Origin and characterization of disks substructures, and their relation to stellar hosts

Planets are formed from the gas and dust content available in planet-forming disks around young stars, creating substructures in their density, thermal, and chemical distribution. Characterizing those substructures can provide constraints on the planet-formation potential of each disk. To improve our understanding of how planets are formed around the stars that are the most common in our galaxy, very low mass stars and binary stars, I studied high spatial resolution observations of dust and gas emission from these objects. To maximize information recovery, I analyzed these datasets with visibility-based methods. The results demonstrate that substructured emission in the dust continuum is present in all spatially resolved disks around very low mass stars, which could be explained by ongoing planet formation. In circumbinary disks, the combination of hydro-models and observations suggest that measuring the eccentricity gradient as a function of radii can be used as a tracer for the presence of Saturn-like planets embedded in the disks. On the other hand, for multiple disk systems, I showed the feasibility of recovering the orbital motion of young objects through the relative movement of their disks, which is crucial to interpreting the emission substructures

A circumplanetary disk around PDS70c

Funding: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 101002188 and No. 832428). J.B. acknowledges support by NASA through the NASA Hubble Fellowship grant #HST-HF2-51427.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. S.F. acknowledges an ESO Fellowship. S.A. acknowledges support from the National Aeronautics and Space Administration under grant No. 17-XRP17 2-0012 issued through the Exoplanets Research Program. A.I. acknowledges support from the National Science Foundation under grant No. AST1715719 and from NASA under grant No. 80NSSC18K0828. J.M.C. acknowledges support from the National Aeronautics and Space Administration under grant No. 15XRP15_20140 issued through the Exoplanets Research Program. N.T.K. and P.P. acknowledge support provided by the Alexander von Humboldt Foundation in the framework of the Sofja Kovalevskaja Award endowed by the Federal Ministry of Education and Research.PDS 70 is a unique system in which two protoplanets, PDS 70 b and c, have been discovered within the dust-depleted cavity of their disk, at ~22 and 34 au, respectively, by direct imaging at infrared wavelengths. Subsequent detection of the planets in the Hα line indicates that they are still accreting material through circumplanetary disks. In this Letter, we present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum emission at 855 μm at high angular resolution (~20 mas, 2.3 au) that aim to resolve the circumplanetary disks and constrain their dust masses. Our observations confirm the presence of a compact source of emission co-located with PDS 70 c, spatially separated from the circumstellar disk and less extended than ~1.2 au in radius, a value close to the expected truncation radius of the circumplanetary disk at a third of the Hill radius. The emission around PDS 70 c has a peak intensity of ~86 ± 16 μJy beam-1, which corresponds to a dust mass of ~0.031 M⊕ or ~0.007 M⊕, assuming that it is only constituted of 1 μm or 1 mm sized grains, respectively. We also detect extended, low surface brightness continuum emission within the cavity near PDS 70 b. We observe an optically thin inner disk within 18 au of the star with an emission that could result from small micron-sized grains transported from the outer disk through the orbits of b and c. In addition, we find that the outer disk resolves into a narrow and bright ring with a faint inner shoulder.Publisher PDFPeer reviewe

Molecules with ALMA at Planet-forming Scales (MAPS). II. CLEAN strategies for synthesizing images of molecular line emission in protoplanetary disks

Funding: I.C. was supported by NASA through NASA Hubble Fellowship grant No. HST-HF2-51405.001-A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. C.W. acknowledges financial support from the University of Leeds, STFC, and UKRI (grant Nos. ST/R000549/1, ST/T000287/1, MR/T040726/1) J.D.I. acknowledges support from STFC under ST/T000287/1.The Molecules with ALMA at Planet-forming Scales Large Program (MAPS LP) surveyed the chemical structures of five protoplanetary disks across more than 40 different spectral lines at high angular resolution (0"15 and 0"30 beams for Bands 6 and 3, respectively) and sensitivity (spanning 0.3-1.3 mJy beam-1 and 0.4-1.9 mJy beam-1 for Bands 6 and 3, respectively). In this article, we describe the multistage workflow-built around the CASA tclean image deconvolution procedure-that we used to generate the core data product of the MAPS LP: the position-position-velocity image cubes for each spectral line. Owing to the expansive nature of the survey, we encountered a range of imaging challenges: some are familiar to the submillimeter protoplanetary disk community, like the need to use an accurate CLEAN mask, and others are less well known, like the incorrect default flux scaling of the CLEAN residual map first described by Jorsater & van Moorsel (the "JvM effect"). We distill lessons learned into recommended workflows for synthesizing image cubes of molecular emission. In particular, we describe how to produce image cubes with accurate fluxes via "JvM correction," a procedure that is generally applicable to any image synthesized via CLEAN deconvolution but is especially critical for low signal-to-noise ratio (S/N) emission. We further explain how we used visibility tapering to promote a common, fiducial beam size and contextualize the interpretation of S/N when detecting molecular emission from protoplanetary disks. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.Publisher PDFPeer reviewe

EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc

Earth-sized exoplanets that transit nearby, late spectral type red dwarfs will be prime targets for atmospheric characterization in the coming decade. Such systems, however, are difficult to find via wide-field transit surveys like Kepler or TESS. Consequently, the presence of such transiting planets is unexplored and the occurrence rates of short-period Earth-sized planets around late M dwarfs remain poorly constrained. Here, we present the deepest photometric monitoring campaign of 22 nearby late M dwarf stars, using data from over 500 nights on seven 1-2 meter class telescopes. Our survey includes all known single quiescent northern late M dwarfs within 15 pc. We use transit-injection-and-recovery tests to quantify the completeness of our survey, successfully identify most ($>80\%$) transiting short-period (0.5-1 d) super-Earths ($R > 1.9 R_\oplus$), and are sensitive ($\sim50\%$) to transiting Earth-sized planets ($1.0-1.2 R_\oplus$). Our high sensitivity to transits with a near-zero false positive rate demonstrates an efficient survey strategy. Our survey does not yield a transiting planet detection, yet it provides the most sensitive upper limits on transiting planets orbiting our target stars. Finally, we explore multiple hypotheses about the occurrence rates of short-period planets (from Earth-sized planets to giant planets) around late M dwarfs. We show, for example, that giant planets at short periods ($<1$ day) are uncommon around our target stars. Our dataset provides some insight into occurrence rates of short-period planets around TRAPPIST-1-like stars, and our results can help test planetary formation and system evolution models, as well as guide future observations of nearby late M dwarfs.Comment: 27 pages, 11 figure

Molecules with ALMA at Planet-forming Scales (MAPS). I. Program overview and highlights

Funding: I.C. was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51405.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. C.W. acknowledges financial support from the University of Leeds, Science and Technology Facilities Council of the United Kingdom (STFC), and UKRI (grant Nos. ST/R000549/1, ST/T000287/1, MR/T040726/1).Planets form and obtain their compositions in dust- and gas-rich disks around young stars, and the outcome of this process is intimately linked to the disk chemical properties. The distributions of molecules across disks regulate the elemental compositions of planets, including C/N/O/S ratios and metallicity (O/H and C/H), as well as access to water and prebiotically relevant organics. Emission from molecules also encodes information on disk ionization levels, temperature structures, kinematics, and gas surface densities, which are all key ingredients of disk evolution and planet formation models. The Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program was designed to expand our understanding of the chemistry of planet formation by exploring disk chemical structures down to 10 au scales. The MAPS program focuses on five disks-around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480-in which dust substructures are detected and planet formation appears to be ongoing. We observed these disks in four spectral setups, which together cover ~50 lines from over 20 different species. This paper introduces the Astrophysical Journal Supplement's MAPS Special Issue by presenting an overview of the program motivation, disk sample, observational details, and calibration strategy. We also highlight key results, including discoveries of links between dust, gas, and chemical substructures, large reservoirs of nitriles and other organics in the inner disk regions, and elevated C/O ratios across most disks. We discuss how this collection of results is reshaping our view of the chemistry of planet formation.Publisher PDFPeer reviewe

Behavioural neurobiology: Chemical love

International audienc

Molecules with ALMA at Planet-forming Scales (MAPS):a circumplanetary disk candidate in molecular-line emission in the AS 209 Disk

We report the discovery of a circumplanetary disk (CPD) candidate embedded in the circumstellar disk of the T Tauri star AS 209 at a radial distance of about 200 au (on-sky separation of 1.″4 from the star at a position angle of 161°), isolated via 13CO J = 2-1 emission. This is the first instance of CPD detection via gaseous emission capable of tracing the overall CPD mass. The CPD is spatially unresolved with a 117 × 82 mas beam and manifests as a point source in 13CO, indicating that its diameter is ≲14 au. The CPD is embedded within an annular gap in the circumstellar disk previously identified using 12CO and near-infrared scattered-light observations and is associated with localized velocity perturbations in 12CO. The coincidence of these features suggests that they have a common origin: an embedded giant planet. We use the 13CO intensity to constrain the CPD gas temperature and mass. We find that the CPD temperature is ≳35 K, higher than the circumstellar disk temperature at the radial location of the CPD, 22 K, suggesting that heating sources localized to the CPD must be present. The CPD gas mass is ≳0.095 M Jup ≃ 30 M ⊕ adopting a standard 13CO abundance. From the nondetection of millimeter continuum emission at the location of the CPD (3σ flux density ≲26.4 μJy), we infer that the CPD dust mass is ≲0.027 M ⊕ ≃ 2.2 lunar masses, indicating a low dust-to-gas mass ratio of ≲9 × 10-4. We discuss the formation mechanism of the CPD-hosting giant planet on a wide orbit in the framework of gravitational instability and pebble accretion