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Publications

Publications by CTM

2013

TLOCI: A fully loaded speckle killing machine

Authors
Marois, C; Correia, C; Veran, JP; Currie, T;

Publication
Proceedings of the International Astronomical Union

Abstract
A new high-contrast imaging subtraction algorithm (TLOCI) is presented to maximize a planet signal-to-noise ratio. The technique uses an input spectrum and template PSFs to optimize the reference image coefficient determination to minimize the flux contamination via self-subtraction (thus maximizing its throughput wavelength per wavelength) of any planet that have a similar spectrum to the template spectrum in the image, while trying, at the same time, to maximize the speckle noise subtraction. The optimization is performed by a correlation matrix conditioning. Using laboratory Gemini Planet Imager data, the new algorithm is shown to be superior to the simple/double difference, polynomial fit and original LOCI algorithm. Copyright © 2013, International Astronomical Union.

2013

Wave-front reconstruction for the non-linear curvature wave-front sensor

Authors
Correia, C; Veran, JP; Guyon, O; Clergeon, C;

Publication
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes

Abstract
Non-linear curvature wave-front sensing (nlCWFS) delivers outstanding sensitivity and high dynamic range by lifting the linearity constraint of standard curvature wave-front sensing and working in the non-linear Fresnel (near-field) regime [Guyon, 2010]. The goals of this paper are twofold: 1) revisit the phase-diversity PD formalism and attempt to use this framework, originally developed for the Fraunhofer (far-field) regime, with nlCWFS signals and 2) develop formulae making explicit use of the Fresnel regime for later use with gradient-based non-linear minimisation methods.

2013

Current status of Raven, a MOAO science demonstrator for subaru

Authors
Lardiere, O; Andersen, D; Bradley, C; Blain, C; Gamroth, D; Jackson, K; Lach, P; Nash, R; Oya, S; Pham, L; Veran, JP; Correia, C;

Publication
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes

Abstract
Raven is a Multi-Object Adaptive Optics (MOAO) scientific demonstrator which will be used on-sky at the Subaru observatory from 2014. Raven is currently being built and tested at the University of Victoria AO Lab. This paper presents an overview of the optomechanical design and the software architecture of Raven, and gives the current status of this project. Raven includes three open loop wavefront sensors (WFSs), a laser guide star WFS and two figure/truth WFSs. Two science channels containing deformable mirrors (DMs) feed light to the Subaru IRCS spectrograph. Central to the Raven is a Calibration Unit which contains multiple sources, a telescope simulator including two phase screens and a ground layer DM that can be used to calibrate and test Raven in the lab. Preliminary results on calibration and open-loop AO correction using a tomographic reconstructor are presented.

2013

Visualization of electric field lines in an engineering education context

Authors
Sousa, RG; Garcia, PJV; Marinho, V; Mouraz, A;

Publication
2013 1ST INTERNATIONAL CONFERENCE OF THE PORTUGUESE SOCIETY FOR ENGINEERING EDUCATION (CISPEE)

Abstract
The electromagnetic theory presents a unifying explanation of electric and magnetic phenomena underlying our technological society. It is a fundamental physical theory taught in engineering schools at university level. In this theory the electromagnetic field is a vector field permeating space. An important aspect relating to students difficulties and misconceptions is the difficulty in visualizing vector fields. With the goal of enhancing student understanding and studying student engagement we have developed high quality 3D visualizations of electromagnetic situations. These make use of accurate computation of the field lines, together with realistic rendering using the open source software Blender. We present examples of electrostatic situations with both an assessment of the student understanding and an evaluation of the students' perceptions of the importance of the visualizations. Complex interplay between visualization specific issues and the abstract notion of the field is identified in the students' conceptions. It is found that the visualizations are not used as substitutes of other learning resources. They are perceived as allowing a quick access to content and prompting motivation. The adequacy of the visualization to the subject content as well as the capacity to use it as self-assessment is valued by the students.

2013

Pre-main-sequence binaries with tidally disrupted discs: the Br gamma in HD 104237

Authors
Garcia, PJV; Benisty, M; Dougados, C; Bacciotti, F; Clausse, JM; Massi, F; Merand, A; Petrov, R; Weigelt, G;

Publication
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Abstract
Active pre-main-sequence binaries with separations of around 10 stellar radii present a wealth of phenomena unobserved in common systems. The study of these objects is extended from classical T Tauri stars to the Herbig Ae star HD 104237. The primary has a mass 2.2 +/- 0.2 M-circle dot and secondary 1.4 +/- 0.3 M-circle dot. Spectrointerferometry with the VLTI/AMBER in the K-band continuum and the Br gamma line is presented. It is found that the K-band continuum squared visibilities are compatible with a circumbinary disc with a radius of similar to 0.5 AU. However, a significant fraction (similar to 50 per cent) of the flux is unresolved and not fully accounted by the stellar photospheres. The stars probably do not hold circumstellar discs, in addition to the circumbinary disc, due to the combined effects of inner magnetospheric truncation and outer tidal truncation. This unresolved flux likely arises in compact structures inside the tidally disrupted circumbinary disc. Most (greater than or similar to 90 per cent) of the Br gamma line emission is unresolved. The line-to-continuum spectroastrometry shifts in time, along the direction of the Ly alpha jet known to be driven by the system. The shift is anticorrelated with the Br gamma equivalent width. It is shown that the unresolved Br gamma emission cannot originate in the jet but instead is compatible with stellar emission from the orbiting binary components. The increase in the absolute value of the equivalent width of the line takes place at periastron passage; it could arise in an accretion burst, a flare or in the increase in effective size of the emission region by the interaction of the magnetospheres. The binary longitude of the ascending node is found to be Omega = (235 +/- 3)degrees and the orbit retrograde. The origin of the jet is revisited. The tidal disruption of the circumstellar discs creates difficulties to ejection models that rely on stellar magnetosphere and disc coupling. A scenario of a stellar wind collimated by a circumbinary disc wind is suggested.

2012

Resource Aware Routing and Intelligent Wavelength Assignment for Cooperative Clustered OBS Networks

Authors
Ul Haq, I; Salgado, HM; Castro, JCS;

Publication
2012 9TH INTERNATIONAL CONFERENCE ON HIGH CAPACITY OPTICAL NETWORKS AND EMERGING/ENABLING TECHNOLOGIES (HONET)

Abstract
Burst loss is a critical issue in Optical Burst Switching (OBS) networks which restrains its deployment. This article presents a novel routing and wavelength assignment strategy for the Cooperative Clustered OBS (C2OBS) network architecture, to proactively avoid contention. In C2OBS, the network topology is divided into several manageable overlapping zones/clusters, with a Zone Head (ZH) node keeping an information base of zone resources. The ZH pre-computes a list of alternate k-shortest disjoint paths for every ingress-egress node pair within the zone. The ZH utilizes both the inferred knowledge about wavelength usage at the zone intermediate nodes and a novel poles apart heuristic for assigning wavelengths to incoming bursts. A route is selected among the pre-computed paths where the selected wavelength is available. As a result, traffic is balanced among the set of pre-computed routes, thus proactively reducing probability of contention. This strategy is called Resource Aware Routing (RAR) and Intelligent Wavelength Assignment (IWA).

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