Multiwavelength analysis of polarized light in HD 100453

TL;DR

This work presents a multiwavelength polarimetric study of HD 100453 from $0.55$ to $2.2~\mu m$, combining SPHERE/ZIMPOL and IRDIS data with reference differential imaging to measure disk polarization and intensity across the ring, spirals, and cavity. By correcting for PSF smearing and employing RADMC-3D radiative transfer with DIANA and Henyey-Greenstein dust parameterizations, the authors constrain how dust scattering evolves with wavelength and varies by disk substructure. They find that the outer disk is dominated by sub-micron, low-porosity grains or irregular grains, with a small cavity populated by grains $a_{\max} \lesssim 0.1~\mu m$, and that spirals show higher polarization indicating region-specific dust processing or porosity changes. The study combines forward modeling with aggregate-dust libraries to connect observed colors and polarization to grain structure, suggesting dust filtration at the cavity edge and differential grain growth in spirals, thereby informing planet-disk interaction scenarios and disk evolution.

Abstract

HD 100453 disk is a prototypical companion-disk interaction system hosting a pair of spirals and a substellar companion. We present new noncoronagraphic high-contrast imaging observations of HD 100453 with $V$ filter on SPHERE/ZIMPOL. We combined high-contrast imaging data of the reflected light from 0.55 to 2.2 $μm$ using the $V$, $I'$, $J$, and $Ks$ band data of ZIMPOL and IRDIS at VLT/SPHERE. For each observational epoch, we corrected for the smearing effect to derive the intrinsic disk-integrated polarized flux. We derived a steady increase with wavelengths from $\hat{Q}_{\varphi}/I_{\star}(V)=0.3\%$ to $\hat{Q}_{\varphi}/I_{\star}(K)=1.2\%$. We applied reference differential imaging to extract the disk intensity for the $V$ and $Ks$ bands using star hopping observations. We obtained the first $V$-band total intensity for HD 100453 with ZIMPOL star hopping. The integrated total flux $I_{\rm disk}/I_{\star}(V)=1.5\%$ increases to $I_{\rm disk}/I_{\star}(K)=4.8\%$. Both the total intensity and the polarization fraction show red colors, and the intrinsic maximum degree of polarization increases moderately from $40\%$ to $55\%$. We then used RADMC-3D radiative transfer modeling with a parametrized Henyey-Greenstein phase function to constrain the dust properties. From the $V$ to $Ks$ band, the dominating dust in the outer disk has an increasing scattering albedo and degree of polarization, while the asymmetry parameter slightly decreases. The outer disk of HD 100453 contains sub-micron-sized low porosity grains/aggregates. The cavity in scattered light is not empty and is replenished with optically thin dust with a maximum size of $\leq 0.1μm$. The linear polarization is higher in the spiral region than in the other regions, suggesting different dust properties in those regions.

Figures (14)

• Figure 1: Polarized intensity images $Q_{\varphi}(x,y)$ and $U_{\varphi}(x,y)$ for $V$, $I'$, $J$, and $Ks$ band. All images are normalized to the integrated stellar intensity $I_{\star}$ and their pixel scale ($3.6\times3.6$ mas$^2$ for ZIMPOL and $12.25\times 12.25$ mas$^2$ for IRDIS). The shared color bar is indicated on the right. All the images are cut to $1.0\times1.0\arcsec$ and the black bar in $Q_{\varphi}(V)$ indicates 0.2. The dashed lines in $U_{\varphi}(V)$ enclose the integration region for the cavity, the rim, and the spiral respectively. The semitransparent circle in K-hop represents the inner working angle (IWA) = 0.125 limited by the coronagraph. North is up and east to the left.
• Figure 2: Intrinsic integrated polarized flux $\hat{Q}_{\varphi}/I_{\star}$ as a function of wavelengths. Values are from Table \ref{['tab: polarised-flux']}.
• Figure 3: Extracted disk intensity map $I_{\rm disk}(x,y)$ for the $V$- and $Ks$-bands, cut to $2.0\times 2.0\arcsec$. The black bar indicates 0.5. The central 0.1 and 0.125 are masked out as the IWA for $V$ and $Ks$ respectively.
• Figure 4: Observed degree of polarization $p_{\rm disk}(x,y)$ for $V$- and $Ks$-bands cut to $1.0\times 1.0\arcsec$. The black bar in the $V$-band subfigure indicates 0.2. The star marker indicates the position of the central host star.
• Figure 5: Radial profiles of polarized intensity $Q_{\varphi}(r)$ along both sides of the major axis (left), near side (middle), and far side (right). All profiles have been normalized to the peak value along the major axis and shifted by one for clarity. The standard deviation among all cycles at a given epoch is indicated as the error bar. The shaded region indicates the cavity region [0.10, 0.13].