2020, Solanki, S.K., del Toro Iniesta, J.C., Woch, J., Gandorfer, A., Hirzberger, J., Alvarez-Herrero, A., Appourchaux, T., Martínez Pillet, V., Pérez-Grande, I., Sanchis Kilders, E., Schmidt, W., Garranzo-García, D., Laguna, H., Martín, J.A., Navarro, R., Villanueva, J., Núñez Peral, A., Royo, M., Sánchez, A., Silva-López, M., Fourmond, J.-J., Berkefeld, Th., Ruiz de Galarreta, C., Bouzit, M., Hervier, V., Le Clec'h, J.C., Szwec, N., Chaigneau, M., Buttice, V., Volkmer, R., Dominguez-Tagle, C., Philippon, A., Baumgartner, J., Boumier, P., Le Cocguen, R., Baranjuk, G., Bell, A., Heidecke, F., Maue, T., Blanco Rodríguez, J., Nakai, E., Scheiffelen, T., Sigwarth, M., Soltau, D., Domingo, V., Fiethe, B., Ferreres Sabater, A., Gasent Blesa, J.L., Rodríguez Martínez, P., Osorno Caudel, D., Bosch, J., Casas, A., Carmona, M., Gómez Cama, J.M., Herms, A., Roma, D., Guan, Y., Alonso, G., Gómez-Sanjuan, A., Piqueras, J., Torralbo, I., Lange, T., Michel, H., Michalik, H., Bonet, J.A., Fahmy, S., Müller, D., Zouganelis, I., Deutsch, W., Busse, D., Fernandez-Rico, G., Grauf, B., Gizon, L., Heerlein, K., Kolleck, M., Lagg, A., Meller, R., Müller, R., Schühle, U., Staub, J., Enge, R., Albert, K., Alvarez Copano, M., Beckmann, U., Bischoff, J., Frahm, S., Germerott, D., Guerrero, L., Löptien, B., Meierdierks, T., Oberdorfer, D., Papagiannaki, I., Ramanath, S., Bellot Rubio, L.R., Schou, J., Werner, S., Yang, D., Zerr, A., Bergmann, M., Bochmann, J., Heinrichs, J., Meyer, S., Monecke, M., Müller, M.-F., Cobos Carracosa, J.P., Sperling, M., Álvarez García, D., Aparicio, B., Balaguer Jiménez, M., Girela, F., Hernández Expósito, D., Herranz, M., Labrousse, P., López Jiménez, A., Orozco Suárez, D., Ramos, J.L., Barandiarán, J., Vera, I., Bastide, L., Campuzano, C., Cebollero, M., Dávila, B., Fernández-Medina, A., García Parejo, P.

This paper describes the Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter, as well as hosting the potential of a rich return in further science. SO/PHI measures the Zeeman effect and the Doppler shift in the FeI 617.3nm spectral line. To this end, the instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO_3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders (LCVRs). The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2kx2k CMOS detector. To save valuable telemetry, the raw data are reduced on board, including being inverted under the assumption of a Milne-Eddington atmosphere, although simpler reduction methods are also available on board. SO/PHI is composed of two telescopes; one, the Full Disc Telescope (FDT), covers the full solar disc at all phases of the orbit, while the other, the High Resolution Telescope (HRT), can resolve structures as small as 200km on the Sun at closest perihelion. The high heat load generated through proximity to the Sun is greatly reduced by the multilayer-coated entrance windows to the two telescopes that allow less than 4% of the total sunlight to enter the instrument, most of it in a narrow wavelength band around the chosen spectral line.

2020, 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.

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.