We present an analysis of the anomalous micro-lensing event,MOA-2010-BLG-073, announced by the Micro-lensing 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. We initially explored a number of purely micro-lensing models for the event but found a residual gradient in the data taken prior to and after the event. The Einstein crossing time of the event, tsubE = 44.3 + or - 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, DL = 2.8 + or - 0.4 kpc, and the masses of the lensing objects.
We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of M sub(h) = 0.11 + or - 0.01 M sub(middot in circle) and M sub(p) = 9.2 + or - 2.2 M ...sub(+ in circle), corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at D sub(L) = 0.81 + or - 0.10 kpc with projected separation r sub(bottom) = 0.92 + or - 0.16 AU. Because of the host's a priori unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions.
We report the discovery of MOA-2013-BLG-220Lb, which has a super-Jupiter mass ratio q = 3.01 + or - 0.02 x 10 super(-3) relative to its host. The proper motion, mu = 12.5 + or - 1 mas yr super(-1), ...is one of the highest for microlensing planets yet discovered, implying that it will be possible to separately resolve the host within ~7 yr. Two separate lines of evidence imply that the planet and host are in the Galactic disk. The planet could have been detected and characterized purely with follow-up data, which has important implications for microlensing surveys, both current and into the Large Synoptic Survey Telescope (LSST) era.
ABSTRACT 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 (Amax ∼ 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 (∼3M⊕) 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.
We present B-, R- and I-band-selected galaxy catalogues based on the Munich Near-Infrared Cluster Survey (MUNICS) which, together with the previously used K-selected sample, serve as an important ...probe of galaxy evolution in the redshift range 0 ≲z≲ 2. Furthermore, used in comparison they are ideally suited to study selection effects in extragalactic astronomy. The construction of the B-, R- and I-selected photometric catalogues, containing ∼9000, ∼9000 and ∼6000 galaxies, respectively, is described in detail. The catalogues reach 50 per cent completeness limits for point sources of B≃ 24.5 mag, R≃ 23.5 mag and I≃ 22.5 mag and cover an area of about 0.3 deg2. Photometric redshifts are derived for all galaxies with an accuracy of δz/(1 +z) ≃ 0.057, very similar to the K-selected sample. Galaxy number counts in the B, V, R, I, J and K bands demonstrate the quality of the data set. The rest-frame colour distributions of galaxies at different selection bands and redshifts suggest that the most-massive galaxies have formed the bulk of their stellar population at earlier times and are essentially in place at redshift unity. We investigate the influence of selection band and environment on the specific star formation rate (SSFR). We find that K-band selection indeed comes close to selection in stellar mass, while B-band selection purely selects galaxies in SFR. We use a galaxy group catalogue constructed on the K-band-selected MUNICS sample to study possible differences of the SSFR between the field and the group environment, finding a marginally lower average SSFR in groups as compared to the field, especially at lower redshifts. The field-galaxy luminosity function in the B and R band as derived from the R-selected sample evolves out to z≃ 2 in the sense that the characteristic luminosity increases but the number density decreases. This effect is smaller at longer rest-frame wavelengths and gets more pronounced at shorter wavelengths. Parametrizing the redshift evolution of the Schechter parameters as M*(z) =M*(0) +a ln (1 +z) and Φ*(z) =Φ*(0) (1 + z)b, we find evolutionary parameters a≃−2.1 and b≃−2.5 for the B band, and a≃−1.4 and b≃−1.8 for the R band.
We analyze MOA-2010-BLG-311, a high magnification (A sub(max) > 600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event ...with both a point lens and a two-body lens model and find that the two-body lens model is a better fit but with only Deltachi super(2) ~ 80. The preferred mass ratio between the lens star and its companion is q = 10 super(-3.7+ or -0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question.
Despite the astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of ...observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of two binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax. The measured masses of the binary components are 0.43 M sub(middot in circle) and 0.39 M sub(middot in circle) for MOA-2011-BLG-090 and 0.57 M sub(middot in circle) and 0.17 M sub(middot in circle) for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. The blended light of OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible to check the microlensing orbital solution by follow-up radial-velocity observation. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future.
ABSTRACT We reanalyze microlensing events in the published list of anomalous events that were observed from the Optical Gravitational Lensing Experiment (OGLE) lensing survey conducted during the ...2004-2008 period. In order to check the existence of possible degenerate solutions and extract extra information, we conduct analyses based on combined data from other survey and follow-up observation and consider higher-order effects. Among the analyzed events, we present analyses of eight events for which either new solutions are identified or additional information is obtained. We find that the previous binary-source interpretations of five events are better interpreted by binary-lens models. These events include OGLE-2006-BLG-238, OGLE-2007-BLG-159, OGLE-2007-BLG-491, OGLE-2008-BLG-143, and OGLE-2008-BLG-210. With additional data covering caustic crossings, we detect finite-source effects for six events including OGLE-2006-BLG-215, OGLE-2006-BLG-238, OGLE-2006-BLG-450, OGLE-2008-BLG-143, OGLE-2008-BLG-210, and OGLE-2008-BLG-513. Among them, we are able to measure the Einstein radii of three events for which multi-band data are available. These events are OGLE-2006-BLG-238, OGLE-2008-BLG-210, and OGLE-2008-BLG-513. For OGLE-2008-BLG-143, we detect higher-order effects induced by the changes of the observer's position caused by the orbital motion of the Earth around the Sun. In addition, we present degenerate solutions resulting from the known close/wide or ecliptic degeneracy. Finally, we note that the masses of the binary companions of the lenses of OGLE-2006-BLG-450 and OGLE-2008-BLG-210 are in the brown-dwarf regime.
PDF
