A Multiwavelength ALMA View of Gas and Dust in Binary Protoplanetary System AS 205: Evidence of Dust Asymmetric Distribution

Abstract We present Atacama Large Millimeter/submillimeter Array observations of multiwavelength dust emissions at 3.1 and 1.3 mm, along with molecular line emissions of CO(2–1), CO(3–2), 13 CO(3–2), and C 18 O(3–2) at spatial resolutions of 7–45 au toward the protoplanetary system AS 205. The dust emissions exhibit two distinct components of AS 205 N and AS 205 S, separated by 1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 3. While gas kinematics within the dust disk regions are dominated by Keplerian rotation, the more extended gas emission displays complex morphology and kinematics strongly affected by the binary gravitational interaction in the outer regions. The stellar masses of AS 205 N and AS 205 S are estimated at 0.78 ± 0.19 and 1.93 ± 0.86 M ⊙ , respectively. Azimuthal variation is observed in the spectral index distribution of both disks. In AS 205 N, the spectral index minimum in the southwest is coincident with the peaks of CO(2–1), CO(3–2), and 13 CO(3–2) integrated intensity and the relative position of its southern counterpart. On the other hand, the spectral index distribution in AS 205 S exhibits two prominent maxima, with the one in the northeast aligning with the peak of 13 CO(3–2), and the peak in the south coinciding with local maxima in CO(2–1) and CO(3–2) azimuthal profiles. These results suggest a correlation between dust grain size and/or optical depth with the gas distributions. Dust trapping along the spiral arms possibly contributes to the spectral index minima in AS 205 N; however, the observed asymmetry across both disks suggests the involvement of additional mechanisms.