Dust evolution in protoplanetary disks

Planet formation models rely on knowledge of the physical conditions and evolutionary processes in protoplanetary disks, in particular the grain size distribution and dust growth timescales. In theoretical models, several barriers exist that prevent grain growth to pebble sizes and beyond, such as the radial drift and fragmentation. Pressure bumps have been proposed to overcome such barriers. In the past decade ALMA has revealed observational evidence for the existence of such pressure bumps in the form of dust traps, such as dust rings, gaps, cavities and crescents through high-resolution millimeter continuum data originating from thermal dust emission of pebble-sized dust grains. These substructures may be related to young protoplanets, either as the starting point or the consequence of early planet formation. Furthermore, disk dust masses have been measured for complete samples of young stars in clusters, which provide initial conditions for the solid mass budget available for planet formation. However, observational biases exist in the selection of high-resolution ALMA observations and uncertainties exist in the derivation of the disk dust mass, which both may affect the observed trends. This chapter describes the latest insights in dust evolution and disk continuum observations. Specifically, disk populations and evolutionary trends are described, as well as the uncertainties therein, and compared with exoplanet demographics.Comment: submitted, invited chapter for the "Handbook of Exoplanets". Comments welcom

Disc population synthesis: decrease of the solid mass reservoir through pebble drift

Surveys of star-forming regions reveal that the dust mass of protoplanetary discs decreases by several orders of magnitude on a timescale of a few million years. This decrease in the mass budget of solids is likely due to the gas-drag-induced radial drift of mm-sized solids, called pebbles. However, quantifying the evolution of this dust component in young stellar clusters is difficult due to the inherent large spread in stellar masses and formation times. Therefore, we aim to model the collective evolution of a cluster to investigate the effectiveness of radial drift in clearing the discs of mm-sized particles. We use a protoplanetary disc model that numerically solves for disc formation, and the viscous evolution and photoevaporative clearing of the gas component, while also including the drift of particles limited in size by fragmentation. We find that discs are born with dust masses between 50 Earth masses and 1000 Earth masses, for stars with, respectively, masses between 0.1 solar masses and 1 solar masses. The majority of this initial dust reservoir is typically lost through drift before photoevaporation opens a gap in the gas disc for models both with and without strong X-ray-driven mass loss rates. We conclude that the decrease in time of the mass locked in fragmentation-limited pebbles is consistent with the evolution of dust masses and ages inferred from nearby star-forming regions when assuming viscous evolution rates corresponding to mean gas disc lifetimes between 3 Myr and 8 Myr.Comment: 16 pages, 11 figures, accepted for publication in A&A. Addressed additional language comment

A concentration of centimeter-sized grains in the Oph IRS 48 dust trap

Azimuthally asymmetric dust distributions observed with ALMA in transition disks have been interpreted as dust traps. We present VLA Ka band (34 GHz or 0.9 cm) and ALMA Cycle 2 Band 9 (680 GHz or 0.45 mm) observations at 0.2" resolution of the Oph IRS 48 disk, which suggest that larger particles could be more azimuthally concentrated than smaller dust grains, assuming an axisymmetric temperature field or optically thin 680 GHz emission. Fitting an intensity model to both data demonstrates that the azimuthal extent of the millimeter emission is 2.3 $\pm0.9$ times as wide as the centimeter emission, marginally consistent with the particle trapping mechanism under the above assumptions. The 34 GHz continuum image also reveals evidence for ionized gas emission from the star. Both the morphology and the spectral index variations are consistent with an increase of large particles in the center of the trap, but uncertainties remain due to the continuum optical depth at 680 GHz. Particle trapping has been proposed in planet formation models to allow dust particles to grow beyond millimeter sizes in the outer regions of protoplanetary disks. The new observations in the Oph IRS 48 disk provide support for the dust trapping mechanism for centimeter-sized grains, although additional data is required for definitive confirmation.Comment: Language editing and addition reference ALMA dat

Outflow forces of low mass embedded objects in Ophiuchus: a quantitative comparison of analysis methods

The outflow force of molecular bipolar outflows is a key parameter in theories of young stellar feedback on their surroundings. The focus of many outflow studies is the correlation between the outflow force, bolometric luminosity and envelope mass. However, it is difficult to combine the results of different studies in large evolutionary plots over many orders of magnitude due to the range of data quality, analysis methods and corrections for observational effects such as opacity and inclination. We aim to determine the outflow force for a sample of low luminosity embedded sources. We will quantify the influence of the analysis method and the assumptions entering the calculation of the outflow force. We use the James Clerk Maxwell Telescope to map 12CO J=3-2 over 2'x2' regions around 16 Class I sources of a well-defined sample in Ophiuchus at 15" resolution. The outflow force is then calculated using seven different methods differing e.g. in the use of intensity-weighted emission and correction factors for inclination. The results from the analysis methods differ from each other by up to a factor of 6, whereas observational properties and choices in the analysis procedure affect the outflow force by up to a factor of 4. For the sample of Class I objects, bipolar outflows are detected around 13 sources including 5 new detections, where the three non-detections are confused by nearby outflows from other sources. When combining outflow forces from different studies, a scatter by up to a factor of 5 can be expected. Although the true outflow force remains unknown, the separation method (separate calculation of dynamical time and momentum) is least affected by the uncertain observational parameters. The correlations between outflow force, bolometric luminosity and envelope mass are further confirmed down to low luminosity sources.Comment: 24 pages, 13 figures, Accepted by A&

Investigating the asymmetric chemistry in the disk around the young star HD 142527

The atmospheric composition of planets is determined by the chemistry of the disks in which they form. Studying the gas-phase molecular composition of disks thus allows us to infer what the atmospheric composition of forming planets might be. Recent observations of the IRS 48 disk have shown that (asymmetric) dust traps can directly impact the observable chemistry, through radial and vertical transport, and the sublimation of ices. The asymmetric HD 142527 disk provides another good opportunity to investigate the role of dust traps in setting the disk's chemical composition. In this work, we use archival ALMA observations of the HD 142527 disk to obtain an as large as possible molecular inventory, which allows us to investigate the possible influence of the asymmetric dust trap on the disk's chemistry. We present the first ALMA detections of [C I], 13C18O, DCO+, H2CO and additional transition of HCO+ and CS in this disk. In addition, we have acquired upper limits for non-detected species such as SO and CH3OH. For the majority of the observed molecules, a decrement in the emission at the location of the dust trap is found. For the main CO isotopologues continuum over-subtraction likely causes the observed asymmetry, while for CS and HCN we propose that the observed asymmetries are likely due to shadows cast by the misaligned inner disk. As the emission of the observed molecules is not co-spatial with the dust trap and no SO or CH3OH are found, thermal sublimation of icy mantles does not appear to play a major role in changing the gas-phase composition of the outer disk in HD 142527 disk. Using our observations of 13C18O and DCO+ and a RADMC-3D model, we determine the CO snowline to be located beyond the dust traps, favouring cold gas-phase formation of H2CO, rather than the hydrogenation of CO-ice and subsequent sublimation.Comment: Accepted for publication in A&A on 12/04/202

Women in physics in the Netherlands:Recent Developments

Although women are still a small minority in physics in the Netherlands, their visibility has increased markedly over the past five years. The measures put in place after the first IUPAP Women in Physics Conference in 2002 have in fact not increased the total number of female staff, but put the spotlight on female talent in physics. Affirmative actions by Dutch science faculties and physics departments have brought about a more than fivefold increase of female full professors: by now only one university is left without a female chair. At the assistant and associate professor levels, the MEERVOUD and ASPASIA programs of NWO (the national funding agency for scientific research) have been a success. The FOm/f program of the Foundation for Fundamental Research on Matter has accomplished its goal of stimulating the participation of women in physics through covering salary costs, giving research funding and postdoctoral positions, and highlighting outstanding female physicists through the MINERVA prize. Despite these success stories, the number of female physics students is still far too low, and even if there is an important influx of foreigners at all career levels from the PhD student upward, reaching 10% women in permanent positions in physics is still a goal for the future