Spatial segregation of dust grains in transition disks

Abstract

Context. The mechanisms governing the opening of cavities in transition disks are not fully understood. Several processes have been proposed, but their occurrence rate is still unknown. Aims. We present spatially resolved observations of two transition disks, and aim at constraining their vertical and radial structure using multiwavelength observations that probe different regions of the disks and can help understanding the origin of the cavities. Methods. We have obtained near-infrared scattered light observations with VLT/SPHERE of the transition disks 2MASS J16083070-3828268 (J1608) and RXJ1852.3-3700 (J1852), located in the Lupus and Corona Australis star-forming regions respectively. We complement our datasets with archival ALMA observations, and with unresolved photometric observations covering a wide range of wavelengths. We performed radiative transfer modeling to analyze the morphology of the disks, and then compare the results with a sample of 20 other transition disks observed with both SPHERE and ALMA. Results. We detect scattered light in J1608 and J1852 up to a radius of 0.54′′ and 0.4′′ respectively. The image of J1608 reveals a very inclined disk (i ~ 74°), with two bright lobes and a large cavity. We also marginally detect the scattering surface from the rear-facing side of the disk. J1852 shows an inner ring extending beyond the coronagraphic radius up to 15 au, a gap and a second ring at 42 au. Our radiative transfer model of J1608 indicates that the millimeter-sized grains are less extended vertically and radially than the micron-sized grains, indicating advanced settling and radial drift. We find good agreement with the observations of J1852 with a similar model, but due to the low inclination of the system, the model remains partly degenerate. The analysis of 22 transition disks shows that, in general, the cavities observed in scattered light are smaller than the ones detected at millimeter wavelengths. Conclusions. The analysis of a sample of transition disks indicates that the small grains, well coupled to the gas, can flow inward of the region where millimeter grains are trapped. While 15 out of the 22 cavities in our sample could be explained by a planet of less than 13 Jupiter masses, the others either require the presence of a more massive companion or of several low-mass planets.

An HST/STIS view of protoplanetary discs in Upper Scorpius: observations of three young M stars

“…Whilst we detect no significant structure around J16090075-1908526, Barenfeld et al (2016) find this disc to be the most extended in CO and in 0.88 mm continuum emission of those observed as part of our study. This indicates that the micron-sized dust grains are poorly coupled to both the CO gas and larger mm-size dust grains at these extended radii, in agreement with results reported in Villenave et al (2019) and Rich et al (2021) and contrasting with the relationship we observe for our detected discs. Again, further characterization via deeper imaging and disc modelling could potentially help to resolve these seemingly contradictory sets of observations.…”

Quantitative polarimetry of the disk around HD 169142

“…The radius of the inner ring is in millimeter wavelengths around 0.22 , which is substantially larger than the radius measured for the inner ring in scattered light. This radius difference between scattered light and thermal light in the millimeter range is often seen in transition disks (e.g., Villenave et al 2019), and this is explained by the accumulation of large grains in the gas pressure maximum of the ring, which is, in transition disks, farther out than the scattered light emission from the inner wall. For the outer ring of HD 169142, the millimeter-wave ring has a radius of about 0.53 , which coincides well with the peak flux radii derived for the scattered light.…”

Perturbers: SPHERE detection limits to planetary-mass companions in protoplanetary disks

“…We use their functional form of the ratio in the cavity size seen in µm-and mm-sized dust for a given planet mass The location of the scattered-light inner edge is usually not provided from the observations. Following Villenave et al (2019), we derive for each gap a minimum planet mass (M p (min)), assuming that the scattered-light edge is at the onehalf distance between the peak of the disk in PDI and the gap minimum, and a maximum planet mass (M p (max)), taking the scattered-light edge as the position of the peak in PDI. We use as R p the location of the gap in scattered light.…”