Poster Presentation

How Reliably Can Multi-band ALMA SED Fitting Recover Dust Grain Sizes in Narrow Disk Rings?

Author(s): Yi Yang (The Astrobiology Center), Yanqin Wu (The University of Toronto)

Presenter: Yi Yang (NINS, The Astrobiology Center)

Dust growth from submillimeter particles to millimeter-sized pebbles is a key step in planet formation. Multi-band ALMA continuum spectral energy distribution (SED) fitting is widely used to constrain the maximum dust grain size, (a_{\max}), in protoplanetary disks. However, the inferred grain size can be affected by degeneracies among (a_{\max}), dust surface density, and temperature, as well as by optical depth, angular resolution, and the selected combination of observing bands. It is therefore important to determine under which observational conditions grain sizes can be reliably recovered.

We investigate this problem through controlled recovery experiments using synthetic multi-band continuum observations of a narrow dust ring. Our fiducial model has a radius of approximately (0.3^{\prime\prime}) and a characteristic width of (0.02^{\prime\prime}). We vary the input (a_{\max}), dust surface density, angular resolution, and ALMA-band combination. The synthetic images are convolved to different resolutions and fitted using a multi-band SED model. Rather than considering only the minimum (\chi^2), we examine the distributions of acceptable solutions and compare them with the known input parameters.

Our preliminary results show that millimeter-sized grains ((a_{\max}\sim1) mm) can generally be recovered under favorable conditions. In contrast, smaller grains ((a_{\max}\sim0.1) mm) frequently produce broad or multiple solution branches, particularly when some observing bands become optically thick or the ring is insufficiently resolved. The ability to distinguish these solutions also depends strongly on the adopted band combination.

These experiments demonstrate that a formally good SED fit does not necessarily correspond to a unique or reliable grain-size measurement. Our results aim to identify the regimes in which multi-band continuum observations of narrow disk rings provide reliable constraints, ambiguous solutions, or biased estimates of dust growth.