258 research outputs found
Pulsating star research and the Gaia revolution
In this article we present an overview of the ESA Gaia mission and of the
unprecedented impact that Gaia will have on the field of variable star
research. We summarise the contents and impact of the first Gaia data release
on the description of variability phenomena, with particular emphasis on
pulsating star research. The Tycho-Gaia astrometric solution, although limited
to 2.1 million stars, has been used in many studies related to pulsating stars.
Furthermore a set of 3,194 Cepheids and RR Lyrae stars with their times series
have been released. Finally we present the plans for the ongoing study of
variable phenomena with Gaia and highlight some of the possible impacts of the
second data release on variable, and specifically, pulsating stars.Comment: 12 pages, 4 figures, proceedings for the 22nd Los Alamos Stellar
Pulsation Conference Series Meeting "Wide field variability surveys: a
21st-century perspective", held in San Pedro de Atacama, Chile, Nov. 28 -
Dec. 2, 201
Large-amplitude variables in Gaia Data Release 2. Multi-band variability characterization
The second data release (DR2) of Gaia provides mean photometry in three bands
for 1.4 billion sources, but light curves and variability properties are
available for only 0.5 million of them. Here, we provide a census of
large-amplitude variables with amplitudes larger than 0.2 mag in the
band for objects with mean brightnesses between 5.5 and 19 mag. To achieve
this, we rely on variability amplitude proxies in , and
computed from the uncertainties on the magnitudes published in DR2. We then
apply successive filters to identify two subsets containing respectively
sources with reliable mean and (for studies using colours)
and sources having compatible amplitude proxies in , and
(for multi-band variability studies). The full catalogue gathers
large-amplitude variable candidates, and the two subsets with increased levels
of purity contain respectively and sources. A
multi-band variability analysis of the catalogue shows that different types of
variable stars can be globally categorized in four groups according to their
colour and blue-to-red amplitude ratios as determined from the ,
and amplitude proxies. The catalogue constitutes the first census of
Gaia large-amplitude variable candidates, extracted from the public DR2
archive. The overview presented here illustrates the added-value of the mission
for multi-band variability studies even at this stage when epoch photometry is
not yet available for all sources. (Abridged abstract)Comment: Final version, A&A, in press. Main text: 20 pages, 26 figures. Four
appendixe
Gaia Data Release 2: Short-timescale variability processing and analysis
The Gaia DR2 sample of short-timescale variable candidates results from the
investigation of the first 22 months of Gaia photometry for a subsample of
sources at the Gaia faint end. For this exercise, we limited ourselves to the
case of suspected rapid periodic variability. Our study combines
fast-variability detection through variogram analysis, high-frequency search by
means of least-squares periodograms, and empirical selection based on the
investigation of specific sources seen through the Gaia eyes (e.g. known
variables or visually identified objects with peculiar features in their light
curves). The progressive definition and validation of this selection criterion
also benefited from supplementary ground-based photometric monitoring of a few
preliminary candidates, performed at the Flemish Mercator telescope (Canary
Islands, Spain) between August and November 2017. We publish a list of 3,018
short-timescale variable candidates, spread throughout the sky, with a
false-positive rate up to 10-20% in the Magellanic Clouds, and a more
significant but justifiable contamination from longer-period variables between
19% and 50%, depending on the area of the sky. Although its completeness is
limited to about 0.05%, this first sample of Gaia short-timescale variables
recovers some very interesting known short-period variables, such as
post-common envelope binaries or cataclysmic variables, and brings to light
some fascinating, newly discovered variable sources. In the perspective of
future Gaia data releases, several improvements of the short-timescale
variability processing are considered, by enhancing the existing variogram and
period-search algorithms or by classifying the identified candidates.
Nonetheless, the encouraging outcome of our Gaia DR2 analysis demonstrates the
power of this mission for such fast-variability studies, and opens great
perspectives for this domain of astrophysics
Gaia Data Release 3. The first Gaia catalogue of eclipsing binary candidates
We present the first Gaia catalogue of eclipsing binary candidates released
in Gaia DR3, describe its content, provide tips for its usage, estimate its
quality, and show illustrative samples. The catalogue contains 2,184,477
sources with G magnitudes up to 20 mag. Candidate selection is based on the
results of variable object classification performed within the Gaia Data
Processing and Analysis Consortium, further filtered using eclipsing
binary-tailored criteria based on the G light curves. To find the orbital
period, a large ensemble of trial periods is first acquired using three
distinct period search methods applied to the cleaned G light curve. The G
light curve is then modelled with up-to two Gaussians and a cosine for each
trial period. The best combination of orbital period and geometric model is
finally selected using Bayesian model comparison based on the BIC. A global
ranking metric is provided to rank the quality of the chosen model between
sources. The catalogue is restricted to orbital periods larger than 0.2 days.
About 530,000 of the candidates are classified as eclipsing binaries in the
literature as well, out of ~600,000 available crossmatches, and 93% of them
have published periods compatible with the Gaia periods. Catalogue completeness
is estimated to be between 25% and 50%, depending on the sky region, relative
to the OGLE4 catalogues of eclipsing binaries towards the Galactic Bulge and
the Magellanic Clouds. The analysis of an illustrative sample of ~400,000
candidates with significant parallaxes shows properties in the observational HR
diagram as expected for eclipsing binaries. The subsequent analysis of a
sub-sample of detached bright candidates provides further hints for the
exploitation of the catalogue. The orbital periods, light curve model
parameters, and global rankings are all published in the catalogue with their
related uncertainties where applicable.Comment: Submitted to A&A. Main text: 23 pages, 35 figures. Four appendices
(17 pages) with 38 figure
The Detection of Transiting Exoplanets by Gaia
Context: The space telescope Gaia is dedicated mainly to performing
high-precision astrometry, but also spectroscopy and epoch photometry which can
be used to study various types of photometric variability. One such variability
type is exoplanetary transits. The photometric data accumulated so far have
finally matured enough to allow the detection of some exoplanets.
Aims: In order to fully exploit the scientific potential of Gaia, we search
its photometric data for the signatures of exoplanetary transits.
Methods: The search relies on a version of the Box-Least-Square (BLS) method,
applied to a set of stars prioritized by machine-learning classification
methods. An independent photometric validation was obtained using the public
full-frame images of TESS. In order to validate the first two candidates,
radial-velocity follow-up observations were performed using the spectrograph
PEPSI of the Large Binocular Telescope (LBT).
Results: The radial-velocity measurements confirm that two of the candidates
are indeed hot Jupiters. Thus, they are the first exoplanets detected by Gaia -
Gaia-1b and Gaia-2b.
Conclusions: Gaia-1b and Gaia-2b demonstrate that the approach presented in
this paper is indeed effective. This approach will be used to assemble a set of
additional exoplanet candidates, to be released in Gaia third data release,
ensuring better fulfillment of the exoplanet detection potential of Gaia.Comment: Accepted for publication in A&A, 8 pages, 8 figure
Gaia Data Release 3: The first Gaia catalogue of variable AGN
One of the novelties of the Gaia-DR3 with respect to the previous data
releases is the publication of the multiband light curves of about 1 million
AGN. The goal of this work was the creation of a catalogue of variable AGN,
whose selection was based on Gaia data only. We first present the
implementation of the methods to estimate the variability parameters into a
specific object study module for AGN. Then we describe the selection procedure
that led to the definition of the high-purity variable AGN sample and analyse
the properties of the selected sources. We started from a sample of millions of
sources, which were identified as AGN candidates by 11 different classifiers
based on variability processing. Because the focus was on the variability
properties, we first defined some pre-requisites in terms of number of data
points and mandatory variability parameters. Then a series of filters was
applied using only Gaia data and the Gaia Celestial Reference Frame 3
(Gaia-CRF3) sample as a reference.The resulting Gaia AGN variable sample, named
GLEAN, contains about 872000 objects, more than 21000 of which are new
identifications. We checked the presence of contaminants by cross-matching the
selected sources with a variety of galaxies and stellar catalogues. The
completeness of GLEAN with respect to the variable AGN in the last Sloan
Digital Sky Survey quasar catalogue is about 47%, while that based on the
variable AGN of the Gaia-CRF3 sample is around 51%. From both a comparison with
other AGN catalogues and an investigation of possible contaminants, we conclude
that purity can be expected to be above 95%. Multiwavelength properties of
these sources are investigated. In particular, we estimate that about 4% of
them are radio-loud. We finally explore the possibility to evaluate the time
lags between the flux variations of the multiple images of strongly lensed
quasars, and show one case.Comment: 19 pages, 31 figures, 2 table. This paper is part of Gaia Data
Release 3 (DR3). In press for A&
Gaia Data Release 2: All-sky classification of high-amplitude pulsating stars
Out of the 1.69 billion sources in the Gaia Data Release 2 (DR2), more than half a million are published with photometric time series that exhibit light variations during 22 months of observation. An all-sky classification of common high-amplitude pulsators (Cepheids, long-period variables, Delta Scuti / SX Phoenicis, and RR Lyrae stars) is provided for stars with brightness variations greater than 0.1 mag in the G band. A semi-supervised classification approach was employed, firstly training multi-stage Random Forest classifiers with sources of known types in the literature, followed by a preliminary classification of the Gaia data and a second training phase that included a selection of the first classification results to improve the representation of some classes, before the application of the improved classifiers to the Gaia data. Dedicated validation classifiers were used to reduce the level of contamination in the published results. A relevant fraction of objects were not yet sufficiently sampled for reliable Fourier series decomposition, so classifiers were based on features derived from statistics of photometric time series in the G, BP, and RP bands, as well as from some astrometric parameters. The published classification results include 195,780 RR Lyrae stars, 150,757 long-period variables, 8550 Cepheids, and 8882 Delta Scuti / SX Phoenicis stars. All of these results represent candidates, whose completeness and contamination are described as a function of variability type and classification reliability. Results are expressed in terms of class labels and classification scores, which are available in the vari_classifier_result table of the Gaia archive
Gaia Data Release 2 Summary of the variability processing and analysis results
Context. The Gaia Data Release 2 (DR2) contains more than half a million sources that are identified as variable stars. Aims. We summarise the processing and results of the identification of variable source candidates of RR Lyrae stars, Cepheids, long-period variables (LPVs), rotation modulation (BY Dra-type) stars, delta Scuti and SX Phoenicis stars, and short-timescale variables. In this release we aim to provide useful but not necessarily complete samples of candidates. Methods. The processed Gaia data consist of the G, G(BP), and G(RP) photometry during the first 22 months of operations as well as positions and parallaxes. Various methods from classical statistics, data mining, and time-series analysis were applied and tailored to the specific properties of Gaia data, as were various visualisation tools to interpret the data. Results. The DR2 variability release contains 228 904 RR Lyrae stars, 11 438 Cepheids, 151 761 LPVs, 147 535 stars with rotation modulation, 8882 delta( )Scuti and SX Phoenicis stars, and 3018 short-timescale variables. These results are distributed over a classification and various Specific Object Studies tables in the Gaia archive, along with the three-band time series and associated statistics for the underlying 550 737 unique sources. We estimate that about half of them are newly identified variables. The variability type completeness varies strongly as a function of sky position as a result of the non-uniform sky coverage and intermediate calibration level of these data. The probabilistic and automated nature of this work implies certain completeness and contamination rates that are quantified so that users can anticipate their effects. This means that even well-known variable sources can be missed or misidentified in the published data. Conclusions. The DR2 variability release only represents a small subset of the processed data. Future releases will include more variable sources and data products; however, DR2 shows the (already) very high quality of the data and great promise for variability studies
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