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    RefPlanets: Search for reflected light from extra-solar planets with SPHERE/ZIMPOL
    (Les Ulis : EDP Sciences , 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.
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    Small-scale structures in neutrals and charged aerosol particles as observed during the ECOMA/MASS rocket campaign
    (München : European Geopyhsical Union, 2009) Strelnikov, B.; Rapp, M.; Strelnikova, I.; Engler, N.; Latteck, R.
    We present results of in situ measurements of neutral temperature during the ECOMA/MASS rocket campaign. We present and compare results of turbulence measurements conducted simultaneously by both in situ and doppler radar techniques. We show that the derived values of the turbulence energy dissipation rates are similar on average. We also find a region with a near adiabatic lapse rate with turbulence detected at the upper and lower edge. We note that it is consistent with expectation for a Kelvin-Helmholtz instability. We also present an estimate of the Schmidt numbers, Sc, for the charged aerosols that utilizes in situ measured small-scale density fluctuations of charged aerosols and both in situ and radar turbulence measurements. The derived Schmidt numbers fall within the range between 100 and 4500. This result agrees with previous estimates based on multi-frequency observations of PMSE (Rapp et al., 2008) and also with estimates of microphysical parameters presented in the companion paper by Rapp et al. (2009).
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    Turbulent energy dissipation rates observed by Doppler MST Radar and by rocket-borne instruments during the MIDAS/MaCWAVE campaign 2002
    (Göttingen : Copernicus GmbH, 2005) Engler, N.; Latteck, R.; Strelnikov, B.; Singer, W.; Rapp, M.
    During the MIDAS/MaCWAVE campaign in summer 2002 we have observed turbulence using Doppler beam steering measurements obtained from the ALWIN VHF radar at Andøya/Northern Norway. This radar was operated in the Doppler beam steering mode for turbulence investigations during the campaign, as well as in spaced antenna mode, for continuously measuring the background wind field. The real-time data analysis of the Doppler radar backscattering provided the launch conditions for the sounding rockets. The spectral width data observed during the occurrence of PMSE were corrected for beam and shear broadening caused by the background wind field to obtain the turbulent part of the spectral width. The turbulent energy dissipation rates determined from the turbulent spectral width vary between 5 and 100 m Wkg-1 in the altitude range of 80-92 km and increase with altitude. These estimations agree well with the in-situ measurements using the CONE sensor which was launched on 3 sounding rockets during the campaign.