Towards Asteroid Detection in Microlensing Surveys with Deep Learning

Asteroids are an indelible part of most astronomical surveys though only a few surveys are dedicated to their detection. Over the years, high cadence microlensing surveys have amassed several terabytes of data while scanning primarily the Galactic Bulge and Magellanic Clouds for microlensing events and thus provide a treasure trove of opportunities for scientific data mining. In particular, numerous asteroids have been observed by visual inspection of selected images. This paper presents novel deep learning-based solutions for the recovery and discovery of asteroids in the microlensing data gathered by the MOA project. Asteroid tracklets can be clearly seen by combining all the observations on a given night and these tracklets inform the structure of the dataset. Known asteroids were identified within these composite images and used for creating the labelled datasets required for supervised learning. Several custom CNN models were developed to identify images with asteroid tracklets. Model ensembling was then employed to reduce the variance in the predictions as well as to improve the generalisation error, achieving a recall of 97.67%. Furthermore, the YOLOv4 object detector was trained to localize asteroid tracklets, achieving a mean Average Precision (mAP) of 90.97%. These trained networks will be applied to 16 years of MOA archival data to find both known and unknown asteroids that have been observed by the survey over the years. The methodologies developed can be adapted for use by other surveys for asteroid recovery and discovery.Comment: 11 pages, 10 figures, submitted to Astronomy and Computin

Identification of the OGLE-2003-BLG-235/MOA-2003-BLG-53 Planetary Host Star

We present the results of HST observations of the host star for the first definitive extrasolar planet detected by microlensing. The light curve model for this event predicts that the lens star should be separated from the source star by ~6mas at the time of the HST images. If the lens star is a late G, K or early M dwarf, then it will be visible in the HST images as an additional source of light that is blended with the source image. Unless the lens and source have exactly the same colors, its presence will also be revealed by a systematic shift between centroids of the source plus lens in different filter bands. The HST data indicates both of these effects: the HST source that matches the position of the source star is 0.21 magnitudes brighter in the ACS/HRC-F814W filter than the microlensing model predicts, and there is an offset of ~0.7mas between the centroid of this source in the F814W and F435W filter bands. We conclude the planetary host star has been detected in these HST images, and this identification of the lens star enables a complete solution of the lens system. The lens parameters are determined with a Bayesian analysis, averaging over uncertainties in the measured parameters, interstellar extinction, and allowing for the possibility of a binary companion to the source star. This yields a stellar mass of M_* = 0.63(+0.07/-0.09) M_solar and a planet mass of M_p = 2.6 (+0.8/-0.6) M_Jup at an orbital separation of 4.3 (+2.5/-0.8) AU. Thus, the lens system resembles our own Solar System, with a planet of ~3 Jupiter-masses in a Jupiter-like orbit around a star of two-thirds of a Solar mass. These conclusions can be tested with future HST images, which should reveal a broadening of the blended source-plus-lens point spread function due to the relative lens-source proper motion.Comment: 11 pages, with 3 figures. to appear in ApJ Lett (Aug 20 issue

Robust synthesis of epoxy resin-filled microcapsules for application to self-healing materials

Mechanically and thermally robust microcapsules containing diglycidyl ether bisphenol A-based epoxy resin and a high-boiling-point organic solvent were synthesized in high yield using in situ polymerization of urea and formaldehyde in an oil-in-water emulsion. Microcapsules were characterized in terms of their size and size distribution, shell surface morphology and thermal resistance to the curing cycles of commercially used epoxy polymers. The size distribution of the capsules and characteristics such as shell thickness can be controlled by the specific parameters of microencapsulation, including concentrations of reagents, stirrer speed and sonication. Selected microcapsules, and separated core and shell materials, were analysed using thermogravimetric analysis and differential scanning calorimetry. It is demonstrated that capsules lose minimal 2.5 wt% at temperatures no higher than 120°C. These microcapsules can be applied to self-healing carbon fibre composite structural materials, with preliminary results showing promising performance

A Comment on "The Far Future of Exoplanet Direct Characterization" - the Case for Interstellar Space Probes

Following on from ideas presented in a recent paper by Schneider et al. (2010) on "The Far Future of Exoplanet Direct Characterization", I argue that they have exaggerated the technical obstacles to performing such 'direct characterization' by means of fast (order 0.1c) interstellar space probes. A brief summary of rapid interstellar spaceflight concepts that may be found in the literature is presented. I argue that the presence of interstellar dust grains, while certainly something which will need to be allowed for in interstellar vehicle design, is unlikely to be the kind of 'show stopper' suggested by Schneider et al. Astrobiology as a discipline would be a major beneficiary of developing an interstellar spaceflight capability, albeit in the longer term, and I argue that astrobiologists should keep an open mind to the possibilities.Comment: Accepted for publication in Astrobiolog

A Second Method to Photometrically Align Multi-Site Microlensing Light Curves: Source Color in Planetary Event MOA-2007-BLG-192

At present, microlensing light curves from different telescopes and filters are photometrically aligned by fitting them to a common model. We present a second method based on photometry of common field stars. If two spectral responses are similar (or the color of the source is known) then this technique can resolve important ambiguities that frequently arise when predicting the future course of the event, and that occasionally persist even when the event is over. Or if the spectral responses are different, it can be used to derive the color of the source when that is unknown. We present the essential elements of this technique and apply it to the case of MOA-2007-BLG-192, an important planetary event for which the system may be a terrestrial planet orbiting a brown dwarf or very low mass star. The refined estimate of the source color that we derive here, V-I=2.36 +- 0.03, will aid in making the estimate of the lens mass more precise.Comment: 16 pages including 3 figures. Submitted to Ap

Search full text options here 2 of 4 KMT-2021-BLG-0912Lb: a microlensing super Earth around a K-type star

Aims. The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very short anomaly relative to a single-lens single-source form. We investigate the light curve for the purpose of identifying the origin of the anomaly. Methods. We model the light curve under various interpretations. From this, we find four solutions, in which three solutions are found under the assumption that the lens is composed of two masses (2L1S models), and the other solution is found under the assumption that the source is comprised of binary stars (1L2S model). The 1L2S model is ruled out based on the contradiction that the faint source companion is bigger than its primary, and one of the 2L1S solutions is excluded from the combination of the poorer fit, blending constraint, and lower overall probability, leaving two surviving solutions with the planet/host mass ratios of q similar to 2.8 x 10(-5) and similar to 1.1 x 10(-5). A subtle central deviation supports the possibility of a tertiary lens component, either a binary companion to the host with a very large or small separation, or a second planet lying near the Einstein ring, but it is difficult to claim a secure detection due to the marginal improvement of the fit, lack of consistency among different data sets, and difficulty in uniquely specifying the nature of the tertiary component. Results. With the observables of the event, it is estimated that the masses of the planet and host are similar to(6.9 M-circle plus, 0.75 M-circle dot) according to one solution and similar to(2.8 M-circle plus, 0.80 M-circle dot) according to the other, indicating that the planet is a super Earth around a K-type star, regardless of the solution. The fact that 16 (including the one reported in this work) out of 19 microlensing planets with M less than or similar to 10 M-circle plus were detected during the last 6 yr nicely demonstrates the importance of high-cadence global surveys in detecting very low-mass planets

A High-Resolution Spectrum of the Highly Magnified Bulge G-Dwarf MOA-2006-BLG-099S

We analyze a high-resolution spectrum of a microlensed G-dwarf in the Galactic bulge, acquired when the star was magnified by a factor of 110. We measure a spectroscopic temperature, derived from the wings of the Balmer lines, that is the same as the photometric temperature, derived using the color determined by standard microlensing techniques. We measure [Fe/H]=0.36 +/-0.18, which places this star at the upper end of the Bulge giant metallicity distribution. In particular, this star is more metal-rich than any bulge M giant with high-resolution abundances. We find that the abundance ratios of alpha and iron-peak elements are similar to those of Bulge giants with the same metallicity. For the first time, we measure the abundances of K and Zn for a star in the Bulge. The [K/Mg] ratio is similar to the value measured in the halo and the disk, suggesting that K production closely tracks alpha production. The [Cu/Fe] and [Zn/Fe] ratios support the theory that those elements are produced in Type II SNe, rather than Type Ia SNe. We also measured the first C and N abundances in the Bulge that have not been affected by first dredge-up. The [C/Fe] and [N/Fe] ratios are close to solar, in agreement with the hypothesis that giants experience only canonical mixing.Comment: 42 pages, 14 figures, submitted to Ap

Apiotrichum terrigenum sp. nov., a novel soil-associated yeast found in both the UK and mainland Europe

Five arthroconidium-producing yeast strains representing a novel Trichosporon-like species were independently isolated from the UK, Hungary and Norway. Two strains (Bio4(T) and Bio21) were isolated from biogas reactors used for processing grass silage, with a third strain (S8) was isolated from soil collected at the same UK site. Two additional strains were isolated in mainland Europe, one from soil in Norway (NCAIM Y.02175) and the other from sewage in Hungary (NCAIM Y.02176). Sequence analyses of the D1/D2 domains of the LSU rRNA gene and internal transcribed spacer (ITS) region indicated that the novel species belongs to the recently reinstated genus Apiotrichum and is most closely related to Apiotrichum scarabaeorum, a beetle-associated species first found in South Africa. Despite having similar physiological characteristics, the two species can be readily distinguished from one another by ITS sequencing. The species name Apiotrichum terrigenum sp. nov. is proposed to accommodate these strains, with Bio4(T) (=CBS 11373(T)=NCYC 3540(T)) designated as the type strain. The Mycobank deposit number is MB817431