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Christoph U. Keller
Professor of Experimental Astrophysics

Leiden Observatory
Leiden University, The Netherlands

RefPlanets: Search for reflected light from extrasolar planets with SPHERE/ZIMPOL

20 Feb 2020

by Hunziker, S., Schmid, H. M., Mouillet, D., Milli, J., Zurlo, A., Delorme, P., Abe, L., Avenhaus, H., Baruffolo, A., Bazzon, A., Boccaletti, A., Baudoz, P., Beuzit, J. L., Carbillet, M., Chauvin, G., Claudi, R., Costille, A., Daban, J.-B., Desidera, S., Dohlen, K., Dominik, C., Downing, M., Engler, N., Feldt, M., Fusco, T., Ginski, C., Gisler, D., Girard, J. H., Gratton, R., Henning, Th., Hubin, N., Kasper, M., Keller, C. U., Langlois, M., Lagadec, E., Martinez, P., Maire, A. L., Menard, F., Meyer, M. R., Pavlov, A., Pragt, J., Puget, P., Quanz, S. P., Rickman, E., Roelfsema, R., Salasnich, B., Sauvage, J.-F., Siebenmorgen, R., Sissa, E., Snik, F., Suarez, M., Szulágyi, J., Thalmann, Ch., Turatto, M., Udry, S., van Holstein, R. G., Vigan, A., Wildi, F., is now available here.

Abstract: Aims: RefPlanets is a guaranteed time observation programme that uses the Zurich IMaging POLarimeter (ZIMPOL) of Spectro-Polarimetric High-contrast Exoplanet REsearch instrument at the Very Large Telescope to perform a blind search for exoplanets in wavelengths from 600 to 900 nm. The goals of this study are the characterisation of the unprecedented high polarimetic contrast and polarimetric precision capabilities of ZIMPOL for bright targets, the search for polarised reflected light around some of the closest bright stars to the Sun, and potentially the direct detection of an evolved cold exoplanet for the first time. Methods: For our observations of α Cen A and B, Sirius A, Altair, ɛ Eri and τ Ceti we used the polarimetricdifferential imaging (PDI) mode of ZIMPOL which removes the speckle noise down to the photon noise limit for angular separations ≿0.6''. We describe some of the instrumental effects that dominate the noise for smaller separations and explain how to remove these additional noise effects in post-processing. We then combine PDI with angular differential imaging as a final layer of post-processing to further improve the contrast limits of our data at these separations. Results: For good observing conditions we achieve polarimetric contrast limits of 15.0-16.3 mag at the effective inner working angle of ~0.13'', 16.3-18.3 mag at 0.5'', and 18.8-20.4 mag at 1.5''. The contrast limits closer in (≾0.6'') display a significant dependence on observing conditions, while in the photon-noise-dominated regime (≿0.6'') the limits mainly depend on the brightness of the star and the total integration time. We compare our results with contrast limits from other surveys and review the exoplanet detection limits obtained with different detection methods. For all our targets we achieve unprecedented contrast limits. Despite the high polarimetric contrasts we are not able to find any additional companions or extended polarised light sources in the data obtained so far. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs: 095.C-0312(B), 096.C-0326(A), 097.C-0524(A), 097.C-0524(B), 098.C-0197(A), 099.C-0127(A), 099.C-0127(B), 0102.C-0435(A).

Polarimetric imaging mode of VLT/SPHERE/IRDIS. II. Characterization and correction of instrumental polarization effects

20 Feb 2020

by van Holstein, R. G., Girard, J. H., de Boer, J., Snik, F., Milli, J., Stam, D. M., Ginski, C., Mouillet, D., Wahhaj, Z., Schmid, H. M., Keller, C. U., Langlois, M., Dohlen, K., Vigan, A., Pohl, A., Carbillet, M., Fantinel, D., Maurel, D., Origné, A., Petit, C., Ramos, J., Rigal, F., Sevin, A., Boccaletti, A., Le Coroller, H., Dominik, C., Henning, T., Lagadec, E., Ménard, F., Turatto, M., Udry, S., Chauvin, G., Feldt, M., Beuzit, J.-L., is now available here.

Abstract: Context. Circumstellar disks and self-luminous giant exoplanets or companion brown dwarfs can be characterized through direct-imaging polarimetry at near-infrared wavelengths. SPHERE/IRDIS at the Very Large Telescope has the capabilities to perform such measurements, but uncalibrated instrumental polarization effects limit the attainable polarimetric accuracy. Aims: We aim to characterize and correct the instrumental polarization effects of the complete optical system, that is, the telescope and SPHERE/IRDIS. Methods: We created a detailed Mueller matrix model in the broadband filters Y, J, H, and Ks and calibrated the model using measurements with SPHERE's internal light source and observations of two unpolarized stars. We developed a data-reduction method that uses the model to correct for the instrumental polarization effects, and applied it to observations of the circumstellar disk of T Cha. Results: The instrumental polarization is almost exclusively produced by the telescope and SPHERE's first mirror and varies with telescope altitude angle. The crosstalk primarily originates from the image derotator (K-mirror). At some orientations, the derotator causes severe loss of signal (> 90% loss in the H- and Ks-band) and strongly offsets the angle of linear polarization. With our correction method we reach, in all filters, a total polarimetric accuracy of ≲0.1% in the degree of linear polarization and an accuracy of a few degrees in angle of linear polarization. Conclusions: The correction method enables us to accurately measure the polarized intensity and angle of linear polarization of circumstellar disks, and is a vital tool for detecting spatially unresolved (inner) disks and measuring the polarization of substellar companions. We have incorporated the correction method in a highly-automated end-to-end data-reduction pipeline called IRDAP, which we made publicly available online. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under program ID 60.A-9800(S), 60.A-9801(S) and 096.C-0248(C). The data-reduction pipeline IRDAP is available at http://https://irdap.readthedocs.io

Polarimetric imaging mode of VLT/SPHERE/IRDIS. I. Description, data reduction, and observing strategy

20 Feb 2020

by de Boer, J., Langlois, M., van Holstein, R. G., Girard, J. H., Mouillet, D., Vigan, A., Dohlen, K., Snik, F., Keller, C. U., Ginski, C., Stam, D. M., Milli, J., Wahhaj, Z., Kasper, M., Schmid, H. M., Rabou, P., Gluck, L., Hugot, E., Perret, D., Martinez, P., Weber, L., Pragt, J., Sauvage, J.-F., Boccaletti, A., Le Coroller, H., Dominik, C., Henning, T., Lagadec, E., Ménard, F., Turatto, M., Udry, S., Chauvin, G., Feldt, M., Beuzit, J.-L., is now available here.

Abstract: Context. Polarimetric imaging is one of the most effective techniques for high-contrast imaging and for the characterization of protoplanetary disks, and it has the potential of becoming instrumental in the characterization of exoplanets. The Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument installed on the Very Large Telescope (VLT) contains the InfraRed Dual-band Imager and Spectrograph (IRDIS) with a dual-beam polarimetric imaging (DPI) mode, which offers the capability of obtaining linear polarization images at high contrast and resolution. Aims: We aim to provide an overview of the polarimetric imaging mode of VLT/SPHERE/IRDIS and study its optical design to improve observing strategies and data reduction. Methods: For H-band observations of TW Hydrae, we compared two data reduction methods that correct for instrumental polarization effects in different ways: a minimization of the "noise" image (Uϕ), and a correction method based on a polarimetric model that we have developed, as presented in Paper II of this study. Results: We use observations of TW Hydrae to illustrate the data reduction. In the images of the protoplanetary disk around this star, we detect variability in the polarized intensity and angle of linear polarization that depend on the pointing-dependent instrument configuration. We explain these variations as instrumental polarization effects and correct for these effects using our model-based correction method. Conclusions: The polarimetric imaging mode of IRDIS has proven to be a very successful and productive high-contrast polarimetric imaging system. However, the instrument performance is strongly dependent on the specific instrument configuration. We suggest adjustments to future observing strategies to optimize polarimetric efficiency in field-tracking mode by avoiding unfavorable derotator angles. We recommend reducing on-sky data with the pipeline called IRDAP, which includes the model-based correction method (described in Paper II) to optimally account for the remaining telescope and instrumental polarization effects and to retrieve the true polarization state of the incident light. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 095.C-0273(D).

A snapshot full-Stokes spectropolarimeter for detecting life on Earth

20 Feb 2020

by Snik, Frans, Keller, Christoph U., Doelman, David S., Kühn, Jonas, Patty, C. H. Lucas, Hoeijmakers, H. Jens, Pallichadath, Vidhya, Stam, Daphne M., Pommerol, Antoine, Poch, Olivier, Demory, Brice-Olivier, is now available here.

Abstract: We present the design of a point-and-shoot non-imaging full-Stokes spectropolarimeter dedicated to detecting life on Earth from an orbiting platform like the ISS. We specifically aim to map circular polarization in the spectral features of chorophyll and other biopigments for our planet as a whole. These non-zero circular polarization signatures are caused by homochirality of the molecular and supramolecular configurations of organic matter, and are considered the most unambiguous biomarker. To achieve a fully solid-state snapshot design, we implement a novel spatial modulation that completely separates the circular and linear polarization channels. The polarization modulator consists of a patterned liquid-crystal quarter-wave plate inside the spectrograph slit, which also constitutes the first optical element of the instrument. This configuration eliminates cross-talk between linear and circular polarization, which is crucial because linear polarization signals are generally much stronger than the circular polarization signals. This leads to a quite unorthodox optical concept for the spectrograph, in which the object and the pupil are switched. We discuss the general design requirements and trade-offs of LSDpol (Life Signature Detection polarimeter), a prototype instrument that is currently under development.

The Young Suns Exoplanet Survey: Detection of a wide-orbit planetary-mass companion to a solar-type Sco-Cen member

19 Jan 2020

by Bohn, A. J., Kenworthy, M. A., Ginski, C., Manara, C. F., Pecaut, M. J., de Boer, J., Keller, C. U., Mamajek, E. E., Meshkat, T., Reggiani, M., Todorov, K. O., Snik, F., is now available here.

Abstract: The Young Suns Exoplanet Survey consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of 15 ± 3 Myr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211-6456207) that is located at a distance of 94.6 ± 0.3 pc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to 1.00± 0.02 M_{⊙ } and an age of 16.7± 1.4 Myr. The companion TYC 8998-760-1 b is detected at a projected separation of 1.71″, which implies a projected physical separation of 162 au. Photometric measurements ranging from Y to M band provide a mass estimate of 14± 3 M_jup by comparison to BT-Settl and AMES-dusty isochrones, corresponding to a mass ratio of q = 0.013 ± 0.003 with respect to the primary. We rule out additional companions to TYC 8998-760-1 that are more massive than 12 M_jup and farther than 12 au away from the host. Future polarimetric and spectroscopic observations of this system with ground and space based observatories will facilitate testing of formation and evolution scenarios shaping the architecture of the circumstellar environment around this `young Sun'.

Overview of focal plane wavefront sensors to correct for the Low Wind Effect on SUBARU/SCExAO

19 Jan 2020

by Vievard, Sebastien, Bos, Steven, Cassaing, Frederic, Ceau, Alban, Guyon, Olivier, Jovanovic, Nemanja, Keller, Christoph U., Lozi, Julien, Martinache, Frantz, Montmerle-Bonnefois, Aurelie, Mugnier, Laurent, NDiaye, Mamadou, Norris, Barnaby, Sahoo, Ananya, Sauvage, Jean-Francois, Snik, Frans, Wilby, Michael J., Wong, Alisson, is now available here.

Abstract: The Low Wind Effect (LWE) refers to a phenomenon that occurs when the wind speed inside a telescope dome drops below $3$m/s creating a temperature gradient near the telescope spider. This produces phase discontinuities in the pupil plane that are not detected by traditional Adaptive Optics (AO) systems such as the pyramid wavefront sensor or the Shack-Hartmann. Considering the pupil as divided in 4 quadrants by regular spiders, the phase discontinuities correspond to piston, tip and tilt aberrations in each quadrant of the pupil. Uncorrected, it strongly decreases the ability of high contrast imaging instruments utilizing coronagraphy to detect exoplanets at small angular separations. Multiple focal plane wavefront sensors are currently being developed and tested on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument at Subaru Telescope: Among them, the Zernike Asymmetric Pupil (ZAP) wavefront sensor already showed on-sky that it could measure the LWE induced aberrations in focal plane images. The Fast and Furious algorithm, using previous deformable mirror commands as temporal phase diversity, showed in simulations its efficiency to improve the wavefront quality in the presence of LWE. A Neural Network algorithm trained with SCExAO telemetry showed promising PSF prediction on-sky. The Linearized Analytic Phase Diversity (LAPD) algorithm is a solution for multi-aperture cophasing and is studied to correct for the LWE aberrations by considering the Subaru Telescope as a 4 sub-aperture instrument. We present the different algorithms, show the latest results and compare their implementation on SCExAO/SUBARU as real-time wavefront sensors for the LWE compensation.

Focal-plane wavefront sensing with the vector-Apodizing Phase Plate

19 Jan 2020

by Bos, S. P., Doelman, D. S., Lozi, J., Guyon, O., Keller, C. U., Miller, K. L., Jovanovic, N., Martinache, F., Snik, F., is now available here.

Abstract: Context. One of the key limitations of the direct imaging of exoplanets at small angular separations are quasi-static speckles that originate from evolving non-common path aberrations (NCPA) in the optical train downstream of the instrument's main wavefront sensor split-off. Aims: In this article we show that the vector-Apodizing Phase Plate (vAPP) coronagraph can be designed such that the coronagraphic point spread functions (PSFs) can act as wavefront sensors to measure and correct the (quasi-)static aberrations without dedicated wavefront sensing holograms or modulation by the deformable mirror. The absolute wavefront retrieval is performed with a non-linear algorithm. Methods: The focal-plane wavefront sensing (FPWFS) performance of the vAPP and the algorithm are evaluated via numerical simulations to test various photon and read noise levels, the sensitivity to the 100 lowest Zernike modes, and the maximum wavefront error (WFE) that can be accurately estimated in one iteration. We apply these methods to the vAPP within SCExAO, first with the internal source and subsequently on-sky. Results: In idealized simulations we show that for 107 photons the root mean square (rms) WFE can be reduced to ˜λ/1000, which is 1 nm rms in the context of the SCExAO system. We find that the maximum WFE that can be corrected in one iteration is ˜λ/8 rms or ˜200 nm rms (SCExAO). Furthermore, we demonstrate the SCExAO vAPP capabilities by measuring and controlling the 30 lowest Zernike modes with the internal source and on-sky. On-sky, we report a raw contrast improvement of a factor ˜2 between 2 and 4 λ/D after five iterations of closed-loop correction. When artificially introducing 150 nm rms WFE, the algorithm corrects it within five iterations of closed-loop operation. Conclusions: FPWFS with the vAPP coronagraphic PSFs is a powerful technique since it integrates coronagraphy and wavefront sensing, eliminating the need for additional probes and thus resulting in a 100% science duty cycle and maximum throughput for the target.

Highly multiplexed Bragg gratings for large field of view gas sensing in planetary atmospheres

19 Jan 2020

by Haffert, S. Y., Por, E. H., Keller, C. U., is now available here.

Abstract: Not Available

RefPlanets: Search for reflected light from extra-solar planets with SPHERE/ZIMPOL

19 Jan 2020

by Hunziker, S., Schmid, H. M., Mouillet, D., Milli, J., Zurlo, A., Delorme, P., Abe, L., Avenhaus, H., Baruffolo, A., Bazzon, A., Boccaletti, A., Baudoz, P., Beuzit, J. L., Carbillet, M., Chauvin, G., Claudi, R., Costille, A., Daban, J. B., Desidera, S., Dohlen, K., Dominik, C., Downing, M., Engler, N., Feldt, M., Fusco, T., Ginski, C., Gisler, D., Girard, J. H., Gratton, R., Henning, Th., Hubin, N., Kasper, M., Keller, C. U., Langlois, M., Lagadec, E., Martinez, P., Maire, A. L., Menard, F., Meyer, M. R., Pavlov, A., Pragt, J., Puget, P., Quanz, S. P., Rickman, E., Roelfsema, R., Salasnich, B., Sauvage, J. F., Siebenmorgen, R., Sissa, E., Snik, F., Suarez, M., Szulagyi, J., Thalmann, Ch., Turatto, M., Udry, S., van Holstein, R. G., Vigan, A., Wildi, F., is now available here.

Abstract: RefPlanets is a guaranteed time observation (GTO) programme that uses the Zurich IMaging POLarimeter (ZIMPOL) of SPHERE/VLT for a blind search for exoplanets in wavelengths from 600-900 nm. The goals of this study are the characterization of the unprecedented high polarimetic contrast and polarimetric precision capabilities of ZIMPOL for bright targets, the search for polarized reflected light around some of the closest bright stars to the Sun and potentially the direct detection of an evolved cold exoplanet for the first time. For our observations of Alpha Cen A and B, Sirius A, Altair, Eps Eri and Tau Ceti we used the polarimetric differential imaging (PDI) mode of ZIMPOL which removes the speckle noise down to the photon noise limit for angular separations >0.6". We describe some of the instrumental effects that dominate the noise for smaller separations and explain how to remove these additional noise effects in post-processing. We then combine PDI with angular differential imaging (ADI) as a final layer of post-processing to further improve the contrast limits of our data at these separations. For good observing conditions we achieve polarimetric contrast limits of 15.0-16.3 mag at the effective inner working angle of about 0.13", 16.3-18.3 mag at 0.5" and 18.8-20.4 mag at 1.5". The contrast limits closer in (<0.6") depend significantly on the observing conditions, while in the photon noise dominated regime (>0.6"), the limits mainly depend on the brightness of the star and the total integration time. We compare our results with contrast limits from other surveys and review the exoplanet detection limits obtained with different detection methods. For all our targets we achieve unprecedented contrast limits. Despite the high polarimetric contrasts we are not able to find any additional companions or extended polarized light sources in the data that has been taken so far.

The polarimetric imaging mode of VLT/SPHERE/IRDIS II: Characterization and correction of instrumental polarization effects

19 Jan 2020

by van Holstein, R. G., Girard, J. H., de Boer, J., Snik, F., Milli, J., Stam, D. M., Ginski, C., Mouillet, D., Wahhaj, Z., Schmid, H. M., Keller, C. U., Langlois, M., Dohlen, K., Vigan, A., Pohl, A., Carbillet, M., Fantinel, D., Maurel, D., Origné, A., Petit, C., Ramos, J., Rigal, F., Sevin, A., Boccaletti, A., Le Coroller, H., Dominik, C., Henning, T., Lagadec, E., Ménard, F., Turatto, M., Udry, S., Chauvin, G., Feldt, M., Beuzit, J.-L., is now available here.

Abstract: Context. Circumstellar disks and self-luminous giant exoplanets or companion brown dwarfs can be characterized through direct-imaging polarimetry at near-infrared wavelengths. SPHERE/IRDIS at the Very Large Telescope has the capabilities to perform such measurements, but uncalibrated instrumental polarization effects limit the attainable polarimetric accuracy. Aims. We aim to characterize and correct the instrumental polarization effects of the complete optical system, i.e. the telescope and SPHERE/IRDIS. Methods. We create a detailed Mueller matrix model in the broadband filters Y-, J-, H- and Ks, and calibrate it using measurements with SPHERE's internal light source and observations of two unpolarized stars. We develop a data-reduction method that uses the model to correct for the instrumental polarization effects, and apply it to observations of the circumstellar disk of T Cha. Results. The instrumental polarization is almost exclusively produced by the telescope and SPHERE's first mirror and varies with telescope altitude angle. The crosstalk primarily originates from the image derotator (K-mirror). At some orientations, the derotator causes severe loss of signal (>90% loss in H- and Ks-band) and strongly offsets the angle of linear polarization. With our correction method we reach in all filters a total polarimetric accuracy of <0.1% in the degree of linear polarization and an accuracy of a few degrees in angle of linear polarization. Conclusions. The correction method enables us to accurately measure the polarized intensity and angle of linear polarization of circumstellar disks, and is a vital tool for detecting unresolved (inner) disks and measuring the polarization of substellar companions. We have incorporated the correction method in a highly-automatic end-to-end data-reduction pipeline called IRDAP which is publicly available at https://irdap.readthedocs.io.

The polarimetric imaging mode of VLT/SPHERE/IRDIS I: Description, data reduction and observing strategy

19 Jan 2020

by de Boer, J., Langlois, M., van Holstein, R. G., Girard, J. H., Mouillet, D., Vigan, A., Dohlen, K., Snik, F., Keller, C. U., Ginski, C., Stam, D. M., Milli, J., Wahhaj, Z., Kasper, M., Schmid, H. M., Rabou, P., Gluck, L., Hugot, E., Perret, D., Martinez, P., Weber, L., Pragt, J., Sauvage, J.-F., Boccaletti, A., Le Coroller, H., Dominik, C., Henning, T., Lagadec, E., Ménard, F., Turatto, M., Udry, S., Chauvin, G., Feldt, M., Beuzit, J.-L., is now available here.

Abstract: Context. Polarimetric imaging is one of the most effective techniques for high-contrast imaging and characterization of protoplanetary disks, and has the potential to be instrumental in characterizing exoplanets. VLT/SPHERE contains the InfraRed Dual-band Imager and Spectrograph (IRDIS) with a dual-beam polarimetric imaging (DPI) mode, which offers the capability to obtain linear polarization images at high contrast and resolution. Aims. We aim to provide an overview of IRDIS/DPI and study its optical design to improve observing strategies and data reduction. Methods. For H-band observations of TW Hya, we compare two data reduction methods that correct for instrumental polarization effects in different ways: a minimization of the noise image, and a polarimetric-model-based correction method that we present in Paper II of this study. Results. We use observations of TW Hya to illustrate the data reduction. In the images of the protoplanetary disk around this star we detect variability in the polarized intensity and angle of linear polarization with pointing-dependent instrument configuration. We explain these variations as instrumental polarization effects and correct for these effects using our model-based correction method. Conclusions. IRDIS/DPI has proven to be a very successful and productive high-contrast polarimetric imaging system. However, the instrument performance depends on the specific instrument configuration. We suggest adjustments to future observing strategies to optimize polarimetric efficiency in field tracking mode by avoiding unfavourable derotator angles. We recommend reducing on-sky data with the pipeline called IRDAP that includes the model-based correction method (described in Paper II) to optimally account for the remaining telescope and instrumental polarization effects and to retrieve the true polarization state of the incident light.

A snapshot full-Stokes spectropolarimeter for detecting life on Earth

19 Jan 2020

by Snik, Frans, Keller, Christoph U., Doelman, David S., Kühn, Jonas, Patty, C. H. Lucas, Hoeijmakers, H. Jens, Pallichadath, Vidhya, Stam, Daphne M., Pommerol, Antoine, Poch, Olivier, Demory, Brice-Olivier, is now available here.

Abstract: We present the design of a point-and-shoot non-imaging full-Stokes spectropolarimeter dedicated to detecting life on Earth from an orbiting platform like the ISS. We specifically aim to map circular polarization in the spectral features of chlorophyll and other biopigments for our planet as a whole. These non-zero circular polarization signatures are caused by homochirality of the molecular and supramolecular configurations of organic matter, and are considered the most unambiguous biomarker. To achieve a fully solid-state snapshot design, we implement a novel spatial modulation that completely separates the circular and linear polarization channels. The polarization modulator consists of a patterned liquid-crystal quarter-wave plate inside the spectrograph slit, which also constitutes the first optical element of the instrument. This configuration eliminates cross-talk between linear and circular polarization, which is crucial because linear polarization signals are generally much stronger than the circular polarization signals. This leads to a quite unorthodox optical concept for the spectrograph, in which the object and the pupil are switched. We discuss the general design requirements and trade-offs of LSDpol (Life Signature Detection polarimeter), a prototype instrument that is currently under development.

Insights into Terrestrial Planet Compositions and Geophysics from Observations of Magma Worlds

19 Jan 2020

by Ridden-Harper, Andrew, Snellen, Ignas, Keller, Christoph, Mollière, Paul, De Mooij, Ernst J. W., Jayawardhana, Ray, de Kok, Remco, Hoeijmakers, H. Jens, Brogi, Matteo, Fridlund, Carl Malcolm, Vermeersen, Bert, Westrenen, Wim, is now available here.

Abstract: There exists a remarkable population of short period transiting rocky exoplanets with temperatures >2,000 K, and masses ranging from about 8 Earth masses, such as the hot super-Earth 55 Cancri e, to that of Mercury or smaller, such as K2-22b. These planets are thought to have mineral atmospheres that are produced by the vaporisation of their magma surfaces, or large exospheres that are produced by sputtering of their atmospheres or exposed surfaces by intense stellar winds. Additionally, the smaller, low surface gravity hot rocky exoplanets have been found to be actively disintegrating and forming 'comet-like' dust tails. Since their atmospheres and released gas and dust can be observationally constrained, these planets present the tantalising prospect of directly probing the composition of rocky planets. Sodium and calcium are promising species to detect given their low sublimation temperatures, large absorption cross-sections, likely presence in terrestrial planet compositions, and presence in Mercury's exosphere. This poster presents the insights we gained from using high-resolution transmission spectroscopy to search for Na and Ca around 55 Cnc e and K2-22 b using several ground based telescopes. For 55 Cne e, we detected a tantilizing 5 σ signal of Ca+ on one night of observation, but a similar signal has not been detected since (despite our unprecedented limits). This may be related to variability of the star-planet system and the planet's magnetic field. For K2-22 b, we did not detect absorption by Na or Ca+, but found lower-limits that are smaller than the expected magnitude of the signal based on the planet's estimated mass-loss rate and assuming a terrestrial composition. We attribute this non-detection to the probed gases being accelerated by the stellar wind and radiation pressure to high velocities, resulting in very broad Doppler shifted absorption signals that are hard to detect. The implications of these results on probing rocky exoplanet compositions, constraining planetary magnetic fields, and understanding the environment around short-period rocky exoplanets are also outlined.

ESA Voyage 2050 White Paper: Detecting life outside our solar system with a large high-contrast-imaging mission

19 Jan 2020

by Snellen, Ignas, Albrecht, Simon, Anglada-Escude, Guillem, Baraffe, Isabelle, Baudoz, Pierre, Benz, Willy, Beuzit, Jean-Luc, Biller, Beth, Birkby, Jayne, Boccaletti, Anthony, van Boekel, Roy, de Boer, Jos, Brogi, Matteo, Buchhave, Lars, Carone, Ludmila, Claire, Mark, Claudi, Riccardo, Demory, Brice-Olivier, Desert, Jean-Michel, Desidera, Silvano, Gaudi, Scott, Gratton, Raffaele, Gillon, Michael, Grenfell, John Lee, Guyon, Olivier, Henning, Thomas, Hinkley, Sasha, Huby, Elsa, Janson, Markus, Helling, Christiane, Heng, Kevin, Kasper, Markus, Keller, Christoph, Kenworthy, Matthew, Krause, Oliver, Kreidberg, Laura, Madhusudhan, Nikku, Lagrange, Anne-Marie, Launhardt, Ralf, Lenton, Tim, Lopez-Puertas, Manuel, Maire, Anne-Lise, Mayne, Nathan, Meadows, Victoria, Mennesson, Bertrand, Micela, Giuseppina, Miguel, Yamila, Milli, Julien, Min, Michiel, de Mooij, Ernst, Mouillet, David, N'Diaye, Mamadou, D'Orazi, Valentina, Palle, Enric, Pagano, Isabella, Piotto, Giampaolo, Queloz, Didier, Rauer, Heike, Ribas, Ignasi, Ruane, Garreth, Selsis, Franck, Snik, Frans, Sozzetti, Alessandro, Stam, Daphne, Stark, Christopher, Vigan, Arthur, de Visser, Pieter, is now available here.

Abstract: In this white paper, we recommend the European Space Agency plays a proactive role in developing a global collaborative effort to construct a large high-contrast imaging space telescope, e.g. as currently under study by NASA. Such a mission will be needed to characterize a sizable sample of temperate Earth-like planets in the habitable zones of nearby Sun-like stars and to search for extraterrestrial biological activity. We provide an overview of relevant European expertise, and advocate ESA to start a technology development program towards detecting life outside the Solar system.

Search for gas from the disintegrating rocky exoplanet K2-22b

19 Jan 2020

by Ridden-Harper, A. R., Snellen, I. A. G., Keller, C. U., Mollière, P., is now available here.

Abstract: Context. The red dwarf star K2-22 is transited every 9.14 h by an object which is best explained by being a disintegrating rocky exoplanet featuring a variable comet-like dust tail. While the dust is thought to dominate the transit light curve, gas is also expected to be present, either from being directly evaporated off the planet or by being produced by the sublimation of dust particles in the tail. Aims: Both ionized calcium and sodium have large cross-sections, and although present at low abundance, exhibit the strongest atomic absorption features in comets. We therefore also identify these species as the most promising tracers of circumplanetary gas in evaporating rocky exoplanets and search for them in the tail of K2-22 b to constrain the gas-loss and sublimation processes in this enigmatic object. Methods: We observed four transits of K2-22 b with X-shooter on the Very Large Telescope operated by ESO to obtain time series of intermediate-resolution (R 11 400) spectra. Our analysis focussed on the two sodium D lines (588.995 and 589.592 nm) and the Ca+ triplet (849.802, 854.209, and 866.214 nm). The stellar calcium and sodium absorption was removed using the out-of-transit spectra. We searched for planet-related absorption in the velocity rest frame of the planet, which changes from approximately -66 to +66 km s-1 during the transit. Results: Since K2-22 b exhibits highly variable transit depths, we analysed the individual nights and their average. By injecting signals we reached 5σ upper limits on the individual nights that range from 11-13% and 1.7-2.0% for the sodium and ionized calcium absorption of the tail, respectively. Night 1 was contaminated by its companion star so we considered weighted averages with and without Night 1 and quote conservative 5σ limits without Night 1 of 9 and 1.4%, respectively. Assuming their mass fractions to be similar to those in the Earth's crust, these limits correspond to scenarios in which 0.04 and 35% of the transiting dust is sublimated and observed as absorbing gas. However, this assumes the gas to be co-moving with the planet. We show that for the high irradiation environment of K2-22 b, sodium and ionized calcium could be quickly accelerated to 100s of km s-1 owing to radiation pressure and entrainment by the stellar wind, making these species much more difficult to detect. No evidence for such possibly broad and blue-shifted signals are seen in our data. Conclusions: Future observations aimed at observing circumplanetary gas should take into account the possible broad and blue-shifted velocity field of atomic and ionized species.

Polarimetric imaging of circumstellar disks. I. Artifacts due to limited angular resolution

19 Jan 2020

by Heikamp, S., Keller, C. U., is now available here.

Abstract: Context. Polarimetric images of circumstellar environments, even when corrected with adaptive optics, have a limited angular resolution. Finite resolution greatly affects polarimetric images because of the canceling of adjacent polarization signals with opposite signs. In radio astronomy this effect is called beam depolarization and is well known. However, radio techniques to mitigate beam depolarization are not directly applicable to optical images as a consequence of the inherent lack of phase information at optical wavelengths. Aims: We explore the effects of a finite point-spread function (PSF) on polarimetric images and the application of Richardson-Lucy deconvolution to polarimetric images. Methods: We simulated polarimetric images of highly simplified, circumstellar disk models and convolved these with simulated and actual SPHERE/ZIMPOL PSFs. We attempted to deconvolve simulated images in orthogonal linear polarizations and polarized intensity images. Results: The most significant effect of finite angular resolution is the loss of polarimetric signal close to the central star where large polarization signals of opposite signs average out. The finite angular resolution can also introduce polarized light in areas beyond the original, polarized signal such as outside of disks. These effects are particularly severe for disks that are not rotationally symmetric. The deconvolution of polarimetric images is far from trivial. Richardson-Lucy deconvolution applied to images in opposite linear polarization states, which are subsequently subtracted from each other, cannot recover the signal close to the star. Sources that lack rotational symmetry cannot be recovered with this deconvolution approach.

Two accreting protoplanets around the young star PDS 70

19 Jan 2020

by Haffert, S. Y., Bohn, A. J., de Boer, J., Snellen, I. A. G., Brinchmann, J., Girard, J. H., Keller, C. U., Bacon, R., is now available here.

Abstract: Newly forming protoplanets are expected to create cavities and substructures in young, gas-rich protoplanetary disks1-3, but they are difficult to detect as they could be confused with disk features affected by advanced image analysis techniques4,5. Recently, a planet was discovered inside the gap of the transitional disk of the T Tauri star PDS 706,7. Here, we report on the detection of strong Hα emission from two distinct locations in the PDS 70 system, one corresponding to the previously discovered planet PDS 70 b, which confirms the earlier Hα detection8, and another located close to the outer edge of the gap, coinciding with a previously identified bright dust spot in the disk and with a small opening in a ring of molecular emission6,7,9. We identify this second Hα peak as a second protoplanet in the PDS 70 system. The Hα emission spectra of both protoplanets indicate ongoing accretion onto the protoplanets10,11, which appear to be near a 2:1 mean motion resonance. Our observations show that adaptive-optics-assisted, medium-resolution integral field spectroscopy with MUSE12 targeting accretion signatures will be a powerful way to trace ongoing planet formation in transitional disks at different stages of their evolution. Finding more young planetary systems in mean motion resonance would give credibility to the Grand Tack hypothesis in which Jupiter and Saturn migrated in a resonance orbit during the early formation period of our Solar System13.

Discovery of a directly imaged disk in scattered light around the Sco-Cen member Wray 15-788

19 Jan 2020

by Bohn, A. J., Kenworthy, M. A., Ginski, C., Benisty, M., de Boer, J., Keller, C. U., Mamajek, E. E., Meshkat, T., Muro-Arena, G. A., Pecaut, M. J., Snik, F., Wolff, S. G., Reggiani, M., is now available here.

Abstract: Context. Protoplanetary disks are the birth environments of planetary systems. Therefore, the study of young, circumstellar environments is essential in understanding the processes taking place in planet formation and the evolution of planetary systems. Aims: We detect and characterize circumstellar disks and potential companions around solar-type, pre-main sequence stars in the Scorpius-Centaurus association (Sco-Cen). Methods: As part of our ongoing survey we carried out high-contrast imaging with VLT/SPHERE/IRDIS to obtain polarized and total intensity images of the young (11-7+16 Myr old) K3IV star Wray 15-788 within the Lower Centaurus Crux subgroup of Sco-Cen. For the total intensity images, we remove the stellar halo via an approach based on reference star differential imaging in combination with principal component analysis. Results: Both total intensity and polarimetric data resolve a disk around the young, solar-like Sco-Cen member Wray 15-788. Modeling of the stellar spectral energy distribution suggests that this is a protoplanetary disk at a transition stage. We detect a bright outer ring at a projected separation of 370 mas (≈56 au), hints of inner substructures at 170 mas (≈28 au), and a gap in between. Within a position angle range of only 60° < ϕ < 240°, we are confident at the 5σ level that we detect actual scattered light flux from the outer ring of the disk; the remaining part is indistinguishable from background noise. For the detected part of the outer ring we determine a disk inclination of i = 21° ± 6° and a position angle of φ = 76° ± 16°. Furthermore, we find that Wray 15-788 is part of a binary system with the A2V star HD 98363 at a separation of 50'' (≈6900 au). Conclusions: The detection of only half of the outer ring might be due to shadowing by a misaligned inner disk. A potential substellar companion can cause the misalignment of the inner structures and can be responsible for clearing the detected gap from scattering material. However, we cannot rule out the possibility of a non-detection due to our limited signal-to-noise ratio (S/N), combined with brightness azimuthal asymmetry. From our data we can exclude companions more massive than 10 Mjup within the gap at a separation of 230 mas (≈35 au). Additional data are required to characterize the disk's peculiar morphology and to set tighter constraints on the potential perturber's orbital parameters and mass. Reduced images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A87Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 099.C-0698(A), 0101.C-0153(A), and 0101.C-0464(A).

SPHERE/ZIMPOL high resolution polarimetric imager. I. System overview, PSF parameters, coronagraphy, and polarimetry

19 Jan 2020

by Schmid, H. M., Bazzon, A., Roelfsema, R., Mouillet, D., Milli, J., Menard, F., Gisler, D., Hunziker, S., Pragt, J., Dominik, C., Boccaletti, A., Ginski, C., Abe, L., Antoniucci, S., Avenhaus, H., Baruffolo, A., Baudoz, P., Beuzit, J. L., Carbillet, M., Chauvin, G., Claudi, R., Costille, A., Daban, J.-B., de Haan, M., Desidera, S., Dohlen, K., Downing, M., Elswijk, E., Engler, N., Feldt, M., Fusco, T., Girard, J. H., Gratton, R., Hanenburg, H., Henning, Th., Hubin, N., Joos, F., Kasper, M., Keller, C. U., Langlois, M., Lagadec, E., Martinez, P., Mulder, E., Pavlov, A., Podio, L., Puget, P., Quanz, S. P., Rigal, F., Salasnich, B., Sauvage, J.-F., Schuil, M., Siebenmorgen, R., Sissa, E., Snik, F., Suarez, M., Thalmann, Ch., Turatto, M., Udry, S., van Duin, A., van Holstein, R. G., Vigan, A., Wildi, F., is now available here.

Abstract: Context. The SPHERE "planet finder" is an extreme adaptive optics (AO) instrument for high resolution and high contrast observations at the Very Large Telescope (VLT). We describe the Zurich Imaging Polarimeter (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance. Aims: We present a detailed characterization of SPHERE/ZIMPOL which should be useful for an optimal planning of observations and for improving the data reduction and calibration. We aim to provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging. Methods: We have analyzed SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and the peak flux attenuation and the off-axis flux transmission are determined. Simultaneous images of the coronagraphic focal plane and the pupil plane are analyzed and the suppression of the diffraction rings by the pupil stop is investigated. We compared the performance at small separation for different coronagraphs with tests for the binary α Hyi with a separation of 92 mas and a contrast of Δm ≈ 6m. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show small (< 1 mas) but disturbing differential polarimetric beam shifts, which can be explained as Goos-Hähnchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr. Results: SPHERE/ZIMPOL reaches routinely an angular resolution (FWHM) of 22-28 mas, and a normalized peak surface brightness of SB0 - mstar ≈ -6.5m arcsec-2 for the V-, R- and I-band. The AO performance is worse for mediocre ≳1.0″ seeing conditions, faint stars mR ≳ 9m, or in the presence of the "low wind" effect (telescope seeing). The coronagraphs are effective in attenuating the PSF peak by factors of > 100, and the suppression of the diffracted light improves the contrast performance by a factor of approximately two in the separation range 0.06″-0.20″. The polarimetric sensitivity is Δp < 0.01% and the polarization zero point can be calibrated to better than Δp ≈ 0.1%. The contrast limits for differential polarimetric imaging for the 400 s I-band data of R Aqr at a separation of ρ = 0.86″ are for the surface brightness contrast SBpol( ρ)-mstar ≈ 8m arcsec-2 and for the point source contrast mpol( ρ)-mstar ≈ 15m and much lower limits are achievable with deeper observations. Conclusions: SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar Hα emission. Based on observations collected at La Silla and Paranal Observatory, ESO (Chile), Program ID: 60.A-9249 and 60.A-9255.

Chromatic transit light curves of disintegrating rocky planets

19 Jan 2020

by Ridden-Harper, A. R., Keller, C. U., Min, M., van Lieshout, R., Snellen, I. A. G., is now available here.

Abstract: Context. Kepler observations have revealed a class of short-period exoplanets, of which Kepler-1520 b is the prototype, which have comet-like dust tails thought to be the result of small, rocky planets losing mass. The shape and chromaticity of the transits constrain the properties of the dust particles originating from the planet's surface, offering a unique opportunity to probe the composition and geophysics of rocky exoplanets. Aims: We aim to approximate the average Kepler long-cadence light curve of Kepler-1520 b and investigate how the optical thickness and transit cross section of a general dust tail can affect the observed wavelength dependence and depth of transit light curves. Methods: We developed a new 3D model that ejects sublimating particles from the planet surface to build up a dust tail, assuming it to be optically thin, and used 3D radiative transfer computations that fully treat scattering using the distribution of hollow spheres (DHS) method, to generate transit light curves between 0.45 and 2.5 μm. Results: We show that the transit depth is wavelength independent of optically thick tails, potentially explaining why only some observations indicate a wavelength dependence. From the 3D nature of our simulated tails, we show that their transit cross sections are related to the component of particle ejection velocity perpendicular to the planets orbital plane and use this to derive a minimum ejection velocity of 1.2 km s-1. To fit the average transit depth of Kepler-1520 b of 0.87%, we require a high dust mass-loss rate of 7-80 M⊕ Gyr-1 which implies planet lifetimes that may be inconsistent with the observed sample. Therefore, these mass loss rates should be considered to be upper limits.

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

19 Jan 2020

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: Aims: To understand planet formation it is necessary to study the birth environment of planetary systems. Resolved imaging of young planet forming disks allows us to study this environment in great detail and find signs of planet-disk interaction and disk evolution. 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, spectral energy distribution modeling suggests significant dust settling, pointing toward an evolved disk that may show signs of ongoing or completed planet formation. Methods: We observed CS Cha with the high contrast imager SPHERE at the ESO Very Large Telescope (VLT) 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 Hubble Space Telescope WFPC2 I-band data. Results: 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 55 au (at 165 pc). We do not detect the inner cavity but find an upper limit for the cavity size of 15 au. Furthermore, we find a faint comoving 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 ± 0.4% in the J band). The J- and H-band magnitudes of the companion are compatible with masses of a few MJup. 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 ( 20 MJup) brown dwarf or high-mass planet with an unresolved disk and dust envelope. Based on observations performed with VLT/SPHERE under program ID 098.C-0760(B) and 099.C-0891(B) and VLT/NACO under program ID 298.C-5054(B) and 076.C-0292(A)The reduced images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A79

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes III: technology opportunities and pathways

19 Jan 2020

by Snik, Frans, Absil, Olivier, Baudoz, Pierre, Beaulieu, Mathilde, Bendek, Eduardo, Cady, Eric, Carlomagno, Brunella, Carlotti, Alexis, Cvetojevic, Nick, Doelman, David, Fogarty, Kevin, Galicher, Raphaël., Guyon, Olivier, Haffert, Sebastiaan, Huby, Elsa, Jewell, Jeffrey, Jovanovic, Nemanja, Keller, Christoph, Kenworthy, Matthew A., Knight, Justin, Kuhn, Jonas, Mazoyer, Johan, Miller, Kelsey, N'Diaye, Mamadou, Norris, Barnaby, Por, Emiel, Pueyo, Laurent, Riggs, A. J. Eldorado, Ruane, Garreth, Sirbu, Dan, Wallace, J. Kent, Wilby, Michael, Ygouf, Marie, is now available here.

Abstract: The Optimal Optical CoronagraphWorkshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 30 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. This contribution is the final part of a series of three papers summarizing the outcomes of the workshop, and presents an overview of novel optical technologies and systems that are implemented or considered for high-contrast imaging instruments on both ground-based and space telescopes. The overall objective of high contrast instruments is to provide direct observations and characterizations of exoplanets at contrast levels as extreme as 10-10. We list shortcomings of current technologies, and identify opportunities and development paths for new technologies that enable quantum leaps in performance. Specifically, we discuss the design and manufacturing of key components like advanced deformable mirrors and coronagraphic optics, and their amalgamation in "adaptive coronagraph" systems. Moreover, we discuss highly integrated system designs that combine contrast-enhancing techniques and characterization techniques (like high-resolution spectroscopy) while minimizing the overall complexity. Finally, we explore extreme implementations using all-photonics solutions for ground-based telescopes and dedicated huge apertures for space telescopes.

Optimization of contrast in adaptive optics for exoplanet imaging

19 Jan 2020

by Radhakrishnan, Vikram Mark, Keller, Christoph U., Doelman, Niek, is now available here.

Abstract: Direct imaging of exoplanets requires overcoming the enormous contrast between the exoplanet and its host star, to distinguish the reflected light from the exoplanet, from the diffracted light of the star. Direct optimization of contrast, using nonlinear optimization techniques of the Adaptive Optics (AO) system coupled with coronagraphy, shows significant promise in achieving high contrast, beyond the limits of what can be achieved with traditional AO systems. Using a coronagraph optic as a "static" phase modifying element, and a deformable mirror as a "dynamic" element, we create an adaptive coronagraph, capable of engineering the point spread function (PSF) of the imaging system, to create a deep, dark hole in the focal plane, within which the exoplanet can be imaged. We present the results of simulations of a system, consisting of a vector Apodizing Phase Plate (vAPP) coronagraph, a deformable mirror (DM), and an imaging camera. The vAPP coronagraph reroutes starlight within the pupil plane, to create a designated dark hole region, which in the ideal case would be devoid of starlight in the focal plane. Off-axis exoplanet light is transmitted through to the dark hole and hence can be imaged. Atmospheric turbulence is simulated to generate a distorted wavefront, and a nonlinear, gradient climbing based optimization algorithm is implemented to drive the DM to optimize a merit function. This merit function is chosen with a dual objective to maximize average raw contrast in the dark hole, while maintaining a sufficiently high Strehl ratio. Preliminary results show that in a setup with a coronagraph designed to create a 6×6 (λ/D)2 rectangular dark hole with a raw contrast of 10-5, the optimization procedure results in a raw contrast of 10-7 at the dark hole while maintaining a Strehl ratio above 40%. It is observed that by tweaking the merit function, this non-linear optimization procedure can be adjusted to result in either higher Strehl or higher contrast. We discuss potential strategies to extend the non-linear optimization techniques to real-time, non-linear control for the AO system, thereby achieving a real-time, dynamic, adaptive coronagraph. Toward this end, we investigate the results of using the fast wavefront sensor data to reconstruct the wavefront phase, virtually propagate this through the science optical path, and optimize contrast on this virtual science image, as opposed to using the slower science camera to optimize contrast on the true science image. One potential approach to implement true real-time control would be to use deep neural networks, trained using deep deterministic policy gradients, to identify and remove speckles of diffracted starlight in the dark hole region in real-time.

On-sky results of the Leiden EXoplanet Instrument (LEXI)

19 Jan 2020

by Haffert, S. Y., Wilby, M. J., Keller, C. U., Snellen, I. A. G., Doelman, D. S., Por, E. H., van Kooten, M., Bos, S. P., Wardenier, J., is now available here.

Abstract: The Leiden EXoplanet Instrument (LEXI) is a bench-mounted high-contrast spectrograph (HCS) and high- contrast imager(HCI). Both science instruments are mounted behind a common adaptive optics (AO) system. The AO can be controlled by several new wavefront sensors for which we will show the first on-sky results. There is a new pupil-plane wavefront sensors; the Generalized Optical Differentiation Wavefront sensor(g-ODWFS). LEXI can switch between two observing modes, the HCI mode or the HD-IFS mode. The spectrograph is very compact because it is fed by single-mode fiber. The HD-IFS is an IFS that covers the spectral range of 600 800 nm with a constant spectral resolving power of 96000. The 2kx3k detector makes it possible to deliver diffraction limited spectra of up to 20 input fibers. The high-dispersion spectra of the HD-IFS allow for robust post-processing technique to remove residual stellar speckles and allows for direct characterization of the faint stellar environment. We will show the first sucesful on-sky results of the injection into a single-mode fiber with LEXI. In HCI mode an Apodizing Phase Plate (APP) is used to create a dark region around the star with an average design contrast of 1E-4. The APP is multiplexed with holographic modes to create the Coronagraphic Modal Wavefront sensor (cMWS) for non-common path error (NCPE) correction. The cMWS creates holographic copies in the focal plane that react linearly to aberrations. The holographic copies are measured simultaneously with the science target. There is no downtime for NCPE correction. We will show the first on-sky closed-loop correction of (NCPEs) with the cMWS.

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes: Part II. Common path wavefront sensing/control and coherent differential imaging

19 Jan 2020

by Jovanovic, Nemanja, Absil, Olivier, Baudoz, Pierre, Beaulieu, Mathilde, Bottom, Michael, Cady, Eric, Carlomagno, Brunella, Carlotti, Alexis, Doelman, David, Fogarty, Kevin, Galicher, Raphaël., Guyon, Olivier, Haffert, Sebastiaan, Huby, Elsa, Jewell, Jeffrey, Keller, Christoph, Kenworthy, Matthew A., Knight, Justin, Kühn, Jonas, Miller, Kelsey, Mazoyer, Johan, N'Diaye, Mamadou, Por, Emiel, Pueyo, Laurent, Riggs, A. J. E., Ruane, Garreth, Sirbu, Dan, Snik, Frans, Wallace, J. K., Wilby, Michael, Ygouf, Marie, is now available here.

Abstract: The Optimal Optical Coronagraph (OOC) Workshop held at the Lorentz Center in September 2017 in Leiden, the Netherlands, gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. In this second installment of a series of three papers summarizing the outcomes of the OOC workshop, we present an overview of common path wavefront sensing/control and Coherent Differential Imaging techniques, highlight the latest results, and expose their relative strengths and weaknesses. We layout critical milestones for the field with the aim of enhancing future ground/space based high contrast imaging platforms. Techniques like these will help to bridge the daunting contrast gap required to image a terrestrial planet in the zone where it can retain liquid water, in reflected light around a G type star from space.

MagAO-X: project status and first laboratory results

19 Jan 2020

by Males, Jared R., Close, Laird M., Miller, Kelsey, Schatz, Lauren, Doelman, David, Lumbres, Jennifer, Snik, Frans, Rodack, Alex, Knight, Justin, Van Gorkom, Kyle, Long, Joseph D., Hedglen, Alex, Kautz, Maggie, Jovanovic, Nemanja, Morzinski, Katie, Guyon, Olivier, Douglas, Ewan, Follette, Katherine B., Lozi, Julien, Bohlman, Chris, Durney, Olivier, Gasho, Victor, Hinz, Phil, Ireland, Michael, Jean, Madison, Keller, Christoph, Kenworthy, Matt, Mazin, Ben, Noenickx, Jamison, Alfred, Dan, Perez, Kevin, Sanchez, Anna, Sauve, Corwynn, Weinberger, Alycia, Conrad, Al, is now available here.

Abstract: MagAO-X is an entirely new extreme adaptive optics system for the Magellan Clay 6.5 m telescope, funded by the NSF MRI program starting in Sep 2016. The key science goal of MagAO-X is high-contrast imaging of accreting protoplanets at Hα. With 2040 actuators operating at up to 3630 Hz, MagAO-X will deliver high Strehls (> 70%), high resolution (19 mas), and high contrast (< 1 × 10-4 ) at Hα (656 nm). We present an overview of the MagAO-X system, review the system design, and discuss the current project status.

High contrast imaging for the enhanced resolution imager and spectrometer (ERIS)

19 Jan 2020

by Kenworthy, Matthew A., Snik, Frans, Keller, Christoph U., Doelman, David, Por, Emiel H., Absil, Olivier, Carlomagno, Brunella, Karlsson, Mikael, Huby, Elsa, Glauser, Adrian M., Quanz, Sascha P., Taylor, William D., is now available here.

Abstract: ERIS is a diffraction limited thermal infrared imager and spectrograph for the Very Large Telescope UT4. One of the science cases for ERIS is the detection and characterization of circumstellar structures and exoplanets around bright stars that are typically much fainter than the stellar diffraction halo. Enhanced sensitivity is provided through the combination of (i) suppression of the diffraction halo of the target star using coronagraphs, and (ii) removal of any residual diffraction structure through focal plane wavefront sensing and subsequent active correction. In this paper we present the two coronagraphs used for diffraction suppression and enabling high contrast imaging in ERIS.

ERIS: revitalising an adaptive optics instrument for the VLT

19 Jan 2020

by Davies, R., Esposito, S., Schmid, H.-M., Taylor, W., Agapito, G., Agudo Berbel, A., Baruffolo, A., Biliotti, V., Biller, B., Black, M., Boehle, A., Briguglio, B., Buron, A., Carbonaro, L., Cortes, A., Cresci, G., Deysenroth, M., Di Cianno, A., Di Rico, G., Doelman, D., Dolci, M., Dorn, R., Eisenhauer, F., Fantinel, D., Ferruzzi, D., Feuchtgruber, H., Förster Schreiber, N., Gao, X., Gemperlein, H., Genzel, R., George, E., Gillessen, S., Giordano, C., Glauser, A., Glindemann, A., Grani, P., Hartl, M., Heijmans, J., Henry, D., Huber, H., Kasper, M., Keller, C., Kenworthy, M., Kühn, J., Kuntschner, H., Lightfoot, J., Lunney, D., MacIntosh, M., Mannucci, F., March, S., Neeser, M., Patapis, P., Pearson, D., Plattner, M., Puglisi, A., Quanz, S., Rau, C., Riccardi, A., Salasnich, B., Schubert, J., Snik, F., Sturm, E., Valentini, A., Waring, C., Wiezorrek, E., Xompero, M., is now available here.

Abstract: ERIS is an instrument that will both extend and enhance the fundamental diffraction limited imaging and spectroscopy capability for the VLT. It will replace two instruments that are now being maintained beyond their operational lifetimes, combine their functionality on a single focus, provide a new wavefront sensing module that makes use of the facility Adaptive Optics System, and considerably improve their performance. The instrument will be competitive with respect to JWST in several regimes, and has outstanding potential for studies of the Galactic Center, exoplanets, and high redshift galaxies. ERIS had its final design review in 2017, and is expected to be on sky in 2020. This contribution describes the instrument concept, outlines its expected performance, and highlights where it will most excel.

Multiplexed holographic aperture masking with liquid-crystal geometric phase masks

19 Jan 2020

by Doelman, D. S., Tuthill, P., Norris, B., Wilby, M. J., Por, E. H., Keller, C. U., Escuti, M. J., Snik, F., is now available here.

Abstract: Sparse Aperture Masking (SAM) allows for high-contrast imaging at small inner working angles, however the performance is limited by the small throughput and the number of baselines. We present the concept and first lab results of Holographic Aperture Masking (HAM) with extreme liquid-crystal geometric phase patterns. We multiplex subapertures using holographic techniques to combine the same subaperture in multiple non-redundant PSFs in combination with a non-interferometric reference spot. This way arbitrary subaperture combinations and PSF configurations can be realized, giving HAM more uv-coverage, better throughput and improved calibration as compared to SAM, at the cost of detector space.

Review of high-contrast imaging systems for current and future ground- and space-based telescopes I: coronagraph design methods and optical performance metrics

19 Jan 2020

by Ruane, G., Riggs, A., Mazoyer, J., Por, E. H., N'Diaye, M., Huby, E., Baudoz, P., Galicher, R., Douglas, E., Knight, J., Carlomagno, B., Fogarty, K., Pueyo, L., Zimmerman, N., Absil, O., Beaulieu, M., Cady, E., Carlotti, A., Doelman, D., Guyon, O., Haffert, S., Jewell, J., Jovanovic, N., Keller, C., Kenworthy, M. A., Kuhn, J., Miller, K., Sirbu, D., Snik, F., Wallace, J. Kent, Wilby, M., Ygouf, M., is now available here.

Abstract: The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. In this first installment of a series of three papers summarizing the outcomes of the OOC workshop, we present an overview of design methods and optical performance metrics developed for coronagraph instruments. The design and optimization of coronagraphs for future telescopes has progressed rapidly over the past several years in the context of space mission studies for Exo-C, WFIRST, HabEx, and LUVOIR as well as ground-based telescopes. Design tools have been developed at several institutions to optimize a variety of coronagraph mask types. We aim to give a broad overview of the approaches used, examples of their utility, and provide the optimization tools to the community. Though it is clear that the basic function of coronagraphs is to suppress starlight while maintaining light from off-axis sources, our community lacks a general set of standard performance metrics that apply to both detecting and characterizing exoplanets. The attendees of the OOC workshop agreed that it would benefit our community to clearly define quantities for comparing the performance of coronagraph designs and systems. Therefore, we also present a set of metrics that may be applied to theoretical designs, testbeds, and deployed instruments. We show how these quantities may be used to easily relate the basic properties of the optical instrument to the detection significance of the given point source in the presence of realistic noise.

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

19 Jan 2020

by Wilby, M. J., Keller, C. U., Sauvage, J.-F., Dohlen, K., Fusco, T., Mouillet, D., Beuzit, J.-L., is now available here.

Abstract: Context. 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 ms-1. The LWE produces bright low-order speckles in the stellar point-spread function (PSF), which severely limit the contrast performance of SPHERE under otherwise optimal observing conditions. Aims: 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) and apply corrections via reference slope offsets on the AO system's Shack-Hartmann wavefront sensor. Methods: We evaluated the closed-loop performance of F&F on the MITHIC high-contrast test-bench, under conditions emulating LWE-affected DTTS images. These results were contrasted with predictive simulations for a variety of convergence tests, in order to assess the expected performance of an on-sky implementation of F&F in SPHERE. Results: The algorithm was found to be capable of returning 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 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. Conclusions: 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.

A Planet with a Disc? A Surprising Detection in Polarised Light with VLT/SPHERE

19 Jan 2020

by Ginski, C., van Holstein, R., Juhász, A., Benisty, M., Schmidt, T., Chauvin, G., de Boer, J., Wilby, M., Manara, C. F., Delorme, P., Ménard, F., Muro-Arena, G., 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: With the Spectro-Polarimetric High- contrast Exoplanet REsearch (SPHERE) instrument at ESO's Very Large Telescope (VLT) we can study the linear polarisation of directly detected planets and brown dwarfs, to learn about their atmospheres and immediate environments. We summarise here the recent discovery of a low-mass companion in polarised light by Ginski et al. (2018). The object shows an extreme degree of polarisation, indicating the presence of a circumplanetary disc.

SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems. From planetary disks to nearby Super Earths

19 Jan 2020

by Boccaletti, Anthony, Schneider, Jean, Traub, Wes, Lagage, Pierre-Olivier, Stam, Daphne, Gratton, Raffaele, Trauger, John, Cahoy, Kerri, Snik, Frans, Baudoz, Pierre, Galicher, Raphael, Reess, Jean-Michel, Mawet, Dimitri, Augereau, Jean-Charles, Patience, Jenny, Kuchner, Marc, Wyatt, Mark, Pantin, Eric, Maire, Anne-Lise, Vérinaud, Christophe, Ronayette, Samuel, Dubreuil, Didier, Min, Michiel, Rodenhuis, Michiel, Mesa, Dino, Belikov, Russ, Guyon, Olivier, Tamura, Motohide, Murakami, Naoshi, Beerer, Ingrid Mary, SPICES Team, Mas, M., Rouan, D., Perrin, G., Lacour, S., Thébault, P., Nguyen, N., Ibgui, L., Arenou, F., Lestrade, J. F., N'Diaye, M., Dohlen, K., Ferrari, M., Hugot, E., Beuzit, J.-L., Lagrange, A.-M., Martinez, P., Barthelemey, M., Mugnier, L., Keller, C., Marley, M., Kalas, P., Stapelfeldt, K., Brown, R., Kane, S., Desidera, S., Sozzetti, A., Mura, A., Martin, E. L., Bouy, H., Allan, A., King, R., Vigan, A., Churcher, L., Udry, S., Matsuo, T., Nishikawa, J., Hanot, C., Wolf, S., Kaltenegger, L., Klahr, H., Pilat-Lohinger, E., is now available here.

Abstract: SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450-900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (˜2 Earth radii, ˜10 M⊕) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.

News ArchiveRefPlanets: Search for reflected light from extrasolar planets with SPHERE/ZIMPOLPolarimetric imaging mode of VLT/SPHERE/IRDIS. II. Characterization and correction of instrumental polarization effectsPolarimetric imaging mode of VLT/SPHERE/IRDIS. I. Description, data reduction, and observing strategyA snapshot full-Stokes spectropolarimeter for detecting life on EarthThe Young Suns Exoplanet Survey: Detection of a wide-orbit planetary-mass companion to a solar-type Sco-Cen memberOverview of focal plane wavefront sensors to correct for the Low Wind Effect on SUBARU/SCExAOFocal-plane wavefront sensing with the vector-Apodizing Phase PlateHighly multiplexed Bragg gratings for large field of view gas sensing in planetary atmospheresRefPlanets: Search for reflected light from extra-solar planets with SPHERE/ZIMPOLThe polarimetric imaging mode of VLT/SPHERE/IRDIS II: Characterization and correction of instrumental polarization effectsThe polarimetric imaging mode of VLT/SPHERE/IRDIS I: Description, data reduction and observing strategyA snapshot full-Stokes spectropolarimeter for detecting life on EarthInsights into Terrestrial Planet Compositions and Geophysics from Observations of Magma WorldsESA Voyage 2050 White Paper: Detecting life outside our solar system with a large high-contrast-imaging missionSearch for gas from the disintegrating rocky exoplanet K2-22bPolarimetric imaging of circumstellar disks. I. Artifacts due to limited angular resolutionTwo accreting protoplanets around the young star PDS 70Discovery of a directly imaged disk in scattered light around the Sco-Cen member Wray 15-788SPHERE/ZIMPOL high resolution polarimetric imager. I. System overview, PSF parameters, coronagraphy, and polarimetryChromatic transit light curves of disintegrating rocky planetsFirst direct detection of a polarized companion outside a resolved circumbinary disk around CS ChamaeleonisReview of high-contrast imaging systems for current and future ground-based and space-based telescopes III: technology opportunities and pathwaysOptimization of contrast in adaptive optics for exoplanet imagingOn-sky results of the Leiden EXoplanet Instrument (LEXI)Review of high-contrast imaging systems for current and future ground-based and space-based telescopes: Part II. Common path wavefront sensing/control and coherent differential imagingMagAO-X: project status and first laboratory resultsHigh contrast imaging for the enhanced resolution imager and spectrometer (ERIS)ERIS: revitalising an adaptive optics instrument for the VLTMultiplexed holographic aperture masking with liquid-crystal geometric phase masksReview of high-contrast imaging systems for current and future ground- and space-based telescopes I: coronagraph design methods and optical performance metricsLaboratory verification of Fast & Furious phase diversity: Towards controlling the low wind effect in the SPHERE instrumentA Planet with a Disc? A Surprising Detection in Polarised Light with VLT/SPHERESPICES: spectro-polarimetric imaging and characterization of exoplanetary systems. From planetary disks to nearby Super EarthsFirst 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