Characterize dust properties in circumstaller disks with quantitative polarimetry

Jie Ma, Hans Martin Schmid, Christian Tschudi

The polarized scattered light images of circumstellar disks are essential in characterizing dust properties to understand dust evolution and to constrain the composition of the forming planet. Many disks have been well-resolved with Polarimetric Differential Imaging (PDI) using AO instruments at large ground-based telescopes, e.g. VLT, Gemini, and Subaru. Simulations focusing on disk geometries reproduce well the various disk morphologies but much fewer studies have been carried out on the characterization of the dust properties based on quantitative measurements of the scattered light.&nbsp;<div>To obtain accurate photo-polarimetric measurements of the reflected light from disks, variable PSF smearing and polarimetric cancellation effects should be considered. We correct for the smearing effect and measure the integrated flux, polarized flux, and fractional polarization for different wavelengths in the transition disk RX J1604. We derive a fractional polarization &gt;20%, and higher polarized intensity in the near-infrared compared to the visual. Such measurements are used as diagnostic tools to characterize the dust properties, based on simulations of the dust scattering in simplified disk models.&nbsp;<div>We also conducted systematic multi-wavelength measurements of the polarized flux of 11 circumstellar disks observed by SPHERE. Using data from the ESO archive, we observe red colors for 7 disks and gray-bluish colors for 4 disks from visible to near-infrared.
We find a correlation between polarized light color and stellar irradiation which might indicate a systematic dust evolution process.&nbsp;</div><div>The derived scattering parameters constrain the dust aggregates' properties and support the possible presence of micron-sized dust aggregates in agreement with dust coagulation. More such data for the dust in different types of disks need to be collected to better understand the dust evolution and the planet formation process.</div></div>

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