among 2227 observed sources, 435 sources were detected in three or more observations. We have also run three 8-hour segments with VLBA for improving positions of 71 ecliptic sources.
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We present here the results of the first part of the VLBI Ecliptic Plane Survey (VEPS) program. The goal of the program is to find all compact sources within $7.5^circ$ of the ecliptic plane which are suitable as calibrators for anticipated phase ref
erencing observations of spacecraft and determine their positions with accuracy at the 1.5~nrad level. We run the program in two modes: the search mode and the refining mode. In the search mode, a complete sample of all sources brighter than 50 mJy at 5 GHz listed in the Parkes-MIT-NRAO (PMN) and Green Bank 6~cm (GB6) catalogs, except those previously detected with VLBI, is observed. In the refining mode, the positions of all ecliptic plane sources, including those found in the search mode, are improved. By October 2016, thirteen 24-hr sessions that targeted all sources brighter than 100~mJy have been observed and analyzed. Among 3320 observed target sources, 555 objects have been detected. We also conducted a number of follow-up VLBI experiments in the refining mode and improved the positions of 249 ecliptic plane sources.
We report the orbital distribution of the Trans-Neptunian objects (TNOs) discovered during the High Ecliptic Latitude (HiLat) extension of the Canada-France Ecliptic Plane Survey (CFEPS), conducted from June 2006 to July 2009. The HiLat component was
designed to address one of the shortcomings of ecliptic surveys (like CFEPS), their lack of sensitivity to high-inclination objects. We searched 701~deg$^2$ of sky ranging from 12$^circ$ to 85$^circ$ ecliptic latitude and discovered lKBO TNOs, with inclinations between 15$^circ$ to 104$^circ$. This survey places a very strong constraint on the inclination distribution of the hot component of the classical Kuiper Belt, ruling out any possibility of a large intrinsic fraction of highly inclined orbits. Using the parameterization of citet{2001AJ....121.2804B}, the HiLat sample combined with CFEPS imposes a width $14^circ le sigma le 15.5^circ$, with a best match for $sigma = 14.5^circ$. HiLat discovered the first retrograde TNO, 2008~KV$_{42}$, with an almost polar orbit with inclination 104$^circ$, and (418993), a scattering object with perihelion in the region of Saturns influence, with $a sim 400$~AU and $i = 68^circ$.
Radio observations using the Very Long Baseline Interferometry (VLBI) technique typically have fields of view of only a few arcseconds, due to the computational problems inherent in imaging larger fields. Furthermore, sensitivity limitations restrict
observations to very compact and bright objects, which are few and far between on the sky. Thus, while most branches of observational astronomy can carry out sensitive, wide-field surveys, VLBI observations are limited to targeted observations of carefully selected objects. However, recent advances in technology have made it possible to carry out the computations required to target hundreds of sources simultaneously. Furthermore, sensitivity upgrades have dramatically increased the number of objects accessible to VLBI observations. The combination of these two developments have enhanced the survey capabilities of VLBI observations such that it is now possible to observe (almost) any point in the sky with milli-arcsecond resolution. In this talk I review the development of wide-field VLBI, which has made significant progress over the last three years.
The SKA will deliver orders of magnitude increases in sensitivity, but most astrometric VLBI observations are limited by systematic errors. In these cases improved sensitivity offers no benefit. The best current solution for improving the accuracy of
the VLBI calibration is MV VLBI, where multiple simultaneous observations around the target are used to deduce the corrections required for the line of sight to the target. We have estimated and quantified the applicability of MV from real-world ionospheric studies, making projections into achievable astrometric accuracies. These predict systematic measurement errors, with calibrators separated by several degrees, of $sim$10uas with current VLBI facilities. For closer calibrators, that are in-beam for single dish VLBI facilities, we predict systematic measurement errors of a few uas. This is the ideal combination, where the sensitivity of the SKA will provide the precision and MV will provide the accuracy. Based on these results we suggest that the SKA design should increase the number of VLBI beams it can form from four to as many as ten.
QUBIC is a unique instrument that crosses the barriers between classical imaging architectures and interferometry taking advantage from both for high sensitivity and systematics mitigation. The scientific target is the detection of the primordial gra
vitational waves imprint on the Cosmic Microwave Background which are the proof of inflation, holy grail of modern cosmology. In this paper, we show the latest advances in the development of the architecture and the sub-systems of the first module of this instrument to be deployed in Dome Charlie Concordia base - Antarctica in 2015.
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