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Publicações

Publicações por Paulo Jorge Garcia

2017

Submilliarcsecond Optical Interferometry of the High-mass X-Ray Binary BP Cru with VLTI/GRAVITY

Autores
Waisberg, I; Dexter, J; Pfuhl, O; Abuter, R; Amorim, A; Anugu, N; Berger, JP; Blind, N; Bonnet, H; Brandner, W; Buron, A; Clenet, Y; de Wit, W; Deen, C; Delplancke Strobele, F; Dembet, R; Duvert, G; Eckart, A; Eisenhauer, F; Fedou, P; Finger, G; Garcia, P; Lopez, RG; Gendron, E; Genzel, R; Gillessen, S; Haubois, X; Haug, M; Haussmann, F; Henning, T; Hippler, S; Horrobin, M; Hubert, Z; Jochum, L; Jocou, L; Kervella, P; Kok, Y; Kulas, M; Lacour, S; Lapeyrere, V; Le Bouquin, JB; Lena, P; Lippa, M; Merand, A; Muller, E; Ott, T; Pallanca, L; Panduro, J; Paumard, T; Perraut, K; Perrin, G; Rabien, S; Ramirez, A; Ramos, J; Rau, C; Rohloff, RR; Rousset, G; Sanchez Bermudez, J; Scheithauer, S; Scholler, M; Straubmeier, C; Sturm, E; Vincent, F; Wank, I; Wieprecht, E; Wiest, M; Wiezorrek, E; Wittkowski, M; Woillez, J; Yazici, S;

Publicação
ASTROPHYSICAL JOURNAL

Abstract
We observe the high-mass X-ray binary (HMXB) BP Cru using interferometry in the near-infrared K band with VLTI/GRAVITY. Continuum visibilities are at most partially resolved, consistent with the predicted size of the hypergiant. Differential visibility amplitude (Delta|V| similar to 5%) and phase (Delta phi similar to 2 degrees) signatures are observed across the He I 2.059 mu m and Br gamma lines, the latter seen strongly in emission, unusual for the donor star's spectral type. For a baseline B similar to 100 m, the differential phase rms similar to 0 degrees 2 corresponds to an astrometric precision of similar to 2 mu as. We generalize expressions for image centroid displacements and variances in the marginally resolved limit of interferometry to spectrally resolved data, and use them to derive model-independent properties of the emission such as its asymmetry, extension, and strong wavelength dependence. We propose geometric models based on an extended and distorted wind and/or a high-density gas stream, which has long been predicted to be present in this system. The observations show that optical interferometry is now able to resolve HMXBs at the spatial scale where accretion takes place, and therefore to probe the effects of the gravitational and radiation fields of the compact object on its environment.

2017

A combined MUSE/X-Shooter study of the TH28 jet

Autores
Murphy, A; Whelan, E; Bacciotti, F; Dougados, C; Ray, T; Coffey, D; Alcalá, J; Garcia, P; Comerón, F; Eislöffel, J;

Publicação
Memorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society

Abstract
Here we present the first results from a MUSE/X-Shooter study of the jet from the classical T Tauri star TH 28. The combination of MUSE and X-Shooter enables us to take advantage of both spectro-imaging and broadband spectroscopy to comprehensively investigate the TH 28 jet. We present a MUSE spectro-image and PV plot of the Ha emission line and use flux ratios from the X-Shooter spectrum to estimate the mass accretion rate at log(?acc) = -9.4. Future work will focus on diagnostic analyses on both sets of data, including estimating the mass outflow rate (?out) and the extinction of the jet. © SAIt 2017.

2018

Maximizing the community exploitation of the VLTI 2nd-generation instruments

Autores
Kraus, S; Garcia, P; Perrin, G;

Publicação
Experimental Astronomy

Abstract

2018

Mind the gap: bridging the transversal and transferable skills chasm in a public engineering school

Autores
Freitas, A; Garcia, P; Lopes, H; de Sousa, A;

Publicação
2018 3RD INTERNATIONAL CONFERENCE OF THE PORTUGUESE SOCIETY FOR ENGINEERING EDUCATION (CISPEE)

Abstract
Transversal and transferable skills are the single most important skill gap identified by employers of engineering graduates. This gap can be a very effective chasm in the early careers of otherwise competent graduates. In this paper we address the end-toend implementation of a transversal and transferable skills training programme in an European public engineering school. The training addresses master and doctoral candidates. The needs assessment, the programme design, delivery and assessment are presented. Relevant stakeholders are involved throughout. They include employers, master and doctoral candidates, faculty, graduate course directors and teaching staff directly involved in the programme. The programme includes methodologies of self-evaluation and course evolution. It is found that the programme is perceived as very important by the trainees and that there is an increasing number of enrolled trainees. The challenges of a sustained delivery of such a growing programme are shortly addressed.

2018

Methods for multiple-telescope beam imaging and guiding in the near-infrared

Autores
Anugu, N; Amorim, A; Gordo, P; Eisenhauer, F; Pfuhl, O; Haug, M; Wieprecht, E; Wiezorrek, E; Lima, J; Perrin, G; Brandner, W; Straubmeier, C; Le Bouquin, JB; Garcia, PJV;

Publicação
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Abstract
Atmospheric turbulence and precise measurement of the astrometric baseline vector between any two telescopes are two major challenges in implementing phase-referenced interferometric astrometry and imaging. They limit the performance of a fibre-fed interferometer by degrading the instrument sensitivity and the precision of astrometric measurements and by introducing image reconstruction errors due to inaccurate phases. A multiple-beam acquisition and guiding camera was built to meet these challenges for a recently commissioned four-beam combiner instrument, GRAVITY, at the European Southern Observatory Very Large Telescope Interferometer. For each telescope beam, it measures (a) field tip-tilts by imaging stars in the sky, (b) telescope pupil shifts by imaging pupil reference laser beacons installed on each telescope using a 2x2 lenslet and (c) higher-order aberrations using a 9x9 Shack-Hartmann. The telescope pupils are imaged to provide visual monitoring while observing. These measurements enable active field and pupil guiding by actuating a train of tip-tilt mirrors placed in the pupil and field planes, respectively. The Shack-Hartmann measured quasi-static aberrations are used to focus the auxiliary telescopes and allow the possibility of correcting the non-common path errors between the adaptive optics systems of the unit telescopes and GRAVITY. The guiding stabilizes the light injection into single-mode fibres, increasing sensitivity and reducing the astrometric and image reconstruction errors. The beam guiding enables us to achieve an astrometric error of less than 50 mu as. Here, we report on the data reduction methods and laboratory tests of the multiple-beam acquisition and guiding camera and its performance on-sky.

2017

Assessing the quality of restored images in optical long-baseline interferometry

Autores
Gomes, N; Garcia, PJV; Thiebaut, E;

Publicação
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Abstract
Assessing the quality of aperture synthesis maps is relevant for benchmarking image reconstruction algorithms, for the scientific exploitation of data from optical long-baseline interferometers, and for the design/upgrade of new/existing interferometric imaging facilities. Although metrics have been proposed in these contexts, no systematic study has been conducted on the selection of a robust metric for quality assessment. This article addresses the question: what is the best metric to assess the quality of a reconstructed image? It starts by considering several metrics and selecting a few based on general properties. Then, a variety of image reconstruction cases are considered. The observational scenarios are phase closure and phase referencing at the Very Large Telescope Interferometer (VLTI), for a combination of two, three, four and six telescopes. End-to-end image reconstruction is accomplished with the MIRA software, and several merit functions are put to test. It is found that convolution by an effective point spread function is required for proper image quality assessment. The effective angular resolution of the images is superior to naive expectation based on the maximum frequency sampled by the array. This is due to the prior information used in the aperture synthesis algorithm and to the nature of the objects considered. The l(1)-norm is the most robust of all considered metrics, because being linear it is less sensitive to image smoothing by high regularization levels. For the cases considered, this metric allows the implementation of automatic quality assessment of reconstructed images, with a performance similar to human selection.

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