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The past few years have seen a revolution in the study of circumstellar disks. New instrumentation in the near-infrared and (sub)millimeter regimes have allowed us to routinely spatially resolve disks around young stars of nearby star-forming regions. As a result, we have found that substructures with scales of sim 10\,au in disks are common. We have also revealed a zoo of different morphologies, sizes, and luminosities that is as complex as the diversity of architectures found in evolved exoplanet systems. We study disk evolutionary trends as they appear in scattered light observations. Scattered light traces the micron-sized particles at the disk surface that are well coupled to the gas. This means that scattered light observations can be used to trace the distribution of the disk gas and its interaction with embedded perturbers. We used VLT/SPHERE to observe 20 systems in the Cha I cloud in polarized scattered light in the near-infrared. We combined the scattered light observations with existing literature data on stellar properties and with archival ALMA continuum data to study trends with system age and dust mass. We also connected resolved near-infrared observations with the spectral energy distributions of the systems. In 13 of the 20 systems included in this study we detected resolved scattered light signals from circumstellar dust. For the CR\,Cha, CT\,Cha, CV\,Cha, SY\,Cha, SZ\,Cha, and VZ\,Cha systems we present the first detailed descriptions of the disks in scattered light. The observations found typically smooth or faint disks, often with little substructure, with the notable exceptions of SZ\,Cha, which shows an extended multiple-ringed disk, and WW\,Cha, which shows interaction with the cloud environment. New high S/N K-band observations of the HD\,97048 system in our survey reveal a significant brightness asymmetry that may point to disk misalignment and subsequent shadowing of outer disk regions, possibly related to the suggested planet candidate in the disk. We resolve for the first time the stellar binary in the CS\,Cha system. Multiple wavelength observations of the disk around CS\,Cha have revealed that the system contains small, compact dust grains that may be strongly settled, consistent with numerical studies of circumbinary disks. We find in our sample that there is a strong anti-correlation between the presence of a (close) stellar companion and the detection of circumstellar material with five of our seven nondetections located in binary systems. We also find a correlation between disk mass, as inferred from millimeter observations, and the detection of scattered light signal. Finally, we find a tentative correlation between relative disk-to-star brightness in scattered light and the presence of a dust cavity in the inner (unresolved) disk, as traced by the system spectral energy distribution. At the same time, faint disks in our sample are generally younger than 2\,Myr.
The past few years have seen a revolution in the study of circumstellar disks. New instrumentation in the near-infrared and (sub)millimeter regimes have allowed us to routinely spatially resolve disks around young stars of nearby star-forming regions. As a result, we have found that substructures with scales of sim 10\,au in disks are common. We have also revealed a zoo of different morphologies, sizes, and luminosities that is as complex as the diversity of architectures found in evolved exoplanet systems. We study disk evolutionary trends as they appear in scattered light observations. Scattered light traces the micron-sized particles at the disk surface that are well coupled to the gas. This means that scattered light observations can be used to trace the distribution of the disk gas and its interaction with embedded perturbers. We used VLT/SPHERE to observe 20 systems in the Cha I cloud in polarized scattered light in the near-infrared. We combined the scattered light observations with existing literature data on stellar properties and with archival ALMA continuum data to study trends with system age and dust mass. We also connected resolved near-infrared observations with the spectral energy distributions of the systems. In 13 of the 20 systems included in this study we detected resolved scattered light signals from circumstellar dust. For the CR\,Cha, CT\,Cha, CV\,Cha, SY\,Cha, SZ\,Cha, and VZ\,Cha systems we present the first detailed descriptions of the disks in scattered light. The observations found typically smooth or faint disks, often with little substructure, with the notable exceptions of SZ\,Cha, which shows an extended multiple-ringed disk, and WW\,Cha, which shows interaction with the cloud environment. New high S/N K-band observations of the HD\,97048 system in our survey reveal a significant brightness asymmetry that may point to disk misalignment and subsequent shadowing of outer disk regions, possibly related to the suggested planet candidate in the disk. We resolve for the first time the stellar binary in the CS\,Cha system. Multiple wavelength observations of the disk around CS\,Cha have revealed that the system contains small, compact dust grains that may be strongly settled, consistent with numerical studies of circumbinary disks. We find in our sample that there is a strong anti-correlation between the presence of a (close) stellar companion and the detection of circumstellar material with five of our seven nondetections located in binary systems. We also find a correlation between disk mass, as inferred from millimeter observations, and the detection of scattered light signal. Finally, we find a tentative correlation between relative disk-to-star brightness in scattered light and the presence of a dust cavity in the inner (unresolved) disk, as traced by the system spectral energy distribution. At the same time, faint disks in our sample are generally younger than 2\,Myr.
The sample of planet-forming disks observed by high-contrast imaging campaigns over the last decade is mature enough to enable the demographical analysis of individual star-forming regions. We present the full census of Taurus sources with VLT/SPHERE polarimetric images available. The whole sample sums up to 43 targets (of which 31 have not been previously published) corresponding to one-fifth of the Class II population in Taurus and about half of such objects that are observable. A large fraction of the sample is apparently made up of isolated faint disks (equally divided between small and large self-shadowed disks). Ambient signal is visible in about one-third of the sample. This probes the interaction with the environment and with companions or the outflow activity of the system. The central portion of the Taurus region almost exclusively hosts faint disks, while the periphery also hosts bright disks interacting with their surroundings. The few bright disks are found around apparently older stars. The overall picture is that the Taurus region is in an early evolutionary stage of planet formation. Yet, some objects are discussed individually, as in an intermediate or exceptional stage of the disk evolution. This census provides a first benchmark for the comparison of the disk populations in different star forming regions.
Disks around intermediate mass stars called Herbig disks are the formation sites of giant exoplanets. Obtaining a complete inventory of these disks will therefore give insights into giant planet formation. However, to date no complete disk survey has been done on Herbig disks in a single star-forming region. Our aim is to obtain the first complete survey of Herbig disks. Orion is the only nearby region with a significant number of Herbig disks (N=35) where such a survey can be carried out. The resulting dust mass distribution is compared to other dust mass distributions of disks around proto- and pre-main sequence stars in Orion. In addition, we ascertain whether previous Atacama Large Millimeter/submillimeter Array (ALMA) observations have been biased toward the most massive and brightest Herbig disks. Using new Northern Extended Millimeter Array (NOEMA) observations of 25 Herbig disks, in combination with ALMA archival data of 10 Herbig disks, resulted in a complete sample of all known Herbig disks in Orion. Using $uv$-plane analysis for the NOEMA observed disks, and literature values of the ALMA observed disks, we obtained the dust masses of all Herbig disks and obtained a cumulative dust mass distribution. Additionally, six disks with new CO isotopolog detections are presented, one of which is detected in C^17O . We calculated the external ultraviolet (UV) irradiance on each disk and compared the dust mass to it. We find a median disk dust mass of 11.7 $M_ for the Herbig disks. Comparing the Herbig disks in Orion to previous surveys for mainly T Tauri disks in Orion, we find that while $ of the Herbig disks have a mass higher than 10 M$_ this is at most 25<!PCT!> for the T Tauri disks. This difference is especially striking when considering that the Herbig disks are around a factor of 2 older than the T Tauri disks. After a comparison to the Herbig disks observed with ALMA from a previous study, no significant difference is found between the distributions. We find a steeper relationship between the dust mass and external UV irradiation (slope of $-7.6$) compared to that of the T Tauri disks (slope of $-1.3$). Comparing our results to a recent SPHERE survey of disks in Orion, we see that the Herbig disks present the largest and brightest disks and have structures indicative of gas-giant formation. Herbig disks are on average more massive compared to T Tauri disks. This work shows the importance of complete samples, giving rise to the need of a complete survey of the Herbig disk population.
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