Access to microarcsecond astrometry is now routine in the radio, infrared (IR), and optical domains. In particular, the publication of the second data release (
Gaia
DR2) from the
Gaia
mission made ...it possible for every astronomer to work with easily accessible, high-precision astrometry for 1.7 billion sources to twenty-first magnitude over the full sky.
Gaia
provides splendid astrometry, but at the limits of the data small systematic errors are present. A good understanding of the Hipparcos-
Gaia
astrometry concept, and of the data collection and processing, provides insights into the origins of the systematic errors and how to mitigate their effects.
A selected set of results from
Gaia
highlight the breadth of exciting science and unexpected results, from the Solar System to the distant Universe, to creative uses of the data.
Gaia
data release 2 provides, for the first time, a dense sampling of Galactic phase space with high-precision astrometry, photometry, and radial velocities, allowing researchers to uncover subtle features in phase space and the observational Hertzsprung-Russell diagram.
In the coming decade, we can look forward to more accurate and richer
Gaia
data releases, and new photometric and spectroscopic surveys coming online that will provide essential complementary data.
The longer term promises exciting new opportunities for microarcsecond astrometry and beyond, including the plans for an IR version of
Gaia
that would offer the dense sampling of phase space deep into the Milky Way's nuclear regions.
Gaia Data Release 2 Luri, X.; Brown, A. G. A.; Sarro, L. M. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Context.
The second
Gaia
data release (
Gaia
DR2) 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 using Bayesian methods. In particular we also show that negative parallaxes, or parallaxes with relatively large uncertainties still contain valuable information. Finally, we provide examples that show more generally how to use astrometric data for parameter estimation, including the combination of proper motions and parallaxes and the handling of covariances in the uncertainties.
Methods.
The paper contains examples based on simulated
Gaia
data to illustrate the problems and the solutions proposed. Furthermore, the developments and methods proposed in the paper are linked to a set of tutorials included in the
Gaia
archive documentation that provide practical examples and a good starting point for the application of the recommendations to actual problems. In all cases the source code for the analysis methods is provided.
Results.
Our main recommendation is to always treat the derivation of (astro-)physical parameters from astrometric data, in particular when parallaxes are involved, as an inference problem which should preferably be handled with a full Bayesian approach.
Conclusions.
Gaia
will provide fundamental data for many fields of astronomy. Further data releases will provide more data, and more precise data. Nevertheless, to fully use the potential it will always be necessary to pay careful attention to the statistical treatment of parallaxes and proper motions. The purpose of this paper is to help astronomers find the correct approach.
ABSTRACT
For stars with unresolved companions, motions of the centre of light and that of mass decouple, causing a single-source astrometric model to perform poorly. We show that such stars can be ...easily detected with the reduced χ2 statistic, or renormalized unit weight error (RUWE), provided as part of Gaia DR2. We convert RUWE into the amplitude of the image centroid wobble, which, if scaled by the source distance, is proportional to the physical separation between companions (for periods up to several years). We test this idea on a sample of known spectroscopic binaries and demonstrate that the amplitude of the centroid perturbation scales with the binary period and the mass ratio as expected. We apply this technique to the Gaia DR2 data and show how the binary fraction evolves across the Hertzsprung–Russell diagram. The observed incidence of unresolved companions is high for massive young stars and drops steadily with stellar mass, reaching its lowest levels for white dwarfs. We highlight the elevated binary fraction for the nearby blue stragglers and blue horizontal branch stars. We also illustrate how unresolved hierarchical triples inflate the relative velocity signal in wide binaries. Finally, we point out a hint of evidence for the existence of additional companions to the hosts of extrasolar hot Jupiters.
Abstract
Double white dwarf (DWD) binaries are expected to be very common in the Milky Way, but their intrinsic faintness challenges the detection of these systems. Currently, only a few tens of ...detached DWDs are know. Such systems offer the best chance of extracting the physical properties that would allow us to address a wealth of outstanding questions ranging from the nature of white dwarfs and thermonuclear supernovae, over stellar and binary evolution to mapping the Galaxy. In this paper, we explore the prospects for detections of ultra-compact (with binary separations of a few solar radii or less) detached DWDs in (1) optical radiation with Gaia and the Large Synoptic Survey Telescope (LSST) and (2) gravitational wave radiation with Large Synoptic Survey Telescope (LISA). We show that Gaia, LSST and LISA have the potential to detect, respectively, around a few hundred, a thousand and 25 thousand DWD systems. Moreover, Gaia and LSST data will extend by, respectively, a factor of 2 and 7 the guaranteed sample of LISA verification sources, binaries detectable in electromagnetic and gravitational wave radiation, opening the era of multimessenger astronomy for these sources.
ABSTRACT The Orion-Eridanus superbubble is the prototypical superbubble owing to its proximity and evolutionary state. Here we provide a synthesis of recent observational data from WISE and Planck ...with archival data, allowing us to draw a new and more complete picture on the history and evolution of the Orion-Eridanus region. We discuss the general morphological structures and observational characteristics of the superbubble and derive quantitative properties of the gas and dust inside Barnard's Loop. We reveal that Barnard's Loop is a complete bubble structure that, together with the λ Ori region and other smaller-scale bubbles, expands within the Orion-Eridanus superbubble. We argue that the Orion-Eridanus superbubble is larger and more complex than previously thought, and that it can be viewed as a series of nested shells, superimposed along the line of sight. During the lifetime of the superbubble, Hii region champagne flows and thermal evaporation of embedded clouds continuously mass-load the superbubble interior, while winds or supernovae from the Orion OB association rejuvenate the superbubble by sweeping up the material from the interior cavities in an episodic fashion, possibly triggering the formation of new stars that form shells of their own. The steady supply of material into the superbubble cavity implies that dust processing from interior supernova remnants is more efficient than previously thought. The cycle of mass loading, interior cleansing, and star formation repeats until the molecular reservoir is depleted or the clouds have been disrupted. While the nested shells come and go, the superbubble remains for tens of millions of years.
We model the formation of the Galactic stellar halo via the accretion of satellite galaxies on to a time-dependent semicosmological galactic potential. Our goal is to characterize the substructure ...left by these accretion events in a close manner to what may be possible with the Gaia mission. We have created a synthetic Gaia solar neighbourhood catalogue by convolving the six-dimensional phase-space coordinates of stellar particles from our disrupted satellites with the latest estimates of the Gaia measurement errors, and included realistic background contamination due to the Galactic disc(s) and bulge. We find that, even after accounting for the expected observational errors, the resulting phase space is full of substructure. We are able to successfully isolate roughly 50 per cent of the different satellites contributing to the ‘solar neighbourhood’ by applying the mean shift clustering algorithm in energy–angular momentum space. Furthermore, a Fourier analysis of the space of orbital frequencies allows us to obtain accurate estimates of the time since accretion for approximately 30 per cent of the recovered satellites.
Abstract
Asteroseismology provides fundamental stellar parameters independent of distance, but subject to systematics under calibration. Gaia DR2 has provided parallaxes for a billion stars, which ...are offset by a parallax zero-point (ϖzp). Red Clump (RC) stars have a narrow spread in luminosity, thus functioning as standard candles to calibrate these systematics. This work measures how the magnitude and spread of the RC in the Kepler field are affected by changes to temperature and scaling relations for seismology, and changes to the parallax zero-point for Gaia. We use a sample of 5576 RC stars classified through asteroseismology. We apply hierarchical Bayesian latent variable models, finding the population-level properties of the RC with seismology, and use those as priors on Gaia parallaxes to find ϖzp. We then find the position of the RC, using published values for ϖzp. We find a seismic temperature-insensitive spread of the RC of ${\sim }0.03\, \rm mag$ in the 2MASS K band and a larger and slightly temperature-dependent spread of ${\sim }0.13\, \rm mag$ in the Gaia G band. This intrinsic dispersion in the K band provides a distance precision of ${\sim } 1{{\ \rm per\ cent}}$ for RC stars. Using Gaia data alone, we find a mean zero-point of $-41\pm 10\, \mu \rm as$. This offset yields RC absolute magnitudes of −1.634 ± 0.018 in K and 0.546 ± 0.016 in G. Obtaining these same values through seismology would require a global temperature shift of ${\sim }-70\, \mathrm{K}$, which is compatible with known systematics in spectroscopy.
ABSTRACT
Satellite galaxies within the Milky Way’s (MW's) virial radius Rvir are typically devoid of cold gas due to ram pressure stripping by the MW’s corona. The density of this corona is poorly ...constrained today and essentially unconstrained in the past, but can be estimated using ram pressure stripping. In this paper, we probe the MW's corona at z ≈ 1.6 using the Draco dwarf spheroidal galaxy. We assume that (i) Draco’s orbit is determined by its interaction with the MW, whose dark matter halo we evolve in time following cosmologically motivated prescriptions, (ii) Draco’s star formation was quenched by ram pressure stripping and (iii) the MW’s corona is approximately smooth, spherical, and in hydrostatic equilibrium. We used Gaia proper motions to set the initial conditions and Draco’s star formation history to estimate its past gas content. We found indications that Draco was stripped of its gas during the first pericentric passage. Using 3D hydrodynamical simulations at a resolution that enables us to resolve individual supernovae and assuming no tidal stripping, which we estimate to be a minor effect, we find a density of the MW corona ≥8 × 10−4 cm−3 at a radius ≈0.72Rvir. This provides evidence that the MW’s corona was already in place at z ≈ 1.6 and with a higher density than today. If isothermal, this corona would have contained all the baryons expected by the cosmological baryon fraction. Extrapolating to today shows good agreement with literature constraints if feedback has removed ≲30 per cent of baryons accreted on to the halo.
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