Planetary Lensing Signals of High-Magnification Events under Severe Finite-Source Effect

We investigate the effect of a finite source on the planetary-lensing signals of high-magnification events. From this, we find that the dependency of the finite-source effect on the caustic shape is weak and perturbations survive even when the source is substantially bigger than the caustic. Specifically, we find that perturbations with fractional magnification excess $\geq 5$ survive when the source star is roughly 4 times bigger than the caustic. We also find characteristic features that commonly appear in the perturbation patterns of planetary lens systems affected by severe finite-source effect and thus can be used for the diagnosis of the existence of a companion. These features form in and around a circle with its center located at the caustic center and a radius corresponding to that of the source star. The light curve of an event where the source crosses these features will exhibit a distinctive signal that is characterized by short-duration perturbations of either positive or negative excess and a flat residual region between these short-duration perturbations.Comment: 5 pages, 3 figure

catena-Poly[[bis­(μ-3-carboxy­benzoato)bis­(1,10-phenanthroline)tricopper(II)]-di-μ3-isophthalato]

The title copper coordination polymer, [Cu3(C8H4O4)2(C8H5O4)2(C10H8N2)2]n, was synthesized by reacting Cu(NO3)2, isophthalic acid and 1,10-phenanthroline under hydro­thermal conditions. The trinuclear unit presents a central almost planar CuO4 chromophore with the cation on a symmetry center, and two symmetry-related CuN2O3 groups with the metal centre in a distorted square-pyramidal environment. These units are bridged by isophthalate ligands into one-dimensional double-chain coordination polymers which are, in turn, connected by various π–π stacking inter­actions (face-to-face distance ca 3.45 Å) and O—H⋯O hydrogen bonds, forming a three-dimensional supra­molecular network

The Importance of Binary Gravitational Microlensing Events Through High-Magnification Channel

We estimate the detection efficiency of binary gravitational lensing events through the channel of high-magnification events. From this estimation, we find that binaries in the separations ranges of 0.1 < s < 10, 0.2 < s < 5, and 0.3 < s < 3 can be detected with ~ 100% efficiency for events with magnifications higher than A=100, 50, and 10, respectively, where s represents the projected separation between the lens components normalized by the Einstein radius. We also find that the range of high efficiency covers nearly the whole mass-ratio range of stellar companions. Due to the high efficiency in wide ranges of parameter space, we point out that majority of binary-lens events will be detected through the high-magnification channel in lensing surveys that focus on high-magnification events for efficient detections of microlensing planets. In addition to the high efficiency, the simplicity of the efficiency estimation makes the sample of these binaries useful in the statistical studies of the distributions of binary companions as functions of mass ratio and separation. We also discuss other importance of these events.Comment: 5 pages, 1 figure, 1 tabl

A Planetary lensing feature in caustic-crossing high-magnification microlensing events

Current microlensing follow-up observations focus on high-magnification events because of the high efficiency of planet detection. However, central perturbations of high-magnification events caused by a planet can also be produced by a very close or a very wide binary companion, and the two kinds of central perturbations are not generally distinguished without time consuming detailed modeling (a planet-binary degeneracy). Hence, it is important to resolve the planet-binary degeneracy that occurs in high-magnification events. In this paper, we investigate caustic-crossing high-magnification events caused by a planet and a wide binary companion. From this study, we find that because of the different magnification excess patterns inside the central caustics induced by the planet and the binary companion, the light curves of the caustic-crossing planetary-lensing events exhibit a feature that is discriminated from those of the caustic-crossing binary-lensing events, and the feature can be used to immediately distinguish between the planetary and binary companions. The planetary-lensing feature appears in the interpeak region between the two peaks of the caustic-crossings. The structure of the interpeak region for the planetary-lensing events is smooth and convex or boxy, whereas the structure for the binary-lensing events is smooth and concave. We also investigate the effect of a finite background source star on the planetary-lensing feature in the caustic-crossing high-magnification events. From this, we find that the convex-shaped interpeak structure appears in a certain range that changes with the mass ratio of the planet to the planet-hosting star.Comment: 14 pages, 4 figures. Accepted for publication in Ap

Detectability of Orbital Motion in Stellar Binary and Planetary Microlenses

A standard binary microlensing event lightcurve allows just two parameters of the lensing system to be measured: the mass ratio of the companion to its host, and the projected separation of the components in units of the Einstein radius. However, other exotic effects can provide more information about the lensing system. Orbital motion in the lens is one such effect, which if detected, can be used to constrain the physical properties of the lens. To determine the fraction of binary lens lightcurves affected by orbital motion (the detection efficiency) we simulate lightcurves of orbiting binary star and star-planet (planetary) lenses and simulate the continuous, high-cadence photometric monitoring that will be conducted by the next generation of microlensing surveys that are beginning to enter operation. The effect of orbital motion is measured by fitting simulated lightcurve data with standard static binary microlensing models; lightcurves that are poorly fit by these models are considered to be detections of orbital motion. We correct for systematic false positive detections by also fitting the lightcurves of static binary lenses. For a continuous monitoring survey without intensive follow-up of high magnification events, we find the orbital motion detection efficiency for planetary events with caustic crossings to be 0.061+-0.010, consistent with observational results, and 0.0130+-0.0055 for events without caustic crossings (smooth events). Similarly for stellar binaries, the orbital motion detection efficiency is 0.098+-0.011 for events with caustic crossings and is 0.048+-0.006 for smooth events. These result in combined (caustic crossing and smooth) orbital motion detection efficiencies of 0.029+-0.005 for planetary lenses and 0.070+-0.006 for stellar binary lenses. We also investigate how various microlensing parameters affect the orbital motion detectability. [Abridged]Comment: 21 pages, 22 figures, 5 table

A New Application of the Astrometric Method to Break Severe Degeneracies in Binary Microlensing Events

When a source star is microlensed by one stellar component of a widely separated binary stellar components, after finishing the lensing event, the event induced by the other binary star can be additionally detected. In this paper, we investigate whether the close/wide degeneracies in binary lensing events can be resolved by detecting the additional centroid shift of the source images induced by the secondary binary star in wide binary lensing events. From this investigation, we find that if the source star passes close to the Einstein ring of the secondary companion, the degeneracy can be easily resolved by using future astrometric follow-up observations with high astrometric precision. We determine the probability of detecting the additional centroid shift in binary lensing events with high magnification. From this, we find that the degeneracy of binary lensing events with a separation of $\lesssim 20.0$ AU can be resolved with a significant efficiency. We also estimate the waiting time for the detection of the additional centroid shift in wide binary lensing events. We find that for typical Galactic lensing events with a separation of $\lesssim 20.0$ AU, the additional centroid shift can be detected within 100 days, and thus the degeneracy of those events can be sufficiently broken within a year.Comment: 13 pages, 4 figures, 1 table, accepted for publication in Ap