arXiv subjects

Ryo Tazaki

Publications and source records attributed to Ryo Tazaki.

At least 19 recordsLinked to original sources

arXiv2026

The colors of protoplanetary disks - Impact of nonspherical dust particles on the polarized and total intensity colors

Dust properties in protoplanetary disks remain poorly understood despite their central role in planet formation. Recent studies based on analyses of scattered-light images and phase functions provide promising insights into dust characterization, but the phase function alone is insufficient to constrain dust properties. Degeneracies between dust remain a major obstacle to linking observations to realistic dust models. We investigate the behavior of the disk color as a function of dust. We used MCFOST to generate synthetic scattered-light images from the visible to the near-infrared, in total and polarized intensity. We considered compact spherical grains using, irregular particles and compact and fractal aggregates using optical properties from the AggScatVIR database. Disk colors were measured from these images. For aggregates larger than the wavelength, monomer size influences color, whereas aggregate size has little effect, especially at low fractal dimensions. Polarized color is more sensitive to dust properties than total intensity color, because it combines the wavelength dependences of scattered intensity and polarization degree. Effective medium theory is reliable only for compact aggregates with small monomers, becoming inaccurate for highly porous aggregates or larger monomers. Effective albedo helps predict disk colors, but radiative transfer is needed to account for multiple scattering. For HD 100546, red optical-to-near-infrared colors exclude compact grains and organic-rich compositions but are consistent with amorphous-carbon aggregates, compact or fractal, containing large monomers. These results show that combining color measurements with polarized scattering phase functions offers a promising way to break degeneracies between dust models. Applying this approach to larger disk samples could better constrain dust properties and evolution.

astro-ph.SR↗

arXiv2026

Formation of Micron-sized Presolar Graphite Grains in Low-energy Supernova Ejecta

Presolar graphite grains with supernova isotopic signatures provide direct evidence that large graphite grains formed in supernova ejecta. However, theoretical calculations of dust formation in supernovae have typically predicted graphite grains smaller than $0.1\,{\rm μm}$, leaving unclear the physical conditions required to form those grains with radii of order $1\,{\rm μm}$. We systematically investigate graphite nucleation and growth in expanding supernova ejecta by varying the explosion energy, ejecta mass, initial ejecta radius, and ejected $^{56}$Ni mass. We use a simplified one-zone model that follows the temperature and density evolution including adiabatic cooling, radiative cooling, and heating by radioactive nickel. We show that the final graphite grain size is mainly determined by the product of the mass density of atomic carbon available for grain growth and the local cooling timescale, both evaluated at a reference temperature of $2000\,{\rm K}$. Our models show that graphite growth is favored by lower explosion energy, larger ejecta mass, and smaller initial ejecta radius, which keep the gas denser near the graphite-condensation temperature. When radioactive heating and radiative cooling are included, explosions with $E_{\rm exp}\sim10^{50}\,{\rm erg}$ and $M_{\rm Ni}\lesssim10^{-3}\,M_\odot$ can form $1$-$10\,μ{\rm m}$ graphite grains in the ejected helium layer or carbon-oxygen core, whereas $E_{\rm exp}\sim10^{51}\,{\rm erg}$ models do not. These results suggest that micron-sized presolar supernova graphite preferentially forms in faint-supernova-like explosions with low explosion energies, little ejected nickel, and helium layer or carbon-oxygen core ejecta.

astro-ph.HE↗

arXiv2026

JWST Imaging of Edge-on Protoplanetary Disks. V. Flux Ratio Reversal and Disk-edge Structure in the Flying Saucer

We present near- and mid-infrared broadband imaging observations of the edge-on protoplanetary disk 2MASS J16281370-2431391, a.k.a. the 'Flying Saucer', obtained with NIRCam and MIRI on board JWST. These data are combined with archival optical and near-IR broadband imaging from HST, millimeter dust continuum emission from ALMA, and optical lightcurves from the K2 and TESS for a comprehensive multi-wavelength study. The JWST observations reveal a reversal of the flux ratio between the two reflection nebulae at near-infrared wavelengths (2-3 $μm$), which can be explained by a misaligned inner disk. For the first time, JWST reveals the bright lining along the disk edge at 2 and 3 $μm$, arising from forward scattering of background photons by dust grains near the $τ\approx 1$ layer. By combining the dust lane thickness measured with HST and JWST, we find the dust grains up to at least $\sim$3$μ$m are vertically mixed throughout the disk and have undergone significant growth. In addition, comparison of earlier HST/NICMOS J and K band images with those from JWST/NIRCam reveals variability in the scattered-light morphology, as well as measurable proper motion of the system with respect to the background stars, confirming that the Flying Saucer is co-moving with the young star population of $ρ$ Ophiuchi.

astro-ph.EP↗

arXiv2026

Searching for Axion-like particle Dark Matter with Time-domain Polarization: Constraints from a protoplanetary disk

Axion-like particles (ALPs) can induce a birefringence effect that rotates the polarization angle of light, offering a probe of ultralight dark matter. We analyze archival near-infrared polarimetric data of the protoplanetary disk (PPD) around HD 163296. Whereas previous studies considered only single-epoch snapshots, we perform a consistent multi-epoch time-series analysis, extracting the polarization angle and its uncertainty from the polarized images. The resulting six-epoch time series is consistent with a constant polarization angle within the measurement uncertainties, while being sensitive to timescales of $\sim 170-400$ days. The typical polarization angle uncertainties are $1.6$--$6.4$ degrees, partly driven by multiple scattering in the optically thick disk, which broadens the intrinsic polarization angle distribution and introduces additional dispersion in the representative polarization angle. Based on these data, we derive the first upper limits on the ALP-photon coupling from PPD polarization variability, $g_{aγ} \lesssim 7.5 \times 10^{-12} (m_a / 10^{-22}\,{\rm eV})\,{\rm GeV}^{-1}$. Furthermore, we forecast that achieving a polarization angle uncertainty of $σ\sim 0.1$ degrees would enable world-leading sensitivity to ALP-induced birefringence.

astro-ph.CO↗

arXiv2026

Dust characterization of the HD 163296 disk with high-resolution multi-wavelength ALMA observations

Context. Planets form through the growth and accumulation of dust grains in protoplanetary disks. Characterizing dust properties such as size, surface density, and temperature is key to understanding planet formation. Aims. We characterize the dust properties of the protoplanetary disk around HD 163296 by performing spectral energy distribution (SED) fitting of multi-wavelength high-resolution observations. Methods. We present new high-resolution ALMA Band 9 (0.45 mm) observations, which are sensitive to the temperature. We performed SED fitting at a common resolution of 0.066 arcsec using these new Band 9 observations along with archival ALMA Band 3, 4, 6, and 7 observations. We compared the fitted results with VLA observations and explored multiple dust models with different optical constants and porosities. Results. The Band 9 image shows the central disk, two rings at 0.67 and 1.00 arcsec, and outer extended emission previously seen at other wavelengths. At higher frequencies, the rings appear wider, the gaps appear shallower, and the extended emission appears brighter, which can be explained by optical-depth effects and/or size segregation. We characterized the dust properties, including temperature, surface density, and dust size, for each dust model. However, the inferred dust properties are dependent on the dust model, and the ALMA data alone do not allow us to determine which dust model is preferred. We identified the DSHARP Zubko (porous) model as the preferred model based on VLA profiles and physical and observational constraints. The outer ring temperature is lower than predicted by a passively irradiated disk model, suggesting shadowing by the inner ring. Although the surface density and dust size depend on the dust model, the preferred model indicates that the central disk, both rings, and the extended disk each contain more than a few Earth masses of dust.

astro-ph.EP↗

arXiv2026

Constraints on the Crystallinity of Water Ice in Planet-forming Disks from Infrared Scattered-Light Spectra

The crystallinity of water ice not only records the thermal history experienced by an astronomical body, but also affects the composition of forming planets by controlling the trapping of volatile materials in amorphous ice and their subsequent transport. An additional structure within the 3~$\rm μm$ water-ice absorption band, known as the Fresnel feature, may serve as a diagnostic of ice crystallinity. Recent observations with the James Webb Space Telescope have detected a Fresnel peak in a debris disk and in Trans-Neptunian Objects (TNOs). Here, we propose a portable expression that translates the observed Fresnel peak strength into the degree of crystallinity of icy grains in debris disks. Our formula targets scattered light at around 90$^{\circ}$ angles, which are easily accessible for spatially resolved debris disks regardless of the inclination angle. Applying this expression, we derive the degree of crystallinity of a debris disk around HD 181327 to be 10-20%. We also study the Fresnel feature in protoplanetary disks and find that it is generally weaker than in debris disks even for the same crystallinity. We then analyzed a scattered light spectrum of the protoplanetary disk around d216-0939, which shows a weak crystalline feature, and inferred a crystallinity of $\sim$50%. We conclude that the Fresnel feature is a reliable observational tracer for ice crystallinity, and future near-IR spectroscopic observations will be crucial to elucidate the crystalline ice evolution.

astro-ph.EP↗

arXiv2026

Probing dust properties through polarized scattered-light images of a sample of ring-shaped protoplanetary disks

The evolution of protoplanetary disks, especially in the early stages of planetary formation, as dust grows, is the cornerstone of the birth of planets. The mechanisms involved in the growth of sub-micrometric dust grains into planetesimals within a very short time frame are a challenging field of study, while the initial conditions remain relatively undefined. One of the main challenges is to unambiguously identify the dust properties within the disk, and our goal is to break this barrier by investigating the light scattered by dust particles lying on the protoplanetary disk surface from many recent promising observations. In this study, we used a set of 30 polarized light images composed of new VLT/SPHERE observations to examine the light scattered by dust grains. For each ring-shaped system, we used the new DRAGyS tool to estimate the disk geometry using the substructures visible on the surface and to extract the limb-brightening-corrected scattering phase function, which encodes the dust grains' physical properties. Finally, we compared our results with the AggScatVIR database of numerical scattering phase functions of nonspherical dust. We combined our measurements of disk geometry to estimate an average disk flaring of about 1.357. First, we recovered the two categories of scattering phase functions based on their shape, as determined in previous studies. Category I is monotonically decreasing and can be explained by fractal organic aggregates with small monomers of 100nm, or compact aggregates with medium porosity and big monomers of 400nm. Category II is defined by a bell-shaped scattering phase function and can be explained by sub-micrometric irregular grains or compact aggregates with low porosity. This statistical study offers general trends about dust populations, but the degeneracy is too strong to apply this method to a unique disk analysis.

astro-ph.SR↗

arXiv2025

Imaging the LkCa 15 system in polarimetry and total intensity without self-subtraction artefacts

Studying young protoplanetary disks is essential for understanding planet formation, but traditional angular differential imaging can introduce self-subtraction artefacts that hinder interpretation of small-scale structures. We present high-resolution total- and polarized-intensity Ks-band images of the LkCa~15 system obtained with SPHERE using near-simultaneous reference-star differential imaging (star-hopping), yielding self-subtraction-free images beyond 0.1 arcsec. LkCa~15 hosts a ~160 au protoplanetary disk and has previously been reported to harbour candidate protoplanets at separations of 15--18 au. We analyse the disk morphology and dust properties and search for super-Jupiter planets beyond 20 au. We first model the near-infrared scattered-light images together with ALMA submillimetre continuum data using RADMC-3D and a two grain-size (micron and millimetre) compact olivine model. While this model broadly reproduces the disk geometry, it overpredicts the degree of forward scattering in the near-infrared. To investigate this discrepancy, we extract the scattering phase function S(theta) and polarized fraction P(theta) from the SPHERE data and compare them with aggregate-scattering models. The observed phase functions disfavour compact Mie spheres and are better matched by porous aggregates (CAHP). Recomputing the scattered-light models with porous CAHP grains in the disk surface layer significantly improves agreement with the observed Ks-band morphology and polarization, while retaining compact millimetre grains to reproduce the ALMA continuum. No new planetary companions are detected; we place upper mass limits of ~1.5 MJ beyond 200 au and ~3.6 MJ in the inner disk. Our results demonstrate that combining star-hopping imaging with phase-function diagnostics provides strong constraints on dust grain properties in protoplanetary disks.

astro-ph.EP↗

arXiv2025

Variation of the disk thickness across ice bands: A method to determine ice abundances in highly inclined protoplanetary disks

The James Webb Space Telescope provides unprecedented information to study ices in protoplanetary disks. However, the saturation of ice bands in highly inclined disks hinders the measurement of ice abundances using classical spectroscopy. This is unfortunate as the presence and more importantly abundance of ices plays a key role in, e.g., the evolution of dust (because it modifies the sticking properties) and the composition of planetesimals and exoplanetary atmospheres. To overcome this issue and quantify the ice abundance within disks, we introduce a new method based on measuring the changes in the apparent disk thickness as a function of wavelength, which is directly and quantitatively related to the grain opacity. Specifically, we expect i) that the increased opacity within ice bands should result in a thicker disk than in the adjacent continuum, and ii) the thickness variations to be proportional to the abundance of ice. We extracted the disk thickness in model images of edge-on disks containing different abundances of water ice, as well as in James Webb Space Telescope spectral imaging of four edge-on disks. For both models and observations, the disk thickness decreases toward longer wavelengths except across the positions of ice absorption features where the thickness is enhanced across the band. In the model images, we demonstrate that this effect increases with ice abundance without any hint of saturation. This definitely demonstrates the presence of the ice species within each disk and confirms our expectation that this method can be applied to estimate ice abundances. Thanks to this method, it will thus be possible to constrain the ice abundance in highly inclined disks with disks model fitting. Unlike spectroscopic analysis, this method is not subject to saturation and should therefore be more robust and applicable to all disks for which the two surfaces can be resolved.

astro-ph.SR↗

arXiv2025

Is cosmic dust porous?

There is a long-standing discussion in the astrophysical/astrochemical community as to the structure and morphology of dust grains in various astrophysical environments (e.g., interstellar clouds, protostellar envelopes, protoplanetary and debris disks, and the atmospheres of exoplanets). Typical grain models assume a compact dust core which becomes covered in a thick ice mantle in cold dense environments. In contrast, less compact cores are likely to exhibit porosity, leading to a pronounced increase in surface area with concomitant much thinner ice films and higher accessibility to the bare grain surface. Several laboratory experimental and theoretical studies have shown that this type of dust structure can have a marked effect on several physico-chemical processes, including adsorption, desorption, mobility, and reactivity of chemical species. Porous grains are thus thought to likely play a particularly important and wide-ranging astrochemical role. Herein, we clarify what is meant by porosity in relation to grains and grain agglomerates, assess the likely astrochemical effects of porosity and ask whether a fractal/porous structural/morphological description of dust grains is appropriate from an astronomical perspective. We provide evidence for high porosity from laboratory experiments and computational simulations of grains and their growth in various astrophysical environments. Finally, we assess the observational constraints and perspectives on cosmic dust porosity. Overall, our paper discusses the effects of including porosity in dust models and the need to use such models for future astrophysical, astrochemical and astrobiological studies involving surface or solid-state processes.

astro-ph.GA↗

arXiv2025

WIde Separation Planets In Time (WISPIT): A Gap-clearing Planet in a Multi-ringed Disk around the Young Solar-type Star WISPIT 2

In the past decades several thousand exoplanet systems have been discovered around evolved, main-sequence stars, revealing a wide diversity in their architectures. To understand how the planet formation process can lead to vastly different outcomes in system architecture we have to study the starting conditions of planet formation within the disks around young stars. In this study we are presenting high resolution direct imaging observations with VLT/SPHERE of the young ($\sim$5 Myr), nearby ($\sim$133 pc), solar-analog designated as WISPIT 2($=$ TYC~5709-354-1). These observations were taken as part of our survey program that explores the formation and orbital evolution of wide-separation gas giants. WISPIT 2 was observed in four independent epochs using polarized light and total intensity observations. They reveal for the first time an extended (380 au) disk in scattered light with a multi-ringed sub-structure. We directly detect a young proto-planet WISPIT 2b, embedded in a disk gap and show that it is co-moving with its host star. Multiple SPHERE epochs demonstrate that it shows orbital motion consistent with Keplerian motion in the observed disk gap. Our $H$ and $K_s$-band photometric data are consistent with thermal emission from a young planet. By comparison with planet evolutionary models, we find a mass of the planet of $4.9^{+0.9}_{-0.6}$ Jupiter masses. This mass is also consistent with the width of the observed disk gap, retrieved from hydrodynamic models. WISPIT 2b is the first unambiguous planet detection in a multi-ringed disk, making the WISPIT 2 system the ideal laboratory to study planet-disk interaction and subsequent evolution.

astro-ph.EP↗

arXiv2025

Multi-Wavelength Dust Characterization of the HL Tau Disk and Implications for Planet Formation

We present a comprehensive analysis of the HL Tau dust disk by modeling its intensity profiles across six wavelengths (0.45 to 7.9 mm) with a resolution of 0.05 arcsec ($\sim7$ au). Using a Markov Chain Monte Carlo (MCMC) approach, we constrain key dust properties including temperature, surface density, maximum grain size, composition, filling factor, and size distribution. The full fitting, with all parameters free, shows a preference for organics-rich dust with a low filling factor in the outer region ($r \gtrsim 40$ au), where the spectral index is $\sim3.7$, but amorphous-carbon-rich dust also reasonably reproduces the observed intensity profiles. Considering the scattering polarization observed at 0.87 mm, compact, amorphous-carbon-rich dust is unlikely, and moderately porous dust is favored. Beyond 40 au, the maximum dust size is likely $\sim100~{\rm μm}$ if dust is compact or amorphous-carbon rich. However, if the dust is moderately porous and organics-rich, both the predicted dust surface density and dust size can be sufficiently large for the pebble accretion rate to reach $\sim10M_{\oplus}~{\rm Myr^{-1}}$ in most regions, suggesting that pebble accretion could be a key mechanism for forming planets in the disk. In contrast, if the dust is amorphous-carbon-rich, forming a giant planet core via pebble accretion is unlikely due to the combined effects of low dust surface density and small dust size required to match the observed emission, suggesting other mechanisms, such as disk fragmentation due to gravitational instability, may be responsible for planet formation in the HL Tau disk.

astro-ph.EP↗

arXiv2025

DRAGyS -- A comprehensive tool to extract scattering phase functions in protoplanetary disks

The early stages of planet formation, involving dust grain growth and planetesimals formation, remain shrouded in mystery. The analysis of the Scattering Phase Function (SPF) measured in disks surrounding young stars holds great potential for revealing crucial information about dust grain properties. Given the increasing number of high-quality datasets available, an efficient method to extract the SPF is required. DRAGyS is a tool designed for the quick and comprehensive analysis of ring-shaped protoplanetary disks. It directly estimates the disk geometry and extracts the total and polarized SPF from scattered light images, without requiring any radiative transfer modeling, a limitation of previous efforts. Key disk parameters (inclination, position angle, aspect ratio) are obtained by fitting ellipses to the disk intensity peaks from the ring surface, assuming the disks are circular. We validated the method using simulated disk images and then applied it to archival polarized-intensity images of nine images for six protoplanetary disks. DRAGyS provides a method to correct for the effect of limb brightening on the SPF. DRAGyS recovers well the injected geometry and the SPF from synthetic images where the parameters are known. When compared to previously published results extracted from images without considering limb brightening, DRAGyS yields similar results for the inclination, position angle, and SPF. We show that the effect of limb brightening on the SPF is significant, with consequences for the inference of dust properties. DRAGyS takes advantage of a fast and purely geometrical approach to estimate ringed-disk geometries. It allows the efficient extraction of SPF either globally or by sectors, allowing it to deal with disk asymmetries. By bypassing the need for a full modeling of the disk geometry before SPF extraction, DRAGyS is well suited to study large samples of disk images.

astro-ph.IM↗

arXiv2025

The role of absorption and scattering in shaping ice bands. Spatially-resolved spectroscopy of protoplanetary disks

The James Webb Space Telescope now enables the spectral study of ices with unprecedented sensitivity and angular resolution. Water ice plays a crucial role in the growth of grains and in planetary formation but its spatial distribution in protoplanetary disks is poorly constrained. To help the interpretation of future observations, we study here for the first time how the water ice band depends on the observer's perspective and the location where spectra are measured within protoplanetary disks. Based on a standard protoplanetary disk model around a T Tauri star, we used the radiative transfer code MCFOST to extract water-ice spectra and to measure the depth and central wavelength of the water-ice band at different locations in the disk. Even in the context of a spatially homogeneous ice mixture, the observed properties of water-ice bands depend on the inclination of the system as well as on the location in the disk from which the spectra are extracted. In particular, the wavelength of the band minimum can change by up to 0.17 μm comparable to the difference expected between amorphous and crystalline ices, for instance. This phenomenon stems from a balance between absorption and scattering and must be taken into account in detailed modeling of spatially-resolved infrared spectroscopy of ices, including CO and CO2.

astro-ph.EP↗

arXiv2025

JWST Imaging of Edge-on Protoplanetary Disks. IV. Mid-infrared Dust Scattering in the HH 30 disk

We present near- and mid-infrared (IR) broadband imaging observations of the edge-on protoplanetary disk around HH 30 with the James Webb Space Telescope/Near Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI). We combine these observations with archival optical/near-IR scattered light images obtained with the Hubble Space Telescope (HST) and a millimeter-wavelength dust continuum image obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) with the highest spatial resolution ever obtained for this target. Our multiwavelength images clearly reveal the vertical and radial segregation of micron-sized and sub-mm-sized grains in the disk. In the near- and mid-IR, the images capture not only bi-reflection nebulae separated by a dark lane but also diverse dynamical processes occurring in the HH 30 disk, such as spiral- and tail-like structures, a conical outflow, and a collimated jet. In contrast, the ALMA image reveals a flat dust disk in the disk midplane. By performing radiative transfer simulations, we show that grains of about 3 $μ$m in radius or larger are fully vertically mixed to explain the observed mid-IR scattered light flux and its morphology, whereas millimeter-sized grains are settled into a layer with a scale height of $\gtrsim1$ au at $100$ au from the central star. We also find a tension in the disk inclination angle inferred from optical/near-IR and mm observations with the latter being closer to an exactly edge-on. Finally, we report the first detection of the proper motion of an emission knot associated with the mid-IR collimated jet detected by combining two epochs of our MIRI 12.8-$μ$m observations.

astro-ph.EP↗

arXiv2024

The grazing angle icy protoplanetary disk PDS 453

PDS 453 is a rare highly inclined disk where the stellar photosphere is seen at grazing incidence on the disk surface. Our goal is take advantage of this geometry to constrain the structure and composition of this disk, in particular the fact that it shows a 3.1 $μ$m water ice band in absorption that can be related uniquely to the disk. We observed the system in polarized intensity with the VLT/SPHERE instrument, as well as in polarized light and total intensity using the HST/NICMOS camera. Infrared archival photometry and a spectrum showing the water ice band are used to model the spectral energy distribution under Mie scattering theory. Based on these data, we fit a model using the radiative transfer code MCFOST to retrieve the geometry and dust and ice content of the disk. PDS 453 has the typical morphology of a highly inclined system with two reflection nebulae where the disk partially attenuates the stellar light. The upper nebula is brighter than the lower nebula and shows a curved surface brightness profile in polarized intensity, indicating a ring-like structure. With an inclination of 80° estimated from models, the line-of-sight crosses the disk surface and a combination of absorption and scattering by ice-rich dust grains produces the water ice band. PDS 453 is seen highly inclined and is composed of a mixture of silicate dust and water ice. The radial structure of the disk includes a significant jump in density and scale height at a radius of 70 au in order to produce a ring-like image. The depth of the 3.1 $μ$m water ice band depends on the amount of water ice, until it saturates when the optical thickness along the line-of-sight becomes too large. Therefore, quantifying the exact amount of water from absorption bands in edge-on disks requires a detailed analysis of the disk structure and tailored radiative transfer modeling.

astro-ph.SR↗

arXiv2024

JWST imaging of edge-on protoplanetary disks. III. Drastic morphological transformation across the mid-infrared in Oph163131

We present JWST broadband images of the highly inclined protoplanetary disk SSTc2d J163131.2-242627 (Oph163131) from 2.0 to 21$μ$m. The images show a remarkable evolution in disk structure with wavelength, quite different from previous JWST observations of other edge-on disks. At 2.0 and 4.4$μ$m, Oph163131 shows two scattering surfaces separated by a dark lane, typical of highly inclined disks. Starting at 7.7$μ$m however, 1) the two linear nebulosities flanking the dark lane disappear; 2) the brighter nebula tracing the disk upper surface transitions into a compact central source distinctly larger than the JWST PSF and whose intrinsic size increases with wavelength; and 3) patches of extended emission appear at low latitudes, and at surprisingly large radii nearly twice that of the scattered light seen with $HST$ and NIRCam, and of the gas. We interpret the compact central source as thermal emission from the star and the inner disk that is not seen directly, but which instead is able to progressively propagate to greater distances at longer wavelengths. The lack of sharp-edged structures in the extended patchy emission argues against the presence of shocks and suggests photoexcitation or stochastic heating of material smoothly flowing away from the star along the disk surface. Finally, the dark lane thickness decreases significantly between 0.6$μ$m and 4.4$μ$m which indicates that the surface layers of Oph163131 lack grains larger than 1$μ$m.

astro-ph.SR↗

arXiv2024

Multiband polarimetric imaging of HD 34700 with SCExAO/CHARIS

We present Subaru/SCExAO + CHARIS broadband (JHK) integral field spectroscopy of HD 34700 A in polarized light. CHARIS has the unique ability to obtain polarized integral field images at 22 wavelength channels in broadband, as the incoming light is first split into different polarization states before passing though the lenslet array. We recover the transition disk around HD 34700 A in multiband polarized light in our data. We combine our polarized intensity data with previous total intensity data to examine the scattering profiles, scattering phase functions and polarized fraction of the disk at multiple wavelengths. We also carry out 3D Monte Carlo radiative transfer simulations of the disk using MCFOST, and make qualitative comparisons between our models and data to constrain dust grain properties. We find that in addition to micron-sized dust grains, a population of sub-micron grains is needed to match the surface brightness in polarized light and polarized fraction. This could indicate the existence of a population of small grains in the disk, or it could be caused by Mie theory simulations using additional small grains to compensate for sub-micron structures of real dust aggregates. We find models that match the polarized fraction of the data but the models do not apply strong constraints on the dust grain type or compositions. We find no models that can match all observed properties of the disk. More detailed modeling using realistic dust aggregates with irregular surfaces and complex structures is required to further constrain the dust properties.

astro-ph.SR↗