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Christoph U. Keller
Professor of Experimental Astrophysics

Leiden Observatory
Leiden University, The Netherlands

First direct detection of a polarized companion outside of a resolved circumbinary disk around CS Cha

5 Jun 2018

by Ginski, C., Benisty, M., van Holstein, R. G., Juhász, A., Schmidt, T. O. B., Chauvin, G., de Boer, J., Wilby, M., Manara, C. F., Delorme, P., Ménard, F., Pinilla, P., Birnstiel, T., Flock, M., Keller, C., Kenworthy, M., Milli, J., Olofsson, J., Pérez, L., Snik, F., Vogt, N., is now available here.

Abstract: In the present study we aim to investigate the circumstellar environment of the spectroscopic binary T Tauri star CS Cha. From unresolved mid- to far-infrared photometry it is predicted that CS Cha hosts a disk with a large cavity. In addition, SED modeling suggests significant dust settling, pointing towards an evolved disk that may show signs of ongoing or completed planet formation. We observed CS Cha with the high contrast imager VLT/SPHERE in polarimetric differential imaging mode to resolve the circumbinary disk in near infrared scattered light. These observations were followed-up by VLT/NACO L-band observations and complemented by archival VLT/NACO K-band and HST/WFPC2 I-band data. We resolve the compact circumbinary disk around CS Cha for the first time in scattered light. We find a smooth, low inclination disk with an outer radius of $\sim$55 au (at 165 pc). We do not detect the inner cavity but find an upper limit for the cavity size of $\sim$15 au. Furthermore, we find a faint co-moving companion with a projected separation of 210 au from the central binary outside of the circumbinary disk. The companion is detected in polarized light and shows an extreme degree of polarization (13.7$\pm$0.4 \% in J-band). The companion's J- and H-band magnitudes are compatible with masses of a few M$_\mathrm{Jup}$. However, K-, L- and I-band data draw this conclusion into question. We explore with radiative transfer modeling whether an unresolved circum-companion disk can be responsible for the high polarization and complex photometry. We find that the set of observations is best explained by a heavily extincted low mass ($\sim 20 \mathrm{M}_\mathrm{Jup}$) brown dwarf or high mass planet with an unresolved disk and dust envelope.

The Single-mode Complex Amplitude Refinement (SCAR) coronagraph: II. Lab verification, and toward the characterization of Proxima b

5 Jun 2018

by Haffert, S. Y., Por, E. H., Keller, C. U., Kenworthy, M. A., Doelman, D. S., Snik, F., Escuti, M. J., is now available here.

Abstract: We present the monochromatic lab verification of the newly developed SCAR coronagraph that combines a phase plate (PP) in the pupil with a microlens-fed single-mode fiber array in the focal plane. The two SCAR designs that have been measured, create respectively a 360 degree and 180 degree dark region from 0.8-2.4 \lambda/D around the star. The 360 SCAR has been designed for a clear aperture and the 180 SCAR has been designed for a realistic aperture with central obscuration and spiders. The 360 SCAR creates a measured stellar null of $2-3 \times 10^{-4}$ , and the 180 SCAR reaches a null of $1 \times 10^{-4}$ . Their monochromatic contrast is maintained within a range of $\pm$ 0.16 \lambda/D peak-to-valley tip-tilt, which shows the robustness against tip-tilt errors. The small inner working angle and tip-tilt stability makes the SCAR coronagraph a very promising technique for an upgrade of current high-contrast instruments to characterize and detect exoplanets in the solar neighborhood.

Laboratory verification of 'Fast & Furious' phase diversity: Towards controlling the low wind effect in the SPHERE instrument

5 Jun 2018

by Wilby, Michael J., Keller, Christoph U., Sauvage, Jean-Francois, Dohlen, Kjetil, Fusco, Thierry, Mouillet, David, Beuzit, Jean-Luc, is now available here.

Abstract: The low wind effect (LWE) refers to a characteristic set of quasi-static wavefront aberrations seen consistently by the SPHERE instrument when dome-level wind speeds drop below 3 m/s. This effect produces bright low-order speckles in the stellar PSF, which severely limit the contrast performance of SPHERE under otherwise optimal observing conditions. In this paper we propose the Fast & Furious (F&F) phase diversity algorithm as a viable software-only solution for real-time LWE compensation, which would utilise image sequences from the SPHERE differential tip-tilt sensor (DTTS). We evaluated the closed-loop performance of F&F on the MITHIC high-contrast test-bench under a variety of conditions emulating LWE-affected DTTS images, in order to assess the expected performance of an on-sky implementation of F&F in SPHERE. The algorithm was found to be capable of returning such LWE-affected images to Strehl ratios of greater than 90% within five iterations, for all appropriate laboratory test cases. These results are highly representative of predictive simulations, and demonstrate the stability of the algorithm against a wide range of factors including low image signal-to-noise ratio (S/N), small image field of view, and amplitude errors. It was also found in simulation that closed-loop stability can be preserved down to image S/N as low as five while still improving overall wavefront quality, allowing for reliable operation even on faint targets. The Fast & Furious algorithm is an extremely promising solution for real-time compensation of the LWE, which can operate simultaneously with science observations and may be implemented in SPHERE without requiring additional hardware. The robustness and relatively large effective dynamic range of F&F also make it suitable for general wavefront optimisation applications, including the co-phasing of segmented ELT-class telescopes.

Atmospheric Implications of Light Alkane Emissions From the U.S. Oil and Natural Gas Sector

5 Jun 2018

by Fischer, E. V., Tzompa Sosa, Z. A., Henderson, B., Travis, K., Keller, C., Sive, B. C., Helmig, D., Fried, A., Herndon, S. C., Yacovitch, T. I., Mahieu, E., Franco, B., is now available here.

Abstract: New efficient drilling techniques triggered a massive growth of unconventional oil and natural gas production in North America starting in 2005. Emissions of a variety of volatile organic compounds (VOCs) from the oil and gas sector occur during well development and production phases, and emissions to the atmosphere also continue when wells are abandoned. Determining VOC emission fluxes in the context of rapid growth of the oil and natural gas industry presents a big challenge for emission inventories. In the U.S., the latest version of the 2011 National Emission Inventory (NEI2011v6.3) includes updates over important oil and natural gas basins and speciation profiles based on the Western Regional Air Partnership. We incorporated the NEI2011v6.3 into the GEOS-Chem chemical transport model to simulate the atmospheric abundances of C2-C5 alkanes over the U.S. attributed to emissions from the oil and gas sector. We present results from a nested high-resolution (0.5 degree x 0.667 degree) simulation over North America. C2-C5 alkane emissions from NEI 2011v6.3 increase across the U.S. compared to the previous NEI 2011 v2 incorporated as default in GEOS-Chem. Ethane (C2H6) and propane (C3H8) emission fluxes increased over important oil and natural gas basins. We compare our simulation to a suite of surface observations, column measurements, and aircraft profiles. Finally, we estimate the contribution that C2-C5 alkanes make to the abundance and production of important secondary species including ozone, peroxy acetyl nitrate, and several ketones.

The Spectropolarimeter for Planetary Exploration: SPEX

5 Jun 2018

by Laan, Erik, Stam, Daphne, Snik, Frans, Karalidi, Theodora, Keller, Christoph, ter Horst, Rik, Navarro, Ramon, Oomen, Gijsbert, de Vries, Johan, Hoogeveen, Ruud, is now available here.

Abstract: SPEX (Spectropolarimeter for Planetary EXploration) is an innovative, compact remotesensing instrument for measuring and characterizing aerosols in the atmosphere. The shoebox size instrument is capable of accurate full linear spectropolarimetry without moving parts or liquid crystals. High precision polarimetry is performed through encoding the degree and angle of linear polarization of the incoming light in a sinusoidal modulation of the spectrum. Measuring this intensity spectrum thus provides the spectral dependence of the degree and angle of linear polarization. Polarimetry has proven to be an excellent tool to study microphysical properties of atmospheric particles. Such information is essential to better understand the weather and climate of a planet. Although SPEX can be used to study any planetary atmosphere, including the Earth's, the current design of SPEX is tailored to study Martian dust and clouds from an orbiting platform. SPEX' 9 entrance pupils can simultaneously measure intensity spectra from 0.4 to 0.8 microns, in different directions along the flight direction (including two limb viewing directions). This way, the scattering phase functions of dust and cloud particles within a ground pixel are sampled while flying over it. SPEX can provide synergy with instruments on rovers and landers, as it provides an overview of spatial and temporal variations of the Martian atmosphere.

SPEX: the Spectropolarimeter for Planetary Exploration

5 Jun 2018

by Rietjens, J. H. H., Snik, F., Stam, D. M., Smit, J. M., van Harten, G., Keller, C. U., Verlaan, A. L., Laan, E. C., ter Horst, R., Navarro, R., Wielinga, K., Moon, S. G., Voors, R., is now available here.

Abstract: We present SPEX, the Spectropolarimeter for Planetary Exploration, which is a compact, robust and low-mass spectropolarimeter designed to operate from an orbiting or in situ platform. Its purpose is to simultaneously measure the radiance and the state (degree and angle) of linear polarization of sunlight that has been scattered in a planetary atmosphere and/or reflected by a planetary surface with high accuracy. The degree of linear polarization is extremely sensitive to the microphysical properties of atmospheric or surface particles (such as size, shape, and composition), and to the vertical distribution of atmospheric particles, such as cloud top altitudes. Measurements as those performed by SPEX are therefore crucial and often the only tool for disentangling the many parameters that describe planetary atmospheres and surfaces. SPEX uses a novel, passive method for its radiance and polarization observations that is based on a carefully selected combination of polarization optics. This method, called spectral modulation, is the modulation of the radiance spectrum in both amplitude and phase by the degree and angle of linear polarization, respectively. The polarization optics consists of an achromatic quarter-wave retarder, an athermal multiple-order retarder, and a polarizing beam splitter. We will show first results obtained with the recently developed prototype of the SPEX instrument, and present a performance analysis based on a dedicated vector radiative transport model together with a recently developed SPEX instrument simulator.

SPEX: a highly accurate spectropolarimeter for atmospheric aerosol characterization

5 Jun 2018

by Rietjens, J. H. H., Smit, J. M., di Noia, A., Hasekamp, O. P., van Harten, G., Snik, F., Keller, C. U., is now available here.

Abstract: Global characterization of atmospheric aerosol in terms of the microphysical properties of the particles is essential for understanding the role aerosols in Earth climate [1]. For more accurate predictions of future climate the uncertainties of the net radiative forcing of aerosols in the Earth's atmosphere must be reduced [2]. Essential parameters that are needed as input in climate models are not only the aerosol optical thickness (AOT), but also particle specific properties such as the aerosol mean size, the single scattering albedo (SSA) and the complex refractive index. The latter can be used to discriminate between absorbing and non-absorbing aerosol types, and between natural and anthropogenic aerosol. Classification of aerosol types is also very important for air-quality and health-related issues [3]. Remote sensing from an orbiting satellite platform is the only way to globally characterize atmospheric aerosol at a relevant timescale of 1 day [4]. One of the few methods that can be employed for measuring the microphysical properties of aerosols is to observe both radiance and degree of linear polarization of sunlight scattered in the Earth atmosphere under different viewing directions [5][6][7]. The requirement on the absolute accuracy of the degree of linear polarization PL is very stringent: the absolute error in PL must be smaller then 0.001+0.005.PL in order to retrieve aerosol parameters with sufficient accuracy to advance climate modelling and to enable discrimination of aerosol types based on their refractive index for air-quality studies [6][7]. In this paper we present the SPEX instrument, which is a multi-angle spectropolarimeter that can comply with the polarimetric accuracy needed for characterizing aerosols in the Earth's atmosphere. We describe the implementation of spectral polarization modulation in a prototype instrument of SPEX and show results of ground based measurements from which aerosol microphysical properties are retrieved.

Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

5 Jun 2018

by Harrington, David M., Snik, Frans, Keller, Christoph U., Sueoka, Stacey R., van Harten, Gerard, is now available here.

Abstract: We outline polarization fringe predictions derived from an application of the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder optics. The DKIST retarder baseline design used six crystals, single-layer antireflection coatings, thick cover windows, and oil between all optical interfaces. This tool estimates polarization fringes and optic Mueller matrices as functions of all optical design choices. The amplitude and period of polarized fringes under design changes, manufacturing errors, tolerances, and several physical factors can now be estimated. This tool compares well with observations of fringes for data collected with the spectropolarimeter for infrared and optical regions at the Dunn Solar Telescope using bicrystalline achromatic retarders as well as laboratory tests. With this tool, we show impacts of design decisions on polarization fringes as impacted by antireflection coatings, oil refractive indices, cover window presence, and part thicknesses. This tool helped DKIST decide to remove retarder cover windows and also recommends reconsideration of coating strategies for DKIST. We anticipate this tool to be essential in designing future retarders for mitigation of polarization and intensity fringe errors in other high spectral resolution astronomical systems.

Combining angular differential imaging and accurate polarimetry with SPHERE/IRDIS to characterize young giant exoplanets

5 Jun 2018

by van Holstein, Rob G., Snik, Frans, Girard, Julien H., de Boer, Jozua, Ginski, C., Keller, Christoph U., Stam, Daphne M., Beuzit, Jean-Luc, Mouillet, David, Kasper, Markus, Langlois, Maud, Zurlo, Alice, de Kok, Remco J., Vigan, Arthur, is now available here.

Abstract: Young giant exoplanets emit infrared radiation that can be linearly polarized up to several percent. This linear polarization can trace: 1) the presence of atmospheric cloud and haze layers, 2) spatial structure, e.g. cloud bands and rotational flattening, 3) the spin axis orientation and 4) particle sizes and cloud top pressure. We introduce a novel high-contrast imaging scheme that combines angular differential imaging (ADI) and accurate near-infrared polarimetry to characterize self-luminous giant exoplanets. We implemented this technique at VLT/SPHEREIRDIS and developed the corresponding observing strategies, the polarization calibration and the data-reduction approaches. The combination of ADI and polarimetry is challenging, because the field rotation required for ADI negatively affects the polarimetric performance. By combining ADI and polarimetry we can characterize planets that can be directly imaged with a very high signal-to-noise ratio. We use the IRDIS pupil-tracking mode and combine ADI and principal component analysis to reduce speckle noise. We take advantage of IRDIS' dual-beam polarimetric mode to eliminate differential effects that severely limit the polarimetric sensitivity (flat-fielding errors, differential aberrations and seeing), and thus further suppress speckle noise. To correct for instrumental polarization effects, we apply a detailed Mueller matrix model that describes the telescope and instrument and that has an absolute polarimetric accuracy <= 0.1%. Using this technique we have observed the planets of HR 8799 and the (sub-stellar) companion PZ Tel B. Unfortunately, we do not detect a polarization signal in a first analysis. We estimate preliminary 1σ upper limits on the degree of linear polarization of ˜ 1% and ˜ 0.1% for the planets of HR 8799 and PZ Tel B, respectively. The achieved sub-percent sensitivity and accuracy show that our technique has great promise for characterizing exoplanets through direct-imaging polarimetry

Three Years of SPHERE: The Latest View of the Morphology and Evolution of Protoplanetary Discs

5 Jun 2018

by Garufi, A., Benisty, M., Stolker, T., Avenhaus, H., de Boer, J.., Pohl, A., Quanz, S. P., Dominik, C., Ginski, C., Thalmann, C., van Boekel, R., Boccaletti, A., Henning, T., Janson, M., Salter, G., Schmid, H. M., Sissa, E., Langlois, M., Beuzit, J.-L., Chauvin, G., Mouillet, D., Augereau, J.-C., Bazzon, A., Biller, B., Bonnefoy, M., Buenzli, E., Cheetham, A., Daemgen, S., Desidera, S., Engler, N., Feldt, M., Girard, J., Gratton, R., Hagelberg, J., Keller, C., Keppler, M., Kenworthy, M., Kral, Q., Lopez, B., Maire, A.-L., Menard, F., Mesa, D., Messina, S., Meyer, M. R., Milli, J., Min, M., Muller, A., Olofsson, J., Pawellek, N., Pinte, C., Szulagyi, J., Vigan, A., Wahhaj, Z., Waters, R., Zurlo, A., is now available here.

Abstract: Spatially resolving the immediate surroundings of young stars is a key challenge for the planet formation community. SPHERE on the VLT represents an important step forward by increasing the opportunities offered by optical or near-infrared imaging instruments to image protoplanetary discs. The Guaranteed Time Observation Disc team has concentrated much of its efforts on polarimetric differential imaging, a technique that enables the efficient removal of stellar light and thus facilitates the detection of light scattered by the disc within a few au from the central star. These images reveal intriguing complex disc structures and diverse morphological features that are possibly caused by ongoing planet formation in the disc. An overview of the recent advances enabled by SPHERE is presented.

Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

5 Jun 2018

by Harrington, David M., Snik, Frans, Keller, Christoph U., Sueoka, Stacey R., van Harten, Gerard, is now available here.

Abstract: We outline polarization fringe predictions derived from a new application of the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder optics. The DKIST retarder baseline design used 6 crystals, singlelayer anti-reflection coatings, thick cover windows and oil between all optical interfaces. This new tool estimates polarization fringes and optic Mueller matrices as functions of all optical design choices. The amplitude and period of polarized fringes under design changes, manufacturing errors, tolerances and several physical factors can now be estimated. This tool compares well with observations of fringes for data collected with the SPINOR spectropolarimeter at the Dunn Solar Telescope using bi-crystalline achromatic retarders as well as laboratory tests. With this new tool, we show impacts of design decisions on polarization fringes as impacted by anti-reflection coatings, oil refractive indices, cover window presence and part thicknesses. This tool helped DKIST decide to remove retarder cover windows and also recommends reconsideration of coating strategies for DKIST. We anticipate this tool to be essential in designing future retarders for mitigation of polarization and intensity fringe errors in other high spectral resolution astronomical systems.

Rigorous vector wave propagation for arbitrary flat media

5 Jun 2018

by Bos, Steven P., Haffert, Sebastiaan Y., Keller, Christoph U., is now available here.

Abstract: Precise modelling of the (off-axis) point spread function (PSF) to identify geometrical and polarization aberrations is important for many optical systems. In order to characterise the PSF of the system in all Stokes parameters, an end-to-end simulation of the system has to be performed in which Maxwell's equations are rigorously solved. We present the first results of a python code that we are developing to perform multiscale end-to-end wave propagation simulations that include all relevant physics. Currently we can handle plane-parallel near- and far-field vector diffraction effects of propagating waves in homogeneous isotropic and anisotropic materials, refraction and reflection of flat parallel surfaces, interference effects in thin films and unpolarized light. We show that the code has a numerical precision on the order of 10-16 for non-absorbing isotropic and anisotropic materials. For absorbing materials the precision is on the order of 10-8. The capabilities of the code are demonstrated by simulating a converging beam reflecting from a flat aluminium mirror at normal incidence.

On-sky Performance Analysis of the Vector Apodizing Phase Plate Coronagraph on MagAO/Clio2

5 Jun 2018

by Otten, Gilles P. P. L., Snik, Frans, Kenworthy, Matthew A., Keller, Christoph U., Males, Jared R., Morzinski, Katie M., Close, Laird M., Codona, Johanan L., Hinz, Philip M., Hornburg, Kathryn J., Brickson, Leandra L., Escuti, Michael J., is now available here.

Abstract: We report on the performance of a vector apodizing phase plate coronagraph that operates over a wavelength range of 2-5 μm and is installed in MagAO/Clio2 at the 6.5 m Magellan Clay telescope at Las Campanas Observatory, Chile. The coronagraph manipulates the phase in the pupil to produce three beams yielding two coronagraphic point-spread functions (PSFs) and one faint leakage PSF. The phase pattern is imposed through the inherently achromatic geometric phase, enabled by liquid crystal technology and polarization techniques. The coronagraphic optic is manufactured using a direct-write technique for precise control of the liquid crystal pattern and multitwist retarders for achromatization. By integrating a linear phase ramp to the coronagraphic phase pattern, two separated coronagraphic PSFs are created with a single pupil-plane optic, which makes it robust and easy to install in existing telescopes. The two coronagraphic PSFs contain a 180° dark hole on each side of a star, and these complementary copies of the star are used to correct the seeing halo close to the star. To characterize the coronagraph, we collected a data set of a bright (mL = 0-1) nearby star with ˜1.5 hr of observing time. By rotating and optimally scaling one PSF and subtracting it from the other PSF, we see a contrast improvement by 1.46 magnitudes at 3.5 λ /D. With regular angular differential imaging at 3.9 μm, the MagAO vector apodizing phase plate coronagraph delivers a 5σ {{Δ }}{mag} contrast of 8.3 (={10}-3.3) at 2 λ /D and 12.2 (={10}-4.8) at 3.5 λ /D.

The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environments

5 Jun 2018

by Wilby, M. J., Keller, C. U., Snik, F., Korkiakoski, V., Pietrow, A. G. M., is now available here.

Abstract: The raw coronagraphic performance of current high-contrast imaging instruments is limited by the presence of a quasi-static speckle (QSS) background, resulting from instrumental Non-Common Path Errors (NCPEs). Rapid development of efficient speckle subtraction techniques in data reduction has enabled final contrasts of up to 10-6 to be obtained, however it remains preferable to eliminate the underlying NCPEs at the source. In this work we introduce the coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront sensor suitable for real-time NCPE correction. This combines the Apodizing Phase Plate (APP) coronagraph with a holographic modal wavefront sensor to provide simultaneous coronagraphic imaging and focal-plane wavefront sensing with the science point-spread function. We first characterise the baseline performance of the cMWS via idealised closed-loop simulations, showing that the sensor is able to successfully recover diffraction-limited coronagraph performance over an effective dynamic range of ±2.5 radians root-mean-square (rms) wavefront error within 2-10 iterations, with performance independent of the specific choice of mode basis. We then present the results of initial on-sky testing at the William Herschel Telescope, which demonstrate that the sensor is capable of NCPE sensing under realistic seeing conditions via the recovery of known static aberrations to an accuracy of 10 nm (0.1 radians) rms error in the presence of a dominant atmospheric speckle foreground. We also find that the sensor is capable of real-time measurement of broadband atmospheric wavefront variance (50% bandwidth, 158 nm rms wavefront error) at a cadence of 50 Hz over an uncorrected telescope sub-aperture. When combined with a suitable closed-loop adaptive optics system, the cMWS holds the potential to deliver an improvement of up to two orders of magnitude over the uncorrected QSS floor. Such a sensor would be eminently suitable for the direct imaging and spectroscopy of exoplanets with both existing and future instruments, including EPICS and METIS for the E-ELT.

The SPEX-airborne multi-angle spectropolarimeter on NASA's ER-2 research aircraft: capabilities, data processing and data products

5 Jun 2018

by Rietjens, J., Smit, M., Hasekamp, O. P., Grim, M., Eggens, M., Eigenraam, A., Keizer, G., van Loon, D., Talsma, J., van der Vlugt, J., Wolfs, R., van Harten, G., Rheingans, B. E., Snik, F., Keller, C. U., Smit, H., is now available here.

Abstract: A multi-angle spectropolarimeter payload, "SPEX-airborne" has been developed for observing and characterizing aerosols from NASA's high-altitude research aircraft ER-2. SPEX-airborne provides autonomously multi-angle snapshot measurements of spectral radiance and degree of linear polarization over a 7 degree swath in the visible part of the optical spectrum. The instrument is unique in the sense that it combines 30 highly accurate polarimetric measurements with hyperspectral radiance measurements at 2.5 nm resolution simultaneously at nine fixed viewing angles and that it offers the possibility to include polarimetric measurements in absorption bands at lower accuracy. This combination of measurements holds great potential for present and new retrieval algorithms to derive aerosol microphysical properties during airborne campaigns. The opto-mechanical subsystem of SPEX-airborne is based on the Spectropolarimeter for Planetary EXploration (SPEX) prototype, which has been developed over recent years by a consortium of Dutch institutes and industry. The polarimetry technique used is spectral polarization modulation, which has been proven to enable high accuracy polarimetric measurements. In laboratory conditions, the SPEX prototype has a demonstrated polarimetric accuracy of 0.002 in the degree of linear polarization. The SPEX prototype has been made fit for autonomous operation on NASA's ER-2 high altitude platform. In this presentation we will present the design and main subsystems of the payload, and address the operational modes. An outline of the data processing chain including calibration data will be given and the foreseen capability and performance will be discussed. We will discuss the quality of the polarimetric measurement in the lab and as recorded during the maiden flight in 2016 when SPEX-airborne was flying together with JPL's AirMSPI imaging polarimeter. Finally, we will give an outlook on the processing of the data of land and ocean scenes, and on the possibilities for aerosol retrieval algorithms that the SPEX-airborne instrument offers, most notably the flexibility in number and center of the wavelength bands, and the incorporation of (polarimetric) O2A-band measurements.

News ArchiveFirst direct detection of a polarized companion outside of a resolved circumbinary disk around CS ChaThe Single-mode Complex Amplitude Refinement (SCAR) coronagraph: II. Lab verification, and toward the characterization of Proxima bLaboratory verification of 'Fast & Furious' phase diversity: Towards controlling the low wind effect in the SPHERE instrumentAtmospheric Implications of Light Alkane Emissions From the U.S. Oil and Natural Gas SectorThe Spectropolarimeter for Planetary Exploration: SPEXSPEX: the Spectropolarimeter for Planetary ExplorationSPEX: a highly accurate spectropolarimeter for atmospheric aerosol characterizationPolarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retardersCombining angular differential imaging and accurate polarimetry with SPHERE/IRDIS to characterize young giant exoplanetsThree Years of SPHERE: The Latest View of the Morphology and Evolution of Protoplanetary DiscsPolarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retardersRigorous vector wave propagation for arbitrary flat mediaOn-sky Performance Analysis of the Vector Apodizing Phase Plate Coronagraph on MagAO/Clio2The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environmentsThe SPEX-airborne multi-angle spectropolarimeter on NASA's ER-2 research aircraft: capabilities, data processing and data productsBP Piscium: its flaring disc imaged with SPHERE/ZIMPOLDusty tails of evaporating exoplanets. II. Physical modelling of the KIC 12557548b light curveMultiple rings in the transition disk and companion candidates around RX J1615.3-3255. High contrast imaging with VLT/SPHEREDirect detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERESearch for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri eNovel instrument concepts for characterizing directly imaged exoplanetsThe Leiden EXoplanet Instrument (LEXI): a high-contrast high-dispersion spectrographEnd-to-end simulations of the E-ELT/METIS coronagraphsA "Fast and Furious'" solution to the low-wind effect for SPHERE at the VLTFocal-plane electric field sensing with pupil-plane hologramsThe ZIMPOL high contrast imaging polarimeter for SPHERE: polarimetric high contrast commissioning resultsDesigning and testing the coronagraphic Modal Wavefront Sensor: a fast non-common path error sensor for high-contrast imagingThe Hera Saturn entry probe missionDesign trade-off and proof of concept for LOUPE, the Lunar Observatory for Unresolved Polarimetry of EarthDirect detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHEREDusty tails of evaporating exoplanets. II. Physical modelling of the KIC 12557548b light curveSearch for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri eFlySPEX: a flexible multi-angle spectropolarimetric sensing systemAccurate spectrally modulating polarimeters for atmospheric aerosol characterizationInstrumemtationInversions of High-Cadence SOLIS-VSM Stokes ObservationsThe Hera Saturn Entry Probe MissionCombining high-dispersion spectroscopy with high contrast imaging: Probing rocky planets around our nearest neighborsMagnetic field topology and chemical spot distributions in the extreme Ap star HD 75049Use of neural networks in ground-based aerosol retrievals from multi-angle spectropolarimetric observationsAtmospheric aerosol characterization with a ground-based SPEX spectropolarimetric instrumentSurprising detection of an equatorial dust lane on the AGB star IRC+10216Mapping atmospheric aerosols with a citizen science network of smartphone spectropolarimetersUse of neural networks in ground-based aerosol retrievals from multi-angle spectropolarimetric observationsFocal-plane wavefront sensing with high-order adaptive optics systemsDrift scanning technique for mid-infrared background subtractionCharacterizing instrumental effects on polarization at a Nasmyth focus using NaCoThe ZIMPOL high contrast imaging polarimeter for SPHERE: system test resultsLOUPE: Spectropolarimetry of the Earth from the surface of the MoonTowards Polarimetric Exoplanet Imaging with ELTsAstronomical Polarimetry: Polarized Views of Stars and PlanetsSearching for signs of habitability with LOUPE, the Lunar Observatory of Unresolved Polarimetry of EarthFocal-plane wavefront sensing with high-order adaptive optics systemsFast & Furious focal-plane wavefront sensingSpectral line polarimetry with a channeled polarimeterOptimization-based wavefront sensorless adaptive optics for multiphoton microscopyAtmospheric aerosol characterization with a ground-based SPEX spectropolarimetric instrumentFive-dimensional optical instrumentation: combining polarimetry with time-resolved integral-field spectroscopySnapshot coherence-gated direct wavefront sensing for multi-photon microscopyInstrumental polarisation at the Nasmyth focus of the E-ELTImaging the circumstellar environment of the young T Tauri star SU AurigaeAnalysis and interpretation of 15 quarters of Kepler data of the disintegrating planet KIC 12557548 bCrowdsourced aerosol measurements using smartphone spectropolarimetersRemote sensing of atmospheric aerosols with the SPEX spectropolarimeterCalibrating a high-resolution wavefront corrector with a static focal-plane cameraIterative linear focal-plane wavefront correctionSPHERE-ZIMPOL system testing: status report on polarimetric high contrast resultsCalibrating a high-resolution wavefront corrector with a static focal-plane cameraThree-dimensional magnetic and abundance mapping of the cool Ap star HD 24712 . I. Spectropolarimetric observations in all four Stokes parametersAre there tangled magnetic fields on HgMn stars?The color dependent morphology of the post-AGB star HD 161796Observing Circumstellar Neighbourhoods with the Extreme PolarimeterSterrekundig Instituut Utrecht: The Last YearsAstronomical Polarimetry: Polarized Views of Stars and PlanetsThe color dependent morphology of the post-AGB star HD161796Magnetically Controlled Accretion on the Classical T Tauri Stars GQ Lupi and TW HydraeHARPS Spectropolarimetry of the Classical T Tauri Stars GQ Lup and TW HyaAstronomical Polarimetry: Polarized Views of Stars and PlanetsObserving the Earth as an exoplanet with LOUPE, the lunar observatory for unresolved polarimetry of EarthSemidefinite programming for model-based sensorless adaptive opticsUnusual Stokes V profiles during flaring activity of a delta sunspotPotential of phase-diversity for metrology of active instrumentsModeling the instrumental polarization of the VLT and E-ELT telescopes with the M&m's codeA spectro-polarimetric integral field spectrograph for EPICS-EPOLThe extreme polarimeter: design, performance, first results and upgradesSearching for signs of habitability with LOUPE, the Lunar Observatory of Unresolved Polarimetry of EarthEvidence for the disintegration of KIC 12557548 bSterrekundig Instituut Utrecht: The Last YearsLinear analytical solution to the phase diversity problem for extended objects based on the Born approximationBilinear solution to the phase diversity problem for extended objects based on the Born approximationExperimental validation of optimization concepts for focal-plane image processing with adaptive opticsFOAM: the modular adaptive optics frameworkExtremely fast focal-plane wavefront sensing for extreme adaptive opticsEvidence for the disintegration of KIC 12557548 bExtremely fast focal-plane wavefront sensing for extreme adaptive opticsConstraining the circumbinary envelope of Z Canis Majoris via imaging polarimetryData driven identification and aberration correction for model-based sensorless adaptive opticsHARPS spectropolarimetry of classical T Tauri starsSPEX2Earth, a novel spectropolarimeter for remote sensing of aerosols and cloudsiSPEX: everybody can measure atmospheric aerosols with a smartphone spectropolarimeteriSPEX: the creation of an aerosol sensor network of smartphone spectropolarimetersObserving the Earth as an exoplanetMultiwavelength imaging polarimetry of Venus at various phase anglesMagnetism, chemical spots, and stratification in the HgMn star ϕ PhoenicisCoherence-gated wavefront sensing for microscopy using fringe analysisSignatures of Water Clouds on Exoplanets: Numerical Simulations.New Insights into Stellar Magnetism from the Spectropolarimetry in All Four Stokes ParametersInnovative Imaging of Young Stars: First Light ExPo ObservationsSimulating Polarized Light from ExoplanetsData Reduction Approach for the Extreme PolarimeterDesign and Prototype Results of the ExPo Imaging PolarimeterPlanetary science: In search of biosignaturesObserving the Earth as an exoplanet with LOUPE, the Lunar Observatory for Unresolved Polarimetry of EarthDirect imaging of a massive dust cloud around R Coronae BorealisSignatures of Water Clouds on Exoplanets: Numerical Simulations.Joint optimization of phase diversity and adaptive optics: demonstration of potentialThe effects of disk and dust structure on observed polarimetric images of protoplanetary disksMagnetism, chemical spots, and stratification in the HgMn star phi PhoenicisSpectropolarimeter for planetary exploration (SPEX): performance measurements with a prototypeNo magnetic field in the spotted HgMn star μ LeporisPrototyping for the Spectropolarimeter for Planetary EXploration (SPEX): calibration and sky measurementsM&m's: an error budget and performance simulator code for polarimetric systemsThe ZIMPOL high contrast imaging polarimeter for SPHERE: sub-system test resultsFast horizontal flows in a quiet sun MHD simulation and their spectroscopic signaturesThe search for magnetic fields in mercury-manganese starsSpectral and polarimetric characterization of gazeous and telluric planets with SEE COASTData-reduction techniques for high-contrast imaging polarimetry. Applications to ExPoData Reduction Techniques for High Contrast Imaging Polarimetry. Applications to ExPoFirst Detection of Linear Polarization in the Line Profiles of Active Cool StarsChemical spots in the absence of magnetic field in the binary HgMn star 66 EridaniThe Polarization Optics for the European Solar TelescopeThe HARPS PolarimeterHARPSpol — The New Polarimetric Mode for HARPSEPOL: the exoplanet polarimeter for EPICS at the E-ELTImaging polarimetry of protoplanetary disks: feasibility and usabilityImaging polarimetry of circumstellar environments with the Extreme PolarimeterThe search for magnetic fields in mercury-manganese starsThe search for magnetic fields in mercury-manganese starsThe HARPS polarimeterObservations of solar scattering polarization at high spatial resolutionThe polarization optics for the European Solar Telescope (EST)EPOL: the exoplanet polarimeter for EPICS at the E-ELTThe ZIMPOL high-contrast imaging polarimeter for SPHERE: design, manufacturing, and testingEPICS: direct imaging of exoplanets with the E-ELTSPEX: the spectropolarimeter for planetary explorationObservations of solar scattering polarization at high spatial resolutionInversions of High-Cadence SOLIS-VSM Stokes ObservationsEPICS, the exoplanet imager for the E-ELTTwo Ways of Improving Stokes InversionsStatistics of Convective Collapse Events in the Photosphere and Chromosphere Observed with the HINODE SOTThe case for spectropolarimetry with SPEX on EJSMStatistics of convective collapse events in the photosphere and chromosphere observed with the Hinode SOTAn IFU for diffraction-limited 3D spectroscopic imaging: laboratory and on-site testsPolarimetric Measurements of Protoplanetary Disks with ExPo Tim van Werkhoven The Prototype of the Small Synoptic Second Solar Spectrum Telescope (S^5T)Polarimetry from the Ground UpVector Magnetic Field Inversions of High Cadence SOLIS-VSM DataSOLIS Vector Spectromagnetograph: Status and ScienceA Brief History of the Second Solar SpectrumStatistics of convective collapse events in the photosphere and chromosphere observed with the Hinode SOTCharacterization of Extra-solar Planets with Direct-Imaging TechniquesPolarization Properties of Real Aluminum Mirrors, I. Influence of the Aluminum Oxide LayerSuper earth explorer: a coronagraphic off-axis space telescopePolarization properties of real aluminum mirrors; I. Influence of the aluminum oxide layerSpectral modulation for full linear polarimetryThe Prototype of the Small Synoptic Second Solar Spectrum Telescope (S5T)An analytical model to demonstrate the reliability of reconstructed `active longitudes'.Polarimetry of Mars with SPEX, an Innovative SpectropolarimeterDiversity among other worlds: characterization of exoplanets by direct detectionA New Era in Solar Thermal-IR Astronomy: the NSO Array Camera (NAC) on the McMath-Pierce TelescopeSPEX: an in-orbit spectropolarimeter for planetary explorationDesign of a laboratory simulator to test exoplanet imaging polarimetryThe Extreme Polarimeter (ExPo): design of a sensitive imaging polarimeterSPHERE ZIMPOL: overview and performance simulationThe upgrade of HARPS to a full-Stokes high-resolution spectropolarimeterDesign of a laboratory simulator to test exoplanet imaging polarimetryThe Extreme Polarimeter (ExPo): design of a sensitive imaging polarimeterSPHERE ZIMPOL: overview and performance simulationThe upgrade of HARPS to a full-Stokes high-resolution spectropolarimeterPolarimetry from the Ground UpNew web page online