Dust settling and grain evolution in edge-on protoplanetary disks: A JWST broadband imaging survey

We report on the initial results of our JWST Cycle 1 program that imaged four edge-on protoplanetary disks in nearby star-forming regions across the wavelength range of 2-21 microns. The goal of our program is to study the extent of vertical settling of dust grains to the disk mid-plane, as well as evidence for grain evolution through the wavelength dependence of the dust opacity and phase function. Prior HST images show that these disks occult direct starlight, appearing as a dust lane between two lobes of reflected light. They possess a range of evolutionary characteristics from prominent envelopes to highly collimated jets to nearly-flat disks with little evidence of accretion. We find that three of the four targets (Tau042021, IRAS 04302, and HH 30) retain the appearance of bipolar nebulae even at MIRI wavelengths, but with enhanced forward scattering. While all three show evidence for a thinner dust lane at NIRCam wavelengths than seen in HST optical images, the first two show a surprising lack of dust lane chromaticity between 4.4-21 microns. An initial exploration with scattered light models shows that to reproduce this behavior, ~10 micron sized grains must remain vertically mixed up to the disks’ outer scattering surfaces at radii of 100-400 AU. Two of the targets also show previously undetected mid-infrared structures above the disk plane. The fourth target shows remarkable changes in appearance at MIRI wavelengths: the two parallel scattered light nebulae disappear, being replaced by a single compact (but resolved) central source. In addition, large irregular patches of emission appear well-outside the disk radius seen with NIRCam and HST. Along with further modeling and interpretation of these results, we will present a preview of our ongoing JWST Cycle 2 program that is studying an additional 13 objects.