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Research Interests: Engineering, Computer Science, Physics, Dark Matter, Astrometry, and 3 moreCosmology, Astronomy, and Ad Astra
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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... 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.
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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... 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.
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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... 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...
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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... 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.”
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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... 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...
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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... 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...
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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... 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...
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Research Interests: Computer Science, Information Retrieval, Astrophysics, Astrometry, Astronomy, and 15 moreBroadband, Calibration, Galaxies, Celestial Mechanics, JSON, Magellanic Clouds, data analysis methods in fMRI, Interoperation, Large Magellanic Cloud, AAP, Gaia Mission, Astronomija, Astronomical Photometry, Catalogs, and Matching statistics
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... 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...
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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... 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
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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)... 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.
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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.... 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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Gaia is an ESA Cornerstone mission, scheduled to be launched in spring 2013, dedicated to precisely measure the positions and motions of over a billion stars in our galaxy: the Milky Way. Gaia Data Processing Center Turin (DPCT), the... more
Gaia is an ESA Cornerstone mission, scheduled to be launched in spring 2013, dedicated to precisely measure the positions and motions of over a billion stars in our galaxy: the Milky Way. Gaia Data Processing Center Turin (DPCT), the Italian DPC, is hosted and operated at ALTEC in Turin. The primary objective of DPCT is to provide the infrastructure and operations support to the Astrometric Verification Unit (AVU) activities for CU3 and the Italian participation to the Gaia data processing tasks. DPCT will archive all of the data, produced for and delivered to DPAC as part of the Italian contribution to the activities of CU4, CU5, CU7, and CU8.
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We present here "IN VIAGGIO FRA LE STELLE" (Journey amongst the Stars), a project to develop an educational application for Microsoft Windows based on multimedia and interactive tools that will be distributed as a CD-ROM. The... more
We present here "IN VIAGGIO FRA LE STELLE" (Journey amongst the Stars), a project to develop an educational application for Microsoft Windows based on multimedia and interactive tools that will be distributed as a CD-ROM. The uniqueness of this project consists in using the making of an astrometric catalogue (GSC II) as its guiding theme in the explanation of many
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The technology of modern astrometric satellites like Gaia assures an accuracy of one microarcsecond in the measurements of angles. At this level, one also has to take into account the general relativistic effects due to most of the Solar... more
The technology of modern astrometric satellites like Gaia assures an accuracy of one microarcsecond in the measurements of angles. At this level, one also has to take into account the general relativistic effects due to most of the Solar System planets and their largest satellites. The aim of the RAMOD project is the construction of a fully general relativistic data reduction scheme consistent with these expectations. The project consists of the development of subsequent models having increasing accuracies and complications. Each model has been used as a testbed for comparison with the successively more advanced models. Here we illustrate only some of the problems already solved or presently under investigation for the fulfillment of our task.
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APOP is the first version of an absolute proper motion catalog achieved using the Digitized Sky Survey Schmidt plate material outside the galactic plane (|b| ≥ 27). The resulting global zero point error is less than 0.6 mas/yr, and the... more
APOP is the first version of an absolute proper motion catalog achieved using the Digitized Sky Survey Schmidt plate material outside the galactic plane (|b| ≥ 27). The resulting global zero point error is less than 0.6 mas/yr, and the precision better than 4.0 mas/yr for objects brighter than RF = 18.5, rising to 9.0 mas/yr for objects with magnitude in the range 18.5 < RF < 20.0. The average position accuracy is about 150 mas (per coordinate) with a systematic deviation from the ICRS around 0.2 mas. The catalog covers 22,525 square degrees and lists 100,777,385 objects to the limiting magnitude of RF ∼ 20.8. Although the Gaia mission is poised to set the new standard in catalog astronomy, the methods and procedures used for APOP will be useful in other reductions to dispel astrometric magnitudeand color-dependent systematic errors from the next generation of ground-based surveys.
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ABSTRACT This paper describes the design and the implementation of the Italian Data Processing Centre multi-tier software and hardware infrastructure, built by ALTEC and funded by ASI, to support the Italian participation to the Gaia data... more
ABSTRACT This paper describes the design and the implementation of the Italian Data Processing Centre multi-tier software and hardware infrastructure, built by ALTEC and funded by ASI, to support the Italian participation to the Gaia data processing tasks. In particular the paper focuses on the software and hardware architectural choices adopted to manage both big data volumes and complex operations scenarios. The DPCT system has been designed as an integrated system whit the capability to manage all data processing pipeline phases: data receiving, data processing, data extraction, data archiving and data sending. In addition, the DPCT system includes also data access and analysis tools allowing Italian scientists to be active system users during operations.
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Improvement of our understanding of Fundamental Physics is more and more based on high precision measurements over significant fractions of our Universe. Among the crucial tests of General Relativity and competing theories is the... more
Improvement of our understanding of Fundamental Physics is more and more based on high precision measurements over significant fractions of our Universe. Among the crucial tests of General Relativity and competing theories is the detection of gravitational waves, which is the subject of advanced modern experiments (LISA, VIRGO, LIGO). Our investigation is focused on a novel concept for pointed observations
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Our understanding of Fundamental Physics benefits of modern techniques for high precision angular measurement. Among the crucial tests of General Relativity and competing theories is the detection of gravitational waves, which is the goal... more
Our understanding of Fundamental Physics benefits of modern techniques for high precision angular measurement. Among the crucial tests of General Relativity and competing theories is the detection of gravitational waves, which is the goal of advanced experiments (LISA, VIRGO, LIGO). Our investigation is focused on a novel concept based on observation of selected astro-nomical objects in our Galaxy, in particular
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We describe a way to compare current relativistic astrometric models accurate to the micro-arcsecond level. The observed stellar direction can be written as a function of several parts, linking the astrometric observables to the... more
We describe a way to compare current relativistic astrometric models accurate to the micro-arcsecond level. The observed stellar direction can be written as a function of several parts, linking the astrometric observables to the relativistic effects associated to the stellar kinematical properties and distances as seen inside the gravitational field of our Solar System, i.e. the so called relativistic astrometric parameters, providing a tool for comparing the RAMOD framework to the pM/pN approaches.
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In this article we outline the structure of a general relativistic astrometric model which has been developed to deduce the position and proper motion of stars from 1 µarcsecond optical observations made by an astrometric satellite... more
In this article we outline the structure of a general relativistic astrometric model which has been developed to deduce the position and proper motion of stars from 1 µarcsecond optical observations made by an astrometric satellite orbiting around the Sun. The basic assumption of our model is that the Solar System is the only source of gravity, hence we show
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GAME (Gamma Astrometric Measurement Experiment) is a concept for a small mission whose main goal is to measure from space the γ parameter of the Parameterized Post-Newtonian formalism, Will (2001)) A satellite, looking as close as... more
GAME (Gamma Astrometric Measurement Experiment) is a concept for a small mission whose main goal is to measure from space the γ parameter of the Parameterized Post-Newtonian formalism, Will (2001)) A satellite, looking as close as possible to the Solar limb, measures the gravitational bending of light in a way similar to that followed by past experiments from the ground during solar eclipses. In the cited formalism, deviations of the γ parameter from unity are interpreted as deviations from the predictions of General Relativity which are foreseen by several competing theories of gravity. In the present theoretical scenario, such deviations are expected to appear in the range between 10−5 and 10−7. The most stringent experimental constraints available up to now are those of the Cassini mission, that gives 1−γ≲10−5 Bertotti et al. (2003), while future space missions are expected to reach the 10−7 level of accuracy. (Vecchiato et al. (2003), Turyshev et al. (2004), Ni (2008))Preliminar...
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Gaia will estimate the astrometric and physical data of approximately one billion objects. The core of this process, the global sphere reconstruction, is represented by the reduction of a subset of these objects, which will constitute the... more
Gaia will estimate the astrometric and physical data of approximately one billion objects. The core of this process, the global sphere reconstruction, is represented by the reduction of a subset of these objects, which will constitute the largest and most precise catalog of absolute astrometry in the history of Astronomy, and will put General Relativity to test by estimating the PPN parameter γ with unprecedented accuracy. As the Hipparcos mission showed, and as it is natural for all kind of absolute measurements, possible errors in the data reduction can hardly be identified at the end of the processing, and can lead to systematic errors in all the works which will use these results. In order to avoid such kind of problems, a Verification Unit was established by the Gaia Data Processing and Analysis Consortium (DPAC). One of its jobs is to implement and perform an independent global sphere reconstruction, parallel to the baseline one, to compare the two results, and to report any s...
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A Basic Angle (BA) of 106.5° separates the view directions of Gaia's two fields of view (FoV). A precise determination of the BA variations (BAV) is essential to guarantee a correct reconstruction of the global astrometric sphere, as... more
A Basic Angle (BA) of 106.5° separates the view directions of Gaia's two fields of view (FoV). A precise determination of the BA variations (BAV) is essential to guarantee a correct reconstruction of the global astrometric sphere, as residual systematic errors would result in, e.g., a bias in the parallaxes of the final Gaia catalog. The Basic Angle Monitoring (BAM) device, which provides a reliable and accurate estimation of BAV, shows that there exists a ~1 mas amplitude, 6-h period BA oscillation. It's essential to verify to what extent this signal is caused by real BAV, or is at least in part an effect of the BAM device itself. Here, we propose an astrometric on-sky approach to re-determine the 6-h periodic BAV. The results of this experiment, which treated a full day (17 Oct 2016) of Gaia astrometric data, recover a value for the 6-h oscillation of 1.856±0.857 mas. This is consistent, within the errors, with the BAM finding for that day.
We use methods of differential astrometry to construct a small field inertial reference frame stable at the micro-arcsecond level. Using Gaia measurements of field angles we look at the influence of the number of reference stars and the... more
We use methods of differential astrometry to construct a small field inertial reference frame stable at the micro-arcsecond level. Using Gaia measurements of field angles we look at the influence of the number of reference stars and the stars magnitude as well as astrometric systematics on the total error budget with the help of Gaia-like simulations around the Ecliptic Pole in a differential astrometric scenario. We find that the systematic errors are modeled and reliably estimated to the μas level even in fields with a modest number of 37 stars with G <13 mag over a 0.24 sq. degrees field of view for short timescales of the order of a day for a perfect instrument and with high-cadence observations. Accounting for large-scale calibrations by including the geometric instrument model over such short timescales requires fainter stars down to G=14 mag without diminishing the accuracy of the reference frame.
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This book offers a detailed and stimulating account of the Lagrangian, or variational, approach to general relativity and beyond. The approach more usually adopted when describing general relativity is to introduce the required concepts... more
This book offers a detailed and stimulating account of the Lagrangian, or variational, approach to general relativity and beyond. The approach more usually adopted when describing general relativity is to introduce the required concepts of differential geometry and derive the field and geodesic equations from purely geometrical properties. Demonstration of the physical meaning then requires the weak field approximation of these equations to recover their Newtonian counterparts. The potential downside of this approach is that it tends to suit the mathematical mind and requires the physicist to study and work in a completely unfamiliar environment. In contrast, the approach to general relativity described in this book will be especially suited to physics students. After an introduction to field theories and the variational approach, individual sections focus on the variational approach in relation to special relativity, general relativity, and alternative theories of gravity. Throughout the text, solved exercises and examples are presented. The book will meet the needs of both students specializing in theoretical physics and those seeking a better understanding of particular aspects of the subject.