Despite its importance for star and planet formation, the physical process(es) that drive disk accretion remain frustratingly unclear. The magnetorotational instability is questioned both theoretically and observationally and disk winds are increasingly invoked. I will describe how the evolution of gas disk sizes from Class I to Class II indicates that some mechanism produces significant disk...
The evolution of protoplanetary disks is set by the conservation of angular momentum, where the accretion of material onto the central star is balanced by viscous expansion of the outer disk or by disk winds extracting angular momentum without changing the disk size. Studying the time evolution of disk sizes allows us therefore to distinguish between viscous stresses or disk winds as the main...
Much of our understanding of star and planet formation hinges on the accuracy of stellar masses and ages derived from pre-main sequence evolutionary track models. Consequently, errors in evolutionary track models could propagate through much of our understanding of star and planet formation. Moreover, there remain few constraints on pre-main sequence evolutionary tracks owing in large part to...
From a theoretical point-of-view, magnetic fields are crucial to the evolution of planet-forming disks. However, profound observational constraints are pending. Presently, the number of cutting-edge polarization observations presenting inconclusive data increases continuously. In very recent years, polarization at mm-wavelengths, the classical tracer of magnetic fields, emerged as highly...
Polarimetric observations of protoplanetary disks at millimeter wavelengths have been dramatically developing owing to its high-sensitivity and high-resolution observations with ALMA. However, the mechanisms of the polarization are under discussion. The proposed mechanisms so far are the self-scattering and the grain alignment, but the alignment directions are possibly with magnetic fields,...
ALMA-DOT is a small campaign devoted to the chemical characterization of disk-outflow sources in Taurus. The sample currently consists of six Class I sources known to drive powerful outflows. The high angular resolution and sensitivity of ALMA allowed us to characterize their chemical composition by separating the disk emission from the outflow and envelope contamination. Six molecules - from...
I will present a novel method to extract azimuthally averaged 3D velocity profiles from ALMA data. Application of this to the well studied source HD 163296 reveals a highly dynamical disk, hosting large flow structures indicative of meridional flows likely driven by three embedded protoplanets. These flows provide an efficient transport mechanism of volatile-rich gas in the disk atmosphere...
Protoplanets and circumplanetary disks are elusive yet they are cornerstones to the most popular interpretations for observed protoplanetary disk structures. The gaseous velocity field also bears the imprint of planet–disk interactions, with non-Keplerian fine structure in the molecular-line channel maps (e.g., wiggles or kinks). Such features could in principle be connected to the perturber...
ALMA is showing that most proto-planetary discs are highly sub-structured and that the most frequent structure consists in azimuthally symmetric "gaps and rings". Rings have attracted a lot of attention since they might be the signature of young planets. But rings are extremely important for another reason: they provide us with a privileged window inside disc physics. Indeed, as shown by the...
The migration of planetary cores embedded in a protoplanetary disk is an important mechanism within planet-formation theory, relevant for the architecture of planetary systems. Consequently, planet migration is actively discussed, yet often results of independent theoretical or numerical studies are unconstrained due to the lack of observational diagnostics designed in light of planet...
Snowlines, in particular the water snowline, are important for the formation of planets in protoplanetary disks. However, locating the water snowline directly is challenging. Firstly, due to the proximity of the water snowline to the host star. But ALMA can now resolve this region for the first time. Secondly, due to the absorption of water in the Earth's atmosphere. A chemical tracer, HCO+,...
Elemental abundance ratios in the inner regions of protoplanetary discs are important for setting the composition of exoplanets, but are likely not to represent the bulk composition of the star's parental cloud. Abundance differences are expected to be driven by the differential transport of chemical species in solid and gaseous form: elements which are mainly concentrated in species with high...
