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A giant planet beyond the snow line in microlensing event OGLE-2011-BLG-0251
Kains, N.,Street, R. A.,Choi, J.-Y.,Han, C.,Udalski, A.,Almeida, L. A.,Jablonski, F.,Tristram, P. J.,Jørgensen, U. G.,Szymań,ski, M. K.,Kubiak, M.,Pietrzyń,ski, G.,Soszyń,ski, I.,Polesk EDP Sciences 2013 Astronomy and astrophysics Vol.552 No.-
A census of variability in globular cluster M 68 (NGC 4590)
Kains, N.,Arellano Ferro, A.,Figuera Jaimes, R.,Bramich, D. M.,Skottfelt, J.,Jørgensen, U. G.,Tsapras, Y.,Street, R. A.,Browne, P.,Dominik, M.,Horne, K.,Hundertmark, M.,Ipatov, S.,Snodgrass, C.,Steele EDP Sciences 2015 Astronomy and astrophysics Vol.578 No.-
<P>Aims. We analyse 20 nights of CCD observations in the V and I bands of the globular cluster M?68 (NGC 4590) and use them to detect variable objects. We also obtained electron-multiplying CCD (EMCCD) observations for this cluster in order to explore its core with unprecedented spatial resolution from the ground. Methods. We reduced our data using difference image analysis to achieve the best possible photometry in the crowded field of the cluster. In doing so, we show that when dealing with identical networked telescopes, a reference image from any telescope may be used to reduce data from any other telescope, which facilitates the analysis significantly. We then used our light curves to estimate the properties of the RR Lyrae (RRL) stars in M?68 through Fourier decomposition and empirical relations. The variable star properties then allowed us to derive the cluster’s metallicity and distance. Results. M?68 had 45 previously confirmed variables, including 42 RRL and 2 SX Phoenicis (SX Phe) stars. In this paper we determine new periods and search for new variables, especially in the core of the cluster where our method performs particularly well. We detect 4 additional SX Phe stars and confirm the variability of another star, bringing the total number of confirmed variable stars in this cluster to 50. We also used archival data stretching back to 1951 to derive period changes for some of the single-mode RRL stars, and analyse the significant number of double-mode RRL stars in M?68. Furthermore, we find evidence for double-mode pulsation in one of the SX Phe stars in this cluster. Using the different classes of variables, we derived values for the metallicity of the cluster of [Fe/H] = −2.07 ±0.06 on the ZW scale, or −2.20 ±0.10 on the UVES scale, and found true distance moduli μ0 = 15.00±0.11 mag (using RR0 stars), 15.00 ± 0.05 mag (using RR1 stars), 14.97 ±0.11 mag (using SX Phe stars), and 15.00±0.07 mag (using the MV[Fe/H] relation for RRL stars), corresponding to physical distances of 10.00 ±0.49, 9.99±0.21, 9.84 ±0.50, and 10.00 ±0.30 kpc, respectively. Thanks to the first use of difference image analysis on time-series observations of M?68, we are now confident that we have a complete census of the RRL stars in this cluster.</P>
RED NOISE VERSUS PLANETARY INTERPRETATIONS IN THE MICROLENSING EVENT OGLE-2013-BLG-446
Bachelet, E.,Bramich, D. M.,Han, C.,Greenhill, J.,Street, R. A.,Gould, A.,D’Ago, G.,AlSubai, K.,Dominik, M.,Jaimes, R. Figuera,Horne, K.,Hundertmark, M.,Kains, N.,Snodgrass, C.,Steele, I. A.,Tsapras, IOP Publishing 2015 The Astrophysical journal Vol.812 No.2
<P>For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing data sets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (A(max) similar to 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (similar to 3M(circle plus)) to the lensing star, leading to substantial follow-up coverage of the light curve. We test and compare different models for the light curve and conclude that the data do not favor the planetary interpretation when systematic errors are taken into account.</P>
MOA-2007-BLG-197: Exploring the brown dwarf desert
Ranc, C.,Cassan, A.,Albrow, M. D.,Kubas, D.,Bond, I. A.,Batista, V.,Beaulieu, J.-P.,Bennett, D. P.,Dominik, M.,Dong, Subo,Fouqué,, P.,Gould, A.,Greenhill, J.,Jørgensen, U. G.,Kains, N.,Menzies, EDP Sciences 2015 Astronomy and astrophysics Vol.580 No.-
MOA-2010-BLG-073L: AN M-DWARF WITH A SUBSTELLAR COMPANION AT THE PLANET/BROWN DWARF BOUNDARY
Street, R. A.,Choi, J.-Y.,Tsapras, Y.,Han, C.,Furusawa, K.,Hundertmark, M.,Gould, A.,Sumi, T.,Bond, I. A.,Wouters, D.,Zellem, R.,Udalski, A.,Snodgrass, C.,Horne, K.,Dominik, M.,Browne, P.,Kains, N.,Br IOP Publishing 2013 The Astrophysical journal Vol.763 No.1
<P>We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source light curve, we demonstrate that it is an irregular variable over timescales >200 days. Its dereddened color, (V - I)(S),(0), is 1.221 +/- 0.051 mag, and from our lens model we derive a source radius of 14.7 +/- 1.3 R-circle dot, suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q = 0.0654 +/- 0.0006. The Einstein crossing time of the event, t(E) = 44.3 +/- 0.1 days, was sufficiently long that the light curve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, D-L = 2.8 +/- 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M-L,M-1 = 0.16 +/- 0.03 M-circle dot, while the companion has M-L,M-2 = 11.0 +/- 2.0 M-J, putting it in the boundary zone between planets and brown dwarfs.</P>