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Register a new user(Ultra) Precise Astrometry today and tomorrow, with Next-generation Observatories
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High precision astrometry provides the foundation to resolve many fundamental problems in astrophysics. The application of astrometric studies spans a wide range of fields, and has undergone enormous growth in recent years. This is as a consequence of the increasing measurement precision and wide applicability, which is due in turn to the development of new techniques. Forthcoming next generation observatories have the potential to further increase the astrometric precision, providing there is a matching improvement in the methods to correct for systematic errors. The EVN and other observatories are providing demonstrations of these and are acting as pathfinders for next-generation telescopes such as the SKA and ngVLA. We will review the perspectives for the coming facilities and examples of the current state-of-the-art for astrometry.
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We present a technique-led review of the progression of precise radio astrometry, from the first demonstrations, half a century ago, until to date and into the future. We cover the developments that have been fundamental to allow high accuracy and precision astrometry to be regularly achieved. We review the opportunities provided by the next-generation of instruments coming online, which are primarily: SKA, ngVLA and pathfinders, along with EHT and other (sub)mm-wavelength arrays, Space-VLBI, Geodetic arrays and optical astrometry from GAIA. From the historical development we predict the future potential astrometric performance, and therefore the instrumental requirements that must be provided to deliver these. The next-generation of methods will allow ultra-precise astrometry to be performed at a much wider range of frequencies (hundreds of MHz to hundreds of GHz). One of the key potentials is that astrometry will become generally applicable, and therefore unbiased large surveys can be performed. The next-generation methods are fundamental in allowing this. We review the small but growing number of major astrometric surveys in the radio, to highlight the scientific impact that such projects can provide. Based on these perspectives, the future of radio astrometry is bright. We foresee a revolution coming from: ultra-high precision radio astrometry, large surveys of many objects, improved sky coverage and at new frequency bands other than those available today. These will enable the addressing of a host of innovative open scientific questions in astrophysics.
Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the opacity barrier of synchrotron self-absorption in AGN and opens the direct view into sub-pc scale regions not accessible before. Since AGN variability is more pronounced at short millimeter wavelength, mm-VLBI can reveal structural changes in very early stages after outbursts. When combined with observations at longer wavelength, global 3mm and 1mm VLBI adds very detailed information. This helps to determine fundamental physical properties at the jet base, and in the vicinity of super-massive black holes at the center of AGN. Here we present new results from multi-frequency mm-VLBI imaging of OJ287 during a major outburst. We also report on a successful 1.3mm VLBI experiment with the APEX telescope in Chile. This observation sets a new record in angular resolution. It also opens the path towards future mm-VLBI with ALMA, which aims at the mapping of the black hole event horizon in nearby galaxies, and the study of the roots of jets in AGN.
Context: Observation of star occultations is a powerful tool to determine shapes and sizes of asteroids. This is key information necessary for studying the evolution of the asteroid belt and to calibrate indirect methods of size determination, such as the models used to analyze thermal infrared observations. Up to now, the observation of asteroid occultations is an activity essentially secured by amateur astronomers equipped with small, portable equipments. However, the accuracy of the available ephemeris prevents accurate predictions of the occultation events for objects smaller than ~100 km. Aims: We investigate current limits in predictability and observability of asteroid occultations, and we study their possible evolution in the future, when high accuracy asteroid orbits and star positions (such as those expected from the mission Gaia of the European Space Agency) will be available. Methods: We use a simple model for asteroid ephemeris uncertainties and numerical algorithms for estimating the limits imposed by the instruments, assuming realistic CCD performances and asteroid size distribution, to estimate the expected occultation rate under different conditions. Results: We show that high accuracy ephemerides which will be available in the future will extend toward much smaller asteroids the possibility of observing asteroid occultations, greatly increasing the number of events and objects involved. A complete set of size measurements down to ~10 km main belt asteroids could be obtained in a few years, provided that a small network of ground-based 1m telescopes are devoted to occultation studies.
In the current view of Gamma-Ray Burst (GRB) phenomena, an emission component extending up to the very-high energy (VHE, E > 30 GeV) domain is though to be a relatively common feature at least in the brightest events. This leads to an unexpected richness of possible theoretical models able to describe such phenomenology. Hints of emission at tens of GeV are indeed known since the EGRET observations during the 90s and confirmed in the Fermi-LAT data. However, our comprehension of these phenomena is still far to be satisfactory. In this respect, the VHE characterization of GRBs may constitute a breakthrough for understanding their physics and, possibly, for providing decisive clues for the discrimination among different proposed emission mechanisms, which are barely distinguishable at lower energies. The current generation of Cherenkov observatories, such as the MAGIC telescopes, have opened the possibility to extend the measurement of GRB emission, and in general to any short time-scale transient phenomena, fromfew tens of GeV up to the TeV energy range, with a higher sensitivity with respect to gamma-ray space-based instruments. In the near future, a crucial role for the VHE observations of GRBs will be played by the Cherenkov Telescope Array (CTA), thanks to its about one order of magnitude better sensitivity and lower energy threshold with respect to current instruments. In this contribution, we present a method aimed at providing VHE detection prospects for observations of GRB-like transient events with Cherenkov telescopes. In particular, we consider the observation of the transient event GRB 090102 as a test case for the method and show the achieved detection prospects under different observational conditions for the MAGIC telescopes and CTA.
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