ABSTRACT
We present photometric observations of four transits in the WASP‐17 planetary system, obtained using telescope defocusing techniques and with scatters reaching 0.5 mmag per point. Our ...revised orbital period is 4.0 ± 0.6 s longer than previous measurements, a difference of 6.6σ, and does not support the published detections of orbital eccentricity in this system. We model the light curves using the jktebop code and calculate the physical properties of the system by recourse to five sets of theoretical stellar model predictions. The resulting planetary radius, Rb = 1.932 ± 0.052 ± 0.010 RJup (statistical and systematic errors, respectively), provides confirmation that WASP‐17 b is the largest planet currently known. All 14 planets with radii measured to be greater than 1.6 RJup are found around comparatively hot (Teff > 5900 K) and massive (MA > 1.15 M⊙) stars. Chromospheric activity indicators are available for eight of these stars, and all imply a low activity level. The planets have small or zero orbital eccentricities, so tidal effects struggle to explain their large radii. The observed dearth of large planets around small stars may be natural but could also be due to observational biases against deep transits, if these are mistakenly labelled as false positives and so not followed up.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven ...groups/clusters at z∼ 0.35, we have measured the blue fraction from the cluster core to the cluster outskirts and the field mainly using wide-field Cerro Tololo Inter-American Observatory images. This sample represents a random selection of a volume complete X-ray selected cluster sample, selected so that there is no physical connection with the studied quantity (blue fraction), to minimize observational biases. In order to statistically assess the significance of the Butcher-Oemler effect, we introduce the tools of Bayesian inference. Furthermore, we have modified the blue fraction definition in order to take into account the reduced age of the Universe at higher redshifts, because we should no longer attempt to reject an unphysical universe in which the age of the Universe does depend on redshift, whereas the age of its content does not. We have measured the blue fraction from the cluster centre to the field and we find that the cluster affects the properties of the galaxies up to two virial radii at z∼ 0.35. Data suggest that during the last 3 Gyr no evolution of the blue fraction, from the cluster core to the field value, is seen beyond that needed to account for the varying age with the redshift of the Universe and of its content. The agreement of the radial profiles of the blue fraction at z= 0 and z∼ 0.35 implies that the pattern infall did not change over the last 3 Gyr, or, at least, its variation has no observational effect on the studied quantity.
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Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the electron multiplying CCD (EMCCD) camera at the ...Danish 1.54 m Telescope at La Silla, Chile. The two variableswere not previously detected by conventional CCD imaging because of their proximity to a bright star. This discovery demonstrates that EMCCDs are a powerful tool for performing high-precision time-series photometry in crowded fields and near bright stars, especially when combined with difference image analysis.
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We present the first high-precision photometry of the transiting extrasolar planetary system WASP-7, obtained using telescope defocussing techniques and reaching a scatter of 0.68 mmag per point. We ...find that the transit depth is greater and that the host star is more evolved than previously thought. The planet has a significantly larger radius (1.330 ± 0.093 RJup versus $\er{0.915}{0.046}{0.040}$ 0.91 5 -0.040 + 0.046 RJup) and much lower density (0.41 ± 0.10 ρJup versus $\er{1.26}{0.25}{0.21}$ 1.2 6 -0.21 + 0.25 ρJup) and surface gravity (13.4 ± 2.6 m s-2 versus $\er{26.4}{4.4}{4.0}$ 26. 4 -4.0 + 4.4 m s-2) than previous measurements showed. Based on the revised properties it is no longer an outlier in planetary mass-radius and period-gravity diagrams. We also obtain a more precise transit ephemeris for the WASP-7 system.
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Aims. We propose a method based on the Principal Component Analysis (PCA) to classify and estimate the redshift of an extinction law in a distant gravitational lens galaxy. Such extinction laws are ...very poorly known and an efficient method to characterize them is badly needed. Methods. We first compute the principal axes of an exhaustive collection of redshifted theoretical extinction laws. Then, we project on these new axes the extinction law we wish to classify. The position of its projection among those redshifted extinction laws from the collection allows us to characterize it and to estimate its redshift. Results. Monte Carlo simulations show that the method is efficient and relatively precise for reasonably good signal-to-noise ratio data. The application of the method to a real case, the gravitational lens system SBS 0909+532, leads to very encouraging results.
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We present the XMM Large-Scale Structure Survey (XMM-LSS) cluster catalogue corresponding to the Canada–France–Hawaii Telescope Legacy Survey D1 area. The list contains 13 spectroscopically ...confirmed, X-ray selected galaxy clusters over 0.8 deg2 to a redshift of unity and so constitutes the highest density sample of clusters to date. Cluster X-ray bolometric luminosities range from 0.03 to 5 × 1044 erg s−1. In this study, we describe our catalogue construction procedure: from the detection of X-ray cluster candidates to the compilation of a spectroscopically confirmed cluster sample with an explicit selection function. The procedure further provides basic X-ray products such as cluster temperature, flux and luminosity. We detected slightly more clusters with (0.5–2.0 keV) X-ray fluxes of >2 × 10−14 erg s−1 cm−2 than we expected based on expectations from deep ROSAT surveys. We also present the luminosity–temperature relation for our nine brightest objects possessing a reliable temperature determination. The slope is in good agreement with the local relation, yet compatible with a luminosity enhancement for the 0.15 < z < 0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying systematically for the first time. The present study permits the compilation of cluster samples from XMM images whose selection biases are understood. This allows, in addition to studies of large-scale structure, the systematic investigation of cluster scaling law evolution, especially for low mass X-ray groups which constitute the bulk of our observed cluster population. All cluster ancillary data (images, profiles, spectra) are made available in electronic form via the XMM-LSS cluster data base.
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Aims. Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X- ray flux, luminosity and redshift within a hard X-ray ...selected sample with wide multiwavelength coverage. Methods. We selected a sample of 136 X-ray sources detected at a significance of \geq3 \sigma in the 2-10 keV band ( F sub(2-10) \ga 10 super(-14) erg cm super(-2) s super(-1)) in a similar to 1 deg super(2) area in the XMM Medium Deep Survey (XMDS). The XMDS area is covered with optical photometry from the VVDS and CFHTLS surveys and infrared Spitzer data from the SWIRE survey. Based on the X-ray luminosity and X-ray to optical ratio, 132 sources are likely AGN, of which 122 have unambiguous optical-IR identification. The observed optical and IR spectral energy distributions of all identified sources are fitted with AGN/galaxy templates in order to classify them and compute photometric redshifts. X-ray spectral analysis is performed individually for sources with a sufficient number of counts and using a stacking technique for subsamples of sources at different flux levels. Hardness ratios are used to estimate X-ray absorption in individual weak sources. Results. 70% of the AGN are fitted by a type 2 AGN or a star forming galaxy template. We group them together in a single class of "optically obscured" AGN. These have "red" optical colors and in about 60% of cases show significant X-ray absorption (N_{\rm H} > 10 super(22) cm super(-2)). Sources with SEDs typical of type 1 AGN have "blue" optical colors and exhibit X-ray absorption in about 30% of cases. The stacked X-ray spectrum of obscured AGN is flatter than that of type 1 AGN and has an average spectral slope of \Gamma = 1.6. The subsample of objects fitted by a star forming galaxy template has an even harder stacked spectrum, with \Gamma \sim 1.2- 1.3. The obscured fraction is larger at lower fluxes, lower redshifts and lower luminosities. X-ray absorption is less common than "optical" obscuration and its incidence is nearly constant with redshift and luminosity. This implies that at high luminosities X-ray absorption is not necessarily related to optical obscuration. The estimated surface densities of obscured, unobscured AGN and type 2 QSOs are respectively 138, 59 and 35 deg super(-2) at 10 logical and --> F > 10 super(-14) erg cm super(-2) s super(-1).
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Aims.Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. Methods.We present a ...sample of 99 spectroscopically identified (R ≤ 22 mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (≥3σ) in the 2-10 keV band with fluxes between 8 $\times$ 10-15 and 8 $\times$ 10-14 erg s-1 cm-2, and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme. Results.Introducing the fourfold point correlation coefficient r, we find a mild correlation between the X-ray and the optical classifications (r = 0.28), as up to 32 X-ray sources out of 99 have differing X-ray and optical classifications: on one hand, 10% of the type 1 sources (7/32) present broad emission lines in their optical spectra and strong absorption (N$_{{\rm H}}$$^{{\rm int}}$ ≥ 1022 cm-2) in the X-rays. These objects are highly luminous AGN lying at high redshift and thus dilution effects by the host galaxy light are totally ruled out, their discrepant nature being an intrinsic property instead. Their X-ray luminosities and redshifts distributions are consistent with those of the unabsorbed X-ray sources with broad emission lines (L2-10 ~ 4 $\times$ 1044 erg s-1; z ~ 1.9). On the other hand, 25/32 are moderate luminosity (L2-10 ≤ 5 $\times$ 1043 erg s-1) AGN, which are both unabsorbed in the X-rays and only present narrow emission lines in their optical spectra. Based on their line ratios in the optical, the majority of them have an optical spectrum which is more representative of the host galaxy rather than of a reddened AGN. We finally infer that dilution of the AGN by the host galaxy seems to account for their nature. 5/25 have been defined as Seyfert 2 based on their optical spectra. In conclusion, most of these 32 discrepant cases can be accounted for by the standard AGN unified scheme, as its predictions are not met for only 12% of the 99 X-ray sources.
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Multiply imaged quasars in the Gaia DR1 Ducourant, C.; Delchambre, L.; Finet, F. ...
Proceedings of the International Astronomical Union,
04/2017, Volume:
12, Issue:
S330
Journal Article
Peer reviewed
Open access
Because of to its exceptional resolving power, Gaia should detect a few thousands gravitational lensed systems. These consist in multiple images of background quasars. The estimated number of lens ...phenomena in the sky, however, depends on the cosmological model considered. By taking into account the observational bias that will restrict the detection of lensed quasars, identification of these up to a given limiting magnitude will constrain the cosmological parameters. We have investigated the known gravitationally lensed quasars present in the Gaia DR1, and found that a significant number of components of these systems have been measured and are present in the Gaia DR1 catalogue although quasi none of them have all their components detected. We additionally examined the immediate surroundings of QSOs from the large Quasar catalogue, LQAC3, and detected several configurations compatible with gravitational lensing phenomena. A more global strategy to systematically detect the potential candidates in the various releases of the Gaia catalogue is presented.
Gaia GraL: Gaia DR2 Gravitational Lens Systems Delchambre, L.; Krone-Martins, A.; Wertz, O. ...
Astronomy and astrophysics (Berlin),
02/2019, Volume:
622, Issue:
622
Journal Article, Web Resource
Peer reviewed
Open access
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.
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