Papers by Alberto Vecchiato
Journal of Astronomical History and Heritage
This paper reviews and updates the accounts of a previous article discussing the possible astrono... more This paper reviews and updates the accounts of a previous article discussing the possible astronomical significance of a peculiar, man-made circular stone structure, located close to the European Southern Observatory in La Silla, Chile, and attributed to the El Molle culture. Thanks to further, higher-accuracy measurements in situ, we can confirm some of the original hypotheses and dismiss others, upholding the main tenets of the original work.
arXiv (Cornell University), Jul 8, 2010
On May 27th 2010, the Italian astronomical community learned with concern that the National Insti... more On May 27th 2010, the Italian astronomical community learned with concern that the National Institute for Astrophysics (INAF) was going to be suppressed, and that its employees were going to be transferred to the National Research Council (CNR). It was not clear if this applied to all employees (i.e. also to researchers hired on short-term contracts), and how this was going to happen in practice. In this letter, we give a brief historical overview of INAF and present a short chronicle of the few eventful days that followed. Starting from this example, we then comment on the current situation and prospects of astronomical research in Italy.
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV
Astrometric Science and Technology Roadmap for Astrophysics (ASTRA) is a bilateral cooperation be... more Astrometric Science and Technology Roadmap for Astrophysics (ASTRA) is a bilateral cooperation between China and Italy with the goal of consolidating astrometric measurement concepts and technologies. In particular, the objectives include critical analysis of the Gaia methodology and performance, as well as principle demonstration experiments aimed at future innovative astrometric applications requiring high precision over large angular separations (one to 180 degrees). Such measurement technologies will be the building blocks for future instrumentation focused on the "great questions" of modern cosmology, like General Relativity validity (including Dark Matter and Dark Energy behavior), formation and evolution of structure like proto-galaxies, and planetary systems formation in bio compatibles environments. We describe three principle demonstration tests designed to address some of the potential showstoppers for high astrometric precision experiments. The three tests are focused on the key concepts of multiple fields telescopes, astrometric metrology and very fine sub-pixel precision (goal: < 1/2000 pixel) in white light.
IAU General Assembly, Aug 1, 2015
Understanding Gaia, 2019
Relative astrometry can reach a very high accuracy, but only in the usually small field visible t... more Relative astrometry can reach a very high accuracy, but only in the usually small field visible through the telescope. If the goal is that of determining a global map of the celestial sphere, then this technique is not the best choice. It is easy to understand why by figuring out a possible approach to celestial map-making that uses relative astrometry.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
Understanding Gaia, 2019
The construction of the Gaia satellite was entrusted to EADS Astrium, now Airbus Defence and Spac... more The construction of the Gaia satellite was entrusted to EADS Astrium, now Airbus Defence and Space, and was begun in 2006 in Toulouse, France. While Astrium was the prime contractor, the development and construction of the spacecraft involved many smaller subcontractors dealing with several different parts, like the CCDs of the focal plane, which were provided by the UK’s e2v Technologies, or the laser interferometers used to monitor the stability of the basic angle, which were awarded to the Dutch TNO, or the micro-propulsion system used for the attitude control, produced by the Italian branch of Thales Alenia Space.
The Astrometric Gravitation Probe mission is a modern version of the 1919 Dyson-Eddington-Davidso... more The Astrometric Gravitation Probe mission is a modern version of the 1919 Dyson-Eddington-Davidson experiment, based on a space-borne telescope with a permanent built-in eclipse, provided by a coronagraphic system. The expected improvement on experimental bounds to General Relativity and competing gravitation theories is by at least two orders of magnitude. The measurement principle is reviewed, in particular the principle of Fizeau-like combination of a set of individual inverted coronagraphs simultaneously feeding a common high resolution telescope. Also, the payload has a dual field of view property, in order to support simultaneous observations of stellar fields either very close, or far away, from the Sun, i.e. fields affected by either high or low light bending. We discuss a set of solutions introduced in the optical design to improve on technical feasibility and robustness of the optical performance against perturbations, in particular induced by manufacturing and alignment t...
Understanding Gaia, 2019
On a clear night, and from a place free from light pollution, it is impossible not to notice a br... more On a clear night, and from a place free from light pollution, it is impossible not to notice a bright, imposing strip stretching across the sky. Ancient Greeks called it Γαλαξίας (Galaxias), which gave origin to the name “Galaxy.” This word means “milky,” because, in Greek mythology, it is the milk spurt from the breasts of Hera, Zeus’s wife, while she was nursing the baby Heracles. The Romans inherited the Greeks’ gods and mythology, and called this spectacular structure “Via Lactea,” which means “Milky Way.”
Astronomy & Astrophysics, 2021
Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun fro... more Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun from the Gaia Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use. Methods. Theselection of objects within 100 pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100 pc is included in the catalogue. Re...
Astronomy & Astrophysics, 2018
Context.TheGaiaESA mission will estimate the astrometric and physical data of more than one billi... more Context.TheGaiaESA mission will estimate the astrometric and physical data of more than one billion objects, providing the largest and most precise catalog of absolute astrometry in the history of astronomy. The core of this process, the so-called global sphere reconstruction, is represented by the reduction of a subset of these objects which will be used to define the celestial reference frame. As the HIPPARCOSmission showed, and as is inherent to all kinds of absolute measurements, possible errors in the data reduction can hardly be identified from the catalog, thus potentially introducing systematic errors in all derived work.Aims.Following up on the lessons learned from HIPPARCOS, our aim is thus to develop an independent sphere reconstruction method that contributes to guarantee the quality of the astrometric results without fully reproducing the main processing chain.Methods.Indeed, given the unfeasibility of a complete replica of the data reduction pipeline, an astrometric ve...
Astronomy & Astrophysics, 2018
Context.The secondGaiadata release (GaiaDR2) provides precise five-parameter astrometric data (po... more Context.The secondGaiadata release (GaiaDR2) provides precise five-parameter astrometric data (positions, proper motions, and parallaxes) for an unprecedented number of sources (more than 1.3 billion, mostly stars). This new wealth of data will enable the undertaking of statistical analysis of many astrophysical problems that were previously infeasible for lack of reliable astrometry, and in particular because of the lack of parallaxes. However, the use of this wealth of astrometric data comes with a specific challenge: how can the astrophysical parameters of interest be properly inferred from these data?Aims.The main focus of this paper, but not the only focus, is the issue of the estimation of distances from parallaxes, possibly combined with other information. We start with a critical review of the methods traditionally used to obtain distances from parallaxes and their shortcomings. Then we provide guidelines on how to use parallaxes more efficiently to estimate distances by usi...
Astronomy & Astrophysics, 2017
Context. A key objective of the ESA Gaia satellite is the realization of a quasi-inertial referen... more Context. A key objective of the ESA Gaia satellite is the realization of a quasi-inertial reference frame at visual wavelengths by means of global astrometric techniques. This requires accurate mathematical and numerical modeling of relativistic light propagation, as well as double-blind-like procedures for the internal validation of the results, before they are released to the scientific community at large. Aims. We aim to specialize the time transfer functions (TTF) formalism to the case of the Gaia observer and prove its applicability to the task of global sphere reconstruction (GSR), in anticipation of its inclusion in the GSR system, already featuring the Relativistic Astrometric MODel (RAMOD) suite, as an additional semi-external validation of the forthcoming Gaia baseline astrometric solutions. Methods. We extended the current GSR framework and software infrastructure (GSR2) to include TTF relativistic observation equations compatible with Gaia's operations. We used simulated data generated by the Gaia Data Processing and Analysis Consortium (DPAC) to obtain different least-squares estimations of the full (five-parameter) stellar spheres and gauge results. These were compared to analogous solutions obtained with the current RAMOD model in GSR2 (RAMOD@GSR2) and to the catalog generated with the Gaia RElativistic Model (GREM), the model baselined for Gaia and used to generate the DPAC synthetic data. Results. Linearized least-squares TTF solutions are based on spheres of about 132 000 primary stars uniformly distributed on the sky and simulated observations spanning the entire 5 yr range of Gaia's nominal operational lifetime. The statistical properties of the results compare well with those of GREM. Finally, comparisons to RAMOD@GSR2 solutions confirmed the known lower accuracy of that model and allowed us to establish firm limits on the quality of the linearization point outside of which an iteration for nonlinearity is required for its proper convergence. This has proved invaluable as RAMOD@GSR2 is prepared to go into operations on real satellite data.
Astronomy & Astrophysics, 2016
Context. The first data release from the Gaia mission contains accurate positions and magnitudes ... more Context. The first data release from the Gaia mission contains accurate positions and magnitudes for more than a billion sources, and proper motions and parallaxes for the majority of the 2.5 million Hipparcos and Tycho-2 stars. Aims. We describe three essential elements of the initial data treatment leading to this catalogue: the image analysis, the construction of a source list, and the near real-time monitoring of the payload health. We also discuss some weak points that set limitations for the attainable precision at the present stage of the mission. Methods. Image parameters for point sources are derived from one-dimensional scans, using a maximum likelihood method, under the assumption of a line spread function constant in time, and a complete modelling of bias and background. These conditions are, however, not completely fulfilled. The Gaia source list is built starting from a large ground-based catalogue, but even so a significant number of new entries have been added, and a large number have been removed. The autonomous onboard star image detection will pick up many spurious images, especially around bright sources, and such unwanted detections must be identified. Another key step of the source list creation consists in arranging the more than 10 10 individual detections in spatially isolated groups that can be analysed individually. Results. Complete software systems have been built for the Gaia initial data treatment, that manage approximately 50 million focal plane transits daily, giving transit times and fluxes for 500 million individual CCD images to the astrometric and photometric processing chains. The software also carries out a successful and detailed daily monitoring of Gaia health.
GAME (Gamma Astrometric Measurement Experiment) is a proposal for a space mission whose main scie... more GAME (Gamma Astrometric Measurement Experiment) is a proposal for a space mission whose main scientific goal is the estimation of the γ parameter of the Parametrized Post-Newtonian (PPN) formalism. A possible configuration as a small mission, and its possible performances for the main scientific case, has already been described in some recent papers (Gai et al. 2009, Vecchiato et al. 2009). However, simple considerations on the applicable observation strategy suggest that GAME can also provide outstanding results on other topics. We address the possible application to another classical test of General Relativity, i.e. the determination of the β parameter of the PPN formalism, or more precisely of the (2γ - β - 1) combination, by means of the reconstruction of the orbit of Mercury. The present accepted limit for this combination is |2γ - β - 1| < 10-3 (Will, 2006), while the proposed ESA Bepi-Colombo Mercury orbiter is expected to improve this limit to 3 × 10-4 after 2020. Prelimi...
The Eleventh Marcel Grossmann Meeting - On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG11 Meeting on General Relativity, 2008
Aim of the RAMOD project is to solve the general relativistic ray-tracing problem in the gravitat... more Aim of the RAMOD project is to solve the general relativistic ray-tracing problem in the gravitational field of the Solar System to the accuracy of a micro-arcsecond in the measurements of angles. The project consists in the construction of a family of models with increasing complexity and accuracy each one acting as test bed for the more advanced ones. The
EAS Publications Series, 2010
Ground-based and Airborne Instrumentation for Astronomy IV, 2012
ABSTRACT The Interferometric Stratospheric Astrometry for Solar system (ISAS) project is designed... more ABSTRACT The Interferometric Stratospheric Astrometry for Solar system (ISAS) project is designed for high precision astrometry on the brightest planets of the Solar System, with reference to many field stars, at the milli-arcsec (mas) level or better. The science goal is the improvement on our knowledge of the dynamics of the Solar System, complementing the Gaia observations of fainter objects. The technical goal is the validation of basic concepts for the proposed Gamma Astrometric Measurement Experiment (GAME) space mission, in particular, combination of Fizeau interferometry and coronagraphic techniques by means of pierced mirrors, intermediate angle dual field astrometry, smart focal plane management for increased dynamic range and pointing correction. We discuss the suitability of the stratospheric environment, close to space conditions, to the astrometric requirements. The instrument concept is a multiple field, multiple aperture Fizeau interferometer, observing simultaneously four fields, in order to improve on the available number of reference stars. Coronagraphic solutions are introduced to allow observation of internal planets (Mercury and Venus), as well as of external planets over a large fraction of their orbit, i.e. also close to conjunction with the Sun. We describe the science motivation, the proposed experiment profile and the expected performance.
Proceedings of the International Astronomical Union, 2007
We present the design of a Fizeau interferometer to be implemented for the GAME mission. The aim ... more We present the design of a Fizeau interferometer to be implemented for the GAME mission. The aim is to measure the PPN γ parameter with the same technique used for the first time by Dyson, Eddington et al., but at a 10−6 accuracy level. GAME will observe about 106 sufficiently bright stars at about 2° from the Sun. A dedicated space mission has the advantage of observing the light bending without waiting for an eclipse.
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Papers by Alberto Vecchiato