Aims. We present high-precision photometry and polarimetry based on visual and near-infrared imaging data for the protoplanetary disk surrounding the Herbig Ae/Be star HD 142527, with a strong focus on determining the light scattering parameters of the dust located at the surface of the large outer disk. Methods. We re-reduced existing polarimetric differential imaging data of HD 142527 in the VBB (735 nm) and H-band (1625 nm) from the ZIMPOL and IRDIS subinstruments of SPHERE at the VLT. With polarimetry and photometry based on reference star differential imaging (RDI), we were able to measure the linearly polarized intensity and the total intensity of the light scattered by the circumstellar disk with high precision. We used simple Monte Carlo simulations of multiple light scattering by the disk surface to derive constraints for three scattering parameters of the dust: the maximum polarization of the scattered light Pmax, the asymmetry parameter g, and the single-scattering albedo ω. Results. We measure a reflected total intensity of 51.4 ± 1.5 mJy and 206 ± 12 mJy and a polarized intensity of 11.3 ± 0.3 mJy and 55.1 ± 3.3 mJy in the VBB and H-band, respectively. We also find in the visual range a degree of polarization that varies between 28% on the far side of the disk and 17% on the near side. In the H-band, the degree of polarization is consistently higher by about a factor of 1.2. The disk also shows a red color for the scattered light intensity and the polarized intensity, which are about twice as high in the near-infrared when compared to the visual. We determine with model calculations the scattering properties of the dust particles and find evidence for strong forward scattering (g ≈ 0.5–0.75), relatively low single-scattering albedo (ω ≈ 0.2–0.5), and high maximum polarization (Pmax ≈ 0.5–0.75) at the surface on the far side of the disk for both observed wavelengths. The optical parameters indicate the presence of large aggregate dust particles, which are necessary to explain the high maximum polarization, the strong forward-scattering nature of the dust, and the observed red disk color.

Context. Many scattered light images of protoplanetary disks have been obtained with the new generation of adaptive optics (AO) systems at large telescopes. The measured scattered radiation can be used to constrain the dust that forms planets in these disks. Aims. We want to constrain the dust particle properties for the bright, pole-on transition disk around HD 169142 with accurate measurements and a quantitative analysis for the polarization and intensity of the scattered radiation. Methods. We investigate high resolution imaging polarimetry of HD 169142 taken in the R and I bands with the SPHERE/ZIMPOL AO instrument. The geometry of this pole-on disk is close to rotational symmetry, and we can use azimuthally averaged radial profiles for our analysis. We describe the dependence of the disk polarimetry on the atmospheric turbulence, which strongly impacts the AO point spread function (PSF). With non-coronagraphic data we can analyze the polarimetric signal of the disk simultaneously with the stellar PSF and determine the polarization of the disk based on simulations of the PSF convolution. We also extract the disk intensity signal and derive the fractional polarization for the R and I bands. We compare the scattered flux from the inner and outer disk rings with the corresponding thermal dust emissions measured in the IR and estimate the ratio between scattered and absorbed radiation. Results. We find for the inner and outer disk rings of HD 169142 mean radii of 170 ± 3 mas and 522 ± 20 mas, respectively, and the same small deviations from a perfect ring geometry as previous studies. The AO performance shows strong temporal variation because of the mediocre seeing of about 1.1 ; this produces PSF peak variations of up to a factor of four and strongly correlated changes for the measured disk polarization of about a factor of two for the inner disk ring and about 1.2 for the more extended outer disk. This variable PSF convolution effect can be simulated and accurately corrected, and we obtain ratios between the integrated disk polarization flux and total system flux ( Q φ /I tot ) of 0.43 ± 0.01 % for the R band and 0.55 ± 0.01 % for the I band. This indicates a reddish color for the light reflection by the dust. The inner disk ring contributes about 75 % and the outer disk about 25 % to the total disk flux. The extraction of the scattered intensity of the disk is only possible for the bright, narrow, inner disk ring, and the obtained fractional polarization p for the scattered radiation is 23.6 ± 3.5 % for the I band and 22.0 ± 5.9 % for the R band. The ratio between scattered disk flux and star flux ( I disk /I ) is about 2.3 ± 0.3 %. This is much smaller than the derived IR excess F fIR /F = 17.6 % for the disk components observed in scattered light. This indicates that only a small fraction of the radiation illuminating the disk is scattered; most is absorbed and reemitted in the IR. Conclusions. We demonstrate the feasibility of accurate quantitative photo-polarimetry of a circumstellar disk with a radius of ...

Context. The characterization of the dust in protoplanetary disks is important for a better understanding of the resulting composition of forming planets and the dust particle evolution in these systems. Aims. We aim to accurately characterize the properties of the dust in the face-on transition disk around RX J1604.3–213010 (RX J1604) by analyzing the multiwavelength scattered light intensity and polarization images obtained with the ZIMPOL and IRDIS subinstruments of VLT/SPHERE. Methods. We used archival data of RX J1604 from the ESO archive and carefully corrected the polarization signal for instrumental effects, also taking the interstellar polarization into account. We measured the radial profiles of the disk for the azimuthal polarization, Qφ(r), in the R, J, and H bands and describe variations in our data due to the seeing and other effects. We derived the intrinsic polarization profiles of the disk, Q^φ(r), by comparing the data with rotationally symmetric models convolved with the point spread functions of the observations. We also measured the disk intensity, Idisk(r), with reference star differential imaging for the J and H bands. This provides the disk-integrated polarized intensity, Q^φ/I⋆, for the R, J, and H bands and the averaged fractional polarization, 〈p^φ〉, for the J and H bands. We investigated the azimuthal dependence of the scattered light and the shadows produced by hot dust near the star. The derived results were finally compared with model calculations to constrain the scattering properties of the reflecting dust in RX J1604. Results. RX J1604 is a dipper source, and the data show different kinds of variability. However, a detailed analysis of repeated measurements shows that the results are not affected by dipping events or atmospheric seeing variations. We derive accurate radial disk profiles for the intrinsic polarized intensity, Q^φ(r)/I⋆, and measure different profile peak radii for different bands because of the wavelength dependence of the dust opacity. The disk-integrated polarization is Q^φ/I⋆ = 0.92 ± 0.04% for the R band and 1.51 ± 0.11% for the J band, indicating a red color for the polarized reflectivity of the disk. The intensity of the disk is Idisk|I* = 3.9 ± 0.5% in the J band, and the fractional polarization is 〈p^φ〉 = 38 ± 4% for the J band and 42 ± 2% for the H band. The comparison with the IR excess for RX J1604 yields an apparent disk albedo of about ΛΙ ≈ 0.16 ± 0.08. We also find that previously described shadows seen in the R band data are likely affected by calibration errors. We derive, using dust scattering models for transition disks, approximate J band values for the scattering albedo ω ≈ 0.5, scattering asymmetry g ≈ 0.5, and scattering polarization pmax ≈ 0.7 for the dust. Conclusions. The bright disk of RX J1604 has a very simple axisymmetric structure and is therefore well suited as a benchmark object for accurate photo-polarimetric measurements. We derive values for the disk polarization, 〈p^φ〉, and the apparent disk albedo, ΛΙ, for the J band. Because 〈p^φ〉 and ΛΙ depend predominantly on dust scattering parameters and only weakly on the disk geometry, these parameters define tight relations for the dust scattering parameters between ω and pmax and between ω and g. The positive R to J band color for the polarized reflectivity, (Q^/I⋆)J ≈ 1.64 ⋅ (Q^/I⋆)R, is mainly a result of the wavelength dependence of dust parameters because the scattering geometry is expected to be very similar for different colors. This work demonstrates the potential of accurate photo-polarimetric measurements of the circumstellar disk RX J1604 for the determination of dust scattering parameters that strongly constrain the physical properties of the dust.