Добірка наукової літератури з теми "Astrometry (Hipparcos. Gaia)"

AbstractA Danish computer, GIER, from 1961 played a vital role in the development of a new method for astrometric measurement. This method, photon counting astrometry, ultimately led to two satellites with a significant role in the modern revolution of astronomy. A GIER was installed at the Hamburg Observatory in 1964 where it was used to implement the entirely new method for the measurement of stellar positions by means of a meridian circle, at that time the fundamental instrument of astrometry. An expedition to Perth in Western Australia with the instrument and the computer was a success. This method was also implemented in space in the first ever astrometric satellite Hipparcos launched by ESA in 1989. The Hipparcos results published in 1997 revolutionized astrometry with an impact in all branches of astronomy from the solar system and stellar structure to cosmic distances and the dynamics of the Milky Way. In turn, the results paved the way for a successor, the one million times more powerful Gaia astrometry satellite launched by ESA in 2013. Preparations for a Gaia successor in twenty years are making progress.

Abstract The USNO Bright Star Catalog (UBSC) is a new astrometric catalog of the 1423 brightest stars covering the entire sky, which is published online. It is nearly complete to V = 3 mag except for three stellar systems. A combined astrometric solution of the Hipparcos Intermediate Astrometry Data and two dedicated ground-based campaigns in 2013–2020 is the basis for this catalog. The astrometric parameters for each star include position coordinates, parallax, and proper motion components, and their covariances on the Hipparcos mean epoch 1991.25. 64% of the catalog are flagged as known or suspected double or binary stars. UBSC lists 68 stars missing in Gaia EDR3 and another 114 stars without Gaia parallaxes or proper motions. The formal precision achieved for proper motions is comparable to that of Gaia.

Abstract We present htof, an open-source tool for interpreting and fitting the intermediate astrometric data (IAD) from both the 1997 and 2007 reductions of Hipparcos, the scanning law of Gaia, and future missions such as the Nancy Grace Roman Space Telescope (NGRST). htof solves the astrometric parameters of any system for any arbitrary combination of absolute astrometric missions. In preparation for later Gaia data releases, htof supports arbitrarily high-order astrometric solutions (e.g., five-, seven-, and nine-parameter fits). Using htof, we find that the IAD of 6617 sources in Hipparcos 2007 might have been affected by a data corruption issue. htof integrates an ad hoc correction that reconciles the IAD of these sources with their published catalog solutions. We developed htof to study masses and orbital parameters of substellar companions, and we outline its implementation in one orbit fitting code (orvara). We use htof to predict a range of hypothetical additional planets in the β Pic system, which could be detected by coupling NGRST astrometry with Gaia and Hipparcos. htof is pip installable and available at https://github.com/gmbrandt/htof.

Abstract We present the SCExAO direct imaging discovery and characterization of a low-mass companion to the nearby young A7IV star, HD 91312. SCExAO/CHARIS JHK (1.1–2.4 μm) spectra and SCExAO/HiCIAO H-band imaging identify the companion over a two year baseline in a highly inclined orbit with a maximum projected separation of 8 au. The companion, HD 91312 B, induces an 8.8σ astrometric acceleration on the star as seen with the Gaia & Hipparcos satellites and a long-term radial-velocity trend as previously identified by Borgniet et al. HD 91312 B’s spectrum is consistent with that of an early-to-mid M dwarf. Hipparcos and Gaia absolute astrometry, radial-velocity data, and SCExAO/CHARIS astrometry constrain its dynamical mass to be 0.337 − 0.044 + 0.042 M ⊙, consistent with - but far more precise than - masses derived from spectroscopy, and favors a nearly edge-on orbit with a semimajor axis of ∼9.7 au. This work is an example of precisely characterizing properties of low-mass companions at solar system-like scales from a combination of direct imaging, astrometry, and radial-velocity methods.

The Hipparcos mission demonstrated the efficiency of space astrometry (in terms of number of objects, accuracy, and uniformity of results) and the fact that a relatively small instrument can have a very large scientific potential in the area of astrometry. However, Hipparcos could probe less than 0.1 per cent of the volume of the Galaxy by direct distance measurements. Using a larger instrument and more efficient detectors, it is now technically feasible to increase the efficiency of a space astrometry mission by several orders of magnitude, thus encompassing a large part of the Galaxy within its horizon for accurate determination of parallaxes and transverse velocities. Such a mission will have immediate and profound impact in the areas of the physics and evolution of individual stars and of the Galaxy as a whole.

In this paper we attempt to study an ongoing astrometry mission of the European Space Agency (ESA), named Gaia, whose aim is to make the largest and most precise three-dimensional map of our Galaxy. We present the scientific goals of Gaia and give a brief description of the spacecraft. We also present a preliminary analysis of comparing distance estimates of Be stars from the first Gaia data release, Gaia DR1, and Hipparcos mission. From our analysis, we confirm that Gaia stands out as a promising mission in terms of the distance measurements when compared to Hipparcos, particularly for distances greater than 1 kpc.

AbstractRadial velocity measurements are a well known high-precision method to obtain the orbits of extrasolar planets or brown dwarfs. However, this method is not able to determine the inclination which could be derived from astrometry. The astrometric effects of those objects are very minute, wherefore the interest of astronomers in astrometric techniques was very poor. This situation changes fundamentally since space astrometry observations are available. HIPPARCOS demonstrated the power of space astrometry and the extremely high accuracy of the DIVA, and especially the GAIA observations allows one to detect Jupiter- and Earth- like objects. The optimal estimation of the parameters of the orbit of extrasolar planets or brown dwarfs is a combination of radial velocity measurements and space astrometry observations. Here it is possible to overcome problems which are inherent in both observation methods, so space astrometry complements radial velocity observations and vice versa. This paper gives a method for the parameter estimation using both types of measurements.

Context. Knowing the distribution of strongly magnetic Ap stars in the Hertzsprung-Russell diagram (HRD) allows us to study the evolution of their magnetic fields across the main sequence (MS). With a newly extended Ap star sample from APOGEE and available Gaia DR2 data, we can now critically review the results of previous studies based on HIPPARCOS data. Aims. To investigate our targets in the Gaia DR2 HRD, we need to define astrometric and photometric quality criteria to remove unreliable data from the HRD. Methods. We used the Gaia DR2 renormalised unit weight error RUWE as our main quality criterion. We considered known (close) binaries in our sample compared to their (partly affected) astrometry and used the Gaia DR2 data to find common parallax and proper motion (CPPM) wide companions and open cluster members. We studied G, BP, and RP variability amplitudes and their significance as a function of magnitude. In colour-magnitude diagrams (CMDs) with absolute G magnitude (determined from inverted parallax) versus BP − RP colour and HRDs, where BP − RP is replaced by effective temperature, we studied the appearance of outliers with respect to their astrometric quality, binarity, and variability. Results. We present a catalogue of 83 previously known and 154 new strongly magnetic Ap stars with Gaia DR2 data, including astrometric quality parameters, binary flags, information on cluster membership, variability amplitudes, and data from HIPPARCOS. Our astrometrically cleaned subsamples include 47 and 46 old and new Ap stars with parallaxes > 2 mas. Most of the known 26 binaries among all 237 stars and 14 out of 15 CMD/HRD outliers were excluded by astrometric criteria. The remaining 11 known binaries and a few highly variable objects mainly appear in the bright and red CMD/HRD parts. A CMD based on HIPPARCOS photometry and Gaia DR2 parallaxes shows a much more narrow distribution in the absolute V magnitudes of 75 common Ap stars over the full B − V colour range than the corresponding CMD based on HIPPARCOS parallaxes.

DIVA (Double Interferometer for Visual Astrometry) is a Fizeau interferometer on a small satellite. It will perform astrometric and photometric observations of at least 4 million stars. A launch in 2002 and a minimum mission length of 24 months are aimed at. A detailed description of the experiment can be obtained from the DIVA homepage at http://www.aip.de:8080/dso/diva. An overview is given by Röser et al., 1997.The limiting magnitude of DIVA is about V = 15 for spectral types earlier than M0, but drops to about V = 17.5 for stars later than M5. Table 1 gives a short overview on DIVA’s performance. DIVA will carry out a skysurvey complete to V = 12.5. For the first time this survey will comprise precise photometry in at least 8 bands in the wavelength range from 400 to 1000 nm.DIVA will improve parallaxes by a factor of 3 compared to Hipparcos; proper motions by at least a factor of 2 and, in combination with the Hipparcos observations, by a factor of 10 for Hipparcos stars. At least 30 times asmany stars as Hipparcos will be observed, and doing this DIVA will fill the gap in observations between Hipparcos and GAIA. DIVA’s combined astrometric and photometric measurements of high precision will have important impacts on astronomy and astrophysics in the next decade.

Context. Under certain conditions, stellar radial velocities can be determined from astrometry, without any use of spectroscopy. This enables us to identify phenomena, other than the Doppler effect, that are displacing spectral lines. Aims. The change of stellar proper motions over time (perspective acceleration) is used to determine radial velocities from accurate astrometric data, which are now available from the Gaia and HIPPARCOS missions. Methods. Positions and proper motions at the epoch of HIPPARCOS are compared with values propagated back from the epoch of the Gaia Early Data Release 3. This propagation depends on the radial velocity, which obtains its value from an optimal fit assuming uniform space motion relative to the solar system barycentre. Results. For 930 nearby stars we obtain astrometric radial velocities with formal uncertainties better than 100 km s−1; for 55 stars the uncertainty is below 10 km s−1, and for seven it is below 1 km s−1. Most stars that are not components of double or multiple systems show good agreement with available spectroscopic radial velocities. Conclusions. Astrometry offers geometric methods to determine stellar radial velocity, irrespective of complexities in stellar spectra. This enables us to segregate wavelength displacements caused by the radial motion of the stellar centre-of-mass from those induced by other effects, such as gravitational redshifts in white dwarfs.

Building upon its success with the Hipparcos space astrometry mission launched in 1989, the European Space Agency has agreed to fund the construction of its successor, Gaia, and its launch in 2011. Despite the similarities between the two missions, Gaia will be orders of magnitude more powerful, more sensitive, but also more complex in terms of data processing. Growing from 120,000 stars with Hipparcos to about 120,000E4 stars with Gaia does not simply mean pushing the computing resources to their limits (1 second of processing per star yields 38 years for the whole Gaia-sky). It also means facing situations that did not occur with Hipparcos either by luck or because those cases were carefully removed from the Hipparcos Input Catalogue.

This manuscript illustrates how some chunks of the foreseen Gaia data reduction pipeline can be trained and assessed using the Hipparcos observations. This is especially true for unresolved binaries because they pop up so far down in the Gaia pipeline that, by the time they get there, there is essentially no difference between Hipparcos and Gaia data. Only the number of such binaries is different, going from two thousand to ten million.

Although the computing time clearly becomes an issue, one cannot sacrifice the robustness and correctness of the reduction pipeline for the sake of speed. However, owing to the requirement that everything must be Gaia-based (no help from ground-based results), the very robustness of the reduction has to be assessed as well. For instance, the underlying assumptions of some statistical tests used to assess the quality of the fits used in the Hipparcos pipeline might no longer hold with Gaia. That may not affect the fit itself but rather the quality indicators usually accompanying those fits. For the final catalogue to be a success, these issues must be addressed as soon as possible.

Agrégation de l'enseignement supérieur, Orientation sciences
info:eu-repo/semantics/nonPublished

La détection des premières exoplanètes dans les années 1990 a ouvert une nouvelle ère dans l'étude des planètes. Aujourd'hui, grâce aux instruments toujours plus performants, plusieurs centaines d'exoplanètes (Jupiters chauds, Super-Terre, systèmes multiples...) sont découvertes chaque année. Grâce à cette grande variété d'exoplanètes, il est possible d'étudier la distribution (distance, masse, excentricité...) de ces objets afin de mieux contraindre les modèles de formation et d'évolution des systèmes planétaires. Néanmoins, chaque méthode de détection a ses limites et ses biais de détection. Un des objectifs de cette thèse fut de mettre en évidence les limites des différentes méthodes de détection, en particulier celles liées aux vitesses radiales (VR), et d'améliorer la caractérisation des compagnons détectés en VR.Dans un premier temps, j'ai testé la solidité des études visant à déterminer la distribution radiale des planètes géantes. L'analyse des données de VR des étoiles abritant des planètes à longues périodes, de l'impact de l'activité stellaire et des hypothèses faites lors des calculs d'exhaustivité, nous a permis de démontrer que les études statistiques en VR n'étaient pas robustes au-delà de 7-8 ua. Par la suite, j'ai combiné des données de VR avec les mesures d'astrométrie absolue et relative disponibles dans le but d'améliorer la caractérisation des compagnons sub-stellaires à longues périodes. Cette étude a permis de contraindre précisément les paramètres orbitaux et, surtout, la masse de sept compagnons détectés en VR. Elle a également permis de mettre en avant l'importance du couplage des données de VR avec d'autres mesures afin de déterminer avec précision la nature d'un compagnon. Pour finir, j'ai utilisé les mesures d'anomalie de mouvements propres (PMa) des étoiles, estimées à partir des mesures astrométriques des télescopes Hipparcos et Gaia, dans le but de rechercher de nouveaux compagnons sub-stellaires dans les archives du spectrographe HARPS/VLT. Cette analyse m'a permis d'améliorer la caractérisation de 14 compagnons sub-stellaires et de découvrir trois nouvelles naines brunes ainsi que sept nouvelles exoplanètes. J'ai également pu démontrer l'efficacité de l'utilisation des mesures de PMa pour optimiser la recherche de compagnons sub-stellaires
The detection of the first exoplanets in the 1990s opened a new era in the study of planets. Today, thanks to increasingly powerful instruments, several hundred exoplanets (hot Jupiters, Super-Earths, multiple systems...) are discovered every year. Thanks to this wide variety of exoplanets, it is possible to study the distribution (distance, mass, eccentricity...) of these objects in order to better constrain the formation and evolution models of planetary system. Nevertheless, each detection method has its own limitations and detection biases. One aim of this thesis was to identify the limitations of the various detection methods, in particular those related to radial velocities (RV), and to improve the characterization of companions detected by RV.As a first step, I tested the robustness of studies aimed at determining the radial distribution of giant planets. Analysis of RV data from stars hosting long-period planets, the impact of stellar activity and the hypothesis made in completeness calculations, allowed us to demonstrate that statistical RV studies were not robust beyond 7-8 AU. Subsequently, I combined RV data with available absolute and relative astrometry measurements to improve the characterization of long-period sub-stellar companions. This study allowed us to precisely constrain the orbital parameters and, above all, the mass of seven companions detected in RV. It also highlighted the importance of coupling RV data with other measurements to accurately determine the nature of a companion. Finally, I used measurements of stars' proper motion anomalies (PMa), derived from Hipparcos and Gaia absolute astrometry, to search for new sub-stellar companions in the HARPS/VLT spectrograph archive. This analysis enabled me to improve the characterization of 14 sub-stellar companions, and to discover three new brown dwarfs and seven new exoplanets. I also demonstrated the effectiveness of using PMa measurements to optimize the search for sub-stellar companions