ABSTRACT
The DSHARP survey evidenced the ubiquity of substructure in the mm dust distribution of large, bright protoplanetary discs. Intriguingly, these data sets have yet higher resolution ...information that is not recovered in a CLEAN image. We first show that the intrinsic performance of the CLEAN algorithm is resolution-limited. Then analysing all 20 DSHARP sources using the 1D, super-resolution code FRANKenstein (FRANK), we accurately fit the 1D visibilities to a mean factor of 4.3 longer baseline than the Fourier transform of the CLEAN images and a factor of 3.0 longer baseline than the transform of the CLEAN component models. This yields a higher resolution brightness profile for each source, identifying new substructure interior to 30 au in multiple discs; resolving known gaps to be deeper, wider, and more structured; and known rings to be narrower and brighter. Across the survey, high contrast gaps are an average $14{{\ \rm per\ cent}}$ wider and $44{{\ \rm per\ cent}}$ deeper in the FRANK profiles relative to CLEAN, and high contrast rings are an average $26{{\ \rm per\ cent}}$ narrower. Categorizing the FRANK brightness profiles into trends, we find that the relative scarcity of features interior to 30 au in the survey’s CLEAN images is an artefact of resolving power, rather than an intrinsic rarity of inner disc (or compact disc) substructure. Finally the rings in the FRANK profiles are narrower than the previously inferred deconvolved widths, indicating smaller α/St ratios in the local gas disc.
We present new Atacama Large Millimeter/submillimeter Array observations for three protoplanetary disks in Taurus at 2.9 mm and comparisons with previous 1.3 mm data both at an angular resolution of ...∼0 1 (15 au for the distance of Taurus). In the single-ring disk DS Tau, double-ring disk GO Tau, and multiring disk DL Tau, the same rings are detected at both wavelengths, with radial locations spanning from 50 to 120 au. To quantify the dust emission morphology, the observed visibilities are modeled with a parametric prescription for the radial intensity profile. The disk outer radii, taken as 95% of the total flux encircled in the model intensity profiles, are consistent at both wavelengths for the three disks. Dust evolution models show that dust trapping in local pressure maxima in the outer disk could explain the observed patterns. Dust rings are mostly unresolved. The marginally resolved ring in DS Tau shows a tentatively narrower ring at the longer wavelength, an observational feature expected from efficient dust trapping. The spectral index ( mm) increases outward and exhibits local minima that correspond to the peaks of dust rings, indicative of the changes in grain properties across the disks. The low optical depths (τ ∼ 0.1-0.2 at 2.9 mm and 0.2-0.4 at 1.3 mm) in the dust rings suggest that grains in the rings may have grown to millimeter sizes. The ubiquitous dust rings in protoplanetary disks modify the overall dynamics and evolution of dust grains, likely paving the way toward the new generation of planet formation.
Abstract
Gas giants’ early (≲5 Myr) orbital evolution occurs in a disc losing mass in part to photoevaporation driven by high energy irradiance from the host star. This process may ultimately ...overcome viscous accretion to disperse the disc and halt migrating giants by starving their orbits of gas, imprinting on giant planet separations in evolved systems. Inversion of this distribution could then give insight into whether the stellar FUV, EUV or X-ray flux dominates photoevaporation, constraining planet formation and disc evolution models. We use a 1D hydrodynamic code in population syntheses for gas giants undergoing Type II migration in a viscously evolving disc subject to either a primarily FUV, EUV or X-ray flux from a pre-solar T Tauri star. The photoevaporative mass loss profile’s unique peak location and width in each energetic regime produces characteristic features in the distribution of giant separations: a severe dearth of ≲2 MJ planets interior to 5 au in the FUV scenario, a sharp concentration of ≲3 MJ planets between ≈1.5–2 au in the EUV case and a relative abundance of ≈2–3.5 MJ giants interior to 0.5 au in the X-ray model. These features do not resemble the observational sample of gas giants with mass constraints, although our results do show some weaker qualitative similarities. We thus assess how the differing photoevaporative profiles interact with migrating giants and address the effects of large model uncertainties as a step to better connect disc models with trends in the exoplanet population.
Abstract
The streaming instability is often invoked as solution to the fragmentation and drift barriers in planetesimal formation, catalysing the aggregation of dust on kyr time-scales to grow ...km-sized cores. However, there remains a lack of consensus on the physical mechanism(s) responsible for initiating it. One potential avenue is disc photoevaporation, wherein the preferential removal of relatively dust-free gas increases the disc metallicity. Late in the disc lifetime, photoevaporation dominates viscous accretion, creating a gradient in the depleted gas surface density near the location of the gap. This induces a local pressure maximum that collects drifting dust particles, which may then become susceptible to the streaming instability. Using a one-dimensional viscous evolution model of a disc subject to internal X-ray photoevaporation, we explore the efficacy of this process to build planetesimals. Over a range of parameters, we find that the amount of dust mass converted into planetesimals is often <1 M⊕ and at most a few M⊕ spread across tens of au. We conclude that photoevaporation may at best be relevant for the formation of debris discs, rather than a common mechanism for the formation of planetary cores. Our results are in contrast to a recent, similar investigation that considered an far-ultra-violet (FUV)-driven photoevaporation model and reported the formation of tens of M⊕ at large (>100 au) disc radii. The discrepancies are primarily a consequence of the different photoevaporation profiles assumed. Until observations more tightly constrain photoevaporation models, the relevance of this process to the formation of planets remains uncertain.
This paper outlines the scientific achievements and insights gained from the International Global Atmospheric Chemistry (IGAC) project, which has been jointly sponsored by the international ...Commission on Atmospheric Chemistry and Global Pollution (iCACGP) and the International Geosphere-Biosphere Programme (IGBP) since 1990. A short history of IGAC is followed by representative key scientific achievements. Over 25 years, IGAC has facilitated international scientific collaborations that have deepened the understanding of how atmospheric composition impacts air quality, climate change, and ecosystems from local to global scales. Activities fostered by IGAC show how the field of atmospheric chemistry has evolved from a focus on the atmosphere as a single natural compartment of the Earth system to an emphasis on its interactions with other Earth components, such as oceans, the cryosphere, the biosphere, and the impact of humans on atmospheric composition. Finally, one of IGAC’s significant accomplishments has been building scientific capacity and cooperation in the field of atmospheric chemistry around the globe, especially through its biennial science conferences. As part of IGBP, IGAC has contributed to improving the current state of knowledge of the Earth system and providing the scientific basis to suggest that we have entered the Anthropocene. IGAC will continue to play this role and expand its connections to the larger global change and sustainability research communities, capitalizing on the transition to Future Earth.
ABSTRACT
We have identified the H
α
absorption feature as a new spectroscopic diagnostic of luminosity class in K- and M-type stars. From high-resolution spectra of 19 stars with well-determined ...physical properties (including effective temperatures and stellar radii), we measured equivalent widths for H
α
and the Ca
ii
triplet and examined their dependence on both luminosity class and stellar radius. H
α
shows a strong relation with both luminosity class and radius that extends down to late M spectral types. This behavior in H
α
has been predicted as a result of the density-dependent overpopulation of the metastable 2s level in hydrogen, an effect that should become dominant for Balmer line formation in non-LTE conditions. We conclude that this new metallicity-insensitive diagnostic of luminosity class in cool stars could serve as an effective means of discerning between populations such as Milky Way giants and supergiant members of background galaxies.
ABSTRACT
Interferometric observations of the mm dust distribution in protoplanetary discs are now showing a ubiquity of annular gap and ring substructures. Their identification and accurate ...characterization are critical to probing the physical processes responsible. We present frankenstein (frank), an open source code that recovers axisymmetric disc structures at a sub-beam resolution. By fitting the visibilities directly, the model reconstructs a disc’s 1D radial brightness profile non-parametrically using a fast (≲1 min) Gaussian process. The code avoids limitations of current methods that obtain the radial brightness profile either by extracting it from the disc image via non-linear deconvolution at the cost of reduced fit resolution or by assumptions placed on the functional forms of disc structures to fit the visibilities parametrically. We use mock Atacama Large Millimeter Array observations to quantify the method’s intrinsic capability and its performance as a function of baseline-dependent signal-to-noise ratio. Comparing the technique to profile extraction from a clean image, we motivate how our fits accurately recover disc structures at a sub-beam resolution. Demonstrating the model’s utility in fitting real high- and moderate-resolution observations, we conclude by proposing applications to address open questions on protoplanetary disc structure and processes.
ABSTRACT
The 1.33-mm survey of protoplanetary discs in the Taurus molecular cloud found annular gaps and rings to be common in extended sources (≳ 55au), when their 1D visibility distributions were ...fit parametrically. We first demonstrate the advantages and limitations of non-parametric visibility fits for data at the survey’s 0.12-arcsec resolution. Then we use the non-parametric model in Frankenstein (frank) to identify new substructure in three compact and seven extended sources. Among the new features, we identify three trends: a higher occurrence rate of substructure in the survey’s compact discs than previously seen, underresolved (potentially azimuthally asymmetric) substructure in the innermost disc of extended sources, and a ‘shoulder’ on the trailing edge of a ring in discs with strong depletion at small radii. Noting the shoulder morphology is present in multiple discs observed at higher resolution, we postulate it is tracing a common physical mechanism. We further demonstrate how a superresolution frank brightness profile is useful in motivating an accurate parametric model, using the highly structured source DL Tau in which frank finds two new rings. Finally, we show that sparse (u, v) plane sampling may be masking the presence of substructure in several additional compact survey sources.
ABSTRACT
Constraining the vertical and radial structure of debris discs is crucial to understanding their formation, evolution, and dynamics. To measure both the radial and vertical structure, a disc ...must be sufficiently inclined. However, if a disc is too close to edge-on, deprojecting its emission becomes non-trivial. In this paper we show how Frankenstein, a non-parametric tool to extract the radial brightness profile of circumstellar discs, can be used to deproject their emission at any inclination as long as they are optically thin and axisymmetric. Furthermore, we extend Frankenstein to account for the vertical thickness of an optically thin disc (H(r)) and show how it can be constrained by sampling its posterior probability distribution and assuming a functional form (e.g. constant h = H/r), while fitting the radial profile non-parametrically. We use this new method to determine the radial and vertical structures of 16 highly inclined debris discs observed by ALMA. We find a wide range of vertical aspect ratios, h, ranging from 0.020 ± 0.002 (AU Mic) to 0.20 ± 0.03 (HD 110058), which are consistent with parametric models. We find a tentative correlation between h and the disc fractional width, as expected if wide discs were more stirred. Assuming discs are self-stirred, the thinnest discs would require the presence of at least 500-km-sized planetesimals. The thickest discs would likely require the presence of planets. We also recover previously inferred and new radial structures, including a potential gap in the radial distribution of HD 61005. Finally, our new extension of Frankenstein also allows constraining how h varies as a function of radius, which we test on 49 Ceti, finding that h is consistent with being constant.
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