Protoplanetary disk demographics
Disks and Proplyds in the Orion Nebula Cluster with ALMA at 3 mm
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VLA cm-wave survey of young stellar objects in the Oph A clusterAudrey Coutens (LAB, Univ. of Bordeaux)We report the first results from a pilot study of young stellar objects in the Oph A cluster as a prelude to a deep SKA1-Mid Band 5 pointing Key Science Project to map the grain growth in proto-planetary discs. Cm-wave studies of the dust emission are the key to finding out where and how in discs the early stages of planet formation manage to overcome the cm grain size barrier. Investigating the radio emission of young stellar objects is also important to understand the other contributions to this emission and their associated phenomena (e.g., jets, disk photo-evaporation, magnetosphere activity) since they can affect the lifetime of disks and the formation of planets. We have carried out high-sensitivity observations of the continuum emission toward the Oph A cluster using the Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6 arcmin with 0.2'' x 0.4" resolution. The reached sensitivity goes down to 5 μJy/beam in the center of the field. Among the eighteen sources detected, sixteen are young stellar objects (3 Class 0, 5 Class I, 6 Class II and 2 Class III) and two are extragalactic candidates. We analyzed the nature of the emission of the young stellar objects at 10 GHz and estimated the dust contribution to be less than or about 30% in most cases. The radio emission is dominated by other types of emission (gyro-synchrotron radiation from active magnetospheres, free–free emission from thermal jets or from the outflowing photoevaporated disk material, etc), which could not be clearly disentangled. Our non-detections towards Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve overtime. With the sensitivity of our data, we cannot exclude that photoevaporation due to the role of X-ray photons is an efficient mechanism for disk dispersal. Deeper surveys with the SKA will have the capacity to provide significant constraints to disk photoevaporation as well as to other aspects related to star and planet formation. |
Five years of VLT/SPHERE: a new view of planet-forming disks in scattered lightAntonio Garufi (Osservatorio Astrofisico di Arcetri, INAF)Sixty planet-forming disks have been imaged in the five years of VLT/SPHERE guaranteed time of observations. The high-contrast scattered-light maps reveal the high occurrence of well-known disk sub-structures such as spirals and rings but also of features of increasing interest like shadows and filaments. On behalf of the SPHERE consortium, I review the main results of the survey on the demographics and morphological characterization of disks in the near-IR. |
ALMA Survey of Protoplanetary Disks in Lynds 1641Sierra Grant (Boston University)
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Characterizing Young, Cool M-Stars and their Planet-Forming DisksJamila Pegues (Center for Astrophysics | Harvard & Smithsonian)M-stars are the most common hosts of planetary systems in the local Galaxy. Observations of protoplanetary disks around these cool stars are remarkable tools for understanding the environment within which their planets form. We present a small sample of protoplanetary disks around M-stars (spectral types M4-M5). Using spectrally and spatially resolved ALMA observations of a range of molecular lines, we measure the dynamical masses of these stars and characterize the chemistry in their disks. We find that dynamical masses for a combined sample of M-stars exceed fiducial stellar evolutionary model predictions, and we use this discrepancy to constrain the nature of young, cool M-stars. We then find that similar patterns of chemistry exist between our M-star disk sample and solar-type disks, and we investigate hydrocarbons as one important possible exception. Finally, we discuss future observations, which are crucial for obtaining a holistic view of the chemistry of planet formation around the "coolest" stars. |
Modeling brown dwarf protoplanetary disks
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The early stages at substellar formation in Lupus 1 and 3Alejandro Santamaría-Miranda (European Southern Observatory)The formation of brown dwarfs is still under debate. While the latest discoveries point towards a scaled-down version of the star formation process, other models, such as embryo ejection or stellar disk fragmentation, may not be discarded. Here we present our latest ALMA cycle 3 (band 6) continuum observations of Lupus 1 and 3 star formation regions based on previous ASTE/AzTEC observations and a set of previously known class II substellar objects from the literature. We classify these sources using the spectral energy distribution obtained from archival data. We report nine new sources that could be classified as either prestellar cores or deeply embedded protostar candidates, three new class I objects, and one new class II. Additionally we also detected six previously known class II systems, some of them in the boundary between brown dwars and very low mass stars. |
A direct link between disk structure, disk evolution and exoplanet demographicsNienke van der Marel (University of Victoria)Structures such as gaps and rings in observations of protoplanetary disks have long been hailed as signposts of planet formation. However, a direct link between exoplanets and protoplanetary disks remains hard to identify. We present a large sample study of ALMA dust disk surveys of nearby star-forming regions in order to disentangle this connection at a statistical level. All disks are classified as either structured (transition, ring, extended) or non-structured (compact) disks. A comparison across ages reveals that structured disks retain high dust masses up to at least 10 Myr, whereas the dust mass of non-structured disks decreases rapidly over time. This decrease can be understood if the dust mass evolves primarily by radial drift, unless drift is prevented by pressure bumps in structured disks. Furthermore, we find that massive stars are more likely to host structured disks, providing a link with giant exoplanets that also occur more frequently around more massive stars. We show that the observed disk structures can be accounted for if transitional disks are created by exoplanets more massive than Jupiter, and ring disk structures by exoplanets more massive than Neptune, under the assumption that most of those planets eventually migrate inwards. On the other hand, the occurrence of close-in super-Earths is anti-correlated with the fractions of structured disks at different stellar masses, consistent with those exoplanets forming through pebble accretion in drift-dominated disks. These findings support an evolutionary scenario where the early formation of giant planets determines the dust disk evolution and its observational appearance. |
Constraining Planet Formation Around 6-8 Solar Mass StarsDimitri Veras (University of Warwick (UK))Identifying planets around O-type and B-type stars is inherently difficult; the most massive known planet host has a mass of only about 3 M⊙. However, planetary systems which survive the transformation of their host stars into white dwarfs can be detected via photospheric trace metals, circumstellar dusty and gaseous discs, and transits of planetary debris crossing our line of sight. These signatures offer the potential to explore planet formation efficiency and chemical composition for host stars with masses up to the core-collapse boundary at ≈ 8 M⊙, a mass regime rarely investigated in planet formation theory. Here, we establish limits on where both major and minor planets must reside around ≈ 6–8 M⊙ stars in order to survive into the white dwarf phase. For this mass range, we find that intact terrestrial or giant planets need to leave the main sequence beyond approximate minimum star–planet separations of, respectively, about 3 and 6 au. Further, in these systems, rubble pile minor planets of radii 10, 1.0, and 0.1 km would have been shorn apart by giant branch radiative YORP spin-up if they formed and remained within, respectively, tens, hundreds, and thousands of au. Overall, we find that planet formation around 6 M⊙-8 M⊙ stars may be feasible, and hence we encourage dedicated planet formation investigations for these systems. |
Disk Population Synthesis
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