Alberto Vecchiato - Profile on Academia.edu (original) (raw)

Papers by Alberto Vecchiato

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Undergraduate lecture notes in physics, 2017

The Geometrical Character of Physics Theories

Undergraduate lecture notes in physics, 2017

One of the powerful features of the variational approach is its generality. It is in fact based o... more One of the powerful features of the variational approach is its generality. It is in fact based on a simple principle, stating that physical laws share the common characteristics of minimizing the action of a system, and as we have seen this can be applied to mechanics (i.e., the dynamics of particles) as well as to the dynamics of fields.

Undergraduate lecture notes in physics, 2017

In Chap. 6 it has been shown that the formulation of relativistic dynamics naturally fits into th... more In Chap. 6 it has been shown that the formulation of relativistic dynamics naturally fits into the Minkowskian geometry, which is covariant with respect to the Lorentz transformations. Then we also showed that special relativity, as any theory of dynamics should do, can handle any interaction, such as the electromagnetic one, with the exception of gravity inasmuch as it leads to incorrect or inconsistent predictions. Finally, in the last section of the last chapter, we show that the difference between the electromagnetic and gravitational fields comes from the equivalence principle, and when, as required by such principle, one tries to "mimic" the presence of a constant gravitational field with a constant acceleration this leads to the same equations of motion. These last two facts imply that gravitation, cannot be reduced to a field of some kind on a Minkowskian background geometry obeying the equivalence principle and, on the other side, that it neither can be explained by translating the equivalence principle in the form of an "acceleration-induced" curved spacetime. This seems to hint that a relativistic theory of gravity has to be found in another way, different from those used for field theories, such as electromagnetism, for which equivalence principle does not apply. A way that, once again, has a geometrical background. 8.1 Gravity and Geometry: Curved Spacetime and General Covariance A clue on the possible missing link for a relativistically correct description of gravity comes by realizing how the electromagnetic force/field, or in general any force is treated in our context. In both Newtonian and relativistic dynamics, we first state that there exists a class of privileged observers (namely the inertial observers) according

Gravity and Special Relativity

Undergraduate lecture notes in physics, 2017

We know that, contrary to electromagnetism, the Newtonian theory of gravity is compatible with Ne... more We know that, contrary to electromagnetism, the Newtonian theory of gravity is compatible with Newtonian dynamics, and because we have just realized that the latter has to be replaced by special relativity, it is easy to understand that the former has to be superseded by another theory of gravity which is compatible with the new dynamics.

Game: A Space Mission for Relativistic Tests Around the Earth

The Thirteenth Marcel Grossmann Meeting, 2014

The Astronomical Journal, 2011

We present new results from the Parallaxes of Southern Extremely Cool dwarfs program to measure p... more We present new results from the Parallaxes of Southern Extremely Cool dwarfs program to measure parallaxes, proper motions and multiepoch photometry of L and early T dwarfs. The observations were made on 108 nights over the course of 8 yr using the Wide Field Imager on the ESO 2.2m telescope. We present 118 new parallaxes of L and T dwarfs of which 52 have no published values and 24 of the 66 published values are preliminary estimates from this program. The parallax precision varies from 1.0 to 15.5 mas with a median of 3.8 mas. We find evidence for two objects with long term photometric variation and 24 new moving group candidates. We cross-match our sample to published photometric catalogues and find standard magnitudes in up to 16 pass-bands from which we build spectral energy distributions and H-R diagrams. This allows us to confirm the theoretically anticipated minimum in radius between stars and brown dwarfs across the hydrogen burning minimum mass. We find the minimum occurs between L2 and L6 and verify the predicted steep dependence of radius in the hydrogen burning regime and the gentle rise into the degenerate brown dwarf regime. We find a relatively young age of ∼2 Gyr from the kinematics of our sample.

Possible Astronomical meaning of some El Molle findings at the ESO Observatory of La Silla

IAU General Assembly, Aug 1, 2015

Monthly Notices of the Royal Astronomical Society, 2013

The discovery and subsequent detailed study of T dwarfs have provided many surprises and pushed t... more The discovery and subsequent detailed study of T dwarfs have provided many surprises and pushed the physics and modelling of cool atmospheres in unpredicted directions. Distance is a critical parameter for studies of these objects to determine intrinsic luminosities, test binarity and measure their motion in the Galaxy. We describe a new observational programme to determine distances across the full range of T-dwarf subtypes using the New Technology Telescope (NTT)/SOFI telescope/instrument combination. We present preliminary results for ten objects, five of which represent new distances.

Undergraduate Lecture Notes in Physics, 2017

In this chapter it is shown how some of the basic equations of classical physics behave with resp... more In this chapter it is shown how some of the basic equations of classical physics behave with respect to the requirements of the fundamental principles we have discussed earlier. In particular the examples have been chosen with the aim of naturally ferrying our reasoning toward the realm of non-Newtonian physics. These exercises therefore want to show: 1. How, contrary to what is commonly expected, in some cases even the Euclidean (i.e., "geometrical") covariance can hardly be regarded as self-evident 2. How the covariance, and therefore the fundamental principles from which it derives, can be used as a "minimum requirement" to guess some properties of the physical laws' equations, but also as a way to explore extensions or different versions of an existing theory 3. That classical electromagnetism is incompatible with the principle of relativity in its Galilean form, whose consequences will lead us to special relativity. It has to be stressed that in this chapter, when necessary, x k are intended as vector components dx k , and not just as coordinates. 4.1 Equations of Motion and Newtonian Gravitational Force Newton's second law of dynamics The very first case to start with is Newton's law of dynamics F = ma. This is a very simple one because the force on the left-hand side of the equation is a vector in the Euclidean and Galilean sense by definition. In other words, we require that for the transformations of the Galilean covariance group (i.e., translations, rotations, and Galilean boosts) and for any transformation of the coordinate system it isF = F.

VizieR Online Data Catalog: Gaia-ESO Survey: NGC6705 (Cantat-Gaudin+, 2014)

We combine new BV photometry with the spectroscopic observations of the Gaia-ESO Survey to study ... more We combine new BV photometry with the spectroscopic observations of the Gaia-ESO Survey to study the open cluster NGC6 705. 1028 stars were observed with the HR15n grating of the GIRAFFE instrument at VLT/UT2. The radial velocities obtained for those stars were used to derive membership probabilities. (1 data file)

Satellite Tracking Astrometric Network (STAN)

IAU General Assembly, Aug 1, 2015

The advent of female astronomers at Turin Observatory

Journal of Astronomical History and Heritage, Apr 1, 2018

In this paper we give an historical presentation of the role of women at the Astronomical Observa... more In this paper we give an historical presentation of the role of women at the Astronomical Observatory of Turin, showing their scientific work and interests, and how their role evolved with time. This exposition is put in its appropriate context with a short summary of the history of the Observatory. In the end we try to give a possible recount of the events that triggered the beginning of female participation in the research and the life of this institution and explain its peculiar character.

Building the Gaia Satellite

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.

Astronomy & Astrophysics, 2016

Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The sp... more Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

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.

Undergraduate Lecture Notes in Physics, 2017

In this chapter the reader is introduced to the concepts and language of the Lagrangian formalism... more In this chapter the reader is introduced to the concepts and language of the Lagrangian formalism of field theories. Only knowledge of the Newtonian theory of gravity, as usually explained in standard undergraduate courses is assumed, although some familiarity with classical mechanics is an asset. The goal is twofold:

Experimental Astronomy, 2021

We propose to locate transponders and atomic clocks in at least three of the Lagrange points of t... more We propose to locate transponders and atomic clocks in at least three of the Lagrange points of the Sun-Earth pair, with the aim of exploiting the time of flight asymmetry between electromagnetic signals travelling in opposite directions along polygonal loops having the Lagrange points at their vertices. The asymmetry is due to the presence of a gravito-magnetic field partly caused by the angular momentum of the Sun, partly originating from the angular momentum of the galactic dark halo in which the Milky Way is embedded. We list also various opportunities which could be associated with the main objective of this Lagrange Dark Halo Detector (LaDaHaD).

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.

Fundamental Principles of Classical Physics

Undergraduate Lecture Notes in Physics, 2017

In Chap. 1 we have shown how the classical Newtonian dynamics and Newtonian gravity can be formul... more In Chap. 1 we have shown how the classical Newtonian dynamics and Newtonian gravity can be formulated as a field theory based on the variational principle of least action.

We review the mathematical models available for relativistic astrometry, discussing the different... more We review the mathematical models available for relativistic astrometry, discussing the different approaches and their accuracies in the context of the modern experiments from space like Gaia and GAME, and we show how these models can be applied to the real world, and their consequences from the mathematical and numerical point of view, with specific reference to the case of Gaia, whose launch is due before the end of the year.

Applications

Undergraduate lecture notes in physics, 2017

The Geometrical Character of Physics Theories

Undergraduate lecture notes in physics, 2017

One of the powerful features of the variational approach is its generality. It is in fact based o... more One of the powerful features of the variational approach is its generality. It is in fact based on a simple principle, stating that physical laws share the common characteristics of minimizing the action of a system, and as we have seen this can be applied to mechanics (i.e., the dynamics of particles) as well as to the dynamics of fields.

Undergraduate lecture notes in physics, 2017

In Chap. 6 it has been shown that the formulation of relativistic dynamics naturally fits into th... more In Chap. 6 it has been shown that the formulation of relativistic dynamics naturally fits into the Minkowskian geometry, which is covariant with respect to the Lorentz transformations. Then we also showed that special relativity, as any theory of dynamics should do, can handle any interaction, such as the electromagnetic one, with the exception of gravity inasmuch as it leads to incorrect or inconsistent predictions. Finally, in the last section of the last chapter, we show that the difference between the electromagnetic and gravitational fields comes from the equivalence principle, and when, as required by such principle, one tries to "mimic" the presence of a constant gravitational field with a constant acceleration this leads to the same equations of motion. These last two facts imply that gravitation, cannot be reduced to a field of some kind on a Minkowskian background geometry obeying the equivalence principle and, on the other side, that it neither can be explained by translating the equivalence principle in the form of an "acceleration-induced" curved spacetime. This seems to hint that a relativistic theory of gravity has to be found in another way, different from those used for field theories, such as electromagnetism, for which equivalence principle does not apply. A way that, once again, has a geometrical background. 8.1 Gravity and Geometry: Curved Spacetime and General Covariance A clue on the possible missing link for a relativistically correct description of gravity comes by realizing how the electromagnetic force/field, or in general any force is treated in our context. In both Newtonian and relativistic dynamics, we first state that there exists a class of privileged observers (namely the inertial observers) according

Gravity and Special Relativity

Undergraduate lecture notes in physics, 2017

We know that, contrary to electromagnetism, the Newtonian theory of gravity is compatible with Ne... more We know that, contrary to electromagnetism, the Newtonian theory of gravity is compatible with Newtonian dynamics, and because we have just realized that the latter has to be replaced by special relativity, it is easy to understand that the former has to be superseded by another theory of gravity which is compatible with the new dynamics.

Game: A Space Mission for Relativistic Tests Around the Earth

The Thirteenth Marcel Grossmann Meeting, 2014

The Astronomical Journal, 2011

We present new results from the Parallaxes of Southern Extremely Cool dwarfs program to measure p... more We present new results from the Parallaxes of Southern Extremely Cool dwarfs program to measure parallaxes, proper motions and multiepoch photometry of L and early T dwarfs. The observations were made on 108 nights over the course of 8 yr using the Wide Field Imager on the ESO 2.2m telescope. We present 118 new parallaxes of L and T dwarfs of which 52 have no published values and 24 of the 66 published values are preliminary estimates from this program. The parallax precision varies from 1.0 to 15.5 mas with a median of 3.8 mas. We find evidence for two objects with long term photometric variation and 24 new moving group candidates. We cross-match our sample to published photometric catalogues and find standard magnitudes in up to 16 pass-bands from which we build spectral energy distributions and H-R diagrams. This allows us to confirm the theoretically anticipated minimum in radius between stars and brown dwarfs across the hydrogen burning minimum mass. We find the minimum occurs between L2 and L6 and verify the predicted steep dependence of radius in the hydrogen burning regime and the gentle rise into the degenerate brown dwarf regime. We find a relatively young age of ∼2 Gyr from the kinematics of our sample.

Possible Astronomical meaning of some El Molle findings at the ESO Observatory of La Silla

IAU General Assembly, Aug 1, 2015

Monthly Notices of the Royal Astronomical Society, 2013

The discovery and subsequent detailed study of T dwarfs have provided many surprises and pushed t... more The discovery and subsequent detailed study of T dwarfs have provided many surprises and pushed the physics and modelling of cool atmospheres in unpredicted directions. Distance is a critical parameter for studies of these objects to determine intrinsic luminosities, test binarity and measure their motion in the Galaxy. We describe a new observational programme to determine distances across the full range of T-dwarf subtypes using the New Technology Telescope (NTT)/SOFI telescope/instrument combination. We present preliminary results for ten objects, five of which represent new distances.

Undergraduate Lecture Notes in Physics, 2017

In this chapter it is shown how some of the basic equations of classical physics behave with resp... more In this chapter it is shown how some of the basic equations of classical physics behave with respect to the requirements of the fundamental principles we have discussed earlier. In particular the examples have been chosen with the aim of naturally ferrying our reasoning toward the realm of non-Newtonian physics. These exercises therefore want to show: 1. How, contrary to what is commonly expected, in some cases even the Euclidean (i.e., "geometrical") covariance can hardly be regarded as self-evident 2. How the covariance, and therefore the fundamental principles from which it derives, can be used as a "minimum requirement" to guess some properties of the physical laws' equations, but also as a way to explore extensions or different versions of an existing theory 3. That classical electromagnetism is incompatible with the principle of relativity in its Galilean form, whose consequences will lead us to special relativity. It has to be stressed that in this chapter, when necessary, x k are intended as vector components dx k , and not just as coordinates. 4.1 Equations of Motion and Newtonian Gravitational Force Newton's second law of dynamics The very first case to start with is Newton's law of dynamics F = ma. This is a very simple one because the force on the left-hand side of the equation is a vector in the Euclidean and Galilean sense by definition. In other words, we require that for the transformations of the Galilean covariance group (i.e., translations, rotations, and Galilean boosts) and for any transformation of the coordinate system it isF = F.

VizieR Online Data Catalog: Gaia-ESO Survey: NGC6705 (Cantat-Gaudin+, 2014)

We combine new BV photometry with the spectroscopic observations of the Gaia-ESO Survey to study ... more We combine new BV photometry with the spectroscopic observations of the Gaia-ESO Survey to study the open cluster NGC6 705. 1028 stars were observed with the HR15n grating of the GIRAFFE instrument at VLT/UT2. The radial velocities obtained for those stars were used to derive membership probabilities. (1 data file)

Satellite Tracking Astrometric Network (STAN)

IAU General Assembly, Aug 1, 2015

The advent of female astronomers at Turin Observatory

Journal of Astronomical History and Heritage, Apr 1, 2018

In this paper we give an historical presentation of the role of women at the Astronomical Observa... more In this paper we give an historical presentation of the role of women at the Astronomical Observatory of Turin, showing their scientific work and interests, and how their role evolved with time. This exposition is put in its appropriate context with a short summary of the history of the Observatory. In the end we try to give a possible recount of the events that triggered the beginning of female participation in the research and the life of this institution and explain its peculiar character.

Building the Gaia Satellite

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.

Astronomy & Astrophysics, 2016

Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The sp... more Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

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.

Undergraduate Lecture Notes in Physics, 2017

In this chapter the reader is introduced to the concepts and language of the Lagrangian formalism... more In this chapter the reader is introduced to the concepts and language of the Lagrangian formalism of field theories. Only knowledge of the Newtonian theory of gravity, as usually explained in standard undergraduate courses is assumed, although some familiarity with classical mechanics is an asset. The goal is twofold:

Experimental Astronomy, 2021

We propose to locate transponders and atomic clocks in at least three of the Lagrange points of t... more We propose to locate transponders and atomic clocks in at least three of the Lagrange points of the Sun-Earth pair, with the aim of exploiting the time of flight asymmetry between electromagnetic signals travelling in opposite directions along polygonal loops having the Lagrange points at their vertices. The asymmetry is due to the presence of a gravito-magnetic field partly caused by the angular momentum of the Sun, partly originating from the angular momentum of the galactic dark halo in which the Milky Way is embedded. We list also various opportunities which could be associated with the main objective of this Lagrange Dark Halo Detector (LaDaHaD).

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.

Fundamental Principles of Classical Physics

Undergraduate Lecture Notes in Physics, 2017

In Chap. 1 we have shown how the classical Newtonian dynamics and Newtonian gravity can be formul... more In Chap. 1 we have shown how the classical Newtonian dynamics and Newtonian gravity can be formulated as a field theory based on the variational principle of least action.

We review the mathematical models available for relativistic astrometry, discussing the different... more We review the mathematical models available for relativistic astrometry, discussing the different approaches and their accuracies in the context of the modern experiments from space like Gaia and GAME, and we show how these models can be applied to the real world, and their consequences from the mathematical and numerical point of view, with specific reference to the case of Gaia, whose launch is due before the end of the year.

This book is the first to provide a comprehensive, readily understandable report on the European ... more This book is the first to provide a comprehensive, readily understandable report on the European Space Agency’s Gaia mission that will meet the needs of a general audience. It takes the reader on an exciting journey of discovery, explaining how such a scientific satellite is made, presenting the scientific results available from Gaia to date, and examining how the collected data will be used and their likely scientific consequences.

The Gaia mission will provide a complete and high-precision map of the positions, distances, and motions of the stars in our galaxy. It will revolutionize our knowledge on the origin and evolution of the Milky Way, on the effects of mysterious dark matter, and on the birth and evolution of stars and extrasolar planets. The Gaia satellite was launched in December 2013 and has a foreseen operational lifetime of five to six years, culminating in a final stellar catalogue in the early 2020s. This book will appeal to all who have an interest in the mission and the profound impact that it will have on astronomy.