Publications of the Astronomical Society of the Pacific
Astrometry at or below the microarcsec level with an imaging telescope assumes that the uncertain... more Astrometry at or below the microarcsec level with an imaging telescope assumes that the uncertainty on the location of an unresolved source can be an arbitrarily small fraction of the detector pixel, given a sufficient photon budget. This paper investigates the geometric limiting precision, in terms of CCD pixel fraction, achieved by a large set of star field images, selected among the publicly available science data of the Transiting Exoplanet Survey Satellite (TESS) mission. The statistics of the distance between selected bright stars (G ≃ 5 mag), in pixel units, is evaluated, using the position estimate provided in the TESS light curve files. The dispersion of coordinate differences appears to be affected by long term variation and noisy periods, at the level of 0.01 pixel. The residuals with respect to low-pass filtered data (tracing the secular evolution), which are interpreted as the experimental astrometric noise, reach the level of a few milli-pixel or below, down to 1/5900 ...
Publications of the Astronomical Society of the Pacific, 2022
Background. Relative astrometry at or below the microarcsec level with a 1 m class space telescop... more Background. Relative astrometry at or below the microarcsec level with a 1 m class space telescope has been repeatedly proposed as a tool for exo-planet detection and characterization, as well as for several topics at the forefront of Astrophysics and Fundamental Physics. Aim. This paper investigates the potential benefits of an instrument concept based on an annular field of view, as compared to a traditional focal plane imaging a contiguous area close to the telescope optical axis. Method. Basic aspects of relative astrometry are reviewed as a function of the distribution on the sky of reference stars brighter than G = 12 mag (from Gaia EDR3). Statistics of field stars for targets down to G = 8 mag is evaluated by analysis and simulation. Results. Observation efficiency benefits from prior knowledge on individual targets, since source model is improved with few measurements. Dedicated observations (10–20 hr) can constrain the orbital inclination of exoplanets to a few degrees. Obs...
Item does not contain fulltextThe files contains lists of possible members of each of the objects... more Item does not contain fulltextThe files contains lists of possible members of each of the objects (75 globular clusters, 9 dwarf spheroidal galaxies, the Bootes I UFD, the LMC and SMC). The stars in these lists have been selected and used to determine the astrometric parameters of the corresponding objects following either the procedures described in Sec. 2.1 (for the clusters and dwarfs) or in Sec. 2.2 (for the LMC and SMC). The first column is the "source_id" as given by Gaia, the ra and declination of the star in degrees, and its G-band magnitude (known as "photgmean_mag" in the Gaia archive). (2 data files)
Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry,... more Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celest...
We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russel... more We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations an...
We have determined and examined the astrometric data for 19 open clusters, ranging from the Hyade... more We have determined and examined the astrometric data for 19 open clusters, ranging from the Hyades at just under 47pc to NGC 2422 at nearly 440pc. The clusters are : the Hyades, Coma Berenices, the Pleiades, Praesepe, alpha Per, IC 2391, IC 2602, Blanco 1, NGC 2451, NGC 6475, NGC 7092, NGC 2516, NGC 2232, IC 4665, NGC 6633, Collinder 140, NGC 2422, NGC 3532 and NGC 2547. (2 data files).
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...
We define a numerical description of the signal model for the Gaia astrometric instrument, encode... more We define a numerical description of the signal model for the Gaia astrometric instrument, encoded in the focal plane to sky mapping (FPSM) function, i.e., the transformation between object and image space, and encoded in terms of discrepancy with respect to the geometric optics. We calculate the FPSM for several spectral types, also deriving the chromaticity map. This model can be extended to take into account dynamic contributions, e.g., attitude or TDI errors. The signal distribution is evaluated to estimate the systematic and random error at the elementary exposure level, and scaled to equivalent final mission performance by means of a simple transformation. We describe the possible future development of the model into a more detailed realistic representation of the Gaia astrometric measurement.
The Focal Plane to Sky Mapping (FPSM) describes the detailed response of the Astro instrument, in... more The Focal Plane to Sky Mapping (FPSM) describes the detailed response of the Astro instrument, including the optical transfer function over the field, the detector response and operations. Its definition at the microarcsecond (µas) level requires good knowledge of inflight instrument parameters. Science data can be used to trace directly the instrument response, taking advantage of the repeated measurements of stars over the field. We discuss the sensitivity of simple data analysis procedures to several instrument parameters, which can be either disentangled from each other or estimated as collective contributions in case of degeneration.
The goals of 21 st century high angular precision experiments rely on the limiting performance as... more The goals of 21 st century high angular precision experiments rely on the limiting performance associated to the selected instrumental configuration and observational strat-egy. Both global and narrow angle micro-arcsec space astrometry require that the instrument contributions to the overall error budget has to be less than the desired micro-arcsec level precision. Appropriate modelling of the astrometric response is required for optimal defini-tion of the data reduction and calibration algorithms, in order to ensure high sensitivity to the astrophysical source parameters and in general high accuracy. We will refer to the framework of the SIM-Lite and the Gaia mission, the most challeng-ing space missions of the next decade in the narrow angle and global astrometry field, re-spectively. We will focus our dissertation on the Gaia data reduction issues and instrument calibration implications. We describe selected topics in the framework of the Astrometric Instrument Modelling for the...
Publications of the Astronomical Society of the Pacific
Astrometry at or below the microarcsec level with an imaging telescope assumes that the uncertain... more Astrometry at or below the microarcsec level with an imaging telescope assumes that the uncertainty on the location of an unresolved source can be an arbitrarily small fraction of the detector pixel, given a sufficient photon budget. This paper investigates the geometric limiting precision, in terms of CCD pixel fraction, achieved by a large set of star field images, selected among the publicly available science data of the Transiting Exoplanet Survey Satellite (TESS) mission. The statistics of the distance between selected bright stars (G ≃ 5 mag), in pixel units, is evaluated, using the position estimate provided in the TESS light curve files. The dispersion of coordinate differences appears to be affected by long term variation and noisy periods, at the level of 0.01 pixel. The residuals with respect to low-pass filtered data (tracing the secular evolution), which are interpreted as the experimental astrometric noise, reach the level of a few milli-pixel or below, down to 1/5900 ...
Publications of the Astronomical Society of the Pacific, 2022
Background. Relative astrometry at or below the microarcsec level with a 1 m class space telescop... more Background. Relative astrometry at or below the microarcsec level with a 1 m class space telescope has been repeatedly proposed as a tool for exo-planet detection and characterization, as well as for several topics at the forefront of Astrophysics and Fundamental Physics. Aim. This paper investigates the potential benefits of an instrument concept based on an annular field of view, as compared to a traditional focal plane imaging a contiguous area close to the telescope optical axis. Method. Basic aspects of relative astrometry are reviewed as a function of the distribution on the sky of reference stars brighter than G = 12 mag (from Gaia EDR3). Statistics of field stars for targets down to G = 8 mag is evaluated by analysis and simulation. Results. Observation efficiency benefits from prior knowledge on individual targets, since source model is improved with few measurements. Dedicated observations (10–20 hr) can constrain the orbital inclination of exoplanets to a few degrees. Obs...
Item does not contain fulltextThe files contains lists of possible members of each of the objects... more Item does not contain fulltextThe files contains lists of possible members of each of the objects (75 globular clusters, 9 dwarf spheroidal galaxies, the Bootes I UFD, the LMC and SMC). The stars in these lists have been selected and used to determine the astrometric parameters of the corresponding objects following either the procedures described in Sec. 2.1 (for the clusters and dwarfs) or in Sec. 2.2 (for the LMC and SMC). The first column is the "source_id" as given by Gaia, the ra and declination of the star in degrees, and its G-band magnitude (known as "photgmean_mag" in the Gaia archive). (2 data files)
Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry,... more Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celest...
We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russel... more We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations an...
We have determined and examined the astrometric data for 19 open clusters, ranging from the Hyade... more We have determined and examined the astrometric data for 19 open clusters, ranging from the Hyades at just under 47pc to NGC 2422 at nearly 440pc. The clusters are : the Hyades, Coma Berenices, the Pleiades, Praesepe, alpha Per, IC 2391, IC 2602, Blanco 1, NGC 2451, NGC 6475, NGC 7092, NGC 2516, NGC 2232, IC 4665, NGC 6633, Collinder 140, NGC 2422, NGC 3532 and NGC 2547. (2 data files).
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...
We define a numerical description of the signal model for the Gaia astrometric instrument, encode... more We define a numerical description of the signal model for the Gaia astrometric instrument, encoded in the focal plane to sky mapping (FPSM) function, i.e., the transformation between object and image space, and encoded in terms of discrepancy with respect to the geometric optics. We calculate the FPSM for several spectral types, also deriving the chromaticity map. This model can be extended to take into account dynamic contributions, e.g., attitude or TDI errors. The signal distribution is evaluated to estimate the systematic and random error at the elementary exposure level, and scaled to equivalent final mission performance by means of a simple transformation. We describe the possible future development of the model into a more detailed realistic representation of the Gaia astrometric measurement.
The Focal Plane to Sky Mapping (FPSM) describes the detailed response of the Astro instrument, in... more The Focal Plane to Sky Mapping (FPSM) describes the detailed response of the Astro instrument, including the optical transfer function over the field, the detector response and operations. Its definition at the microarcsecond (µas) level requires good knowledge of inflight instrument parameters. Science data can be used to trace directly the instrument response, taking advantage of the repeated measurements of stars over the field. We discuss the sensitivity of simple data analysis procedures to several instrument parameters, which can be either disentangled from each other or estimated as collective contributions in case of degeneration.
The goals of 21 st century high angular precision experiments rely on the limiting performance as... more The goals of 21 st century high angular precision experiments rely on the limiting performance associated to the selected instrumental configuration and observational strat-egy. Both global and narrow angle micro-arcsec space astrometry require that the instrument contributions to the overall error budget has to be less than the desired micro-arcsec level precision. Appropriate modelling of the astrometric response is required for optimal defini-tion of the data reduction and calibration algorithms, in order to ensure high sensitivity to the astrophysical source parameters and in general high accuracy. We will refer to the framework of the SIM-Lite and the Gaia mission, the most challeng-ing space missions of the next decade in the narrow angle and global astrometry field, re-spectively. We will focus our dissertation on the Gaia data reduction issues and instrument calibration implications. We describe selected topics in the framework of the Astrometric Instrument Modelling for the...
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Papers by D. Busonero