Publications (17)13.61 Total impact
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Article: Gravitation Astrometric Measurement Experiment
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ABSTRACT: The Gravitation Astrometric Measurement Experiment (GAME) is a mission concept based on astronomical techniques (astrometry and coronagraphy) for Fundamental Physics measurements, namely the \gamma\ and \beta\ parameters of the Parametrized Post-Newtonian formulation of gravitation theories extending the General Relativity. The science case also addresses cosmology, extra-solar planets, Solar system objects and fundamental stellar parameters. The mission concept is described, including the measurement approach and the instrument design.03/2012; -
Article: A general relativistic model for the light propagation in the gravitational field of the Solar System: the dynamical case
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ABSTRACT: Modern astrometry is based on angular measurements at the micro-arcsecond level. At this accuracy a fully general relativistic treatment of the data reduction is required. This paper concludes a series of articles dedicated to the problem of relativistic light propagation, presenting the final microarcsecond version of a relativistic astrometric model which enable us to trace back the light path to its emitting source throughout the non-stationary gravity field of the moving bodies in the Solar System. The previous model is used as test-bed for numerical comparisons to the present one. Here we also test different versions of the computer code implementing the model at different levels of complexity to start exploring the best trade-off between numerical efficiency and the micro-arcsecond accuracy needed to be reached.10/2006; -
Chapter: FINITO: A Fringe Sensor for VLTI in Two and Three Beam Configuration
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ABSTRACT: ESO and the Astronomical Observatory of Torino (OATo) are collaborating for development of a Fringe Sensor Unit (FSU) for the Very Large Telescope Interferometer (VLTI, see [1] and references therein): FINITO (Fringe-tracking Instrument of NIce and Torino), derived from the concept demonstrated by a prototype from the Observatoire de la Côte d’Azur. It will be used for stabilisation of the Optical Path Difference (OPD) between telescope beams for the first generation scientific interferometers (AMBER, MIDI, VINCI), providing an improvement of up to five magnitudes in limiting sensitivity, thanks to the integration time increased from a few ten milliseconds up to minutes. Accordingly to current planning, FINITO is the only FSU able to support three-beam observations, allowing closure phase measurements in the near and mid IR range.02/2006: pages 328-330; -
Chapter: Extra-Solar Planets with GAIA
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ABSTRACT: GAIA, like Hipparcos, is a global astrometric mission which will survey the sky several times during the 5 years of its nominal lifetime. GAIA is being actively studied by ESA as a possible candidate for the next Cornerstone-class mission to be launched around 2009 and possibly earlier. Results from detailed simulations show that GAIA would detect giant planets (M p ~ _p \sim M J ) around normal stars up to a distance of ~ 200\sim 200 pc. This horizon includes over 500,000 dwarf stars earlier than K5 to be screened for planets. The same simulations predict that the main orbital parameters (semi-major axis, eccentricity, period, and inclination) of a significant fraction of the detected planets should be measurable to better than 30% up to 200 pc. Our results indicate that GAIA’s contribution would uniquely complement the expectations from other spectroscopic and astrometric surveys for ground breaking science in the fields of formation and evolution of planetary systems.02/2006: pages 479-491; -
Article: Astronomical Telescopes and Instrumentation
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ABSTRACT: The design and performance of a Fizeau interferometer with long focal length and large field of view are discussed. The optical scheme presented is well suited for very accurate astrometric measurements from space, being optimised, in terms of geometry and aberrations, to observe astronomical targets down to the visual magnitude mV=20, with a measurement accuracy of 10 microarcseconds at mV=15. This study is in the context of the next generation astrometric space missions, in particular for a mission profile similar to that of the Gaia mission of the European Space Agency. Beyond the accuracy goal, the great effort in optical aberrations reduction, particularly distortion, aims at the optimal exploitation of data acquisition done with CCD arrays working in Time Delay Integration mode. The design solution we present reaches the astrometric goals with a field of view of 0.5 square degrees.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.10/2004; -
Article: Astronomical Telescopes and Instrumentation
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ABSTRACT: We describe a software tool developed to simulate the behaviour of the angle between two lines of sight in a dual view telescope assembly (usually referred to as basic angle) due to optical misalignments induced by thermo-mechanical fluctuations. The tool applies to a variety of reflective optical designs. In principle, not only the basic angle behaviour can be simulated, but also other optical parameters. As a practical example, we present and discuss results obtained from application of our software to the case of the Gaia baseline optical design. We show that the final error can be severely degraded by fluctuations of the basic angle due to thermo-mechanical effects.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.09/2004; -
Article: Fizeau interferometer for global astrometry in space.
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ABSTRACT: We discuss the design and the performance of a Fizeau interferometer with a long focal length and a large field of view that is well suited for a global astrometry space mission. Our work focuses on the geometric optimization and minimization of aberration of such an astrometric interferometer, which is able to observe astronomical targets down to the visual magnitude (mag) mv = 20 mag, with an accuracy in the measurements of 10 micro-arcseconds at mv = 15 mag. We assume a mission profile similar to that of the Global Astrometric Interferometer for Astrophysics mission of the European Space Agency. In this framework, data acquisition is performed by an array of CCDs working in time-delay integration mode. Optical aberrations, particularly distortion and coma, play a crucial role in the efficiency of this technique. We present a design solution that meets the requirements for the best possible exploitation of the time-delay integration mode over a field of view of 0.7 degrees x 0.7 degrees.Applied Optics 03/2004; 43(4):721-8. · 1.41 Impact Factor -
Article: Some aspects of Relativistic Astrometry from within the Solar System
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ABSTRACT: 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-microarcsecond 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 how we modeled the satellite observations in a many-body perturbative approach limiting ourselves to the order of accuracy of $(v/c)^2$. The microarcsecond observing scenario outlined is that for the GAIA astrometric mission.06/2003; -
Article: Testing general relativity by micro-arcsecond global astrometry
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ABSTRACT: The global astrometric observations of a GAIA-like satellite were modeled within the PPN formulation of Post-Newtonian gravitation. An extensive experimental campaign based on realistic end-to-end simulations was conducted to establish the sensitivity of global astrometry to the PPN parameter \gamma, which measures the amount of space curvature produced by unit rest mass. The results show that, with just a few thousands of relatively bright, photometrically stable, and astrometrically well behaved single stars, among the ~10^9 objects that will be observed by GAIA, \gamma can be estimated after 1 year of continuous observations with an accuracy of ~10^{-5} at the 3\sigma level. Extrapolation to the full 5-year mission of these results based on the scaling properties of the adjustment procedure utilized suggests that the accuracy of \simeq 2x10^{-7}, at the same 3\sigma level, can be reached with \~10^6 single stars, again chosen as the most astrometrically stable among the millions available in the magnitude range V=12-13. These accuracies compare quite favorably with recent findings of scalar-tensor cosmological models, which predict for \gamma a present-time deviation, |1-\gamma|, from the General Relativity value between 10^{-5} and 10^{-7}.02/2003; -
Article: Potential applications of GSC-2 for GAIA operations
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ABSTRACT: The second guide star catalog (GSC-2) is a project that aims to create a complete catalog of stars and galaxies to about the 18th magnitude, and would contain colors, magnitudes, positions and proper motions. The catalog would provide an object list for the construction of an input catalog for possible future astrometric satellites, such as the global astrometric interferometer for astrophysics (GAIA) satellite. With a schedule that is compatible with the projected timeframe of GAIA, the GSC-2 could be available in time to support the preparatory astrophysical observations for an input catalog. The availability of the digitalized images for the preparation of finding charts would improve the efficiency of this task.10/1995; -
Article: Pt. 1: A Halo symbiotic binary not related to the globular cluster NGC 6401
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ABSTRACT: We present absolute 4000-9000 A spectrophotometry and astrometry of the emission line object Pt 1, originally discovered as a planetary nebula possibly associated with the Bulge globular cluster NGC 6401 and later discussed as a symbiotic star. The radial velocity (-350 +/- 10 km/sec), the distance (2.7 +/- 1.2 kpc) and possibly also the metallicity of the late type giant all deny association of Pt 1 with NGC 6401. The extreme values derived both from absorption and emission features make Pt 1 the symbiotic star with the highest known radial velocity and strongly suggest that it belongs to the Halo population of the Galaxy. It is then seen projected against NGC 6401 and quite close to the galactic center by a mere coincidence. Our kinematic data on Pt 1 suggest an extremely eccentric galactocentric orbit with an orbital period of several 108 yr. The limited number of passages through the Bulge over the lifetime of the Galaxy supports the possibility that Pt 1 is a first generation Halo binary.Astronomy and Astrophysics 11/1994; 292:501-506. · 4.59 Impact Factor -
Article: Flexures of conventional Cassegrain-fed spectrographs
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ABSTRACT: The flexure patterns of two classical Cassegrain-fed spectrographs are derived by cross-correlating CCD spectra. After a detailed description of the method used to derive the flexure models, emphasis is given to the fact that extreme care must be used in compensating for those flexures when high precision is sought in wavelength-calibration and radial-velocity work involving instrumentation similar to that investigated here. If not fully accounted for, the flexures can introduce spurious shifts up to one hundred times the typical error of the cross-correlation technique usually used to compare the spectra. With the aid of the present models, it is now possible to remove most of the flexure biases from spectra taken with both spectrographs of the Asiago Astrophysical Observatory over a large fraction of the sky accessible to the telescope derived with the cross-correlation technique. A brief discussion on possible ways to monitor in real time the flexure pattern of a telescope + spectrograph combination is given.Publications of the Astronomical Society of the Pacific 01/1992; 104:121-126. · 3.58 Impact Factor -
Article: Memberships and CM diagrams of young open clusters. I - NGC 225
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ABSTRACT: Results are presented on astrometric, photometric, and spectroscopic studies of the loose young open cluster NGC 225, conducted on the basis of observations and archived plate material. The main cluster parameters derived in this study are presented in the form of a table. Astrometric member candidates were checked against photometric and spectroscopic criteria, yielding an enhanced list of cluster members which is suitable for further and more extensive investigations.The Astronomical Journal 06/1991; 102:177-199. · 4.03 Impact Factor -
Article: A second epoch survey of the southern sky, and sky surveys: The ST ScI program for the 1990s
07/1989; -
Article: Comparisons with Galaxy Models in the NGP Field
127:153. -
Article: MIDI observations of 1459 Magnya: First attempt of interferometric observations of asteroids with the VLTI
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ABSTRACT: The Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) can be used to obtain direct determination of the sizes and the albedos of asteroids. We present results of the first attempt to carry out interferometric observations of asteroids with the Mid Infrared Interferometric Instrument (MIDI) at the VLTI. Our target was 1459 Magnya. This is the only V-type asteroid known to exist in the outer main-belt, and its IRAS-albedo turns out to be rather low for an object of this taxonomic class. Interferometric fringes were not detected, very likely due to the fact that the flux emitted by the asteroid was lower than expected and below the MIDI threshold for fringe detection. However, by fitting the Standard Thermal Model to the N-band infrared flux measured by MIDI in photometric mode and to the visible absolute magnitude, obtained from quasi-simultaneous B- and V-band photometric observations, we have derived a geometric visible albedo of 0.37±0.06 and an effective diameter of 17±1 km. This new estimate of the albedo differs from that previously obtained by IRAS and is more consistent with the V-type taxonomic classification of 1459 Magnya.Icarus. -
Article: Parallaxes and physical properties of 11 mid-to-late T dwarfs
http://dx.doi.org/10.1051/0004-6361/201015394.
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Institutions
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1991–1992
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Space Telescope Science Institute
Baltimore, MD, USA
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