725 research outputs found
Hydrogen gas embrittlement and the disc pressure test
A disc pressure test has been used to study the influenced of a hydrogen gas environment on the mechanical properties of three high strength superalloys, Inconel 718, L-605 and A-286, in static and dynamic conditions. The influence of the hydrogen pressure, loading rate, temperature, mechanical and thermal fatigue has investigated. The permeation characteristics of Inconel 718 have been determined in collaboration with the French AEC. The results complemented by a fractographic study are consistent either with a stress-sorption or with an internal embrittlement type of mechanism
A brown dwarf orbiting an M-dwarf: MOA 2009–BLG–411L
Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted.
Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit.
Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components.
Results. We find that the source star is a giant G star with radius 9 R_⊙. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s^(-1). We find that the lens is composed of a brown dwarf secondary of mass M_S = 0.05 M_⊙ orbiting a primary M-star of mass M_P = 0.18 M_⊙. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries.
Conclusions. As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf
Difference image analysis: The interplay between the photometric scale factor and systematic photometric errors
Context: Understanding the source of systematic errors in photometry is
essential for their calibration. Aims: We investigate how photometry performed
on difference images can be influenced by errors in the photometric scale
factor. Methods: We explore the equations for difference image analysis (DIA)
and we derive an expression describing how errors in the difference flux, the
photometric scale factor and the reference flux are propagated to the object
photometry. Results: We find that the error in the photometric scale factor is
important, and while a few studies have shown that it can be at a significant
level, it is currently neglected by the vast majority of photometric surveys
employing DIA. Conclusions: Minimising the error in the photometric scale
factor, or compensating for it in a post-calibration model, is crucial for
reducing the systematic errors in DIA photometry.Comment: Accepted A&
Red Noise Versus Planetary Interpretations in the Microlensing Event Ogle-2013-BLG-446
For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing data sets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (A_(max) ~ 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (~3M_⊕) to the lensing star, leading to substantial follow-up coverage of the light curve. We test and compare different models for the light curve and conclude that the data do not favor the planetary interpretation when systematic errors are taken into account
A mixed ultrasoft/normconserved pseudopotential scheme
A variant of the Vanderbilt ultrasoft pseudopotential scheme, where the
normconservation is released for only one or a few angular channels, is
presented. Within this scheme some difficulties of the truly ultrasoft
pseudopotentials are overcome without sacrificing the pseudopotential softness.
i) Ghost states are easily avoided without including semicore shells. ii) The
ultrasoft pseudo-charge-augmentation functions can be made more soft. iii) The
number of nonlocal operators is reduced. The scheme will be most useful for
transition metals, and the feasibility and accuracy of the scheme is
demonstrated for the 4d transition metal rhodium.Comment: 4 pages, 2 figure
Gravitational Microlensing Events from the First Year of the Northern Galactic Plane Survey by the Zwicky Transient Facility
The Zwicky Transient Facility (ZTF) (Bellm et al. 2019; Graham et al. 2019; Masci et al. 2019) is currently surveying the entire northern sky, including dense Galactic plane fields. Here, we present preliminary results of the search for gravitational microlensing events in the ZTF data collected from the beginning of the survey (2018 March 20) through 2019 June 30
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