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Context.Acetone (CH₃COCH₃) is one of the most abundant three-carbon oxygen-bearing complex organic molecules (O-COMs) that have been detected in space. The previous detections were made in the gas phase toward star-forming regions that are chemically rich, mostly in protostellar systems. Recently, acetone ice has also been reported as (tentatively) detected toward two low-mass protostars, allowing comparisons in acetone abundances between gas and ice. The detection of acetone ice warrants a more systematic study of its gaseous abundances which is currently lacking. Aims.We aim to measure the gas-phase abundances of acetone in a large sample obtained from the CoCCoA program, and investigate the chemical evolution of acetone from ice to gas in protostellar systems. Methods.We fit the ALMA spectra to determine the column density, excitation temperature, and line width of acetone in 12 high-mass protostars as part of CoCCoA. We also constrained the physical properties of propanal (C₂H₅CHO), ketene (CH₂CO), and propyne (CH₃CCH), which might be chemically linked with acetone. We discuss the possible formation pathways of acetone by making comparisons in its abundances between gas and ice and between observations and simulations. Results.We firmly detect acetone, ketene, and propyne in the 12 high-mass protostars. The observed gas-phase abundances of acetone are surprisingly high compared to those of two-carbon O-COMs (especially aldehydes). Propanal is considered as tentatively detected due to lack of unblended lines covered in our data. The derived physical properties suggest that acetone, propanal, and ketene have the same origin from hot cores as other O-COMs, while propyne tends to trace the more extended outflows. The acetone-to-methanol ratios are higher in the solid phase than in the gas phase by one order of magnitude, which suggests gas-phase reprocessing after sublimation. There are several suggested formation pathways of acetone (in both ice and gas) from acetaldehyde, ketene, and propylene. The observed ratios between acetone and these three species are rather constant across the sample, and can be well reproduced by astrochemical simulations. Conclusions.On the one hand, the observed high gas-phase abundances of acetone along with dimethyl ether (CH₃OCH₃) and methyl formate (CH₃OCHO) may hint at specific chemical mechanisms that favor the production of ethers, esters, and ketones over alcohols and aldehydes. On the other hand, the overall low gas-phase abundances of aldehydes may result from destruction pathways that are overlooked or underestimated in previous studies. The discussed formation pathways of acetone from acetaldehyde, ketene, and propylene seem plausible from observations and simulations, but more investigations are needed to draw more solid conclusions. We emphasize the importance of studying acetone, which is an abundant COM that deserves more attention in the future. 

We present high-resolution millimeter continuum ALMA observations of the disks around the T Tauri stars LkCa 15 and 2MASS J16100501-2132318 (hereafter, J1610). These transition disks host dust-depleted inner regions, which have possibly been carved by massive planets, and they are of prime interest to the study of the imprints of planet-disk interactions. While at moderate angular resolution, they appear as a broad ring surrounding a cavity, the continuum emission resolves into multiple rings at a resolution of ~60 × 40 mas (~7.5 au for LkCa 15, ~6 au for J1610) and ~7 μ Jy beam −1 rms at 1.3 mm. In addition to a broad extended component, LkCa 15 and J1610 host three and two narrow rings, respectively, with two bright rings in LkCa 15 being radially resolved. LkCa 15 possibly hosts another faint ring close to the outer edge of the mm emission. The rings look marginally optically thick, with peak optical depths of ~0.5 (neglecting scattering), in agreement with high angular resolution observations of full disks. We performed hydrodynamical simulations with an embedded, sub-Jovian-mass planet and show that the observed multi-ringed substructure can be qualitatively explained as the outcome of the planet-disk interaction. We note, however, that the choice of the disk cooling timescale alone can significantly impact the resulting gas and dust distributions around the planet, leading to different numbers of rings and gaps and different spacings between them. We propose that the massive outer disk regions of transition disks are favorable places for planetesimals, and possibly second-generation planet formation of objects with a lower mass than the planets carving the inner cavity (typically few M Jup ), and that the annular substructures observed in LkCa 15 and J1610 may be indicative of planetary core formation within dust-rich pressure traps. Current observations are compatible with other mechanisms contributing to the origin of the observed substructures, in particular with regard to narrow rings generated (or facilitated) at the edge of the CO and N 2 snowlines.