Alejandro Santamaría Miranda

arXiv2026

AB Aur, a Rosetta stone for studies of planet formation (IV): C/O estimates from CS and SO interferometric observations

Context. Protoplanetary disks are the birthplace of planets. As such, they set the initial chemical abundances available for planetary atmosphere formation. Thus, studying elemental abundances, molecular compositions, and abundance ratios in protoplanetary disks is key to linking planetary atmospheres to their formation sites. Aims. We aim to derive the sulfur abundance and the C/O ratio in the AB Aur disk using interferometric observations of CS and SO. Methods. New NOEMA observations of CS 3-2 towards AB Aur are presented. We used velocity-integrated intensity maps to determine the inclination and position angles. Keplerian masks were constructed for all observed species to assess the presence of non-Keplerian motions. We use the CS/SO ratio to study the C/O ratio. We compare our present and previous interferometric observations of AB Aur with a NAUTILUS disk model to gain insight into the S elemental abundance and C/O ratio. Results. We derive an observational CS/SO ratio ranging from 1.8 to 2.6. Only NAUTILUS models with C/O > 1 can reproduce such ratios. The comparison with models points to strong sulfur depletion, with [S/H]=8e-8, but we note that no single model can simultaneously fit all observed species.

astro-ph.EP↗

arXiv2025

Hints of Disk Substructure in the First Brown Dwarf with a Dynamical Mass Constraint

We present high-resolution ALMA observations at 0.89 mm of the Class II brown dwarf 2MASS J04442713+2512164 (2M0444), achieving a spatial resolution of 0$.\!\!^{\prime\prime}$046 ($\sim$6.4 au at the distance to the source). These observations targeted continuum emission together with $^{12}$CO (3-2) molecular line. The line emission traces a Keplerian disk, allowing us to derive a dynamical mass between 0.043-0.092 M${_{\odot}}$ for the central object. We constrain the gas-to-dust disk size ratio to be $\sim$7, consistent with efficient radial drift. However, the observed dust emission suggest that a dust trap is present, enough to retain some dust particles. We perform visibility fitting of the continuum emission, and under the assumption of annular substructure, our best fit shows a gap and a ring at 98.1$^{+4.2}_{-8.4}$ mas ($\sim$14 au) and 116.0$^{+4.2}_{-4.8}$ mas ($\sim$16 au), respectively, with a gap width of 20 mas ($\sim$3 au). To ensure robustness, the data were analyzed through a variety of methods in both the image and uv plane, employing multiple codes and approaches. This tentative disk structure could be linked to a possible planetary companion in the process of formation. These results provide the first dynamical mass of the lowest mass object to date, together with the possible direct detection of a substructure, offering new insights into disk dynamics and planet formation in the very low-mass regime. Future higher spatial resolution ALMA observations will be essential to confirm these findings and further investigate the link between substructures and planet formation in brown dwarf disks.

astro-ph.SR↗