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See detailVortex Image Processing (VIP) package for high-contrast direct imaging
Gómez González, Carlos ULiege; Absil, Olivier ULiege; Wertz, Olivier ULiege et al

Poster (2016, May 16)

VIP is a Python instrument-agnostic toolbox featuring a flexible framework for reproducible and robust data reduction. VIP currently supports three high-contrast imaging observational techniques: angular ... [more ▼]

VIP is a Python instrument-agnostic toolbox featuring a flexible framework for reproducible and robust data reduction. VIP currently supports three high-contrast imaging observational techniques: angular, reference-star and multi-spectral differential imaging. The code can be downloaded from our git repository on Github: http://github.com/vortex-exoplanet/VIP [less ▲]

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See detailLow-rank plus sparse decomposition for exoplanet detection in direct-imaging ADI sequences. The LLSG algorithm
Gómez González, Carlos ULiege; Absil, Olivier ULiege; Absil, P.-A. et al

in Astronomy and Astrophysics (2016), 589

Context. Data processing constitutes a critical component of high-contrast exoplanet imaging. Its role is almost as important as the choice of a coronagraph or a wavefront control system, and it is ... [more ▼]

Context. Data processing constitutes a critical component of high-contrast exoplanet imaging. Its role is almost as important as the choice of a coronagraph or a wavefront control system, and it is intertwined with the chosen observing strategy. Among the data processing techniques for angular differential imaging (ADI), the most recent is the family of principal component analysis (PCA) based algorithms. It is a widely used statistical tool developed during the first half of the past century. PCA serves, in this case, as a subspace projection technique for constructing a reference point spread function (PSF) that can be subtracted from the science data for boosting the detectability of potential companions present in the data. Unfortunately, when building this reference PSF from the science data itself, PCA comes with certain limitations such as the sensitivity of the lower dimensional orthogonal subspace to non-Gaussian noise. <BR /> Aims: Inspired by recent advances in machine learning algorithms such as robust PCA, we aim to propose a localized subspace projection technique that surpasses current PCA-based post-processing algorithms in terms of the detectability of companions at near real-time speed, a quality that will be useful for future direct imaging surveys. <BR /> Methods: We used randomized low-rank approximation methods recently proposed in the machine learning literature, coupled with entry-wise thresholding to decompose an ADI image sequence locally into low-rank, sparse, and Gaussian noise components (LLSG). This local three-term decomposition separates the starlight and the associated speckle noise from the planetary signal, which mostly remains in the sparse term. We tested the performance of our new algorithm on a long ADI sequence obtained on β Pictoris with VLT/NACO. <BR /> Results: Compared to a standard PCA approach, LLSG decomposition reaches a higher signal-to-noise ratio and has an overall better performance in the receiver operating characteristic space. This three-term decomposition brings a detectability boost compared to the full-frame standard PCA approach, especially in the small inner working angle region where complex speckle noise prevents PCA from discerning true companions from noise. [less ▲]

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See detailErratum to A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry
Arellano Ferro, A.; Bramich, D. M.; Figuera Jaimes, R. et al

in Monthly Notices of the Royal Astronomical Society (2016), 458(2), 1188-1189

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See detailHigh-precision photometry by telescope defocussing - VIII.WASP-22, WASP-41,WASP-42 andWASP-55
Southworth, J.; Tregloan-Reed, J.; Andersen, M. I. et al

in Monthly Notices of the Royal Astronomical Society (2016), 457(4), 4205-4217

We present 13 high-precision and four additional light curves of four bright southernhemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55 ... [more ▼]

We present 13 high-precision and four additional light curves of four bright southernhemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55, these are the first follow-up observations since their discovery papers. We present refined measurements of the physical properties and orbital ephemerides of all four systems. No indications of transit timing variations were seen. All four planets have radii inflated above those expected from theoretical models of gas-giant planets; WASP-55 b is the most discrepant with a mass of 0.63MJup and a radius of 1.34 RJup. WASP-41 shows brightness anomalies during transit due to the planet occulting spots on the stellar surface. Two anomalies observed 3.1 d apart are very likely due to the same spot. We measure its change in position and determine a rotation period for the host star of 18.6 ± 1.5 d, in good agreement with a published measurement from spot-induced brightness modulation, and a sky-projected orbital obliquity of λ = 6 ± 11°. We conclude with a compilation of obliquity measurements from spot-tracking analyses and a discussion of this technique in the study of the orbital configurations of hot Jupiters. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. [less ▲]

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See detailSPITZER PARALLAX of OGLE-2015-BLG-0966: A COLD NEPTUNE in the GALACTIC DISK
Street, R. A.; Udalski, A.; Novati, S. C. et al

in Astrophysical Journal (2016), 819(2),

We report the detection of a cold Neptune mplanet = 21 ± 2 M⊕ orbiting a 0.38 Mo M dwarf lying 2.5-3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations ... [more ▼]

We report the detection of a cold Neptune mplanet = 21 ± 2 M⊕ orbiting a 0.38 Mo M dwarf lying 2.5-3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real-time protocols described by Yee et al., which aim to maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey and follow up teams successfully combined their efforts within the framework of these protocols to detect this planet. This is the second planet in the Spitzer Galactic distribution sample. Both are in the near to mid-disk and are clearly not in the Galactic bulge. © 2016. The American Astronomical Society. All rights reserved. [less ▲]

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See detailSPITZER OBSERVATIONS of OGLE-2015-BLG-1212 REVEAL A NEW PATH TOWARD BREAKING STRONG MICROLENS DEGENERACIES
Bozza, V.; Shvartzvald, Y.; Udalski, A. et al

in Astrophysical Journal (2016), 820(1),

Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively break a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered ... [more ▼]

Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively break a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter space. These models clearly indicate that the lens is a stellar binary system possibly located within the bulge of our Galaxy, ruling out the planetary alternative. We argue that several types of discrete degeneracies can be broken via such space-based parallax observations. © 2016. The American Astronomical Society. All rights reserved.. [less ▲]

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See detailThe XXL Survey: I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme
Pierre, M.; Pacaud, F.; Adami, C. et al

in Astronomy and Astrophysics (2016), 592

Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum ... [more ▼]

Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have supported numerous studies of X-ray-selected clusters of galaxies, active galactic nuclei (AGNs), and the X-ray background. The present paper is the first in a series reporting results of the XXL-XMM survey; it comes at a time when the Planck mission results are being finalised. Aims. We present the XXL Survey, the largest XMM programme totaling some 6.9 Ms to date and involving an international consortium of roughly 100 members. The XXL Survey covers two extragalactic areas of 25 deg2 each at a point-source sensitivity of ∼5 × 10-15 erg s-1 cm-2 in the [0.5-2] keV band (completeness limit). The survey's main goals are to provide constraints on the dark energy equation of state from the space-time distribution of clusters of galaxies and to serve as a pathfinder for future, wide-area X-ray missions. We review science objectives, including cluster studies, AGN evolution, and large-scale structure, that are being conducted with the support of approximately 30 follow-up programmes. Methods. We describe the 542 XMM observations along with the associated multi-λ and numerical simulation programmes. We give a detailed account of the X-ray processing steps and describe innovative tools being developed for the cosmological analysis. Results. The paper provides a thorough evaluation of the X-ray data, including quality controls, photon statistics, exposure and background maps, and sky coverage. Source catalogue construction and multi-λ associations are briefly described. This material will be the basis for the calculation of the cluster and AGN selection functions, critical elements of the cosmological and science analyses. Conclusions. The XXL multi-λ data set will have a unique lasting legacy value for cosmological and extragalactic studies and will serve as a calibration resource for future dark energy studies with clusters and other X-ray selected sources. With the present article, we release the XMM XXL photon and smoothed images along with the corresponding exposure maps. © ESO, 2016. [less ▲]

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See detailPlanet Formation Imager (PFI): Science vision and key requirements
Kraus, S.; Monnier, J. D.; Ireland, M. J. et al

in Proceedings of SPIE (2016)

The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that ... [more ▼]

The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to ∼100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs. © 2016 SPIE. [less ▲]

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See detailErratum: Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry (Astronomy and Astrophysics (2013) 555 (A36))
Kains, N.; Bramich, D. M.; Arellano Ferro, A. et al

in Astronomy and Astrophysics (2016), 588

[No abstract available]

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See detailPhysical properties of the planetary systems WASP-45 and WASP-46 from simultaneous multiband photometry
Ciceri, S.; Mancini, L.; Southworth, J. et al

in Monthly Notices of the Royal Astronomical Society (2016), 456(1), 990-1002

Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large variety ... [more ▼]

Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large variety of exoplanets and planetary-system configurations that have been observed. We present a study of the planetary systemsWASP-45 andWASP-46, both composed of a mainsequence star and a close-in hot Jupiter, based on 29 new high-quality light curves of transits events. In particular, one transit of WASP-45 b and four of WASP-46 b were simultaneously observed in four optical filters, while one transit of WASP-46 b was observed with the NTT obtaining a precision of 0.30 mmag with a cadence of roughly 3 min. We also obtained five new spectra of WASP-45 with the FEROS spectrograph. We improved by a factor of 4 the measurement of the radius of the planet WASP-45 b, and found that WASP-46 b is slightly less massive and smaller than previously reported. Both planets now have a more accurate measurement of the density (0.959 ± 0.077 ρJup instead of 0.64 ± 0.30 ρJup for WASP-45 b, and 1.103 ± 0.052 ρJup instead of 0.94 ± 0.11 ρJup for WASP-46 b). We tentatively detected radius variations with wavelength for both planets, in particular in the case of WASP-45 b we found a slightly larger absorption in the redder bands than in the bluer ones. No hints for the presence of an additional planetary companion in the two systems were found either from the photometric or radial velocity measurements. © 2015 The Authors. [less ▲]

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See detailThe XXL Survey XIV. AAOmega Redshifts for the Southern XXL Field
Lidman, C.; Ardila, F.; Owers, M. et al

in Publications of the Astronomical Society of Australia (2016), 33

We present a catalogue containing the redshifts of 3 660 X-ray selected targets in the XXL southern field. The redshifts were obtained with the AAOmega spectrograph and 2dF fibre positioner on the Anglo ... [more ▼]

We present a catalogue containing the redshifts of 3 660 X-ray selected targets in the XXL southern field. The redshifts were obtained with the AAOmega spectrograph and 2dF fibre positioner on the Anglo-Australian Telescope. The catalogue contains 1 515 broad line AGN, 528 stars, and redshifts for 41 out of the 49 brightest X-ray selected clusters in the XXL southern field. Copyright © Astronomical Society of Australia 2016. [less ▲]

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See detailThe XXL Survey: XII. Optical spectroscopy of X-ray-selected clusters and the frequency of AGN in superclusters
Koulouridis, E.; Poggianti, B.; Altieri, B. et al

in Astronomy and Astrophysics (2016), 592

Context. This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg2 fields in the XXL Survey, which were selected on the basis of ... [more ▼]

Context. This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg2 fields in the XXL Survey, which were selected on the basis of their high density of X-ray-detected clusters. The observations were obtained with the AutoFib2+WYFFOS (AF2) wide-field fibre spectrograph mounted on the 4.2 m William Herschel Telescope. Aims. The paper first describes the scientific rationale, the preparation, the data reduction, and the results of the observations, and then presents a study of active galactic nuclei (AGN) within three superclusters. Methods. To determine the redshift of galaxy clusters and AGN, we assign high priority to a) the brightest cluster galaxies (BCGs), b) the most probable cluster galaxy candidates, and c) the optical counterparts of X-ray point-like sources. We use the outcome of the observations to study the projected (2D) and the spatial (3D) overdensity of AGN in three superclusters. Results. We obtained redshifts for 455 galaxies in total, 56 of which are counterparts of X-ray point-like sources. We were able to determine the redshift of the merging supercluster XLSSC-e, which consists of six individual clusters at z ~ 0.43, and we confirmed the redshift of supercluster XLSSC-d at z ~ 0.3. More importantly, we discovered a new supercluster, XLSSC-f, that comprises three galaxy clusters also at z ~ 0.3. We find a significant 2D overdensity of X-ray point-like sources only around the supercluster XLSSC-f. This result is also supported by the spatial (3D) analysis of XLSSC-f, where we find four AGN with compatible spectroscopic redshifts and possibly one more with compatible photometric redshift. In addition, we find two AGN (3D analysis) at the redshift of XLSSC-e, but no AGN in XLSSC-d. Comparing these findings with the optical galaxy overdensity we conclude that the total number of AGN in the area of the three superclusters significantly exceeds the field expectations. All of the AGN found have luminosities below 7 × 1042 erg s-1. Conclusions. The difference in the AGN frequency between the three superclusters cannot be explained by the present study because of small number statistics. Further analysis of a larger number of superclusters within the 50 deg2 of the XXL is needed before any conclusions on the effect of the supercluster environment on AGN can be reached. © ESO, 2016. [less ▲]

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See detailGravitational microlensing as a probe for dark matter clumps
Fedorova, E.; Sliusar, V. M.; Zhdanov, V. I. et al

in Monthly Notices of the Royal Astronomical Society (2016), 457(4), 4147-4159

Extended dark matter (DM) substructures may play the role of microlenses in the Milky Way and in extragalactic gravitational lens systems (GLSs).We compare microlensing effects caused by point masses ... [more ▼]

Extended dark matter (DM) substructures may play the role of microlenses in the Milky Way and in extragalactic gravitational lens systems (GLSs).We compare microlensing effects caused by point masses (Schwarzschild lenses) and extended clumps of matter using a simple model for the lens mapping. A superposition of the point mass and the extended clump is also considered. For special choices of the parameters, this model may represent a cusped clump of coldDM, a cored clump of self-interacting darkmatter (SIDM) or an ultra-compact minihalo of DMsurrounding a massive point-like object.We built the resulting micro-amplification curves for various parameters of one clump moving with respect to the source in order to estimate differences between the light curves caused by clumps and by point lenses. The results show that it may be difficult to distinguish between thesemodels. However, some region of the clump parameters can be restricted by considering the high amplification events at the present level of photometric accuracy. Then we estimate the statistical properties of the amplification curves in extragalactic GLSs. For this purpose, an ensemble of amplification curves is generated yielding the autocorrelation functions (ACFs) of the curves for different choices of the system parameters.We find that there can be a significant difference between these ACFs if the clump size is comparable with typical Einstein radii; as a rule, the contribution of clumps makes the ACFs less steep. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. [less ▲]

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See detailExploring the crowded central region of ten Galactic globular clusters using EMCCDs: Variable star searches and new discoveries
Figuera Jaimes, R.; Bramich, D. M.; Skottfelt, J. et al

in Astronomy and Astrophysics (2016), 588

Aims. We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs ... [more ▼]

Aims. We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. Methods. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. Results. The light curves of 12 541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center. © ESO, 2016. [less ▲]

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See detailHigh-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP): I. Lucky imaging observations of 101 systems in the southern hemisphere
Evans, D. F.; Southworth, J.; Maxted, P. F. L. et al

in Astronomy and Astrophysics (2016), 589

Context. Wide binaries are a potential pathway for the formation of hot Jupiters. The binary fraction among host stars is an important discriminator between competing formation theories, but has not been ... [more ▼]

Context. Wide binaries are a potential pathway for the formation of hot Jupiters. The binary fraction among host stars is an important discriminator between competing formation theories, but has not been well characterised. Additionally, contaminating light from unresolved stars can significantly affect the accuracy of photometric and spectroscopic measurements in studies of transiting exoplanets. Aims. We observed 101 transiting exoplanet host systems in the Southern hemisphere in order to create a homogeneous catalogue of both bound companion stars and contaminating background stars, in an area of the sky where transiting exoplanetary systems have not been systematically searched for stellar companions. We investigate the binary fraction among the host stars in order to test theories for the formation of hot Jupiters. Methods. Lucky imaging observations from the Two Colour Instrument on the Danish 1.54 m telescope at La Silla were used to search for previously unresolved stars at small angular separations. The separations and relative magnitudes of all detected stars were measured. For 12 candidate companions to 10 host stars, previous astrometric measurements were used to evaluate how likely the companions are to be physically associated. Results. We provide measurements of 499 candidate companions within 20 arcsec of our sample of 101 planet host stars. 51 candidates are located within 5 arcsec of a host star, and we provide the first published measurements for 27 of these. Calibrations for the plate scale and colour performance of the Two Colour Instrument are presented. Conclusions. We find that the overall multiplicity rate of the host stars is 38-13 +17%, consistent with the rate among solar-type stars in our sensitivity range, suggesting that planet formation does not preferentially occur in long period binaries compared to a random sample of field stars. Long period stellar companions (P > 10 yr) appear to occur independently of short period companions, and so the population of close-in stellar companions is unconstrained by our study. © ESO, 2016. [less ▲]

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See detailTHE SPITZER MICROLENSING PROGRAM AS A PROBE for GLOBULAR CLUSTER PLANETS: ANALYSIS of OGLE-2015-BLG-0448
Poleski, R.; Zhu, W.; Christie, G. W. et al

in Astrophysical Journal (2016), 823(1),

The microlensing event OGLE-2015-BLG-0448 was observed by Spitzer and lay within the tidal radius of the globular cluster NGC 6558. The event had moderate magnification and was intensively observed, hence ... [more ▼]

The microlensing event OGLE-2015-BLG-0448 was observed by Spitzer and lay within the tidal radius of the globular cluster NGC 6558. The event had moderate magnification and was intensively observed, hence it had the potential to probe the distribution of planets in globular clusters. We measure the proper motion of NGC 6558 ((μcl (N, E) = +0.36 ± 0.10, +1.42 ± 0.10 mas yr-1) as well as the source and show that the lens is not a cluster member. Even though this particular event does not probe the distribution of planets in globular clusters, other potential cluster lens events can be verified using our methodology. Additionally, we find that microlens parallax measured using Optical Gravitational Lens Experiment (OGLE) photometry is consistent with the value found based on the light curve displacement between the Earth and Spitzer. © 2016. The American Astronomical Society. All rights reserved. [less ▲]

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See detailMultiply imaged quasi-stellar objects in the Gaia survey
Finet, F.; Surdej, Jean ULiege

in Astronomy and Astrophysics (2016), 590

Aims. We report a study on the statistical properties of the multiply imaged quasi-stellar objects (QSOs) to be detected within the Gaia survey. Methods. We considered two types of potential deflectors ... [more ▼]

Aims. We report a study on the statistical properties of the multiply imaged quasi-stellar objects (QSOs) to be detected within the Gaia survey. Methods. We considered two types of potential deflectors, the singular isothermal sphere (SIS) and the singular isothermal ellipsoid (SIE), to estimate the number of multiply imaged quasars as well as the normalized distributions of the redshifts of the lensed sources and of their associated deflectors. We also investigated the distribution of the lensing events as a function of their angular size and apparent magnitude. We compared the Gaia survey for multiply imaged quasars to typical ground-based surveys and to an ideal survey that would be carried out with a perfect instrument from space. Results. Of the 6.64 × 105 QSOs brighter than G = 20 to be detected by Gaia, we expect the discovery of about 2886 multiply imaged sources, 450 of which are expected to be produced by a late-type galaxy. We expect only ∼1600 of these multiply imaged quasars to have an angular separation between their images that is large enough to be resolved from seeing-limited observations, and ∼80 of them to have more than two lensed images. © ESO, 2016. [less ▲]

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See detailMASS MEASUREMENTS of ISOLATED OBJECTS from SPACE-BASED MICROLENSING
Zhu, W.; Calchi Novati, S.; Gould, A. et al

in Astrophysical Journal (2016), 825(1),

We report on the mass and distance measurements of two single-lens events from the 2015 Spitzer microlensing campaign. With both finite-source effect and microlens parallax measurements, we find that the ... [more ▼]

We report on the mass and distance measurements of two single-lens events from the 2015 Spitzer microlensing campaign. With both finite-source effect and microlens parallax measurements, we find that the lens of OGLE-2015-BLG-1268 is very likely a brown dwarf (BD). Assuming that the source star lies behind the same amount of dust as the Bulge red clump, we find the lens is a 45 ±7 BD at 5.9 ±1.0 kpc. The lens of of the second event, OGLE-2015-BLG-0763, is a 0.50 ±0.04 star at 6.9 ±1.0 kpc. We show that the probability to definitively measure the mass of isolated microlenses is dramatically increased once simultaneous ground- and space-based observations are conducted. © 2016. The American Astronomical Society. All rights reserved. [less ▲]

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See detailMany new variable stars discovered in the core of the globular cluster NGC 6715 (M 54) with EMCCD observations
Figuera Jaimes, R.; Bramich, D. M.; Kains, N. et al

in Astronomy and Astrophysics (2016), 592

Context. We show the benefits of using electron-multiplying CCDs and the shift-and-add technique as a tool to minimise the effects of atmospheric turbulence, such as blending between stars in crowded ... [more ▼]

Context. We show the benefits of using electron-multiplying CCDs and the shift-and-add technique as a tool to minimise the effects of atmospheric turbulence, such as blending between stars in crowded fields, and to avoid saturated stars in the fields observed. We intend to complete, or improve on, the census of the variable star population in globular cluster NGC 6715. Aims. Our aim is to obtain high-precision time-series photometry of the very crowded central region of this stellar system via the collection of better angular resolution images than has been previously achieved with conventional CCDs on ground-based telescopes. Methods. Observations were carried out using the Danish 1.54-m telescope at the ESO La Silla observatory in Chile. The telescope is equipped with an electron-multiplying CCD that enables short-exposure-time images to be obtained (ten images per second) that were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). The high precision photometry was performed via difference image analysis employing the DanDIA pipeline. We attempted automatic detection of variable stars in the field. Results. We statistically analysed the light curves of 1405 stars in the crowded central region of NGC 6715 to automatically identify the variable stars present in this cluster. We found light curves for 17 previously known variable stars near the edges of our reference image (16 RR Lyrae and 1 semi-regular) and we discovered 67 new variables (30 RR Lyrae, 21 irregular (long-period type), 3 semi-regular, 1 W Virginis, 1 eclipsing binary, and 11 unclassified). Photometric measurements for these stars are available in electronic form through the Strasbourg Astronomical Data Centre. © 2016 ESO. [less ▲]

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See detailOGLE-2015-BLG-0479LA,B: BINARY GRAVITATIONAL MICROLENS CHARACTERIZED by SIMULTANEOUS GROUND-BASED and SPACE-BASED OBSERVATIONS
Han, C.; Udalski, A.; Gould, A. et al

in Astrophysical Journal (2016), 828(1),

We present a combined analysis of the observations of the gravitational microlensing event OGLE-2015-BLG-0479 taken both from the ground and by the Spitzer Space Telescope. The light curves seen from the ... [more ▼]

We present a combined analysis of the observations of the gravitational microlensing event OGLE-2015-BLG-0479 taken both from the ground and by the Spitzer Space Telescope. The light curves seen from the ground and from space exhibit a time offset of ∼13 days between the caustic spikes, indicating that the relative lens-source positions seen from the two places are displaced by parallax effects. From modeling the light curves, we measure the space-based microlens parallax. Combined with the angular Einstein radius measured by analyzing the caustic crossings, we determine the mass and distance of the lens. We find that the lens is a binary composed of two G-type stars with masses of ∼1.0 M⊙ and ∼0.9 M⊙ located at a distance of ∼3 kpc. In addition, we are able to constrain the complete orbital parameters of the lens thanks to the precise measurement of the microlens parallax derived from the joint analysis. In contrast to the binary event OGLE-2014-BLG-1050, which was also observed by Spitzer, we find that the interpretation of OGLE-2015-BLG-0479 does not suffer from the degeneracy between (±, ±) and (±, ∓) solutions, confirming that the four-fold parallax degeneracy in single-lens events collapses into the two-fold degeneracy for the general case of binary-lens events. The location of the blend in the color-magnitude diagram is consistent with the lens properties, suggesting that the blend is the lens itself. The blend is bright enough for spectroscopy and thus this possibility can be checked from future follow-up observations. © 2016. The American Astronomical Society. All rights reserved. [less ▲]

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