Context. The Gaia Data Release 1 (GDR1) is a first, important step on the path of evolution of astrometric accuracy towards a much improved situation. Although asteroids are not present in GDR1, this ...intermediate release already impacts asteroid astrometry. Aims. Our goal is to investigate how the GDR1 can change the approach to a few typical problems, including the determination of orbits from short-arc astrometry, the exploitation of stellar occultations, and the impact risk assessment. Methods. We employ optimised asteroid orbit determination tools, and study the resulting orbit accuracy and post-fit residuals. For this goal, we use selected ground-based asteroid astrometry, and occultation events observed in the past. All measurements are calibrated by using GDR1 stars. Results. We show that, by adopting GDR1, very short measurement arcs can already provide interesting orbital solutions, capable of correctly identifying near-Earth asteroids (NEAs) and providing a much more accurate risk rating. We also demonstrate that occultations, previously used to derive asteroid size and shapes, now reach a new level of accuracy at which they can be fruitfully used to obtain astrometry at the level of accuracy of Gaia star positions.
The European Space Agency astrometric Gaia mission, due for a launch in late 2012, will observe a large number of asteroids (>250 000 to V= 20 mag) over five years with an unprecedented positional ...accuracy (at the submilliarcsecond level). Among them, there will be a subset of near-Earth asteroids (NEAs), all sensitive to the tiny non-gravitational force due to the Yarkovsky effect, hardly detectable with ground based astrometry. Here we investigate the potential of Gaia to detect the Yarkovsky effect. From realistic simulated data on the currently known NEAs observable by Gaia, we performed a variance analysis from the observation residuals on a data model linearized with respect to the initial position and velocity of the asteroid and its semimajor axis drift rate (da/dt)- the main secular effect due to the Yarkovsky effect. The partial derivatives necessary to evaluate the expected accuracy with Gaia observations of (da/dt) are obtained by a numerical integration of the variational equations. We thus give the list of the most promising 64 NEAs for the detection of the Yarkovsky effect by Gaia, with an expected precision on (da/dt) better than 5 × 10−4 au Myr−1 (from underestimated astrometric precision). We also add for each asteroid, the physical parameters to be precisely estimated from complementary ground-based observations (photometric, radar) to accurately model the Yarkovsky effect.
Overview of the determination of astronomical distances from a metrological standpoint. Distances are considered from the Solar System (planetary distances) to extragalactic distances, with a special ...emphasis on the fundamental step of the trigonometric stellar distances and the giant leap recently experienced in this field thanks to the ESA space astrometry missions Hipparcos and Gaia.
Aims. In this work, we aim to provide a reliable list of gravitational lens candidates based on a search performed over the entire Gaia Data Release 2 (Gaia DR2). We also aim to show that the ...astrometric and photometric information coming from the Gaia satellite yield sufficient insights for supervised learning methods to automatically identify strong gravitational lens candidates with an efficiency that is comparable to methods based on image processing. Methods. We simulated 106 623 188 lens systems composed of more than two images, based on a regular grid of parameters characterizing a non-singular isothermal ellipsoid lens model in the presence of an external shear. These simulations are used as an input for training and testing our supervised learning models consisting of extremely randomized trees (ERTs). These trees are finally used to assign to each of the 2 129 659 clusters of celestial objects extracted from the Gaia DR2 a discriminant value that reflects the ability of our simulations to match the observed relative positions and fluxes from each cluster. Once complemented with additional constraints, these discriminant values allow us to identify strong gravitational lens candidates out of the list of clusters. Results. We report the discovery of 15 new quadruply-imaged lens candidates with angular separations of less than 6″ and assess the performance of our approach by recovering 12 of the 13 known quadruply-imaged systems with all their components detected in Gaia DR2 with a misclassification rate of fortuitous clusters of stars as lens systems that is below 1%. Similarly, the identification capability of our method regarding quadruply-imaged systems where three images are detected in Gaia DR2 is assessed by recovering 10 of the 13 known quadruply-imaged systems having one of their constituting images discarded. The associated misclassification rate varies between 5.83% and 20%, depending on the image we decided to remove.
We report the spectroscopic confirmation and modeling of the quadruply imaged quasar GRAL 113100–441959, the first gravitational lens (GL) to be discovered from a machine learning technique that only ...relies on the relative positions and fluxes of the observed images without considering colour informations. Follow-up spectra obtained with Keck/LRIS reveal the lensing nature of this quadruply imaged quasar with redshift zs = 1.090 ± 0.002, but show no evidence of the central lens galaxy. Using the image positions and G-band flux ratios provided by Gaia Data Release 2 as constraints, we modeled the system with a singular power-law elliptical mass distribution (SPEMD) plus external shear, to different levels of complexity. We show that relaxing the isothermal constraint of the SPEMD does not lead to statistically significant different results in terms of fitting the lensing data. We thus simplified the SPEMD to a singular isothermal ellipsoid to estimate the Einstein radius of the main lens galaxy θE = 0.″851 θ E =0 . ″ 851 $ \theta_{{\rm E}} = 0{{\overset{\prime\prime}{.}}}851 $ , the intensity and position angle of the external shear (γ,θγ) = (0.044, 11.°5) (γ, θ γ )=(0.044,11 . ° 5) $ (\gamma,\theta_{\gamma}) = (0.044,11{{\overset{\circ}{.}}}5) $ , and we predict the lensing galaxy position to be (θgal,1, θgal,2) = (−0.″424, −0.″744) ( θ gal,1 , θ gal,2 )=(−0 . ″ 424,−0 . ″ 744) $ (\theta_{{\rm gal},1},\theta_{{\rm gal},2}) = (-0{{\overset{\prime\prime}{.}}}424,-0{{\overset{\prime\prime}{.}}}744) $ with respect to image A. We provide time delay predictions for pairs of images, assuming a plausible range of lens redshift values zl between 0.5 and 0.9. Finally, we examine the impact on time delays of the so-called source position transformation, a family of degeneracies existing between different mass density profiles that reproduce most of the lensing observables equally well. We show that this effect contributes significantly to the time delay error budget and cannot be ignored during the modeling. This has implications for robust cosmography applications of lensed systems. GRAL 113100–441959 is the first in a series of seven new spectroscopically confirmed GLs discovered from Gaia Data Release 2.
Asteroid masses and improvement with Gaia Mouret, S.; Hestroffer, D.; Mignard, F.
Astronomy and astrophysics (Berlin),
09/2007, Letnik:
472, Številka:
3
Journal Article
Recenzirano
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Context.The ESA astrometric mission Gaia, due for launch in late 2011, will observe a very large number of asteroids ($\thicksim$350 000 brighter than V = 20) with an unprecedented positional ...precision (at the sub-milliarcsecond level). Aims.Gaia will yield masses of the hundred largest asteroids from gravitational perturbations during close approaches with target asteroids. The objective is to develop a global method to obtain these masses which will use simultaneously all perturbers together with their target asteroids. In this paper, we outline the numerical and statistical methodology and show how to estimate the accuracy. Methods.The method that we use is the variance analysis from the formulation of observed minus calculated position (O-C). We assume a linear relationship between the (O-C) and the fitted parameters which are the initial position and velocity of the asteroids and the masses of perturbers. The matrix giving the partial derivatives with respect to the positions and masses is computed by numerical integration of the variational equations. Results.We show that with Gaia it will be possible to derive more than 100 masses of minor planets 42 of which with a precision better than 10%.
Context. Multiply imaged gravitationally lensed quasars are among the most interesting and useful observable extragalactic phenomena. Because their study constitutes a unique tool in various fields ...of astronomy, they are highly sought, but difficult to find. Even in this era of all-sky surveys, discovering them remains a great challenge, with barely a few hundred systems currently known. Aims. We aim to discover new multiply imaged quasar candidates in the recently published Gaia Data Release 2 (DR2), which is the astrometric and photometric all-sky survey with the highest spatial resolution that achieves effective resolutions from 0.4″ to 2.2″. Methods. We cross-matched a merged list of quasars and candidates with Gaia DR2 and found 1 839 143 counterparts within 0.5″. We then searched matches with more than two Gaia DR2 counterparts within 6″. We further narrowed the resulting list using astrometry and photometry compatibility criteria between the Gaia DR2 counterparts. A supervised machine-learning method, called extremely randomized trees, was finally adopted to assign a probability of being lensed to each remaining system. Results. We report the discovery of two quadruply imaged quasar candidates that are fully detected in Gaia DR2. These are the most promising new quasar lens candidates from Gaia DR2 and a simple singular isothermal ellipsoid lens model is able to reproduce their image positions to within ~1 mas. This Letter demonstrates the discovery potential of Gaia for gravitational lenses.
The rapid proper motion of the α Cen pair (≈ 3.7 arcsec yr −1) and its location close to the galactic plane on a rich stellar background combine constructively to make them excellent candidates for ...close stellar conjunctions with more distant stars. Adding new differential astrometry to archival data, we have refined the orbital parameters, barycentric proper motion and parallax of α Cen and compute its apparent trajectory on sky over the coming decades. Based on NTT/SUSI2, NTT/SOFI and VLT/NACO maps of the field stars around the trajectories of α Cen A and B, we present a catalog of the expected close conjunctions until 2050. An exceptional event will take place in early May 2028, when α Cen A will come within ρ min = 0.015 ± 0.135 arcseconds of the m K = 7.8 star 2MASS 14392160-6049528 (hereafter S5). In terms of impact parameter and contrast, this is the most favorable stellar conjunction of α Cen within at least the next three decades. With an angular diameter of θ LD = 0.47 ± 0.05 mas, it is likely that S5 is a red giant or super-giant located at several kiloparsecs. The approached stars will act as moving light probes in transmission through the environment of α Cen. The observation of these close conjunctions holds great promises to search for planets and other low mass objects in the α Cen system using photometry and astrometry. The relativistic displacement of the approached star images will be observable, with significant deflection angles in the milliarcsecond range. The small impact parameter of the conjunction with S5 means that this star has a probability of 45% of entering the Einstein ring of α Cen A. The gravitational amplification of the flux of S5 could reach a factor five for the combination of the two lensed images. The proper motion, orbital parameters and parallax of α Cen will be measurable with an extreme accuracy from differential astrometry with the S stars. This will be valuable, for example to prepare the recently announced Breakthrough Starshot initiative to send interstellar nanocrafts to α Centauri.
Gaia Data Release 1 Moitinho, A.; Krone-Martins, A.; Savietto, H. ...
Astronomy and astrophysics (Berlin),
09/2017, Letnik:
605
Journal Article
Recenzirano
Odprti dostop
Context. The first Gaia data release (DR1) delivered a catalogue of astrometry and photometry for over a billion astronomical sources. Within the panoplyof methods used for data exploration, ...visualisation is often the starting point and even the guiding reference for scientific thought. However, this is a volume of data that cannot be efficiently explored using traditional tools, techniques, and habits. Aims. We aim to provide a global visual exploration service for the Gaia archive, something that is not possible out of the box for most people. The service has two main goals. The first is to provide a software platform for interactive visual exploration of the archive contents, using common personal computers and mobile devices available to most users. The second aim is to produce intelligible and appealing visual representations of the enormous information content of the archive. Methods. The interactive exploration service follows a client-server design. The server runs close to the data, at the archive, and is responsible for hiding as far as possible the complexity and volume of the Gaia data from the client. This is achieved by serving visual detail on demand. Levels of detail are pre-computed using data aggregation and subsampling techniques. For DR1, the client is a web application that provides an interactive multi-panel visualisation workspace as well as a graphical user interface. Results. The Gaia archive Visualisation Service offers a web-based multi-panel interactive visualisation desktop in a browser tab. It currently provides highly configurable 1D histograms and 2D scatter plots of Gaia DR1 and the Tycho-Gaia Astrometric Solution (TGAS) with linked views. An innovative feature is the creation of ADQL queries from visually defined regions in plots. These visual queries are ready for use in the Gaia Archive Search/data retrieval service. In addition, regions around user-selected objects can be further examined with automatically generated SIMBAD searches. Integration of the Aladin Lite and JS9 applications add support to the visualisation of HiPS and FITS maps. The production of the all-sky source density map that became the iconic image of Gaia DR1 is described in detail. Conclusions. On the day of DR1, over seven thousand users accessed the Gaia Archive visualisation portal. The system, running on a single machine, proved robust and did not fail while enabling thousands of users to visualise and explore the over one billion sources in DR1. There are still several limitations, most noticeably that users may only choose from a list of pre-computed visualisations. Thus, other visualisation applications that can complement the archive service are examined. Finally, development plans for Data Release 2 are presented.
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