Disk Structures Research Articles

Evidence for a sub-Jovian planet in the young TWA 7 disk

Planets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion years, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies1,2. Tens of debris disks, with sizes of tens, sometimes hundreds, of astronomical units have been resolved with high-spatial-resolution, high-contrast imagers at optical and near-infrared or (sub)millimetre interferometers3,4. They commonly show cavities, ring-like structures and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals2,5. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2–10 MJ) of high-contrast imaging instruments (see, for example, refs. 6, 7, 8–9) before the James Webb Space Telescope. Here we have used the unprecedented sensitivity of the James Webb Space Telescope’s Mid-Infrared Instrument10,11 in the thermal infrared to search for such planets in the disk of the approximately 6.4-Myr-old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arcsec from the star, which is best interpreted as a cold, sub-Jupiter-mass planet. Its estimated mass (about 0.3 MJ) and position (about 52 au, de-projected) can thoroughly account for the main disk structures.

Shadow-based Framework for Estimating Transition Disk Geometries

Abstract Some transition disks host misaligned inner disks with radii of several astronomical units. Understanding the geometric and physical properties of these misaligned disks is essential for advancing terrestrial planet formation models. This study introduces a novel method to infer the three-dimensional structures of both inner and outer disks by analyzing nonaxisymmetric shadows and the horizon in optical and infrared scattered light images of the outer disk. This method was applied to the HD 100453 system, in which infrared scattered light images from the Very Large Telescope revealed disk shadows. These results indicate that the inner disk is misaligned by ∼70° relative to the outer disk, which is consistent with the results of previous studies. The aspect ratio of the inner disk surface was estimated to be 0.17, which may reflect the surface height of the optically thick dusty component due to vertical lofting by MHD winds or turbulence. In addition, the surface height distribution of the outer disk was characterized, providing novel insights into its vertical structure.

Analysis of Forbidden Neon Emission lines in HAeBe Stars using Spitzer IRS spectra

Abstract We analyzed high-resolution mid-infrared spectra of 78 well-known Herbig Ae/Be (HAeBe) stars using Spitzer InfraRed Spectrograph data, focusing on the detection of [Ne ii] and [Ne iii] emission lines as indicators of ionized outflows or disk winds. Emission from [Ne ii] at 12.81 μm or [Ne iii] at 15.55 μm was identified in 25 sources, constituting the largest sample of HAeBe stars with these detected lines. Our analysis revealed a higher detection frequency of [Ne ii] in sources with lower relative accretion luminosity (Lacc/L* < 0.1), suggesting a connection to the disk dispersal phase. We examined correlations between neon lines and various spectral features and investigated [Ne iii]-to-[Ne ii] line flux ratios to explore potential emission mechanisms. Neon emission is predominantly observed in Group I sources (75%), where their flared disk geometry likely contributes to the observed emission, potentially originating from the irradiated disk atmosphere. Interestingly, we also find that Group II sources exhibit a higher median relative [Ne ii] line luminosity (L[Ne II]/L*), suggesting enhanced photoevaporation rates possibly associated with their more settled disk structures. However, larger samples and higher-resolution spectra are required to confirm this trend definitively. The high detection rate of the [Fe ii] and [S iii] lines, commonly associated with EUV-dominated regions, alongside a [Ne iii]-to-[Ne ii] emission ratio greater than 0.1 in sources where both lines detected, suggests that EUV radiation is the primary driver of neon emission in our sample.

Probability of detection and anomaly distribution modeling for surface defects in tenon-groove structures of aeroengine disks

Probability of detection and anomaly distribution modeling for surface defects in tenon-groove structures of aeroengine disks

Structure and material composition of oral disc structures in selected Anuran tadpoles (Amphibia).

Structure and material composition of oral disc structures in selected Anuran tadpoles (Amphibia).

Confirmation of a ring structure in the disk around MP Mus (PDS 66) with ALMA Band 7 observations

Context. Young stellar objects (YSOs) are surrounded by protoplanetary disks, which are the birthplace of young planets. Ring and gap structures are observed among evolved protoplanetary disks, often interpreted as a consequence of planet formation. Aims. The pre-Main Sequence (pre-MS) star MP Mus hosts one of the few known examples of protoplanetary disks within 100 pc. Previously, a disk ring structure, with a radius of 80–85 au, was detected in scattered light via near-infrared polarimetric imaging. This ring structure may be indicative of the disk clearing process. Although such ring structures were not seen in the ALMA Band 6 images, some features were detected at ∼50 au. Methods. In this paper, we analyzed new ALMA Band 7 observations of MP Mus in order to investigate the details of its disk substructures. Results. By subtracting the continuum profile generated from Band 7 data, we discovered a ring structure in the Band 7 dust continuum image at ∼50 au. We calculated the overall dust mass as 28.4 ± 2.8 M⊕ at 0.89 mm and 26.3 ± 2.6 M⊕ at 1.3 mm and the millimeter spectral index α0.89–1.3 mm ∼2.2 ± 0.3 between 0.89 mm and 1.3 mm. Moreover, we display the spatial distribution of the spectral index (αmm), estimating values ranging from 1.3 at the inner disk to 4.0 at a large radius. Additionally, we observed an extended gas disk up to ∼120 au, in contrast with a compact continuum millimeter extent of ∼60 au. Conclusions. We conclude that there are strong indicators for an active radial drift process within the disk. However, we cannot discard the possibility of a dust evolution process and a grain growth process as responsible for the outer disk structures observed in the ALMA continuum imaging.

An energy approach to pulsar–disc interaction: disc stability and implications for transitional millisecond pulsars

ABSTRACT The stability of an accretion disc surrounding a millisecond pulsar is analysed from an energetic point of view, using magnetohydrodynamic simulations that consider realistic disc structures and a variety of magnetic field inclination angles. The time-averaged components of the magnetic field interact with the disc through ohmic dissipation, which causes heating and partial evaporation of its innermost region. The stability of the disc right after the magnetic field is turned on is analysed as a function of the location of the inner radius of the disc and the magnetic inclination angle. Our results show that the disc is severely altered in those cases where its inner radius lies well beyond the light cylinder and the magnetic axis is not totally aligned with the neutron star spin axis. Overall, the results of the simulations agree with those obtained in previous works where analytical or semi-analytical energy models were also used to discuss the stability of the disc. The implications for the understanding of the transitional millisecond pulsars are discussed. We briefly mention implications of our results for low-mass X-ray binaries and supernova fallback discs.

A changing of the garden: evaluating the performance and ecosystem functionality of alternative oyster garden structures in residential waterways

Oyster gardening, in which hanging oyster recruitment substrates are suspended from docks, has become an increasingly common and accessible technique for coastal communities to support local oyster populations for biodiversity enhancement, habitat restoration, and ecological functions including water filtration. However, little research has been done to evaluate materials and methods for oyster garden structures regarding cost, ease of assembly, durability, and ecosystem benefits, making it difficult to scale up efforts and maximize project success and sustainability. We conducted a field experiment in a residential canal system on Sanibel Island, Florida where we deployed a variety of oyster garden structure types to evaluate their performance in oyster recruitment, durability, water filtration rate, and biodiversity. Additionally, the occurrence of Hurricane Ian during the deployment provided an opportunity to evaluate how these structures resisted severe storm events. We tested a total of five structures: (1) a conventional design made of drilled oyster shell on steel wire (shell structures); and four alternatives, (2) GROW concrete discs (disc structures); (3) jute fiber coated with calcium sulfoaluminate cement (jute structures); (4) BESE biodegradable plastic matrix panels (BESE matrix panel structures); and (5) BESE biodegradable plastic mesh bags filled with oyster cultch (bag structures). All structures survived Hurricane Ian; however, both BESE structure types ultimately disintegrated without recruiting oysters. Disc, jute, and shell wire structures demonstrated similarly high levels of durability, oyster recruitment and growth, and biofiltration. Thus, we conclude that structure type selection may be based on material and labor availability and whether cost and biodegradability are prioritized. We show that oyster gardening can provide ecosystem services, including biofiltration, in residential canal sites that have lost “natural” shoreline morphology. Investments in oyster gardening are low risk in the face of natural hazards, supporting the use of the practice in storm-prone areas. However, residential canals are prone to adverse water quality, including low dissolved oxygen, which we show may undermine oyster survival and growth in certain cases; location and season thus need to be considered for garden deployment. Our results reveal material options for providing sustainability, durability, oyster recruitment, and biodiversity for oyster gardening projects while minimizing adverse environmental impacts.

The edge-on disc Tau 042021: Icy grains at high altitudes and a wind containing astronomical polycyclic aromatic hydrocarbons

Context. Spectra of the nearly edge-on protoplanetary discs observed with the JWST have shown ice absorption bands of varying optical depths and peculiar profiles, challenging radiative transfer modelling and our understanding of dust and ice in discs. Aims. With the aim of constraining the underlying disc’s structure and evolutionary state, we build models including dust grain size, shape, and composition to reproduce JWST IFU spectroscopy of a well-characterised, massive, and large edge-on disc, Tau 042021. Specifically, we aim to match its spectral energy distribution, the spatial distribution of the dust and ice, and the spectral characteristics of the dust continuum and ice bands profiles, as well as test for the presence of astronomical polycyclic aromatic hydrocarbons (PAH) band carriers. Methods. We explored radiative transfer models using different dust grain size distributions, including grains with effective radii of aeff = 0.005–3000 μm. Mass absorption and scattering coefficients for distributions of triaxial ellipsoidal grains were calculated using the discrete dipole approximation (DDA) for small size parameters (2πaeff/λ < 10), whereas the hollow sphere approximation was used for larger size parameters. We considered compositions including silicates, amorphous carbon, and mixtures of water, carbon dioxide, and carbon monoxide. The resulting orientation-averaged scattering matrices were input into RADMC-3D Monte Carlo radiative transfer models of Tau 042021 to simulate the spectral cubes observed with JWST-NIRSpec and MIRI. We compared the calculated optical depth distributions and profiles of the main ice bands to observations, including water at 3.05 μm, carbon monoxide at 4.67 μm, and carbon dioxide at 4.26 μm. We also compared these results to archival JWST-NIRCam and ALMA continuum images. We tested three increasingly complex disc structures, starting from a standard model and adding first an extended atmosphere, then a disc wind containing astro-PAHs. Results. The observed near- to mid-infrared spectral energy distribution requires efficient scatterers, implying dust distributions that include grains of up to several tens of microns in size. The intensity distribution perpendicular to the disc exhibits emission profile wings extending into the upper disc atmosphere at altitudes exceeding the classical scale height expected in the isothermal hydrostatic limit. We produce ice absorption images that demonstrate the presence of icy dust grains up to altitudes high above the disc midplane, more than three hydrostatic equilibrium scale heights. We demonstrate the presence of a wind containing the carriers of astronomical PAH bands. The wind appears as an X-shaped emission at 3.3, 6.2, 7.7, and 11.3 μm, characteristic wavelengths associated with the infrared astronomical PAH bands. We associate the spatial distribution of this component with carriers of astronomical PAH bands that form a layer of emission at the interface with the H2 wind.

Connecting a Magnetized Disk to a Convective Low-mass Protostar: A Global 3D Model of Boundary Layer Accretion

Abstract In the early stages of star formation, boundary layer accretion, where protostars accrete material from disks extending down to their surfaces, plays a crucial role. Understanding how a magnetorotational-instability (MRI)-active disk connects to a protostar’s surface remains a significant challenge. To investigate the mechanisms of mass and angular momentum transfer, we develop a global, 3D magnetohydrodynamic model of boundary layer accretion around a magnetized, convective low-mass protostar. Our results reveal that angular momentum transport mechanisms transition significantly from the outer MRI-active disk to the protostellar surface. Various mechanisms—MRI, spiral shocks, coronal accretion, jets, and disk winds—contribute to angular momentum transfer, resulting in three distinct disk structures: (1) the MRI-active disk, (2) the transition layer, and (3) the boundary layer. The simulated protostar is strongly magnetized due to the accumulation of the disk fields, wrapping by disk toroidal fields, and stellar dynamo activity. Magnetic concentrations analogous to starspots form on the protostar and interact with the rotating disk gas to generate spiral shocks. These shocks play a key role in driving accretion. These findings demonstrate the necessity of global MHD models for a comprehensive understanding of angular momentum transport. Additionally, we identify explosive events triggered by magnetic reconnection in both the protostar and the disk atmosphere. We also find decretion flows in the disk midplane, which may be important for the radial transport of refractory materials, such as calcium-aluminum-rich inclusions precursor gas, to the outer disk.

Long-term evolution of the temperature structure in magnetized protoplanetary disks and its implication for the dichotomy of planetary composition

Context. The thermal structure and evolution of protoplanetary disks play a crucial role in planet formation. In addition to stellar irradiation, accretion heating is also thought to significantly affect the disk thermal structure and planet formation processes. Aims. We present the long-term evolution (from the beginning of Class II to disk dissipation) of thermal structures in laminar magnetized disks to investigate where and when accretion heating is a dominant heat source. In addition, we demonstrate that the difference in the disk structures affects the water content of forming planets. Methods. We considered the mass loss by magnetohydrodynamic (MHD) and photoevaporative disk winds to investigate the influence of wind mass loss on the accretion rate profile. Our model includes the recent understanding of accretion heating, that is, accretion heating in laminar disks is less efficient than that in turbulent disks because the surface is heated at optically thinner altitudes and energy is removed by disk winds. Results. We find that accretion heating is weaker than irradiation heating at about 1–10 au even in the early Class II disk, but it can affect the temperature in the inner 1 au region. We also find that the magnetohydrodynamic wind mass loss in the inner region can significantly reduce the accretion rate compared with the rate in the outer region, which in turn reduces accretion heating. Furthermore, using evolving disk structures, we demonstrate that when accretion heating models are updated, the evolution of protoplanets is affected. In particular, we find that our model produces a dichotomy of the planetary water fraction of 1–10 M⊕.

Protoplanetary disk insights from the first ERIS/vAPP survey at 4 μm

Aims. We present high-contrast imaging observations of seven protoplanetary disks at 4 μm using the Enhanced Resolution Imager and Spectrograph (ERIS) on the Very Large Telescope. This study focuses on detecting scattered light from micron-sized dust particles and assessing the potential of the grating vector Apodizing Phase Plat (gvAPP) coronagraph for disk and planet characterization. Methods. Observations were performed in pupil-stabilized mode with the vAPP coronagraph. Data were reduced using reference differential imaging and angular differential imaging techniques, incorporating principal component analysis for point-source detection. Contrast curves and detection limits were computed for planetary companions and disk features. Results. The infrared disk signal was resolved in all systems, with first-time 4 μm detections around AS 209 and Elias 2-24, revealing mostly axisymmetric structures extending up to 60 au. Two gaps were detected in the radial profiles of TW Hya (22 au, 35 au) and AS 209 (50 au, 100 au). For Elias 2-24, scattered light emission matched ALMA observations of inner disk structures, marking their first mid-infrared detection. In the case of HD 100546, the vAPP uncovered flared disk structures and faint spiral arms consistent with previous observations. HD 163296 shows a bright inner dust ring, confirming disk asymmetries and features, but we did not detect any planet candidate within the achieved contrast limits. The disk around PDS 70 exhibits clear features, with faint structures detected within the cavity. The observations achieved contrasts enabling the detection of planets down to 800 K, but no companions were detected, implying either low-mass planets, cooler formation scenarios, or a large dust extinction of AV ≳ 20 mag. Conclusions. The vAPP performed robustly for imaging structures in protoplanetary disks at 4 μm, providing critical insights into disk morphology and constraints on planet formation processes. No planetary-mass companions with temperatures >1000 K are present in our sample.

ExoALMA. XVII. Characterizing the Gas Dynamics around Dust Asymmetries

Abstract The key planet-formation processes in protoplanetary disks remain an active matter of research. One promising mechanism to radially and azimuthally trap millimeter-emitting dust grains, enabling them to concentrate and grow into planetesimals, is anticyclonic vortices. While dust observations have revealed crescent structures in several disks, observations of their kinematic signatures are still lacking. Studying the gas dynamics is, however, essential to confirm the presence of a vortex and understand its dust trapping properties. In this work, we make use of the high-resolution and sensitivity observations conducted by the exoALMA large program to search for such signatures in the 12CO and 13CO molecular line emission of four disks with azimuthal dust asymmetries: HD 135344B, HD 143006, HD 34282, and MWC 758. To assess the vortex features, we constructed an analytical vortex model and performed hydrodynamical simulations. For the latter, we assumed two scenarios: a vortex triggered at the edge of a dead zone and of a gap created by a massive embedded planet. These models reveal a complex kinematical morphology of the vortex. When compared to the data, we find that none of the sources show a distinctive vortex signature around the dust crescents in the kinematics. HD 135344B exhibits a prominent feature similar to the predictions from the simulations, thus making this the most promising target for sensitive follow-up studies at higher resolution and in particular with less abundant molecules at higher resolution and sensitivity to trace closer to the disk midplane.

ExoALMA. IX. Regularized Maximum Likelihood Imaging of Non-Keplerian Features

Abstract The planet-hunting Atacama Large Millimeter/submillimeter Array (ALMA) large program exoALMA observed 15 protoplanetary disks at ∼ 0 . ″ 15 angular resolution and ∼100 m s−1 spectral resolution, characterizing disk structures and kinematics in enough detail to detect non-Keplerian features (NKFs) in the gas emission. As these features are often small and low-contrast, robust imaging procedures are critical for identifying and characterizing NKFs, including determining which features may be signatures of young planets. The exoALMA collaboration employed two different imaging procedures to ensure the consistent detection of NKFs: CLEAN, the standard iterative deconvolution algorithm, and regularized maximum likelihood (RML) imaging. This Letter presents the exoALMA RML images, obtained by maximizing the likelihood of the visibility data given a model image and subject to regularizer penalties. Crucially, in the context of exoALMA, RML images serve as an independent verification of marginal features seen in the fiducial CLEAN images. However, best practices for synthesizing RML images of multichanneled (i.e., velocity-resolved) data remain undefined, as prior work on RML imaging for protoplanetary disk data has primarily addressed single-image cases. We used the open-source Python package MPoL to explore RML image validation methods for multichanneled data and synthesize RML images from the exoALMA observations of seven protoplanetary disks with apparent NKFs in the 12CO J = 3–2 CLEAN images. We find that RML imaging methods independently reproduce the NKFs seen in the CLEAN images of these sources, suggesting that the NKFs are robust features rather than artifacts from a specific imaging procedure.

Continuum Reverberation in Active Galactic Nuclei Disks Only with Sufficient X-Ray Luminosity and Low Albedo

Abstract Disk continuum reverberation mapping is one of the primary ways we learn about active galactic nuclei (AGN) accretion disks. Reverberation mapping assumes that time-varying X-rays incident on the accretion disk drive variability in UV–optical light curves emitted by AGN disks and uses lags between X-ray and UV–optical variability on the light-crossing timescale to measure the radial temperature profile and extent of AGN disks. However, recent reverberation mapping campaigns have revealed oddities in some sources, such as weakly correlated X-ray and UV light curves, longer than anticipated lags, and evidence of intrinsic variability from disk fluctuations. To understand how X-ray reverberation works with realistic accretion disk structures, we perform 3D multifrequency radiation magnetohydrodynamic simulations of X-ray reprocessing by the UV-emitting region of an AGN disk using sophisticated opacity models that include line opacities for both the X-ray and UV radiation. We find there are two important factors that determine whether X-ray irradiation and UV emission will be well-correlated: the ratio of X-ray to UV luminosity and significant absorption. When these factors are met, the reprocessing of X-rays into UV is nearly instantaneous, as is often assumed, although linear reprocessing models are insufficient to fully capture X-ray reprocessing in our simulations. Nevertheless, we can still easily recover mock lags in our light curves using software that assumes linear reprocessing. Finally, the X-rays in our simulation heat the disk, increasing temperatures by a factor of 2–5 in the optically thin region, which could help explain the discrepancy between measured and anticipated lags.

Deep Extragalactic VIsible Legacy Survey (DEVILS): the size–mass relation of galaxies and their components in HST-COSMOS over the last 8 billion years

ABSTRACT We present the evolution of the size–mass relation since $z=1$ in the COSMOS region of the Deep Extragalactic VIsible Legacy Survey (DEVILS). We combine structural decomposition measurements with stellar mass estimates from fitting spectral energy distributions to multiwavelength photometry. We implement a novel technique to fit 2D light profiles to repeated observations, removing the requirement to co-add images, which maximises the effective signal-to-noise ratio and avoids issues arising when averaging point spread functions. The sample is then separated into distinct morphological classifications, which reveals that the size–mass relation of disc-dominated galaxies shows an overall flattened slope with very little redshift evolution over $0.3 < z < 1.0$. In contrast, spheroid-dominated morphologies show a much steeper relation and are generally more compact at a given stellar mass. The size–mass relations of bulge and disc components are also examined revealing that diffuse bulges occupy a similar region to disc structures, in stark contrast to the size–mass relation of compact bulges. Furthermore, the size–mass relation of discs becomes steeper in the presence of a compact bulge, whereas the relation for discs hosting a diffuse bulge is identical to that of pure-discs. The lack of evolution in disc-dominated galaxies (i.e. $R_\mathrm{eff} \propto (1+z)^{-0.13\pm 0.02}$) is inherent to their self-similar assembly. In contrast, the size–mass relation of spheroid-dominated morphologies is rapidly evolving despite minimal growth in the individual compact bulge components, with average sizes increasing at a pace of $R_\mathrm{eff} \propto (1 + z)^{-3.0\pm 0.2}$ and a slope that flattens with time as $\mathrm{ d}\log _{10}(R_\mathrm{eff})/\mathrm{ d}\log _{10}(M_{\star }) \propto (1 + z)^{2.8\pm 0.2}$.

Cup and Disc Segmentation in Smartphone Handheld Ophthalmoscope Images with a Composite Backbone and Double Decoder Architecture.

Glaucoma is a visual disease that affects millions of people, and early diagnosis can prevent total blindness. One way to diagnose the disease is through fundus image examination, which analyzes the optic disc and cup structures. However, screening programs in primary care are costly and unfeasible. Neural network models have been used to segment optic nerve structures, assisting physicians in this task and reducing fatigue. This work presents a methodology to enhance morphological biomarkers of the optic disc and cup in images obtained by a smartphone coupled to an ophthalmoscope through a deep neural network, which combines two backbones and a dual decoder approach to improve the segmentation of these structures, as well as a new way to combine the loss weights in the training process. The models obtained were numerically evaluated through Dice and IoU measures. The dice values obtained in the experiments reached a Dice of 95.92% and 85.30% for the optical disc and cup and an IoU of 92.22% and 75.68% for the optical disc and cup, respectively, in the BrG dataset. These findings indicate promising architectures in the fundus image segmentation task.

Hα Variability of AB Aur b with the Hubble Space Telescope: Probing the Nature of a Protoplanet Candidate with Accretion Light Echoes

Abstract Giant planets generate accretion luminosity as they form. Much of this energy is radiated in strong Hα line emission, which has motivated direct imaging surveys at optical wavelengths to search for accreting protoplanets. However, compact disk structures can mimic accreting planets by scattering emission from the host star. This can complicate the interpretation of Hα point sources, especially if the host star itself is accreting. We describe an approach to distinguish accreting protoplanets from scattered-light disk features using “accretion light echoes.” This method relies on variable Hα emission from a stochastically accreting host star to search for a delayed brightness correlation with a candidate protoplanet. We apply this method to the candidate protoplanet AB Aur b with a dedicated Hubble Space Telescope Wide Field Camera 3 program designed to sequentially sample the host star and the candidate planet in Hα while accounting for the light travel time delay and orbital geometry of the source within the protoplanetary disk. Across five epochs spanning 14 months, AB Aur b is over 20 times more variable than its host star; AB Aur’s Hα emission changes by 15% while AB Aur b varies by 330%. These brightness changes are not correlated, which rules out unobstructed scattered starlight from the host star as the only source of AB Aur b’s Hα emission and is consistent with tracing emission from an independently accreting protoplanet, inner disk shadowing effects, or a physically evolving compact disk structure. More broadly, accretion light echoes offer a novel tool to explore the nature of protoplanet candidates with well-timed observations of the host star prior to deep imaging in Hα.

Functional genomics of Campylobacter -host interactions in an intestinal tissue model reveals a small lipoprotein essential for flagellar assembly.

Campylobacter jejuni is currently the most common cause of bacterial gastroenteritis worldwide. However, its genome provides few clues about how it interacts with the host. Moreover, infection screens have often been limited to classical cell culture or animal models. To identify C. jejuni genes involved in host cell interactions, we applied transposon sequencing in a humanized 3D intestinal infection model based on tissue engineering. This revealed key proteins required for host cell adherence and/or internalization, including an Rrf2 family transcriptional regulator as well as three so far uncharacterized genes ( pflC / Cj1643 , pflD / Cj0892c , pflE / Cj0978c ), which we demonstrate to encode factors essential for motility. Deletion mutants of pflC / D / E are non-motile but retain intact, paralysed flagella filaments. We demonstrate that two of these newly identified motility proteins, PflC and PflD, are components of the C. jejuni 's periplasmic disk structures of the high torque motor. The third gene, pflE , encodes a small protein of only 57 aa. Using CryoET imaging we uncovered that the small protein has a striking effect on motor biogenesis, leading to a complete loss of the flagellar disk and motor structures upon its deletion. While PflE does not appear to be a structural component of the motor itself, our data suggests that it is a lipoprotein and supports localization of the main basal disk protein FlgP, which is the first assembly step of the flagellar disk structure. Despite being annotated as a lipoprotein, we find that C. jejuni FlgP instead relies on PflE for its association with the outer membrane. Overall, our genome-wide screen revealed novel C. jejuni host interaction factors including a transcriptional regulator as well as two structural components and a small protein crucial for biogenesis of the C. jejuni high torque flagella motor. Since the flagella machinery is a critical virulence determining factor for C. jejuni , our work demonstrates how such a small protein can, quite literally, bring a bacterial pathogen to a halt.

Star Formation from Low to High Mass: A Comparative View

Star formation has often been studied by separating the low- and high-mass regimes with an approximate boundary at 8 M⊙. Although some of the outcomes of the star-formation process are different between the two regimes, it is less clear whether the physical processes leading to these outcomes are that different at all. Here, we systematically compare low- and high-mass star formation by reviewing the most important processes and quantities from an observational and theoretical point of view. We identify three regimes in which processes are either similar, quantitatively, or qualitatively different between low- and high-mass star formation. ▪ Similar characteristics can be identified for the turbulent gas properties and density structures of the star-forming regions. Many of the observational characteristics also do not depend that strongly on the environment. ▪ Quantitative differences can be found for outflow, infall, and accretion rates as well as mean column and volume densities. Also, the multiplicity significantly rises from low- to high-mass stars. The importance of the magnetic field for the formation processes appears still less well constrained. ▪ Qualitative differences between low- and high-mass star formation relate mainly to the radiative and ionizing feedback that occurs almost exclusively in regions forming high-mass stars. Nevertheless, accretion apparently can continue via disk structures in ionized accretion flows. Finally, we discuss to what extent a unified picture of star formation over all masses is possible and which issues need to be addressed in the future.