ABSTRACT We report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012. We determine the survey sensitivity as ...a function of planet-star mass ratio, q, and projected planet-star separation, s, in Einstein radius units. We find that the mass-ratio function is not a single power law, but has a change in slope at q ∼ 10−4, corresponding to ∼20 M⊕ for the median host-star mass of ∼0.6 . We find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the MOA-II survey data alone. Data from other groups are used only to characterize planetary signals that have been identified in the MOA data alone. The distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model of the form for q > qbr and for q < qbr, where qbr is the mass ratio of the break. We also combine this analysis with the previous analyses of Gould et al. and Cassan et al., bringing the total sample to 30 planets. This combined analysis yields , n = −0.93 0.13, , and for qbr 1.7 × 10−4. The unbroken power-law model is disfavored with a p-value of 0.0022, which corresponds to a Bayes factor of 27 favoring the broken power-law model. These results imply that cold Neptunes are likely to be the most common type of planets beyond the snow line.
Abstract
We report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar ...remnants. We used the
Hubble Space Telescope
to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ∼2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper, we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. This demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolar planets, using precise ground- and space-based observations.
Studies have shown that the remnants of destroyed planets and debris-disk planetesimals can survive the volatile evolution of their host stars into white dwarfs, but few intact planetary bodies ...around white dwarfs have been detected. Simulations predict that planets in Jupiter-like orbits around stars of ≲8 Mꙩ (solar mass) avoid being destroyed by the strong tidal forces of their stellar host, but as yet, there has been no observational confirmation of such a survivor. Here we report the non-detection of a main-sequence lens star in the microlensing event MOA-2010-BLG-477Lb using near-infrared observations from the Keck Observatory. We determine that this system contains a 0.53 ± 0.11 Mꙩ white-dwarf host orbited by a 1.4 ± 0.3 Jupiter-mass planet with a separation on the plane of the sky of 2.8 ± 0.5 astronomical units, which implies a semi-major axis larger than this. This system is evidence that planets around white dwarfs can survive the giant and asymptotic giant phases of their host’s evolution, and supports the prediction that more than half of white dwarfs have Jovian planetary companions. Located at approximately 2.0 kiloparsecs towards the center of our Galaxy, it is likely to represent an analogue to the end stages of the Sun and Jupiter in our own Solar System.
Self-healing is receiving increasing interest worldwide as a technology to autonomously address the effects of damage in composite materials. This paper describes the results of four point bend ...flexural testing (ASTM-D6272-02) of T300/914 carbon fibre reinforced epoxy with resin filled embedded hollow glass fibres (HGF) which provided a self-healing functionality. The study investigated the effect of the embedded HGF on the host CFRP mechanical properties and also the healing efficiency of the laminates after they were subjected to quasi-static impact. Specimens were tested in the undamaged, damaged and healed conditions using a commercial two-part epoxy healing agent (Cytec Cycom 823). Microscopic characterisation of the embedded HGF was also undertaken to characterise the effect on the host laminate fibre architecture.
An investigation is described concerning the interaction of propagating interlaminar cracks with embedded strips of interleaved materials in E-glass fibre reinforced epoxy composites. The approach ...deploys interlayer strips of a thermoplastic film, thermoplastic particles, chopped fibres, glass/epoxy prepreg, thermoset adhesive film and thermoset adhesive particles ahead of the crack path on mid-plane of Double Cantilever Beam (DCB) specimens. During these mode I tests, the interlayers were observed to confer an apparent increase in the toughness of the host material. The crack arrest performance of individual inclusion types are discussed and the underlying mechanisms for energy absorption and the behaviour of the crack at the interaction point of the interleave edge were analysed using scanning electron microscopy.
This study considers the embedment of a bioinspired vasculature within a composite structure that is capable of delivering functional agents from an external reservoir to regions of internal damage. ...Breach of the vascules, by propagating cracks, is a crucial pre-requisite for such a self-healing system to be activated. Two segregated vascule fabrication techniques are demonstrated, and their interactions with propagating Mode I and II cracks determined. The vascule fabrication route adopted played a significant role on the resulting laminate morphology which in-turn dictated the crack–vascule interactions. Embedment of the vascules did not lower the Mode I or II fracture toughness of the host laminate, with vascules orientated transverse to the crack propagation direction leading to significant increases in
G
I
and
G
II
through crack arrest. Large resin pockets were found to redirect the crack around the vascules under Mode II conditions, therefore, it is recommended to avoid this configuration for self-healing applications.
Impact damage can significantly reduce the strength of composite sandwich panels, giving rise to large factors of safety in design. A self-healing sandwich panel was designed and manufactured. ...Specimens were tested in edgewise compression-after-impact to prove the concept. The self-healing system consists of vascular networks carrying the two liquid components of an epoxy resin system. After damage and autonomous self-healing, the specimens could be restored to their undamaged strength. Key influences on healing efficiency, and the need for further improvements in reliability were identified. A simple specific strength analysis suggested that the mass penalty of self-healing could, in some cases, be offset by the improved design allowables permitted.
This paper presents the design considerations for successful incorporation of bioinspired vascules into a carbon fibre-reinforced epoxy composite laminate. A vasculature capable of delivering ...functional agents from an external reservoir to regions of internal damage potentially offers the host structure an autonomous self-healing function without incurring a mass penalty. Minimising disruption to the host laminate, in terms of fibre architecture, is key to the successful implementation of such a technology. Two vascule fabrication techniques are demonstrated. The resulting effective internal defects are characterised along with their interaction with a 10
J damage event, determined via non-destructive C-scanning and a compression after impact test protocol. The effects of vascule diameter, orientation and interface location are also considered. Vascule orientation was found to be the controlling factor, in terms of maintaining compression performance, regardless of the fabrication route used. However, the fabrication route adopted plays a significant role on the morphology of the impact damage and subsequent vascule-damage connectivity, a pre-requisite for self-healing.
An investigation is described concerning the interaction of propagating inter-laminar cracks with embedded strips of interleaved materials in E-glass fibre reinforced epoxy composite. The approach ...deploys inter-ply strips of thermoplastic film, chopped aramid fibres, pre-impregnated fibre reinforced tape and thermosetting adhesive film, ahead of the crack path on the mid-plane of end loaded split (ELS) specimens promoting energy absorbing mechanisms, at low strain rates, through interfacial toughening ahead of the propagating crack.
Following experimental mode II tests, the features were observed to imbue an apparent increase in the toughness of the parent material and suppression of crack growth. The mechanism behind the energy absorption and the behaviour of the crack interaction at the boundary of the interleave edge on ingress and egress were analysed using fractographic processes.
Based on high-resolution spectra obtained during gravitational microlensing events we present a detailed elemental abundance analysis of 32 dwarf and subgiant stars in the Galactic bulge. Combined ...with the sample of 26 stars from the previous papers in this series, we now have 58 microlensed bulge dwarfs and subgiants that have been homogeneously analysed. The results from the microlensed bulge dwarf stars in combination with other findings in the literature, in particular the evidence that the bulge has cylindrical rotation, indicate that the Milky Way could be an almost pure disk galaxy. The bulge would then just be a conglomerate of the other Galactic stellar populations, residing together in the central parts of the Galaxy, influenced by the Galactic bar.
PDF
