J. Young

University of Cambridge, Cambridge, England, United Kingdom

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Publications (15)14.58 Total impact

  • J. Young, C. Haniff, D. Buscher
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    ABSTRACT: Inteferometric imaging with arrays of telescopes is now a routine technique in optical/infrared astronomy, delivering images with nano-radian resolution. Sensitive next generation arrays, such as the Magdalena Ridge Observatory Interferometer, thus offer a potentially important capability for space situational awareness, allowing satellites in geo-synchronous Earth orbit (GEO) to be inspected after launch. A critical factor for such observations is a lack of short spacings between the telescopes comprising the interferometric array. Large GEO satellites are frequently 20-30m in size, hence ideally the shortest spacings used for the observations should be between 1.2-1.8m for observations at 1 μm wavelength. These cannot easily be realised with existing separated-element arrays. In this paper we explore the approach of combining observations from a separated-element interferometer with interferometric data obtained by optical masking of a “single-dish” telescope. We present simulations that demonstrate that substantial improvements in image fidelity can be achieved in this way. Two shapes of generic satellite shape are investigated, intended to be representative of the majority of bright GEO targets, and the efficacy of the method is assessed for these different target shapes and differing brightness levels.
    Aerospace Conference, 2013 IEEE; 01/2013
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    ABSTRACT: The number of publications of aperture-synthesis images based on optical long-baseline interferometry measurements has recently increased due to easier access to visible and infrared interferometers. The interferometry technique has now reached a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. In writing this paper our motivation was twofold: 1) review and publicize emblematic excerpts of the impressive corpus accumulated in the field of optical interferometry image reconstruction; 2) discuss future prospects for this technique by selecting four representative astrophysical science cases in order to review the potential benefits of using optical long baseline interferometers. For this second goal we have simulated interferometric data from those selected astrophysical environments and used state-of-the-art codes to provide the reconstructed images that are reachable with current or soon-to-be facilities. The image reconstruction process was "blind" in the sense that reconstructors had no knowledge of the input brightness distributions. We discuss the impact of optical interferometry in those four astrophysical fields. We show that image reconstruction software successfully provides accurate morphological information on a variety of astrophysical topics and review the current strengths and weaknesses of such reconstructions. We investigate how to improve image reconstruction and the quality of the image possibly by upgrading the current facilities. We finally argue that optical interferometers and their corresponding instrumentation, existing or to come, with 6 to 10 telescopes, should be well suited to provide images of complex sceneries.
    Astronomy and Astrophysics Review 04/2012; 20(1). · 9.50 Impact Factor
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    ABSTRACT: All of the design work and major construction has been completed for the Magdalena Ridge Observatory interferometer (MROI). The majority of the subsystems are currently (2012) being assembled. When completed, the array will consist of 10 fully transportable 1.4 m telescopes. These will support multiple array configurations, with baselines from 7.8 m to 346 m to give sub-milliarcsecond angular resolution. We provide an assessment of the potential imaging capability of the MRO interferometer with regard to geosynchronous targets. Our preliminary results suggest that a significant proportion of GEO targets may be accessible and that it may be possible to routinely extract key satellite diagnostics with an imaging capability that would be able to distinguish, for example, 70 cm features on a 5-meter satellite bus and payload, 30 cm features on a 2-meter satellite bus or similarly sized structure, as well as precise quantitative information on much larger structures such as 10 m long solar panels. Optimised observation and data reduction strategies are likely to allow these limits to be improved in due course.
    Aerospace Conference, 2012 IEEE; 01/2012
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    ABSTRACT: All of the design work and major construction has been completed for the Magdalena Ridge Observatory interferometer (MROI). The majority of the subsystems are currently (2011) being assembled. When completed, the array will consist of 10 fully transportable 1.4 m telescopes. These will support multiple array configurations, with baselines from 7.8 m to 350 m to give sub-milliarcsecond angular resolution. We assess the potential imaging capability of the MRO interferometer with regard to geosynchronous targets. We conclude that a significant proportion of GEO targets may be accessible and that it may be possible to routinely extract key satellite diagnostics with 7 × 7 pixel imaging. This would distinguish, for example, 70 cm features on a 5-meter satellite, or 30 cm features on a 2-meter satellite.
    Aerospace Conference, 2011 IEEE; 04/2011
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    ABSTRACT: This report focuses on recent developments at the Magdalena Ridge Observatory Interferometer (MROI) in three major areas: 1) telescope delivery and array infrastructure construction, 2) installation of the first vacuum delay line and 3) laboratory fringe measurements with the first fringe beam combiner. Construction of the telescope foundations and utilities began in August of 2010 and will be complete in September of 2011 for delivery of the first of ten telescopes. The MROI now has the longest (100m) evacuated fast delay line in the world. Initial performance tests that began in November of 2010 are reported here. First broadband fringe measurements have been recorded in the laboratory with the fringe tracking beam combiner. These measurements demonstrate high optical quality, and visibilities matching the predicted values for its architecture type.
    01/2011;
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    ABSTRACT: The Magdalena Ridge Observatory Interferometer is a 10 x 1.4 meter aperture long baseline optical and near-infrared interferometer being built at 3,200 meters altitude on Magdalena Ridge, west of Socorro, NM. The interferometer layout is an equilateral "Y" configuration to complement our key science mission, which is centered on imaging faint and complex astrophysical targets. This paper serves as an overview and update on the status of the observatory and our progress towards first light and first fringes in 2012.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    07/2010;
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    ABSTRACT: The MROI fringe tracking beam combiner will be the first fringe instrument for the interferometer. It was designed to utilize the array geometry and maximize sensitivity to drive the interferometer for faint source imaging. Two primary concerns have driven the design philosophy: 1) maintaining high throughput and visibilities in broadband polarized light, and 2) mechanical stability. The first concern was addressed through tight fabrication tolerances of the combiner substrates, and custom coatings. In order to optimize mechanical stability, a unique modular design approach was taken that minimizes the number of internal adjustments. This paper reports initial laboratory fringe and stability measurements.
    Proc SPIE 07/2010;
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    ABSTRACT: We report on the status of the Magdalena Ridge Observatory Interferometer fringe tracker. The instrument design is complete, and is under construction at MRO. It consists of a dedicated, near-IR, fringe tracking beam combiner and spectrographs. It will utilize the "Y" geometry of the array to stabilize fringes on shorter "nearest neighbor" baselines, allowing for increased integration times on the longer baselines and the buildup of signal to noise in the science instrument. The beam combiner has been designed to accommodate light from a maximum of ten telescopes (three in each array arm, one at the "Y" vertex), but can operate with fewer without having to change the overall layout. A single spectrograph will multiplex up to five nearest neighbor combinations onto a single detector. Identical spectrographs are located at both combiner outputs to simultaneously sample combination pairs that are pi radians out of phase with respect to one another.
    01/2010;
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    ABSTRACT: Context. The star HD 87643, exhibiting the “B[e] phenomenon”, has one of the most extreme infrared excesses for this object class. It harbours a large amount of both hot and cold dust, and is surrounded by an extended reflection nebula. Aims. One of our major goals was to investigate the presence of a companion in HD87643. In addition, the presence of close dusty material was tested through a combination of multi-wavelength high spatial resolution observations. Methods. We observed HD 87643 with high spatial resolution techniques, using the near-IR AMBER/VLTI interferometer with baselines ranging from 60 m to 130 m and the mid-IR MIDI/VLTI interferometer with baselines ranging from 25 m to 65 m. These observations are complemented by NACO/VLT adaptive-optics-corrected images in the K and L-bands, and ESO-2.2m optical Wide-Field Imager large-scale images in the B, V and R-bands. Results. We report the direct detection of a companion to HD 87643 by means of image synthesis using the AMBER/VLTI instrument. The presence of the companion is confirmed by the MIDI and NACO data, although with a lower confidence. The companion is separated by ~34 mas with a roughly north-south orientation. The period must be large (several tens of years) and hence the orbital parameters are not determined yet. Binarity with high eccentricity might be the key to interpreting the extreme characteristics of this system, namely a dusty circumstellar envelope around the primary, a compact dust nebulosity around the binary system and a complex extended nebula suggesting past violent ejections.
    Caries Research - CARIES RES. 01/2009; 507(1):317-326.
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    ABSTRACT: Context: The star HD 87643, exhibiting the ``B[e] phenomenon'', has one of the most extreme infrared excesses for this object class. It harbours a large amount of both hot and cold dust, and is surrounded by an extended reflection nebula. Aims: One of our major goals was to investigate the presence of a companion in HD87643. In addition, the presence of close dusty material was tested through a combination of multi-wavelength high spatial resolution observations. Methods: We observed HD 87643 with high spatial resolution techniques, using the near-IR AMBER/VLTI interferometer with baselines ranging from 60 m to 130 m and the mid-IR MIDI/VLTI interferometer with baselines ranging from 25 m to 65 m. These observations are complemented by NACO/VLT adaptive-optics-corrected images in the K and L-bands, and ESO-2.2m optical Wide-Field Imager large-scale images in the B, V and R-bands. Results: We report the direct detection of a companion to HD 87643 by means of image synthesis using the AMBER/VLTI instrument. The presence of the companion is confirmed by the MIDI and NACO data, although with a lower confidence. The companion is separated by ~34 mas with a roughly north-south orientation. The period must be large (several tens of years) and hence the orbital parameters are not determined yet. Binarity with high eccentricity might be the key to interpreting the extreme characteristics of this system, namely a dusty circumstellar envelope around the primary, a compact dust nebulosity around the binary system and a complex extended nebula suggesting past violent ejections. Based on observations made with the ESO very large telescope at Paranal Observatory under programs 076.D-0575, 077.D-0095, 076.D-0141, 380.D-0340, and 280.C-5071, with the ESO 1.52-m and archival ESO data. Appendix is only available in electronic form at http://www.aanda.org
    Astronomy and Astrophysics 01/2009; 507(1):317-326. · 5.08 Impact Factor
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    ABSTRACT: The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility. The concept of VSI consists on 6 sub-systems: a common path distributing the light between the fringe tracker and the scientific instrument, the fringe tracker ensuring the co-phasing of the array, the scientific instrument delivering the interferometric observables and a calibration tool providing sources for internal alignment and interferometric calibrations. The two remaining sub-systems are the control system and the observation support software dedicated to the reduction of the interferometric data. This paper presents the global concept of VSI science path including the common path, the scientific instrument and the calibration tool. The scientific combination using a set of integrated optics multi-way beam combiners to provide high-stability visibility and closure phase measurements are also described. Finally we will address the performance budget of the global VSI instrument. The fringe tracker and scientific spectrograph will be shortly described.
    07/2008;
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    ABSTRACT: The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13 will be imaged without requiring a brighter nearby reference object. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysic including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return. Comment: 12 pages, to be published in Proc. SPIE conference 7013 "Optical and Infrared Interferometry", Schoeller, Danchi, and Delplancke, F. (eds.). See also http://vsi.obs.ujf-grenoble.fr
    07/2008;
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    ABSTRACT: We present the results of the third Optical/IR Interferometry Imaging Beauty Contest. A formal comparison is presented of the performance of algorithms used for imaging data from optical/infrared long-baseline interferometers. The contest consists of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test data consisted of datasets on two objects each "observed" in J, H, and K bands. The majority of the entries produced accurate reconstructions of the initial models. Each of the methods presented is discussed.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2008
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    ABSTRACT: Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain. This instrument will provide information complementary to what is obtained at the same time with ALMA at different wavelengths and the extreme large telescopes.
    01/2008;
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    ABSTRACT: The Magdalena Ridge Observatory Interferometer is a 10-element 1.4 meter aperture optical and near-infrared interferometer being built at 3,200 meters altitude on Magdalena Ridge, west of Socorro, NM. The interferometer layout is an equilateral "Y" configuration to complement our key science mission, which is centered around imaging faint and complex astrophysical targets. This paper serves as an overview and update on the status of the observatory and our progress towards first light and first fringes in the next few years.