Analyse de cartes de profondeur pour la navigation active dans un volume image

Nous proposons une méthode de navigation automatique d'un endoscope virtuel à l'intérieur d'un volume image. Cette navigation est basée sur la vision, la décision de déplacement repose sur une perception locale des configurations spatiales sans traitement préalable (segmentation, modélisation) du volume. En effet nous privilégions ici une analyse de l'image -obtenue par lancer de rayons- à partir de sa carte de profondeur. De ce traitement nous obtenons la détection automatique des branchements et une information structurelle sur la scène observée

Review of patient-specific simulations of transcatheter aortic valve implantation

International audienceTranscatheter Aortic Valve Implantation (TAVI) accounts for one of the most promising new cardiovascular procedures. This minimally invasive technique is still at its early stage and is constantly developing thanks to imaging techniques, computer science, biomechanics and technologies of prosthesis and delivery tools. As a result, patient-specific simulation can find an exciting playground in TAVI. It canexpress its potential by providing the clinicians with powerful decision support, offering great assistance in their workflow. Through a review of the current scientific field, we try to identify the challenges and future evolutions of patient-specific simulation for TAVI. This review article is an attempt to summarize and coordinate data scattered across the literature about patient-specific biomechanical simulation for TAVI

<i>Gaia</i> Data Release 1. Summary of the astrometric, photometric, and survey properties

Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues – a realisation of the Tycho-Gaia Astrometric Solution (TGAS) – and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1 for the proper motions. A systematic component of ∼0.3 mas should be added to the parallax uncertainties. For the subset of ∼94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr−1. For the secondary astrometric data set, the typical uncertainty of the positions is ∼10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼0.03 mag over the magnitude range 5 to 20.7. Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data

Gaia Data Release 3: G_RVS photometry from the RVS spectra

Gaia Data Release 3 (DR3) contains the first release of magnitudes estimated from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample of about 32.2 million stars brighter than G_RVS~14 mag (or G~15 mag). In this paper, we describe the data used and the approach adopted to derive and validate the G_RVS magnitudes published in DR3. We also provide estimates of the G_RVS passband and associated G_RVS zero-point. We derived G_RVS photometry from the integration of RVS spectra over the wavelength range from 846 to 870 nm. We processed these spectra following a procedure similar to that used for DR2, but incorporating several improvements that allow a better estimation of G_RVS. These improvements pertain to the stray-light background estimation, the line spread function calibration, and the detection of spectra contaminated by nearby relatively bright sources. We calibrated the G_RVS zero-point every 30 hours based on the reference magnitudes of constant stars from the Hipparcos catalogue, and used them to transform the integrated flux of the cleaned and calibrated spectra into epoch magnitudes. The G_RVS magnitude of a star published in DR3 is the median of the epoch magnitudes for that star. We estimated the G_RVS passband by comparing the RVS spectra of 108 bright stars with their flux-calibrated spectra from external spectrophotometric libraries. The G_RVS magnitude provides information that is complementary to that obtained from the G, G_BP, and G_RP magnitudes, which is useful for constraining stellar metallicity and interstellar extinction. The median precision of G_RVS measurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5 < G_RVS < 6.5 mag) to 0.125 mag at the faint end. The derived G_RVS passband shows that the effective transmittance of the RVS is approximately 1.23 times better than the pre-launch estimate.Comment: 16 pages, 18 figures. Accepted for publication in A&

X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope

X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope(VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R~4,000 - 17,000, depending on wavelength and slit width) with fixed echelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8"x4" Integral Field Unit as an alternative to the 11" long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.Comment: accepted for publication in A&

Gaia Data Release 3

CONTEXT: Gaia Data Release 3 (Gaia DR3) contains the second release of the combined radial velocities. It is based on the spectra collected during the first 34 months of the nominal mission. The longer time baseline and the improvements of the pipeline made it possible to push the processing limit from GRVS = 12 in Gaia DR2 to GRVS = 14 mag. AIMS: We describe the new functionalities implemented for Gaia DR3, the quality filters applied during processing and post-processing, and the properties and performance of the published velocities. METHODS: For Gaia DR3, several functionalities were upgraded or added to the spectroscopic pipeline. The calibrations were improved in order to better model the temporal evolution of the straylight and of the instrumental point spread function (PSF). The overlapped spectra, which were mostly discarded in Gaia DR2, are now handled by a dedicated module. The hot star template mismatch, which prevented publication of hot stars in Gaia DR2, is largely mitigated now, down to GRVS = 12 mag. The combined radial velocity of stars brighter than or equal to GRVS = 12 mag is calculated in the same way as in Gaia DR2, that is, as the median of the epoch radial velocity time series. The combined radial velocity of the fainter stars is measured from the average of the cross-correlation functions. RESULTS: Gaia DR3 contains the combined radial velocities of 33 812 183 stars. With respect to Gaia DR2, the temperature interval has been expanded from Teff ∈ [3600, 6750] K to Teff ∈ [3100, 14 500] K for the bright stars (GRVS ≤ 12 mag) and [3100, 6750] K for the fainter stars. The radial velocities sample a significant part of the Milky Way: they reach a few kiloparsecs beyond the Galactic centre in the disc and up to about 10−15 kpc vertically into the inner halo. The median formal precision of the velocities is 1.3 km s−1 at GRVS = 12 and 6.4 km s−1 at GRVS = 14 mag. The velocity zeropoint exhibits a small systematic trend with magnitude that starts around GRVS = 11 mag and reaches about 400 m s−1 at GRVS = 14 mag. A correction formula is provided that can be applied to the published data. The Gaia DR3 velocity scale agrees satisfactorily with APOGEE, GALAH, GES, and RAVE; the systematic differences mostly remain below a few hundred m s−1. The properties of the radial velocities are also illustrated with specific objects: open clusters, globular clusters, and the Large Magellanic Cloud. For example, the precision of the data allows mapping the line-of-sight rotational velocities of the globular cluster 47 Tuc and of the Large Magellanic Cloud

Gaia Focused Product Release: Asteroid orbital solution: Properties and assessment

CONTEXT: We report the exploitation of a sample of Solar System observations based on data from the third Gaia Data Release (Gaia DR3) of nearly 157 000 asteroids. It extends the epoch astrometric solution over the time coverage planned for the Gaia DR4, which is not expected before the end of 2025. This data set covers more than one full orbital period for the vast majority of these asteroids. The orbital solutions are derived from the Gaia data alone over a relatively short arc compared to the observation history of many of these asteroids. AIMS: The work aims to produce orbital elements for a large set of asteroids based on 66 months of accurate astrometry provided by Gaia and to assess the accuracy of these orbital solutions with a comparison to the best available orbits derived from independent observations. A second validation is performed with accurate occultation timings. METHODS: We processed the raw astrometric measurements of Gaia to obtain astrometric positions of moving objects with 1D sub-mas accuracy at the bright end. For each asteroid that we matched to the data, an orbit fitting was attempted in the form of the best fit of the initial conditions at the median epoch. The force model included Newtonian and relativistic accelerations to derive the observation equations, which were solved with a linear least-squares fit. RESULTS: Orbits are provided in the form of state vectors in the International Celestial Reference Frame for 156 764 asteroids, including near-Earth objects, main-belt asteroids, and Trojans. For the asteroids with the best observations, the (formal) relative uncertainty σa/a is better than 10-10. Results are compared to orbits available from the Jet Propulsion Laboratory and MPC. Their orbits are based on much longer data arcs, but from positions of lower quality. The relative differences in semi-major axes have a mean of 5 × 10-10 and a scatter of 5 × 10-

Gaia Data Release 3: Exploring and mapping the diffuse interstellar band at 862 nm

Context. Diffuse interstellar bands (DIBs) are common interstellar absorption features in spectroscopic observations but their origins remain unclear. DIBs play an important role in the life cycle of the interstellar medium (ISM) and can also be used to trace Galactic structure. Aims. Here, we demonstrate the capacity of the Gaia-Radial Velocity Spectrometer (RVS) in Gaia DR3 to reveal the spatial distribution of the unknown molecular species responsible for the most prominent DIB at 862 nm in the RVS passband, exploring the Galactic ISM within a few kiloparsecs from the Sun. Methods. The DIBs are measured within the GSP-Spec module using a Gaussian profile fit for cool stars and a Gaussian process for hot stars. In addition to the equivalent widths and their uncertainties, Gaia DR3 provides their characteristic central wavelength, width, and quality flags. Results. We present an extensive sample of 476 117 individual DIB measurements obtained in a homogeneous way covering the entire sky. We compare spatial distributions of the DIB carrier with interstellar reddening and find evidence that DIB carriers are present in a local bubble around the Sun which contains nearly no dust. We characterised the DIB equivalent width with a local density of 0.19 ± 0.04 kpc1 and a scale height of 98.60 8.46+11.10 pc. The latter is smaller than the dust scale height, indicating that DIBs are more concentrated towards the Galactic plane. We determine the rest-frame wavelength with unprecedented precision (?0 = 8620.86 ± 0.019 in air) and reveal a remarkable correspondence between the DIB velocities and the CO gas velocities, suggesting that the 862 nm DIB carrier is related to macro-molecules. Conclusions. We demonstrate the unique capacity of Gaia to trace the spatial structure of the Galactic ISM using the 862 nm DIB