References of "von Essen, C"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailGaia Data Release 2. The celestial reference frame (Gaia-CRF2)
Gaia Collaboration; Mignard, F.; Klioner, S. A. et al

in Astronomy and Astrophysics (2018), 616(A), 14

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical ... [more ▼]

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. <BR /> Aims: We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. <BR /> Methods: Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. <BR /> Results: Gaia-CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ≃ 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = mag. Large- scale systematics are estimated to be in the range 20 to 30 μas. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. <BR /> Conclusions: Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator. [less ▲]

Detailed reference viewed: 30 (3 ULiège)
Full Text
Peer Reviewed
See detailGaia Data Release 2. Observations of solar system objects
Gaia Collaboration; Spoto, F.; Tanga, P. et al

in Astronomy and Astrophysics (2018), 616(A), 13

Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the ... [more ▼]

Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. <BR /> Aims: We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. <BR /> Methods: To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). <BR /> Results: The overall astrometric performance is close to the expectations, with an optimal range of brightness G 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects. [less ▲]

Detailed reference viewed: 28 (4 ULiège)
Full Text
Peer Reviewed
See detailGaia Data Release 2. Kinematics of globular clusters and dwarf galaxies around the Milky Way
Gaia Collaboration; Helmi, A.; van Leeuwen, F. et al

in Astronomy and Astrophysics (2018), 616(A), 12

Context. <BR /> Aims: The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics ... [more ▼]

Context. <BR /> Aims: The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. <BR /> Methods: Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. <BR /> Results: Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.1[SUB]-2.6[/SUB][SUP]+6.2[/SUP] × 10[SUP]11[/SUP] M[SUB]☉[/SUB] based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. <BR /> Conclusions: All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release. Full Table D.3 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://cdsarc.u-strasbg.fr">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/616/A12">http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/616/A12</A> [less ▲]

Detailed reference viewed: 30 (3 ULiège)
Full Text
Peer Reviewed
See detailGaia Data Release 2. Mapping the Milky Way disc kinematics
Gaia Collaboration; Katz, D.; Antoja, T. et al

in Astronomy and Astrophysics (2018), 616(A), 11

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars ... [more ▼]

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G[SUB]RVS[/SUB] = 12 mag. Both samples provide a full sky coverage. <BR /> Aims: To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. <BR /> Methods: We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (σ[SUB]ϖ[/SUB]/ϖ ≤ 20%), and precise Galactic cylindrical velocities (median uncertainties of 0.9-1.4 km s[SUP]-1[/SUP] and 20% of the stars with uncertainties smaller than 1 km s[SUP]-1[/SUP] on all three components). From this sample, we extracted a sub-sample of 3.2 million giant stars to map the velocity field of the Galactic disc from 5 kpc to 13 kpc from the Galactic centre and up to 2 kpc above and below the plane. We also study the distribution of 0.3 million solar neighbourhood stars (r < 200 pc), with median velocity uncertainties of 0.4 km s[SUP]-1[/SUP], in velocity space and use the full sample to examine how the over-densities evolve in more distant regions. <BR /> Results: Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. <BR /> Conclusions: Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non- axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential. [less ▲]

Detailed reference viewed: 27 (5 ULiège)
Full Text
Peer Reviewed
See detailGaia Data Release 2. Observational Hertzsprung-Russell diagrams
Gaia Collaboration; Babusiaux, C.; van Leeuwen, F. et al

in Astronomy and Astrophysics (2018), 616(A), 10

Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and ... [more ▼]

Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented. <BR /> Aims: We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. <BR /> Methods: We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. <BR /> Results: The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. <BR /> Conclusions: Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD- based studies. The full Table A.1 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://cdsarc.u-strasbg.fr">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/616/A10">http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/616/A10</A> [less ▲]

Detailed reference viewed: 23 (3 ULiège)
Full Text
Peer Reviewed
See detailGaia Data Release 2. Summary of the contents and survey properties
Gaia Collaboration; Brown, A. G. A.; Vallenari, A. et al

in Astronomy and Astrophysics (2018), 616(A1), 1-22

Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than ... [more ▼]

Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. <BR /> Aims: A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. <BR /> Methods: The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. <BR /> Results: Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G[SUB]BP[/SUB] (330-680 nm) and G[SUB]RP[/SUB] (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. <BR /> Conclusions: Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy. [less ▲]

Detailed reference viewed: 43 (6 ULiège)
Full Text
See detailVizieR Online Data Catalog: WASP-22, WASP-41, WASP-42, WASP-55 (Southworth+, 2016)
Southworth, J.; Tregloan-Reed, J.; Andersen, M. I. et al

in Monthly Notices of the Royal Astronomical Society (2018), 745

17 light curves of transits of the extrasolar planetary systems WASP-22, WASP-41, WASP-42 and WASP-55 are presented. 13 of the light curves were obtained using the Danish 1.54m telescope at ESO La Silla ... [more ▼]

17 light curves of transits of the extrasolar planetary systems WASP-22, WASP-41, WASP-42 and WASP-55 are presented. 13 of the light curves were obtained using the Danish 1.54m telescope at ESO La Silla, Chile, in the Bessell R or Bessell I passbands. The other 4 light curves were obtained using the 84cm telescope at Observatorio Cerro Armazones, Chile, using either an R filter or no filter. The errorbars for each transit have been scaled so the best-fitting model (obtained using the JKTEBOP code) has a reduced chi-squared value of 1.0. (4 data files). [less ▲]

Detailed reference viewed: 16 (1 ULiège)
Full Text
Peer Reviewed
See detailHigh-resolution imaging of transiting extrasolar planetary systems (HITEP) II. Lucky imaging results from 2015 and 2016
Evans, D. F.; Southworth, J.; Smalley, B. et al

in Astronomy and Astrophysics (2018), 610

Context. The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from ... [more ▼]

Context. The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from both binary companions and unassociated stars can significantly bias the results of planet characterisation studies, but can be corrected for if the properties of the contaminating star are known. Aims. We search for binary companions to known transiting exoplanet host stars, in order to determine the multiplicity properties of hot Jupiter host stars. We also search for and characterise unassociated stars along the line of sight, allowing photometric and spectroscopic observations of the planetary system to be corrected for contaminating light. Methods. We analyse lucky imaging observations of 97 Southern hemisphere exoplanet host stars, using the Two Colour Instrument on the Danish 1.54 m telescope. For each detected companion star, we determine flux ratios relative to the planet host star in two passbands, and measure the relative position of the companion. The probability of each companion being physically associated was determined using our two-colour photometry. Results. A catalogue of close companion stars is presented, including flux ratios, position measurements, and estimated companion star temperature. For companions that are potential binary companions, we review archival and catalogue data for further evidence. For WASP-77AB and WASP-85AB, we combine our data with historical measurements to determine the binary orbits, showing them to be moderately eccentric and inclined to the line of sight (and hence planetary orbital axis). Combining our survey with the similar Friends of Hot Jupiters survey, we conclude that known hot Jupiter host stars show a deficit of high mass stellar companions compared to the field star population; however, this may be a result of the biases in detection and target selection by ground-based surveys. ©ESO 2018. [less ▲]

Detailed reference viewed: 21 (1 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 29 (1 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 37 (1 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 43 (1 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 15 (0 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 15 (1 ULiège)
Full Text
Peer Reviewed
See detailHigh-precision photometry by telescope defocusing - VII. The ultrashort period planet WASP-103
Southworth, J.; Mancini, L.; Ciceri, S. et al

in Monthly Notices of the Royal Astronomical Society (2014), 447(1), 711-721

We present 17 transit light curves of the ultrashort period planetary system WASP-103, a strong candidate for the detection of tidally-induced orbital decay. We use these to establish a high-precision ... [more ▼]

We present 17 transit light curves of the ultrashort period planetary system WASP-103, a strong candidate for the detection of tidally-induced orbital decay. We use these to establish a high-precision reference epoch for transit timing studies. The time of the reference transit mid-point is now measured to an accuracy of 4.8 s, versus 67.4 s in the discovery paper, aiding future searches for orbital decay. With the help of published spectroscopic measurements and theoretical stellar models, we determine the physical properties of the system to high precision and present a detailed error budget for these calculations. The planet has a Roche lobe filling factor of 0.58, leading to a significant asphericity; we correct its measured mass and mean density for this phenomenon. A high-resolution Lucky Imaging observation shows no evidence for faint stars close enough to contaminate the point spread function of WASP-103. Our data were obtained in the Bessell RI and the SDSS griz passbands and yield a larger planet radius at bluer optical wavelengths, to a confidence level of 7.3σ. Interpreting this as an effect of Rayleigh scattering in the planetary atmosphere leads to a measurement of the planetary mass which is too small by a factor of 5, implying that Rayleigh scattering is not the main cause of the variation of radius with wavelength. © 2014 The Authors. [less ▲]

Detailed reference viewed: 36 (1 ULiège)