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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 ∆m ≈ 6 m . 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 SB 0 − m star ≈ −6.5 m arcsec −2 for the V-, R-and I-band. The AO performance is worse for mediocre 1.0 seeing conditions, faint stars m R 9 m , 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 ∆p < 0.01% and the polarization zero point can be calibrated to better than ∆p ≈ 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 SB pol ( ρ)−m star ≈ 8 m arcsec −2 and for the point source contrast m pol ( ρ)−m star ≈ 15 m and much lower limits are achievable with deeper observations. Conclusions. SPHERE/ZIMPOL achieves imaging performances ...

This article estimates the marginal value of safety based on contingent values obtained in a labormarket-oriented national random-sample mail survey. Thus, worker preferences for safety are assessed directly, in contrast to the hedonic price method that has been used almost exclusively in related studies. Key aspects of this article are that (1) contingent values are obtained for small changes in risks of job-related fatal accidents perceived by respondents, and (2) relationships are analyzed between respondents' marginal safety values and their income, socioeconomic/demographic characteristics, union membership status, and initial levels of risk faced.

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Context. A complex environment exists in the inner few astronomical units of planet-forming disks. High-angular-resolution observations play a key role in our understanding of the disk structure and the dynamical processes at work. Aims. In this study we aim to characterize the mid-infrared brightness distribution of the inner disk of the young intermediate-mass star HD 163296 from early VLTI/MATISSE observations taken in the L- and N-bands. We put special emphasis on the detection of potential disk asymmetries. Methods. We use simple geometric models to fit the interferometric visibilities and closure phases. Our models include a smoothed ring, a flat disk with an inner cavity, and a 2D Gaussian. The models can account for disk inclination and for azimuthal asymmetries as well. We also perform numerical hydrodynamical simulations of the inner edge of the disk. Results. Our modeling reveals a significant brightness asymmetry in the L-band disk emission. The brightness maximum of the asymmetry is located at the NW part of the disk image, nearly at the position angle of the semimajor axis. The surface brightness ratio in the azimuthal variation is 3.5 ± 0.2. Comparing our result on the location of the asymmetry with other interferometric measurements, we confirm that the morphology of the r < 0.3 au disk region is time-variable. We propose that this asymmetric structure, located in or near the inner rim of the dusty disk, orbits the star. To find the physical origin of the asymmetry, we tested a hypothesis where a vortex is created by Rossby wave instability, and we find that a unique large-scale vortex may be compatible with our data. The half-light radius of the L-band-emitting region is 0.33 ±0.01 au, the inclination is 52°−7°+5°, and the position angle is 143° ± 3°. Our models predict that a non-negligible fraction of the L-band disk emission originates inside the dust sublimation radius for μm-sized grains. Refractory grains or large (≳10 μm-sized) grains could be the origin of this emission. N-band observations may also support a lack of small silicate grains in the innermost disk (r ≲ 0.6 au), in agreement with our findings from L-band data.