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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 similar to 74 degrees), with two bright lobes and a large cavity. We also marginally detect the scattering surface from the rearfacing 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. ; ANR of France [ANR-16-CE31-0013]; European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme [757957]; ICM (Iniciativa Cientifica Milenio) via the Nucleo Milenio de Formacion Planetaria grant; Universidad de Valparaiso; Fondecyt [1180395]; CONICYT [Basal AFB-170002]; FONDECYT Iniciacion project [11181068]; CONICYT + PAI/Convocatoria nacional subvencion a la instalacion en la academia [2017 + Folio PAI77170087]; Spanish MINECO [AyA2017-84089]; ESO; CNRS (France); MPIA (Germany); INAF (Italy); FINES (Switzerland); NOVA (Netherlands); European Commission [RII3-Ct-2004-001566, 226604, 312430]; Programme National de Planetologie (PNP) of CNRS-INSU in France; Programme National de Physique Stellaire (PNPS) of CNRS-INSU in France; French Labex OSUG2020 (Investissements d'avenir) [ANR10 LABX56]; CNRS, by the Agence Nationale de la Recherche [ANR-14-CE33-0018]; Swiss National Science Foundation (SNSF); SNSF ; Open access journal. ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.

Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity that are intimately connected to the evolution of protoplanetary disks and the formation of planets. We carried out sensitive continuum observations toward the Ophiuchus A star-forming region, using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6′ and with a spatial resolution of θmaj ×θmin ∼ 0.′′4 × 0.′′2. We achieved a 5 μJy beam-1 rms noise level at the center of our mosaic field of view. Among the 18 sources we detected, 16 were YSOs (three Class 0, five Class I, six Class II, and two Class III) and two were extragalactic candidates. We find that thermal dust emission generally contributed less than 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission, such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photoevaporated disk material, and synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections for 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 over time. The sensitivity of our data cannot exclude photoevaporation due to the role of X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys using the Square Kilometre Array (SKA) will have the capacity to provide significant constraints to disk photoevaporation. © A. Coutens et al. ; H2020 Marie SkÅ odowska-Curie Actions, MSCA: 823823 ; Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica, FONDECYT: 11181068 ; Russian Science Foundation, RSF: 18-12-00351 ; Horizon 2020 Framework Programme, H2020 ; University of Leeds ; Natural Sciences and Engineering Research Council of Canada, NSERC ; CUP C52I13000140001 ; Consejo Nacional de Ciencia y Tecnología, Paraguay, El CONACYT ; Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México, DGAPA, UNAM: IN112417 ; Comisión Nacional de Investigación Científica y Tecnológica, CONICYT: AFB-170002 ; Deutsche Forschungsgemeinschaft, DFG: SPP 1833, ERC-2013-ADG ; Deutsche Forschungsgemeinschaft, DFG ; Science and Technology Facilities Council, STFC: ST/R000549/1 ; Deutsche Forschungsgemeinschaft, DFG ; National Research Council Canada, NRC ; European Research Council, ERC: PALs 320620 ; Science and Technology Facilities Council, STFC: ST/L004801 ; of Life Science Working Group of the SKA. The authors thank Hsieh Tien-Hao for providing the results of the classification method presented in Hsieh & Lai (2013). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities. A.C. postdoctoral grant is funded by the ERC Starting Grant 3DICE (grant agreement 336474). I.J.-S. acknowledges the financial support received from the STFC through an Ernest Rutherford Fellowship (proposal number ST/L004801). L.L. acknowledges the financial support of DGAPA, UNAM (project IN112417), and CONACyT, México. A.C.T. acknowledges the financial support of the European Research Council (ERC; project PALs 320620). D.J. is supported by the National Research Council Canada and by an NSERC Discovery Grant. L.M.P. acknowledges support from CONICYT project Basal AFB-170002 and from FONDECYT Iniciación project #11181068. A.P. acknowledges the support of the Russian Science Foundation project 18-12-00351. D.S. acknowledges support by the Deutsche Forschungsgemeinschaft through SPP 1833: Building a Habitable Earth (SE 1962/6-1). M.T. has been supported by the DISCSIM project, grant agreement 341137 funded by the European Research Council under ERC-2013-ADG. C.W. acknowledges support from the University of Leeds and the Science and Technology Facilities Council under grant number ST/R000549/1. This work was partly supported by the Italian Ministero dell'Istruzione, Università e Ricerca through the grant Progetti Premiali 2012 – iALMA (CUP C52I13000140001), by the Deutsche Forschungs-gemeinschaft (DFG, German Research Foundation) – Ref no. FOR 2634/1 TE 1024/1-1, and by the DFG cluster of excellence Origin and Structure of the Universe (www.universe-cluster.de). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 823823. This project has also been supported by the PRIN-INAF 2016 "The Cradle of Life - GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA)".