S. Morel

University of Santiago, Chile, CiudadSantiago, Santiago, Chile

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Publications (87)115.64 Total impact

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    ABSTRACT: The quality of data obtained by VLTI instruments may be refined by analyzing the continuous data supplied by the Reflective Memory Network (RMN). Based on 5 years experience providing VLTI instruments (PACMAN, AMBER, MIDI) with RMN data, the procedure has been generalized to make the synchronization with observation trouble-free. The present software interface saves not only months of efforts for each instrument but also provides the benefits of software frameworks. Recent applications (GRAVITY, MATISSE) supply feedback for the software to evolve. The paper highlights the way common features been identified to be able to offer reusable code in due course.
    SPIE; 07/2014
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    ABSTRACT: We present the latest update of the European Southern Observatory's Very Large Telescope interferometer (VLTI). The operations of VLTI have greatly improved in the past years: reduction of the execution time; better offering of telescopes configurations; improvements on AMBER limiting magnitudes; study of polarization effects and control for single mode fibres; fringe tracking real time data, etc. We present some of these improvements and also quantify the operational improvements using a performance metric. We take the opportunity of the first decade of operations to reflect on the VLTI community which is analyzed quantitatively and qualitatively. Finally, we present briefly the preparatory work for the arrival of the second generation instruments GRAVITY and MATISSE.
    07/2014;
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    ABSTRACT: The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory. After the first fringes obtained in 2011 with the commissioning instrument VINCI and with siderostats, the VLTI has seen an important number of systems upgrades, paving the path towards reaching the infrastructure level and scientific results it had been designed for. The current status of the VLTI operation all year round with up to four telescopes simultaneously and real imaging capability demonstrates the powerful interferometric infrastructure that has been delivered to the astronomical community. Reaching today's level of robustness and operability of the VLTI has been a long journey, with a lot of lessons learned and gained experience. In 2007, the Paranal Observatory recognized the need for a global system approach for the VLTI, and a dedicated system engineering team was set to analyse the status of the interferometer, identify weak points and area where performances were not met, propose and apply solutions. The gains of this specific effort can be found today in the very good operability level with faster observations executions, in the decreased downtime, in the improved performances, and in the better reliability of the different systems. We will present an historical summary of the system engineering effort done at the VLTI, showing the strategy used, and the implemented upgrades and technical solutions. Improvements in terms of scientific data quality will be highlighted when possible. We will conclude on the legacy of the VLTI system engineering effort, for the VLTI and for future systems.
    SPIE Astronomical Telescopes + Instrumentation 2014, Montreal; 06/2014
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    ABSTRACT: Context: A turbulent atmosphere causes atmospheric piston variations leading to rapid changes in the optical path difference of an interferometer, which causes correlated flux losses. This leads to decreased sensitivity and accuracy in the correlated flux measurement. Aims: To stabilize the N band interferometric signal in MIDI (MID-infrared Interferometric instrument), we use an external fringe tracker working in K band, the so-called FSU-A (fringe sensor unit) of the PRIMA (Phase-Referenced Imaging and Micro-arcsecond Astrometry) facility at VLTI. We present measurements obtained using the newly commissioned and publicly offered MIDI+FSU-A mode. A first characterization of the fringe-tracking performance and resulting gains in the N band are presented. In addition, we demonstrate the possibility of using the FSU-A to measure visibilities in the K band. Methods: We analyzed FSU-A fringe track data of 43 individual observations covering different baselines and object K band magnitudes with respect to the fringe-tracking performance. The N band group delay and phase delay values could be predicted by computing the relative change in the differential water vapor column density from FSU-A data. Visibility measurements in the K band were carried out using a scanning mode of the FSU-A. Results: Using the FSU-A K band group delay and phase delay measurements, we were able to predict the corresponding N band values with high accuracy with residuals of less than 1 micrometer. This allows the coherent integration of the MIDI fringes of faint or resolved N band targets, respectively. With that method we could decrease the detection limit of correlated fluxes of MIDI down to 0.5 Jy (vs. 5 Jy without FSU-A) and 0.05 Jy (vs. 0.2 Jy without FSU-A) using the ATs and UTs, respectively. The K band visibilities could be measured with a precision down to ~2%.
    06/2014;
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    ABSTRACT: The science operations process of the VLT Survey Telescope (VST) camera, OmegaCAM, is described. OmegaCAM is a 267-megapixel CCD camera imaging a 1 × 1 degree field of view with a pixel scale of 0.21 arcseconds. It began operations in October 2011. The telescope and camera provide a survey speed that is five times greater than the now-decommissioned Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla. OmegaCAM is currently used for three public surveys, guaranteed time observations for the OmegaCAM and VST consortia, and Chilean programmes. The execution of OmegaCAM observations, real-time quality control and the calibration plan are outlined.
    11/2013;
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    ABSTRACT: The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Since January 2011 the integration and individual testing of the different subsystem has come to a necessary minimum. At the same time the astrometric commissioning phase has begun. In this contribution we give an update on the status of the facility and present some highlights and difficulties on our way from first dual-feed fringe detection to first astrometric measurements. We focus on technical and operational aspects. In particular, within the context of the latter we are going to present a modified mode of operation that scans across the fringes. We will show that this mode, originally only intended for calibration purposes, facilitates the detection of dual-fringes.
    Proc SPIE 07/2012;
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    ABSTRACT: PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer (ESO, Chile) using an integrated optics combiner. The instrument has been integrated at IPAG starting in December 2009 and commissioned at the Paranal Observatory in October 2010. It provides scientific observations since November 2010. In this paper, we detail the instrumental concept, we describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries deltaSco and HIP11231. PIONIER provides 6 visibilities and 3 independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R=40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag=7 in dispersed mode under median atmospheric conditions (seeing<1", tau0>3ms) with the 1.8m Auxiliary Telescopes. We demonstrate a precision of 0.5deg on the closure phases. The precision on the calibrated visibilities ranges from 3 to 15% depending on the atmospheric conditions. PIONIER has been installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8m Unit Telescopes in March 2011 demonstrates that VLTI is ready for 4-telescope operation.
    Astronomy & Astrophysics - ASTRON ASTROPHYS. 09/2011; 535.
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    ABSTRACT: PIONIER (Precision Integrated Optics Near-infrared Imaging ExpeRiment) is a visitor instrument that performs the interferometric beam combination in the near infrared of the light delivered by the 4 main telescopes (8m) or auxiliary telescopes (1.8m) of the VLTI on the ESO Paranal site (Chile). The heart of the instrument is a photonics device optimized for H band operation (1.5 - 1.8μm) that was developed at LETI in collaboration with IPAG (formerly LAOG). This silica-on-silicon integrated optics component splits the signals coming from the 4 telescopes and recombines them, providing for each of the 6 baselines 4 phase states, thanks to integrated phase shifting functions, for a total of 24 outputs. The overall component transmission over the complete H band is 65%. These outputs are imaged on a PICNIC IR camera.
    Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference; 01/2011
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    ABSTRACT: The fringe sensor unit (FSU) is the central element of the phase referenced imaging and micro-arcsecond astrometry (PRIMA) dual-feed facility for the Very Large Telescope interferometer (VLTI). It has been installed at the Paranal observatory in August 2008 and is undergoing commissioning and preparation for science operation. Commissioning observations began shortly after installation and first results include the demonstration of spatially encoded fringe sensing and the increase in VLTI limiting magnitude for fringe tracking. However, difficulties have been encountered because the FSU does not incorporate real-time photometric correction and its fringe encoding depends on polarisation. These factors affect the control signals, especially their linearity, and can disturb the tracking control loop. To account for this, additional calibration and characterisation efforts are required. We outline the instrument concept and give an overview of the commissioning results obtained so far. We describe the effects of photometric variations and beam-train polarisation on the instrument operation and propose possible solutions. Finally, we update on the current status in view of the start of astrometric science operation with PRIMA. Comment: 12 pages, 11 figures, SPIE 2010 conference proceedings
    Proc SPIE 12/2010;
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    ABSTRACT: PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD integrated optics combiner that can also be used in scanning mode. It provides low spectral resolution in H and K band. PIONIER is designed for imaging with a specific emphasis on fast fringe recording to allow closure-phases and visibilities to be precisely measured. In this work we provide the detailed description of the instrument and present its updated status. Comment: Proceedings of SPIE conference Optical and Infrared Interferometry II (Conference 7734) San Diego 2010
    08/2010;
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    ABSTRACT: The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the operation, the instruments developments are pursued, and new modes are studied and commissioned to offer a wider range of scientific possibilities to the community. New configurations of the ATs array are discussed with the science users of the VLTI and implemented to optimize the scientific return. The monitoring and improvement of the different systems of the VLTI is a continuous work. The PRIMA instrument, bringing astrometry capability to the VLTI and phase referencing to the instruments has been successfully installed and the commissioning is ongoing. The possibility for visiting instruments has been opened to the VLTI facility.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2010
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    ABSTRACT: We report first results obtained from observations using a PRIMA FSU (Fringe Sensor Unit) as a fringe tracker for MIDI on the VLTI when operating with the 1.8-m ATs. Interferometric observations require the correction of the disturbance in the optical path induced by atmospheric turbulence ("piston"). The PRIMA FSU is able to compensate for such disturbances in real-time which makes it a suitable facility to stabilize the fringe signal for other VLTI instruments, like AMBER, MIDI or later MATISSE. Currently, the atmospheric coherence time in the N band (8 to 13 μm) observed by MIDI, as well as the thermal background in this band, require a minimum target flux of 20 Jy and a correlated flux of 10 Jy (in PRISM/HIGH SENSE mode and using the ATs under standard conditions) to allow self-fringe-tracking and data reduction. However, we show that if the fringes are stabilized by the FSU, coherent integration allows a reliable data reduction even for the observation of faint targets (Fcorr <10 Jy) with MIDI at standard detector exposure times. We were able to measure the correlated flux of a 0.5 Jy source, which pushes the current limits of MIDI down to regions where numerous new targets become accessible on ATs. For faint object observations we will discuss the usage of VISIR photometry for calibration purposes. The observational tests done so far and the obtained results represent a first step towards Phase Referenced Imaging with the VLTI in the mid-infrared.
    Proc SPIE 07/2010;
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    ABSTRACT: The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Most of the tests have been concentrated on the characterization of the Fringe Sensor Unit (FSU) and on the automation of the fringe tracking in preparation of dual-field observations. The status of the facility, an analysis of the FSU performance and the first attempts towards dual-field observations will be presented in this paper. In the FSU, the phase information is spatially encoded into four independent combined beams (ABCD) and the group delay comes from their spectral dispersion over 5 spectral channels covering the K-band. During fringe tracking the state machine of the optical path difference controller is driven by the Signal to Noise Ratio (SNR) derived from the 4 ABCD measurements. We will describe the strategy used to define SNR thresholds depending on the star magnitude for automatically detecting and locking the fringes. Further, the SNR as well as the phase delay measurements are affected by differential effects occurring between the four beams. We will shortly discuss the contributions of these effects on the measured phase and SNR noises. We will also assess the sensitivity of the group delay linearity to various instrumental parameters and discuss the corresponding calibration procedures. Finally we will describe how these calibrations and detection thresholds are being automated to make PRIMA as much as possible a user-friendly and efficient facility.
    Proc SPIE 07/2010;
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    ABSTRACT: Performed in November 2007 as a part of the MIDI Guaranteed Time Observation exoplanet program, the observation of the hot Jupiter-like exoplanet Gliese 86b constituted the first attempt of exoplanet detection with the VLTI instrument MIDI. It is also a technical achievement as the first VLTI observation using AMBER and MIDI simultaneously. Fringes were obtained for both instruments with the aim to correct the phase in N-band from the dispersion using the fringes in K-band. In N-band, the parent star has an estimated magnitude of 3.8, and a flux ratio planet/star of about 10-3 is expected. After simulating the effect of the data reduction process of MIDI (EWS), it appears that the theoretical interferometric phase spectrum is a curved-like function with an amplitude (that we call arrow) of about 0.05°. According to the phase spectra of the calibrator HD9362, taken during the first night of observation, we estimate that a precision on the curvature measurement of about 0.33° is currently reached. Consequently, we are at least at a factor 6 from a possible detection. The AMBER data, obtained in parallel, were too noisy to be used to extrapolate and remove the corresponding dispersion in N band at the required level of precision.
    Proc SPIE 01/2010;
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    ABSTRACT: Aims. The emission of warm dust dominates the mid-infrared spectra of active galactic nuclei (AGN). Only interferometric observations provide the necessary angular resolution to resolve the nuclear dust and to study its distribution and properties. The investigation of dust in AGN cores is hence one of the main science goals for the MID-infrared Interferometric instrument MIDI at the VLTI. As the first step, the feasibility of AGN observations was verified and the most promising sources for detailed studies were identified. Methods: This was carried out in a ``snapshot survey'' with MIDI using Guaranteed Time Observations. In the survey, observations were attempted for 13 of the brightest AGN in the mid-infrared which are visible from Paranal. Results: The results of the three brightest, best studied sources have been published in separate papers. Here we present the interferometric observations for the remaining 10, fainter AGN. For 8 of these, interferometric measurements could be carried out. Size estimates or limits on the spatial extent of the AGN-heated dust were derived from the interferometric data of 7 AGN. These indicate that the dust distributions are compact, with sizes on the order of a few parsec. The derived sizes roughly scale with the square root of the luminosity in the mid-infrared, s∝√{LMIR}, with no clear distinction between type 1 and type 2 objects. This is in agreement with a model of nearly optically thick dust structures heated to T 300 K. For three sources, the 10 mum feature due to silicates is tentatively detected either in emission or in absorption. Conclusions: The faint AGN of the snapshot survey are at the sensitivity limit of observations with MIDI. Thus, the data set presented here provides a good insight into the observational difficulties and their implications for the observing strategy and data analysis. Based on the results for all AGN studied with MIDI so far, we conclude that in the mid-infrared the differences between individual galactic nuclei are greater than the generic differences between type 1 and type 2 objects. Based on Guaranteed Time Observations of the MIDI consortium collected at the European Southern Observatory, Chile, programme numbers 076.B-0038(A), 077.B-0026(B), 078.B-0031(A), 079.B-0180(A), 080.B-0258(A) and 081.D-0092(A).
    Astronomy and Astrophysics 01/2009; · 5.08 Impact Factor
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    ABSTRACT: Aims. The emission of warm dust dominates the mid-infrared spectra of active galactic nuclei (AGN). Only interferometric observations provide the necessary angular resolution to resolve the nuclear dust and to study its distribution and properties. The investigation of dust in AGN cores is hence one of the main science goals for the MID-infrared Interferometric instrument MIDI at the VLTI. As the first step, the feasibility of AGN observations was verified and the most promising sources for detailed studies were identified.Methods. This was carried out in a “snapshot survey” with MIDI using Guaranteed Time Observations. In the survey, observations were attempted for 13 of the brightest AGN in the mid-infrared which are visible from Paranal.Results. The results of the three brightest, best studied sources have been published in separate papers. Here we present the interferometric observations for the remaining 10, fainter AGN. For 8 of these, interferometric measurements could be carried out. Size estimates or limits on the spatial extent of the AGN-heated dust were derived from the interferometric data of 7 AGN. These indicate that the dust distributions are compact, with sizes on the order of a few parsec. The derived sizes roughly scale with the square root of the luminosity in the mid-infrared, $s\propto\sqrt{L_{{\rm MIR}}}$, with no clear distinction between type 1 and type 2 objects. This is in agreement with a model of nearly optically thick dust structures heated to $T$ ~ 300 K. For three sources, the 10 $\mu$m feature due to silicates is tentatively detected either in emission or in absorption.Conclusions. The faint AGN of the snapshot survey are at the sensitivity limit of observations with MIDI. Thus, the data set presented here provides a good insight into the observational difficulties and their implications for the observing strategy and data analysis. Based on the results for all AGN studied with MIDI so far, we conclude that in the mid-infrared the differences between individual galactic nuclei are greater than the generic differences between type 1 and type 2 objects.
    http://dx.doi.org/10.1051/0004-6361/200811607. 01/2009;
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    ABSTRACT: We present first results of an experiment to combine data from Keck aperture masking and the Infrared-Optical Telescope Array to image the circumstellar environments of evolved stars with ~20 mas resolution. The unique combination of excellent Fourier coverage at short baselines and high-quality long-baseline fringe data allows us to determine the location and clumpiness of the innermost hot dust in the envelopes and to measure the diameters of the underlying stars themselves. We find evidence for large-scale inhomogeneities in some dust shells and also significant deviations from uniform brightness for the photospheres of the most evolved M stars. Deviations from spherically symmetric mass loss in the red supergiant NML Cyg could be related to recent evidence for dynamically important magnetic fields and/or stellar rotation. We point out that dust shell asymmetries, like those observed here, can qualitatively explain the difficulty recent workers have had in simultaneously fitting the broadband spectral energy distributions and high-resolution spatial information, without invoking unusual dust properties or multiple distinct shells (from hypothetical "superwinds"). This paper is the first to combine optical interferometry data from multiple facilities for imaging, and we discuss the challenges and potential for the future of this method, given current calibration and software limitations.
    The Astrophysical Journal 12/2008; 605(1):436. · 6.73 Impact Factor
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    ABSTRACT: Nine bright O-rich Mira stars and five semiregular variable cool M giants have been observed with the Infrared and Optical Telescope Array (IOTA) interferometer in both K' (~2.15 μm) and L' (~3.8 μm) broadband filters, in most cases at very close variability phases. All of the sample Mira stars and four of the semiregular M giants show strong increases, from 20% to 100%, in measured uniform-disk (UD) diameters between the K' and L' bands. (A selection of hotter M stars does not show such a large increase.) There is no evidence that K' and L' broadband visibility measurements should be dominated by strong molecular bands, and cool expanding dust shells already detected around some of these objects are also found to be poor candidates for producing these large apparent diameter increases. Therefore, we propose that this must be a continuum or pseudocontinuum opacity effect. Such an apparent enlargement can be reproduced using a simple two-component model consisting of a warm (1500-2000 K), extended (up to 3 stellar radii), optically thin (τ 0.5) layer located above the classical photosphere. The Planck weighting of the continuum emission from the two layers will suffice to make the L' UD diameter appear larger than the K' UD diameter. This two-layer scenario could also explain the observed variation of Mira UD diameters versus infrared wavelength—outside of strong absorption bands—as already measured inside the H, K, L, and N atmospheric windows. This interpretation is consistent with the extended molecular gas layers (H2O, CO, etc.) inferred around some of these objects from previous IOTA K'-band interferometric observations obtained with the Fiber Linked Unit for Optical Recombination (FLUOR) and from Infrared Space Observatory and high-resolution ground-based FTS infrared spectra. The two-component model has immediate implications. For example, the Mira photosphere diameters are smaller than previously recognized—this certainly implies higher effective temperatures, and it may favor fundamental mode pulsation. Also, the UD model fails generally to represent the brightness distribution and has very limited applicability for Mira stars. The presence of a very extended gas layer extending up to 3 stellar radii seems now well established on a fair sample of asymptotic giant branch stars ranging from late-type giants to long-period variables, with some probable impact on stellar model atmospheres and mass-loss mechanisms.
    The Astrophysical Journal 12/2008; 579(1):446. · 6.73 Impact Factor
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    ABSTRACT: FINITO (the VLTI three beam fringe-tracker) has been offered in September 2007 to the astronomical community for observations with the scientific instruments AMBER and MIDI. In this paper, we describe the last improvements of the fringe-tracking loop and its actual performance when operating with the 1.8m Auxiliary Telescopes. We demonstrate the gain provided to the scientific observations. Finally, we discuss how FINITO real-time data could be used in post-processing to enhance the scientific return of the facility.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2008
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    ABSTRACT: Building on technological developments over the last 35 years, intensity interferometry now appears a feasible option by which to achieve diffraction-limited imaging over a square-kilometer synthetic aperture. Upcoming Atmospheric Cherenkov Telescope projects will consist of up to 100 telescopes, each with ~100m2 of light gathering area, and distributed over ~1km2. These large facilities will offer thousands of baselines from 50m to more than 1km and an unprecedented (u,v) plane coverage. The revival of interest in Intensity Interferometry has recently led to the formation of a IAU working group. Here we report on various ongoing efforts towards implementing modern Stellar Intensity Interferometry.
    Proc SPIE 07/2008;

Publication Stats

873 Citations
115.64 Total Impact Points

Institutions

  • 2005–2014
    • University of Santiago, Chile
      CiudadSantiago, Santiago, Chile
  • 1970–2008
    • European Southern Observatory
      Arching, Bavaria, Germany
  • 2004
    • University of Amsterdam
      • Astronomical Institute Anton Pannekoek
      Amsterdam, North Holland, Netherlands
  • 2001
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2000
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States