OGLE-2018-BLG-0022: First Prediction of an Astrometric Microlensing Signal from a Photometric Microlensing Event

In this work, we present the analysis of the binary microlensing event OGLE-2018-BLG-0022 that is detected toward the Galactic bulge field. The dense and continuous coverage with the high-quality photometry data from ground-based observations combined with the space-based Spitzer observations of this long timescale event enables us to uniquely determine the masses M_1 = 0.40 ± 0.05 M⊙ and M_2 = 0.13 ± 0.01 M⊙ of the individual lens components. Because the lens-source relative parallax and the vector lens-source relative proper motion are unambiguously determined, we can likewise unambiguously predict the astrometric offset between the light centroid of the magnified images (as observed by the Gaia satellite) and the true position of the source. This prediction can be tested when the individual-epoch Gaia astrometric measurements are released

KMT-2016-BLG-2052L: Microlensing Binary Composed of M Dwarfs Revealed from a Very Long Timescale Event

We present the analysis of a binary microlensing event, KMT-2016-BLG-2052, for which the lensing-induced brightening of the source star lasted for two seasons. We determine the lens mass from the combined measurements of the microlens parallax, π_E, and angular Einstein radius, θ_E. The measured mass indicates that the lens is a binary composed of M dwarfs with masses of M_1 ~ 0.34 M⊙ and M_2 ~ 0.17 M⊙. The measured relative lens-source proper motion of μ ~ 3.9 mas yr^(−1) is smaller than ~5 mas yr−1 of typical Galactic lensing events, while the estimated angular Einstein radius of θ E ~ 1.2 mas is substantially greater than the typical value of ~0.5 mas. Therefore, it turns out that the long timescale of the event is caused by the combination of the slow μ and large θ_E rather than the heavy mass of the lens. From the simulation of Galactic lensing events with very long timescales (t_E ≳ 100 days), we find that the probabilities that long timescale events are produced by lenses with masses ≥1.0 M⊙ and ≥3.0 M⊙ are ~19% and 2.6%, respectively, indicating that events produced by heavy lenses comprise a minor fraction of long timescale events. The results indicate that it is essential to determine lens masses by measuring both π_E and θ_E in order to firmly identify heavy stellar remnants, such as neutron stars and black holes

Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60±0.03M⊙ star with D_(LS) = 0.53±0.11 kpc, where D_(LS) is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a 0.51^(+0.12)_(−0.10)M⊙ star with D_(LS) = 0.40±0.12 kpc or a 0.38^(+0.13)_(−0.12)M⊙ star with D_(LS) = 0.53±0.19 kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurrence in single lens events

Spitzer Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M Dwarf

We report the discovery of a Spitzer microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio q ~ 2 × 10^(−4). The planetary signal, which is characterized by a short (~1 day) "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from Gaia, the Spitzer satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of M_p = 13.9 ± 1.6 M⊕ orbiting a mid M-dwarf with a mass of M_h = 0.23 ± 0.03 M⊙. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields M_p = 1.2 ± 0.2 M⊕ and M_h = 0.15 ± 0.02 M⊙. By combining the microlensing and Gaia data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance D_L ~ 6 ± 1 kpc. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy

Biofouling and its control for in situ lab-on-a-chip marine environmental sensors

Biofouling is the process by which biological organisms attach to surfaces in an aqueous environment. This occurs on nearly all surfaces in all natural aquatic environments, and can cause problems with the functioning of scientific equipment exposed to the marine environment for extended periods. At the National Oceanographic Centre in Southampton (NOCS), the Centre for Marine Microsystems (CMM) is developing lab-on-chip micro-sensors to monitor the chemical and biological environment in situ in the oceans. Due to the long periods (up to several months) that these sensors will be deployed, biofouling by microbial biofilms is an important concern for the efficient running of these sensors. The aim of this project was therefore to determine the potential level of fouling within the sensors and to investigate the potential use of low-concentration diffusible molecules (LCDMs) to remediate biofouling.Many of the sensors in development by CMM are designed to sense specific chemical species and they use various chemical reagents to achieve this. The effects of some of these reagents on the formation of biofilms by mixed marine communities were investigated. It was shown that Griess reagent and ortho-phthadialdehyde (OPA), used to sense nitrites and ammonium respectively, effectively stop biofilm formation by killing microorganisms before they can attach to surfaces.Biofouling on two different polymers, cyclic olefin copolymer (COC) and poly (methyl methacrylate) (PMMA), used in the construction of micro-sensors, was compared with biofouling on glass. No differences were observed between COC and PMMA, however a small but significant difference in surface coverage was observed between glass and COC at the early stages of exposure to the marine environment. The lack of differences between the two polymers suggests that biofouling is not an important consideration when deciding whether to construct sensors from COC or PMMA. However, the larger degree of fouling on hydrophobic COC compared with hydrophilic glass indicates a potential use of surface modifications as an antifouling strategy.The effects on biofouling of the LCDMs nitric oxide (NO), cis-2-decenoic acid (CDA) and patulin, were investigated to evaluate their potential for anti-fouling in marine micro sensors. All three molecules were shown to reduce the formation of biofilms by mixed marine communities, but colony counts suggested that the effect of patulin was due to toxicity as opposed to a physiological effect. Investigation of biofilm growth in the light and the dark revealed that there was less biofilm formation in the light that the dark and this effect was determined to be due to an interaction with the polystyrene growth substratum.Analysis of the biofilm communities grown in the presence of LCDMs by denaturing gradient gel electrophoresis (DGGE), showed no clear differences in community profiles depending on the LCDMs. However those biofilms grown in the light appeared to have a greater proportion of Alphaproteobacteria than those grown in the dark.Further study is needed to determine the level of fouling and the applicability of LCDMs in real micro-sensor systems. However, this study has shown that LCDMs have the potential to remediate, at least in part, the biofouling of marine micro-sensors

KMT-2016-BLG-2052L: Microlensing Binary Composed of M Dwarfs Revealed from a Very Long Timescale Event

We present the analysis of a binary microlensing event, KMT-2016-BLG-2052, for which the lensing-induced brightening of the source star lasted for two seasons. We determine the lens mass from the combined measurements of the microlens parallax, π_E, and angular Einstein radius, θ_E. The measured mass indicates that the lens is a binary composed of M dwarfs with masses of M_1 ~ 0.34 M⊙ and M_2 ~ 0.17 M⊙. The measured relative lens-source proper motion of μ ~ 3.9 mas yr^(−1) is smaller than ~5 mas yr−1 of typical Galactic lensing events, while the estimated angular Einstein radius of θ E ~ 1.2 mas is substantially greater than the typical value of ~0.5 mas. Therefore, it turns out that the long timescale of the event is caused by the combination of the slow μ and large θ_E rather than the heavy mass of the lens. From the simulation of Galactic lensing events with very long timescales (t_E ≳ 100 days), we find that the probabilities that long timescale events are produced by lenses with masses ≥1.0 M⊙ and ≥3.0 M⊙ are ~19% and 2.6%, respectively, indicating that events produced by heavy lenses comprise a minor fraction of long timescale events. The results indicate that it is essential to determine lens masses by measuring both π_E and θ_E in order to firmly identify heavy stellar remnants, such as neutron stars and black holes

OGLE-2018-BLG-0022: First Prediction of an Astrometric Microlensing Signal from a Photometric Microlensing Event

In this work, we present the analysis of the binary microlensing event OGLE-2018-BLG-0022 that is detected toward the Galactic bulge field. The dense and continuous coverage with the high-quality photometry data from ground-based observations combined with the space-based Spitzer observations of this long timescale event enables us to uniquely determine the masses M_1 = 0.40 ± 0.05 M⊙ and M_2 = 0.13 ± 0.01 M⊙ of the individual lens components. Because the lens-source relative parallax and the vector lens-source relative proper motion are unambiguously determined, we can likewise unambiguously predict the astrometric offset between the light centroid of the magnified images (as observed by the Gaia satellite) and the true position of the source. This prediction can be tested when the individual-epoch Gaia astrometric measurements are released