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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>
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>
Bozza, V.,Dominik, M.,Rattenbury, N. J.,Jørgensen, U. G.,Tsapras, Y.,Bramich, D. M.,Udalski, A.,Bond, I. A.,Liebig, C.,Cassan, A.,Fouqué,, P.,Fukui, A.,Hundertmark, M.,Shin, I.‐,G.,Lee, S. Blackwell Publishing Ltd 2012 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.424 No.2
<P><B>ABSTRACT</B></P><P>The microlensing event OGLE‐2008‐BLG‐510 is characterized by an evident asymmetric shape of the peak, promptly detected by the Automated Robotic Terrestrial Exoplanet Microlensing Search (ARTEMiS) system in real time. The skewness of the light curve appears to be compatible both with binary‐lens and binary‐source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrate that: (1) automated real‐time detection of weak microlensing anomalies with immediate feedback is feasible, efficient and sensitive, (2) rather common weak features intrinsically come with ambiguities that are not easily resolved from photometric light curves, (3) a modelling approach that finds all features of parameter space rather than just the ‘favourite model’ is required and (4) the data quality is most crucial, where systematics can be confused with real features, in particular small higher order effects such as orbital motion signatures. It moreover becomes apparent that events with weak signatures are a silver mine for statistical studies, although not easy to exploit. Clues about the apparent paucity of both brown‐dwarf companions and binary‐source microlensing events might hide here.</P>
Evans, D. F.,Southworth, J.,Smalley, B.,Jørgensen, U. G.,Dominik, M.,Andersen, M. I.,Bozza, V.,Bramich, D. M.,Burgdorf, M. J.,Ciceri, S.,D’Ago, G.,Figuera Jaimes, R.,Gu, S.-H.,Hinse, T. C.,Henning, Th Springer-Verlag 2018 Astronomy and astrophysics Vol.610 No.-
<P><I>Context.</I> 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.</P><P><I>Aim.</I> 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.</P><P><I>Methods.</I> 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.</P><P><I>Results.</I> 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.</P>
Physical properties of the WASP-67 planetary system from multi-colour photometry
Mancini, L.,Southworth, J.,Ciceri, S.,Calchi Novati, S.,Dominik, M.,Henning, Th.,Jørgensen, U. G.,Korhonen, H.,Nikolov, N.,Alsubai, K. A.,Bozza, V.,Bramich, D. M.,D’Ago, G.,Figuera Jaimes, R.,Galianni EDP Sciences 2014 Astronomy and astrophysics Vol.568 No.2