Determining Dust Properties in Protoplanetary Disks: SED-derived Masses and Settling With ALMA

TL;DR

This study models the spectral energy distributions of 338 protoplanetary disks around T Tauri stars to better estimate their masses and dust settling, revealing that previous (sub)mm surveys likely underestimated disk masses due to optical thickness assumptions.

Contribution

It introduces SED modeling as a more accurate method for disk mass estimation, challenging the reliance on (sub)mm fluxes and providing insights into dust evolution and planetary system formation timelines.

Findings

SED-derived masses are 1.5-5 times higher than (sub)mm estimates.

Disks in younger regions are more massive but show similar dust settling levels.

Significant dust evolution occurs early, suggesting earlier planet formation.

Abstract

We present spectral energy distribution (SED) modeling of 338 disks around T Tauri stars from eleven star-forming regions, ranging from $\sim$0.5 to 10 Myr old. The disk masses we infer from our SED models are typically greater than those reported from (sub)mm surveys by a factor of 1.5-5, with the discrepancy being generally higher for the more massive disks. Masses derived from (sub)mm fluxes rely on the assumption that the disks are optically thin at all millimeter wavelengths, which may cause the disk masses to be underestimated since the observed flux is not sensitive to the whole mass in the disk; SED models do not make this assumption and thus yield higher masses. Disks with more absorbing material should be optically thicker at a given wavelength; which could lead to a larger discrepancy for disks around massive stars when the disk temperature is scaled by the stellar luminosity. We also compare the disk masses and degree of dust settling across the different star-forming regions and find that disks in younger regions have more massive disks than disks in older regions, but a similar degree of dust settling. Together, these results offer potential partial solutions to the "missing" mass problem: disks around T Tauri stars may indeed have enough material to form planetary systems, though previous studies have underestimated the mass by assuming the disks to be optically thin; these planetary systems may also form earlier than previously theorized since significant dust evolution (i.e., settling) is already apparent in young disks.