Identifying microlensing events using neural networks

Current gravitational microlensing surveys are observing hundreds of millions of stars in the Galactic bulge - which makes finding rare microlensing events a challenging tasks. In almost all previous works, microlensing events have been detected either by applying very strict selection cuts or manually inspecting tens of thousands of light curves. However, the number of microlensing events expected in the future space-based microlensing experiments forces us to consider fully-automated approaches. They are especially important for selecting binary-lens events that often exhibit complex light curve morphologies and are otherwise difficult to find. There are no dedicated selection algorithms for binary-lens events in the literature, which hampers their statistical studies. Here, we present two simple neural-network-based classifiers for detecting single and binary microlensing events. We demonstrate their robustness using OGLE-III and OGLE-IV data sets and show they perform well on microlensing events detected in data from the Zwicky Transient Facility (ZTF). Classifiers are able to correctly recognize ≈98% of single-lens events and 80-85% of binary-lens events

OGLE-2013-BLG-0911Lb: A Secondary on the Brown-dwarf Planet Boundary around an M Dwarf

We present the analysis of the binary-lens microlensing event OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of q 0.03, which differs from that reported in Shvartzvald et al. The event suffers from the well-known close/wide degeneracy, resulting in two groups of solutions for the projected separation normalized by the Einstein radius of s ~ 0.15 or s ~ 7. The finite source and the parallax observations allow us to measure the lens physical parameters. The lens system is an M dwarf orbited by a massive Jupiter companion at very close (M_(host) = 0.30^(+0.08)_(-0.06)M⊙, M_(comp) = 10.1^(+2.9)_(-2.2)M_(Jup), a_(exp) = 0.40^(+0.05)_(-0.04) au) or wide (M_(host) = 0.28^(+0.10)_(-0.08) M⊙, M_(comp) = 9.9^(+3.8)_(-3.5)M_(Jup), a(exp) = 18.0^(+3.8)_(3.5) au) separation. Although the mass ratio is slightly above the planet-brown dwarf (BD) mass-ratio boundary of q = 0.03, which is generally used, the median physical mass of the companion is slightly below the planet-BD mass boundary of 13M_(Jup). It is likely that the formation mechanisms for BDs and planets are different and the objects near the boundaries could have been formed by either mechanism. It is important to probe the distribution of such companions with masses of ~13M_(Jup) in order to statistically constrain the formation theories for both BDs and massive planets. In particular, the microlensing method is able to probe the distribution around low-mass M dwarfs and even BDs, which is challenging for other exoplanet detection methods

Mapping the Northern Galactic Disk Warp with Classical Cepheids

We present an updated three dimensional map of the Milky Way based on a sample of 2431 classical Cepheid variable stars, supplemented with about 200 newly detected classical Cepheids from the OGLE survey. The new objects were discovered as a result of a dedicated observing campaign of the ≈280 square degree extension of the OGLE footprint of the Galactic disk during 2018-2019 observing seasons. These regions cover the main part of the northern Galactic warp that has been deficient in Cepheids so far. We use direct distances to the sample of over 2390 classical Cepheids to model the distribution of the young stellar population in the Milky Way and recalculate the parameters of the Galactic disk warp. Our data show that its northern part is very prominent and its amplitude is ≈10% larger than that of the southern part. By combining Gaia astrometric data with the Galactic rotation curve and distances to Cepheids from our sample, we construct a map of the vertical component of the velocity vector for all Cepheids in the Milky Way disk. We find large-scale vertical motions with amplitudes of 10-20 km/s, such that Cepheids located in the northern warp exhibit large positive vertical velocity (toward the north Galactic pole), whereas those in the southern warp - negative vertical velocity (toward the south Galactic pole)

Evaluation of the Possibility of Applying Thermal Barrier Coatings to AlSi7Mg Alloy Castings

This paper analyses the possibility of applying thermal barrier coatings (TBCs) onto a substrate made of the AlSi7Mg alloy, intended for, among other things, internal combustion engine components. Engine components made of aluminum-silicon alloys, especially pistons and valve heads, are exposed to high temperature, pressure and thermal shock resulting from the combustion of the fuel-air mixture. These factors cause degradation of these components and can lead to damage. To minimize the risk of damage to engine components caused by heat stress, one way is to apply TBCs. Applying TBCs coatings to engine components improves their durability, increases power output and reduces fuel consumption. The research scope includes the application of an Al2O3-TiO3 coating via the APS (Air Plasma Spraying or Atmospheric Plasma Spraying) method onto a substrate of the AlSi7Mg alloy, analysis of the microstructure and chemical composition of the substrate and coating material, and assessment of the quality of the coating's bond with the AlSi7Mg alloy substrate using the scratch test method

Over 78 000 RR Lyrae Stars in the Galactic Bulge and Disk from the OGLE Survey

We present an upgrade of the OGLE Collection of RR Lyrae stars in the Galactic bulge and disk. The size of our sample has been doubled and reached 78 350 RR Lyr variables, of which 56 508 are fundamental-mode pulsators (RRab stars), 21 321 pulsate solely in the first-overtone (RRc stars), 458 are classical double-mode pulsators (RRd stars), and 63 are anomalous RRd variables (including six triple-mode pulsators). For all the newly identified RR Lyr stars, we publish time-series photometry obtained during the OGLE Galaxy Variability Survey. We present the spatial distribution of RR Lyr stars on the sky, provide a list of globular clusters hosting RR Lyr variables, and discuss the Petersen diagram for multimode pulsators. We find new RRd stars belonging to a compact group in the Petersen diagram (with period ratios P₁₀/P_F ≈ 0.74 and fundamental-mode periods P_F ≈ 0.44 d) and we show that their spatial distribution is roughly spherically symmetrical around the Milky Way center