Search

Complex Organic Molecules (COMs) have been found toward low-mass protostars but the origins of the COM emission are still unclear. It can be associated with, for example, hot corinos, outflows, and/or accretion shock/disk atmosphere. We have conducted NOEMA observations toward SVS13A from the PROtostars & DIsks: Global Evolution (PRODIGE) program. Our previous \ce{DCN} observations reveal a possible infalling streamer, which may affect the chemistry of the central protobinary by inducing accretion outbursts and/or shocked gas. Here, we further analyze six O-bearing COMs: CH3OH, aGg'-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrain the source sizes to $\lesssim0.3-0.4$ arcsec (90$-$120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral resolution data reveal complex line profiles with multiple peaks showing differences between these six O-bearing COMs. The LTE fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conduct multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. Up to 6 velocity components are found from the LTE modeling. The temperature, column density, and source size of these components from each COM are obtained. We find a variety in excitation temperatures ($100-500$ K) and source sizes (D$\sim10-70$ au) from these kinematic components from different COMs. The emission of each COM can trace several components and different COMs most likely trace different regions. Given this complex structure, we suggest that the central region is inhomogeneous and unlikely to be heated by only protostellar radiation. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission., Comment: 29 pages, 18 figures, accepted to A&A

Extreme debris discs (EDDs) are bright and warm circumstellar dusty structures around main sequence stars. They may represent the outcome of giant collisions occuring in the terrestrial region between large planetesimals or planetary bodies, and thus provide a rare opportunity to peer into the aftermaths of these events. Here, we report on results of a mini-survey we conducted with the aim to increase the number of known EDDs, investigate the presence of solid-state features around 10{\mu}m in eight EDDs, and classify them into the silica or silicate dominated groups. We identify four new EDDs and derive their fundamental properties. For these, and for four other previously known discs, we study the spectral energy distribution around 10{\mu}m by means of VLT/VISIR photometry in three narrow-band filters and conclude that all eight objects likely exhibit solid-state emission features from sub-micron grains. We find that four discs probably belong to the silicate dominated subgroup. Considering the age distribution of the entire EDD sample, we find that their incidence begins to decrease only after 300 Myr, suggesting that the earlier common picture that these objects are related to the formation of rocky planets may not be exclusive, and that other processes may be involved for older objects (>100 Myr). Because most of the older EDD systems have wide, eccentric companions, we suggest that binarity may play a role in triggering late giant collisions., Comment: 20 pages, 9 figures, published in MNRAS

Dynamical masses of young planets aged between 10 and 200 Myr detected in imaging play a crucial role in shaping models of giant planet formation. Regrettably, only a few such objects possess these characteristics. Furthermore, the evolutionary pattern of young sub-stellar companions in near-infrared colour-magnitude diagrams might diverge from free-floating objects, possibly due to differing formation processes. The recent identification of a giant planet around AF Lep, part of the beta Pic moving group (BPMG), encouraged us to re-examine these points. We considered updated dynamical masses and luminosities for the sub-stellar objects in the BPMG. In addition, we compared the properties of sub-stellar companions and free-floating objects in the BPMG and other young associations remapping the positions of the objects in the colour-magnitude diagram into a dustiness-temperature plane. We found that cold-start evolutionary models do not reproduce the mass-luminosity relation for sub-stellar companions in the BPMG. This aligns rather closely with predictions from 'hot start' scenarios and is consistent with recent planet formation models. We obtain rather good agreement with masses from photometry and the remapping approach compared to actual dynamical masses. We also found a strong suggestion that the near-infrared colour-magnitude diagram for young companions is different from that of free-floating objects belonging to the same young associations. If confirmed by further data, this last result would imply that cloud settling - which likely causes the transition between L and T spectral type - occurs at a lower effective temperature in young companions than in free-floating objects. This might tentatively be explained with a different chemical composition., Comment: Accepted on Astronomy and Astrophysics. 19 pages, 12 figures

Recently, combining high-contrast imaging and space astrometry we found that Jupiter-like (JL) planets are frequent in the beta Pic moving group (BPMG) around those stars where their orbit can be stable, prompting further analysis and discussion. We broaden our previous analysis to other young nearby associations to determine the frequency, mass, and separation of companions in general and JL in particular and their dependencies on the mass and age of the associations. We collected available data about companions including those revealed by visual observations, eclipses, spectroscopy, and astrometry. We determined search completeness and found that it is very high for stellar companions, while completeness corrections are still large for JL companions. Once these corrections are included, we found a high frequency of companions, both stellar (>0.52+/-0.03) and JL (0.57+/-0.11). The two populations are separated by a gap that corresponds to the brown dwarf desert. Within the population of massive companions, we found trends in frequency, separation, and mass ratios with stellar mass. Planetary companions pile up in the region just outside the ice line and we found them to be frequent once completeness was considered. The frequency of JL planets decreases with the overall mass and possibly the age of the association. We tentatively identify the two populations as due to disk fragmentation and core accretion, respectively. The distributions of stellar companions with a semi-major axis <1000 au is well reproduced by a simple model of formation by disk fragmentation. The observed trends with stellar mass can be explained by a shorter but much more intense phase of accretion onto the disk of massive stars and by a more steady and prolonged accretion on solar-type stars. Possible explanations for the trends in the population of JL planets with association mass and age are briefly discussed., Comment: Accepted by Astronomy and Astrophysics, 52 pages, 23 figures

The goal of this paper is to derive the so-called five gradients inequality for optimal transport theory for general cost functions on two class of differentiable manifolds: locally compact Lie groups and compact Riemannian manifolds., Comment: 32 pages -- accepted in Journal de Math\'ematiques Pures et Appliqu\'ees

Aims. Using the direct imaging technique we searched for low mass companions around the star AF Lep that presents a significant proper motion anomaly (PMa) signal obtained from the comparison of Hipparcos and Gaia eDR3 catalogs. Methods. We observed AF Lep in two epochs with VLT/SPHERE using its subsystems IFS and IRDIS in the near-infrared (NIR) covering wavelengths ranging from the Y to the K spectral bands (between 0.95 and 2.3 {\mu}m). The data were then reduced using the high-contrast imaging techniques angular differential imaging (ADI) and spectral differential imaging (SDI) to be able to retrieve the signal from low mass companions of the star. Results. A faint companion was retrieved at a separation of ~0.335" from the star and with a position angle of ~70.5 deg in the first epoch and with a similar position in the second epoch. This corresponds to a projected separation of ~9 au. The extracted photometry allowed us to estimate for the companion a mass between 2 and 5 MJup. This mass is in good agreement with what is expected for the dynamic mass of the companion deduced using astrometric measures (5.2-5.5 MJup). This is the first companion with a mass well below the deuterium burning limit discovered coupling direct imaging with PMa measures. Orbit fitting done using the orvara tool allowed to further confirm the companion mass and to define its main orbital parameters., Comment: 10 pages, 8 Figures, accepted for publication on A&A

Aims. We present high sensitivity and high-spectral resolution NOEMA observations of the Class 0/I binary system SVS13A, composed of the low-mass protostars VLA4A and VLA4B with a separation of ~90 au. VLA4A is undergoing an accretion burst that enriches the chemistry of the surrounding gas. This gives us an excellent opportunity to probe the chemical and physical conditions as well as the accretion process. Methods. We observe the (12K-11K) lines of CH3CN and CH313CN, the DCN (3-2) line, and the C18O (2-1) line toward SVS13A using NOEMA. Results. We find complex line profiles at disk scales which cannot be explained by a single component or pure Keplerian motion. By adopting two velocity components to model the complex line profiles, we find that the temperatures and densities are significantly different between these two components. This suggests that the physical conditions of the emitting gas traced via CH3CN can change dramatically within the circumbinary disk. In addition, combining our observations of DCN (3-2) with previous ALMA high-angular-resolution observations, we find that the binary system (or VLA4A) might be fed by an infalling streamer from envelope scales (~700 au). If this is the case, this streamer contributes to the accretion of material onto the system with a rate of at least 1.4x10-6 Msun yr-1. Conclusions. We conclude that the CH3CN emission in SVS13A traces hot gas from a complex structure. This complexity might be affected by a streamer that is possibly infalling and funneling material into the central region., Comment: 20 pages, 19 figures, accepted to A&A

$\kappa$CrB is a ${\sim}2.5\,$Gyr old K1 sub-giant star, with an eccentric exo-Jupiter at ${\sim}2.8\,$au and a debris disc at tens of au. We present ALMA Band 6 ($1.3\,$mm) and HST scattered light ($0.6\,\mu$m) images, demonstrating $\kappa$CrB's broad debris disc, covering an extent $50{-}180\,$au in the millimetre (peaking at $110\,$au), and $51{-}280\,$au in scattered light (peaking at $73\,$au). By modelling the millimetre emission, we estimate the dust mass as ${\sim}0.016\,M{\oplus}$, and constrain lower-limit planetesimal sizes as $D_{\rm{max}}{>}1\,$km and the planetesimal belt mass as $M_{\rm{disc}}{>}1\,M_{\oplus}$. We constrain the properties of an outer body causing a linear trend in 17 years of radial velocity data to have a semi-major axis $8{-}66\,$au and a mass $(0.4{-}120)\,M_{\rm{Jup}}$. There is a large inner cavity seen in the millimetre emission, which we show is consistent with carving by such an outer massive companion with a string of lower mass planets. Our scattered light modelling shows that the dust must have a high anisotropic scattering factor ($g{\sim}0.8{-}0.9$) but an inclination ($i{\sim}30{-}40\,$degrees) that is inferred to be significantly lower than the $i{\sim}61\,$degrees millimetre inclination. The origin of such a discrepancy is unclear, but could be caused by a misalignment in the micron and millimetre sized dust. We place an upper limit on the CO gas mass of $M_{\rm{CO}}{<}(4.2{-}13){\times}10^{-7}\,M_{\oplus}$, and show this to be consistent with levels expected from planetesimal collisions, or from CO-ice sublimation as $\kappa$CrB begins its giant branch ascent., Comment: Accepted for publication in MNRAS. 21 pages, 14 figures

Context. In the past few years, there has been a rise in the detection of streamers, asymmetric flows of material directed toward the protostellar disk with material from outside the star's natal core. It is unclear how they affect the process of mass accretion, in particular beyond the Class 0 phase. Aims. We investigate the gas kinematics around Per-emb-50, a Class I source in the crowded star-forming region NGC 1333. Our goal is to study how the mass infall proceeds from envelope to disk scales in this source. Results. We discover a streamer delivering material toward Per-emb-50 in H$_2$CO and C$^{18}$O emission. The streamer's emission can be well described by the analytic solutions for an infalling parcel of gas along a streamline with conserved angular momentum, both in the image plane and along the line of sight velocities. The streamer has a mean infall rate of $1.3 \times 10^{ -6}$ M$_{ \odot}$ yr$^{ -1}$, $5 -10$ times higher than the current accretion rate of the protostar. SO and SO$_2$ emission reveal asymmetric infall motions in the inner envelope, additional to the streamer around Per-emb-50. Furthermore, the presence of SO$_2$ could mark the impact zone of the infalling material. Conclusions. The streamer delivers sufficient mass to sustain the protostellar accretion rate and might produce an accretion burst, which would explain the protostar's high luminosity with respect to other Class I sources. Our results highlight the importance of late infall for protostellar evolution: streamers might provide a significant amount of mass for stellar accretion after the Class 0 phase., Comment: 20 pages, 14 figures, accepted for publication in A&A

Aims. This work aims at constraining the masses and separations of potential substellar companions to five accelerating stars (HIP 1481, HIP 88399, HIP 96334, HIP 30314 and HIP 116063) using multiple data sets acquired with different techniques. Methods. Our targets were originally observed as part of the SPHERE/SHINE survey, and radial velocity (RV) archive data were also available for four of the five objects. No companions were originally detected in any of these data sets, but the presence of significant proper motion anomalies (PMa) for all the stars strongly suggested the presence of a companion. Combining the information from the PMa with the limits derived from the RV and SPHERE data, we were able to put constraints on the characteristics of the unseen companions. Results. Our analysis led to relatively strong constraints for both HIP 1481 and HIP 88399, narrowing down the companion masses to 2-5 M_Jup and 3-5 M_Jup and separations within 2-15 au and 3-9 au, respectively. Because of the large age uncertainties for HIP 96334, the poor observing conditions for the SPHERE epochs of HIP 30314 and the lack of RV data for HIP 116063, the results for these targets were not as well defined, but we were still able to constrain the properties of the putative companions within a reasonable confidence level. Conclusions. For all five targets, our analysis has revealed that the companions responsible for the PMa signal would be well within reach for future instruments planned for the ELT (e.g., MICADO), which would easily achieve the required contrast and angular resolution. Our results therefore represent yet another confirmation of the power of multi-technique approaches for both the discovery and characterisation of planetary systems., Comment: 11 pages, 7 figures, accepted for publications on A&A

Bright debris discs can contain large amounts of CO gas. This gas was thought to be a protoplanetary remnant until it was recently shown that it could be released in collisions of volatile-rich solids. As CO is released, interstellar UV radiation photodissociates CO producing CI, which can shield CO allowing a large CO mass to accumulate. However, this picture was challenged because CI is inefficient at shielding if CO and CI are vertically mixed. Here, we study for the first time the vertical evolution of gas to determine how vertical mixing affects the efficiency of shielding by CI. We present a 1D model that accounts for gas release, photodissociation, ionisation, viscous evolution, and vertical mixing due to turbulent diffusion. We find that if the gas surface density is high and the vertical diffusion weak ($\alpha_{\rm v}/\alpha<[H/r]^2$) CO photodissociates high above the midplane, forming an optically thick CI layer that shields the CO underneath. Conversely, if diffusion is strong ($\alpha_{\rm v}/\alpha>[H/r]^2$) CI and CO become well mixed, shortening the CO lifetime. Moreover, diffusion could also limit the amount of dust settling. High-resolution ALMA observations could resolve the vertical distribution of CO and CI, and thus constrain vertical mixing and the efficiency of CI shielding. We also find that the CO and CI scale heights may not be good probes of the mean molecular weight, and thus composition, of the gas. Finally, we show that if mixing is strong the CO lifetime might not be long enough for CO to spread interior to the planetesimal belt where gas is produced., Comment: Accepted for publication in MNRAS (18 pages, 14 figures)

Stellar binaries represent a substantial fraction of stellar systems, especially among young stellar objects. Accordingly, binaries play an important role in setting the architecture of a large number of protoplanetary discs. Binaries in coplanar and polar orientations with respect to the circumbinary disc are stable configurations and could induce non-axisymmetric structures in the dust and gas distributions. In this work, we suggest that the structures shown in the central region of the protoplanetary disc HD 169142 are produced by the presence of an inner stellar binary and a circumbinary (P-type) planet. We find that a companion with a mass-ratio of 0.1, semi-major axis of 9.9 au, eccentricity of 0.2, and inclination of 90{\deg}, together with a 2 Jupiter Mass coplanar planet on a circular orbit at 45 au reproduce the structures at the innermost ring observed at 1.3 mm and the shape of spiral features in scattered light observations. The model predicts changes in the disc's dust structure, and star's astrometric parameters, which would allow testing its veracity by monitoring this system over the next 20 years., Comment: 11 pages, 7 figures, accepted for publication in MNRAS

The question of what determines the width of Kuiper belt analogues (exoKuiper belts) is an open one. If solved, this understanding would provide valuable insights into the architecture, dynamics, and formation of exoplanetary systems. Recent observations by ALMA have revealed an apparent paradox in this field, the presence of radially narrow belts in protoplanetary discs that are likely the birthplaces of planetesimals, and exoKuiper belts nearly four times as wide in mature systems. If the parent planetesimals of this type of debris disc indeed form in these narrow protoplanetary rings via streaming instability where dust is trapped, we propose that this width dichotomy could naturally arise if these dust traps form planetesimals whilst migrating radially, e.g. as caused by a migrating planet. Using the dust evolution software DustPy, we find that if the initial protoplanetary disc and trap conditions favour planetesimal formation, dust can still effectively accumulate and form planetesimals as the trap moves. This leads to a positive correlation between the inward radial speed and final planetesimal belt width, forming belts up to $\sim$100 au over 10 Myr of evolution. We show that although planetesimal formation is most efficient in low viscosity ($\alpha = 10^{-4}$) discs with steep dust traps to trigger the streaming instability, the large widths of most observed planetesimal belts constrain $\alpha$ to values $\geq4\times 10^{-4}$ at tens of au, otherwise the traps cannot migrate far enough. Additionally, the large spread in the widths and radii of exoKuiper belts could be due to different trap migration speeds (or protoplanetary disc lifetimes) and different starting locations, respectively. Our work serves as a first step to link exoKuiper belts and rings in protoplanetary discs., Comment: Accepted for publication in MNRAS. 15 pages,12 figures

We present \textit{ALMA} 1.3 mm and 0.86 mm observations of the nearby (17.34 pc) F9V star q1 Eri (HD 10647, HR 506). This system, with age ${\sim}1.4$ Gyr, hosts a ${\sim}2$ au radial velocity planet and a debris disc with the highest fractional luminosity of the closest 300 FGK type stars. The \textit{ALMA} images, with resolution ${\sim}0.5''$, reveal a broad (34{-}134 au) belt of millimeter emission inclined by $76.7{\pm}1.0$ degrees with maximum brightness at $81.6{\pm}0.5$ au. The images reveal an asymmetry, with higher flux near the southwest ansa, which is also closer to the star. Scattered light observed with the Hubble Space Telescope is also asymmetric, being more radially extended to the northeast. We fit the millimeter emission with parametric models and place constraints on the disc morphology, radius, width, dust mass, and scale height. We find the southwest ansa asymmetry is best fitted by an extended clump on the inner edge of the disc, consistent with perturbations from a planet with mass $8 M_{\oplus} {-} 11 M_{\rm Jup}$ at ${\sim}60$ au that may have migrated outwards, similar to Neptune in our Solar System. If the measured vertical aspect ratio of $h{=}0.04{\pm}0.01$ is due to dynamical interactions in the disc, then this requires perturbers with sizes ${>}1200$ km. We find tentative evidence for an 0.86 mm excess within 10 au, $70{\pm}22\, \mu$Jy, that may be due to an inner planetesimal belt. We find no evidence for CO gas, but set an upper bound on the CO gas mass of $4{\times}10^{-6}$ M$_{\oplus}$ ($3\,\sigma$), consistent with cometary abundances in the Solar System., Comment: Accepted for publication in MNRAS. Paper: 21 pages, appendix: 4 pages. 16 figures

Recent observations of resolved cold debris disks at tens of au have revealed that gaps could be a common feature in these Kuiper belt analogues. Such gaps could be evidence for the presence of planets within the gaps or closer-in near the edges of the disk. We present SPHERE observations of HD 92945 and HD 107146, two systems with detected gaps. We constrained the mass of possible companions responsible for the gap to 1-2 M Jup for planets located inside the gap and to less than 5 M Jup for separations down to 20 au from the host star. These limits allow us to exclude some of the possible configurations of the planetary systems proposed to explain the shape of the disks around these two stars. In order to put tighter limits on the mass at very short separations from the star, where direct imaging data are less effective, we also combined our data with astrometric measurements from Hipparcos and Gaia and radial velocity measurements. We were able to limit the separation and the mass of the companion potentially responsible for the proper motion anomaly of HD 107146 to values of 2-7 au and 2-5 M Jup , respectively., Comment: 17 pages, 14 Figures, accepted for publication on MNRAS

Young giant planets and brown dwarf companions emit near-infrared radiation that can be linearly polarized up to several percent. This polarization can reveal the presence of a circumsubstellar accretion disk, rotation-induced oblateness of the atmosphere, or an inhomogeneous distribution of atmospheric dust clouds. We measured the near-infrared linear polarization of 20 known directly imaged exoplanets and brown dwarf companions with the high-contrast imager SPHERE-IRDIS at the VLT. We reduced the data using the IRDAP pipeline to correct for the instrumental polarization and crosstalk with an absolute polarimetric accuracy <0.1% in the degree of polarization. We report the first detection of polarization originating from substellar companions, with a polarization of several tenths of a percent for DH Tau B and GSC 6214-210 B in H-band. By comparing the measured polarization with that of nearby stars, we find that the polarization is unlikely to be caused by interstellar dust. Because the companions have previously measured hydrogen emission lines and red colors, the polarization most likely originates from circumsubstellar disks. Through radiative transfer modeling, we constrain the position angles of the disks and find that the disks must have high inclinations. The presence of these disks as well as the misalignment of the disk of DH Tau B with the disk around its primary star suggest in situ formation of the companions. For the 18 other companions, we do not detect significant polarization and place subpercent upper limits on their degree of polarization. These non-detections may indicate the absence of circumsubstellar disks, a slow rotation rate of young companions, the upper atmospheres containing primarily submicron-sized dust grains, and/or limited cloud inhomogeneity. Finally, we present images of the circumstellar disks of DH Tau, GQ Lup, PDS 70, Beta Pic, and HD 106906., Comment: Accepted for publication in A&A. Shortened abstract. 29 pages, 22 figures

We observed the K7 class III star NO Lup in an ALMA survey of the 1-3 Myr Lupus association and detected circumstellar dust and CO gas. Here we show that the J = 3-2 CO emission is both spectrally and spatially resolved, with a broad velocity width ${\sim}19$kms$^{-1}$ for its resolved size ${\sim}1''$ (${\sim}130$ au). We model the gas emission as a Keplerian disc, finding consistency, but only with a central mass of ${\sim}11M_{\odot}$, which is implausible given its spectral type and X-Shooter spectrum. A good fit to the data can also be found by modelling the CO emission as outflowing gas with a radial velocity ${\sim}22$kms$^{-1}$. We interpret NO Lup's CO emission as the first imaged class III circumstellar disc with outflowing gas. We conclude that the CO is continually replenished, but cannot say if this is from the break-up of icy planetesimals or from the last remnants of the protoplanetary disc. We suggest further work to explore the origin of this CO, and its higher than expected velocity in comparison to photoevaporative models., Comment: 6 pages, 4 figures. Accepted for publication in MNRAS following peer review (this is a pre-copyedited, author-produced PDF version)

Radial substructure in the form of rings and gaps has been shown to be ubiquitous among protoplanetary discs. This could be the case in exoKuiper belts as well, and evidence for this is emerging. In this paper we present ALMA observations of the debris/planetesimal disc surrounding HD 206893, a system that also hosts two massive companions at 2 and 11 au. Our observations reveal a disc extending from 30 to 180 au, split by a 27 au wide gap centred at 74 au, and no dust surrounding the reddened brown dwarf (BD) at 11 au. The gap width suggests the presence of a 0.9 M$_\mathrm{Jup}$ planet at 74 au, which would be the third companion in this system. Using previous astrometry of the BD, combined with our derived disc orientation as a prior, we were able to better constrain its orbit finding it is likely eccentric ($0.14^{+0.05}_{-0.04}$). For the innermost companion, we used RV, proper motion anomaly and stability considerations to show its mass and semi-major axis are likely in the range 4-100 M$_\mathrm{Jup}$ and 1.4-4.5 au. These three companions will interact on secular timescales and perturb the orbits of planetesimals, stirring the disc and potentially truncating it to its current extent via secular resonances. Finally, the presence of a gap in this system adds to the growing evidence that gaps could be common in wide exoKuiper belts. Out of 6 wide debris discs observed with ALMA with enough resolution, 4-5 show radial substructure in the form of gaps.

Class III stars are those in star forming regions without large non-photospheric infrared emission, suggesting recent dispersal of their protoplanetary disks. We observed 30 class III stars in the 1-3 Myr Lupus region with ALMA at ${\sim}856\mu$m, resulting in 4 detections that we attribute to circumstellar dust. Inferred dust masses are $0.036{-}0.093M_\oplus$, ${\sim}1$ order of magnitude lower than any previous measurements; one disk is resolved with radius ${\sim}80$ au. Two class II sources in the field of view were also detected, and 11 other sources, consistent with sub-mm galaxy number counts. Stacking non-detections yields a marginal detection with mean dust mass ${\sim}0.0048M_\oplus$. We searched for gas emission from the CO J=3-2 line, and present its detection to NO Lup inferring a gas mass ($4.9 {\pm} 1.1$) ${\times}10^{-5} M_\oplus$ and gas-to-dust ratio $1.0{\pm}0.4$. Combining our survey with class II sources shows a gap in the disk mass distribution from $0.09{-}2M_\oplus$ for ${>}0.7M_\odot$ Lupus stars, evidence of rapid dispersal of mm-sized dust from protoplanetary disks. The class III disk mass distribution is consistent with a population model of planetesimal belts that go on to replenish the debris disks seen around main sequence stars. This suggests that planetesimal belt formation does not require long-lived protoplanetary disks, i.e., planetesimals form within ${\sim}$2 Myr. While all 4 class III disks are consistent with collisional replenishment, for two the gas and/or mid-IR emission could indicate primordial circumstellar material in the final stages of protoplanetary disk dispersal. Two class III stars without sub-mm detections exhibit hot emission that could arise from ongoing planet formation processes inside ${\sim}1$ au., Comment: 30 pages, 20 figures. This is a pre-copyedited, author-produced PDF of an article accepted for publication in MNRAS following peer review

The presence of CO gas around 10-50 Myr old A stars with debris discs has sparked debate on whether the gas is primordial or secondary. Since secondary gas released from planetesimals is poor in H$_2$, it was thought that CO would quickly photodissociate never reaching the high levels observed around the majority of A stars with bright debris discs. Kral et al. 2019 showed that neutral carbon produced by CO photodissociation can effectively shield CO and potentially explain the high CO masses around 9 A stars with bright debris discs. Here we present a new model that simulates the gas viscous evolution, accounting for carbon shielding and how the gas release rate decreases with time as the planetesimal disc loses mass. We find that the present gas mass in a system is highly dependant on its evolutionary path. Since gas is lost on long timescales, it can retain a memory of the initial disc mass. Moreover, we find that gas levels can be out of equilibrium and quickly evolving from a shielded onto an unshielded state. With this model, we build the first population synthesis of gas around A stars, which we use to constrain the disc viscosity. We find a good match with a high viscosity ($\alpha\sim0.1$), indicating that gas is lost on timescales $\sim1-10$ Myr. Moreover, our model also shows that high CO masses are not expected around FGK stars since their planetesimal discs are born with lower masses, explaining why shielded discs are only found around A stars. Finally, we hypothesise that the observed carbon cavities could be due to radiation pressure or accreting planets., Comment: Accepted for publication in MNRAS, 23 pages, 13 figures

Low mass stars might offer today the best opportunities to detect and characterise planetary systems, especially those harbouring close-in low mass temperate planets. Among those stars, TRAPPIST-1 is exceptional since it has seven Earth-sized planets, of which three could sustain liquid water on their surfaces. Here we present new and deep ALMA observations of TRAPPIST-1 to look for an exo-Kuiper belt which can provide clues about the formation and architecture of this system. Our observations at 0.88 mm did not detect dust emission, but can place an upper limit of 23$\mu$Jy if the belt is smaller than 4 au, and 0.15 mJy if resolved and 100 au in radius. These limits correspond to low dust masses of $\sim10^{-5}-10^{-2}$ $M_\oplus$, which are expected after 8 Gyr of collisional evolution unless the system was born with a $>20$ $M_\oplus$ belt of 100 km-sized planetesimals beyond 40 au or suffered a dynamical instability. This $20$ $M_\oplus$ mass upper limit is comparable to the combined mass in TRAPPIST-1 planets, thus it is possible that most of the available solid mass in this system was used to form the known planets. A similar analysis of the ALMA data on Proxima Cen leads us to conclude that a belt born with a mass $\gtrsim1$ $M_\oplus$ in 100 km-sized planetesimals could explain its putative outer belt at 30 au. We recommend that future characterisations of debris discs around low mass stars should focus on nearby and young systems if possible., Comment: accepted for publication in MNRAS, 7 pages, 5 figures

In the last few years, multiwavelength observations have revealed the ubiquity of gaps/rings in circumstellar discs. Here we report the first ALMA observations of HD 92945 at 0.86 mm, that reveal a gap at about 73$\pm$3 au within a broad disc of planetesimals that extends from 50 to 140 au. We find that the gap is $20^{+10}_{-8}$ au wide. If cleared by a planet in situ, this planet must be less massive than 0.6 $M_\mathrm{Jup}$, or even lower if the gap was cleared by a planet that formed early in the protoplanetary disc and prevented planetesimal formation at that radius. By comparing opposite sides of the disc we also find that the disc could be asymmetric. Motivated by the asymmetry and the fact that planets might be more frequent closer to the star in exoplanetary systems, we show that the gap and asymmetry could be produced by two planets interior to the disc through secular resonances. These planets excite the eccentricity of bodies at specific disc locations, opening radial gaps in the planetesimal distribution. New observations are necessary to confirm if the disc is truly asymmetric, thus favouring the secular resonance model, or if the apparent asymmetry is due to a background galaxy, favouring the in-situ planet scenario. Finally, we also report the non-detection of CO and HCN gas confirming that no primordial gas is present. The CO and HCN non-detections are consistent with the destruction of volatile-rich Solar System-like comets., Comment: Accepted for publication in MNRAS, 13 pages, 8 figures

While detecting low mass exoplanets at tens of au is beyond current instrumentation, debris discs provide a unique opportunity to study the outer regions of planetary systems. Here we report new ALMA observations of the 80-200 Myr old Solar analogue HD 107146 that reveal the radial structure of its exo-Kuiper belt at wavelengths of 1.1 and 0.86 mm. We find that the planetesimal disc is broad, extending from 40 to 140 au, and it is characterised by a circular gap extending from 60 to 100 au in which the continuum emission drops by about 50%. We also report the non-detection of the CO J=3-2 emission line, confirming that there is not enough gas to affect the dust distribution. To date, HD 107146 is the only gas-poor system showing multiple rings in the distribution of millimeter sized particles. These rings suggest a similar distribution of the planetesimals producing small dust grains that could be explained invoking the presence of one or more perturbing planets. Because the disk appears axisymmetric, such planets should be on circular orbits. By comparing N-body simulations with the observed visibilities we find that to explain the radial extent and depth of the gap, it would be required the presence of multiple low mass planets or a single planet that migrated through the disc. Interior to HD 107146's exo-Kuiper belt we find extended emission with a peak at ~20 au and consistent with the inner warm belt that was previously predicted based on 22$\mu$m excess as in many other systems. This warm belt is the first to be imaged, although unexpectedly suggesting that it is asymmetric. This could be due to a large belt eccentricity or due to clumpy structure produced by resonant trapping with an additional inner planet., Comment: Accepted for publication in MNRAS, 19 pages, 11 figures

Resolved observations of millimetre-sized dust, tracing larger planetesimals, have pinpointed the location of 26 Edgeworth-Kuiper belt analogs. We report that a belt's distance $R$ to its host star correlates with the star's luminosity $L_{\star}$, following $R\propto L^{0.19}_{\star}$ with a low intrinsic scatter of $\sim$17%. Remarkably, our Edgeworth-Kuiper belt in the Solar System and the two CO snow lines imaged in protoplanetary disks lie close to this $R$-$L_{\star}$ relation, suggestive of an intrinsic relationship between protoplanetary disk structures and belt locations. To test the effect of bias on the relation, we use a Monte Carlo approach and simulate uncorrelated model populations of belts. We find that observational bias could produce the slope and intercept of the $R$-$L_{\star}$ relation, but is unable to reproduce its low scatter. We then repeat the simulation taking into account the collisional evolution of belts, following the steady state model that fits the belt population as observed through infrared excesses. This significantly improves the fit by lowering the scatter of the simulated $R$-$L_{\star}$ relation; however, this scatter remains only marginally consistent with the one observed. The inability of observational bias and collisional evolution alone to reproduce the tight relationship between belt radius and stellar luminosity could indicate that planetesimal belts form at preferential locations within protoplanetary disks. The similar trend for CO snow line locations would then indicate that the formation of planetesimals and/or planets in the outer regions of planetary systems is linked to the volatility of their building blocks, as postulated by planet formation models., Comment: Accepted for publication in ApJ. 23 pages, 9 figures

HR8799 is a benchmark system for direct imaging studies. It hosts two debris belts, which lie internally and externally to four giant planets. This paper considers how the four known planets and a possible fifth planet, interact with the external population of debris through N-body simulations. We find that when only the known planets are included, the inner edge of the outer belt predicted by our simulations is much closer to the outermost planet than recent ALMA observations suggest. We subsequently include a fifth planet in our simulations with a range of masses and semi-major axes, which is external to the outermost known planet. We find that a fifth planet with a mass and semi-major axis of 0.1$\mathrm{M_J}$ and 138au predicts an outer belt that agrees well with ALMA observations, whilst remaining stable for the lifetime of HR8799 and lying below current direct imaging detection thresholds. We also consider whether inward scattering of material from the outer belt can input a significant amount of mass into the inner belt. We find that for the current age of HR8799, only $\sim$1\% of the mass loss rate of the inner disk can be replenished by inward scattering. However we find that the higher rate of inward scattering during the first $\sim$10Myr of HR8799 would be expected to cause warm dust emission at a level similar to that currently observed, which may provide an explanation for such bright emission in other systems at $\sim10$Myr ages., Comment: 16 pages, 13 figures. Accepted for publication in MNRAS

A decade of surveys has hinted at a possible higher occurrence rate of debris discs in systems hosting low mass planets. This could be due to common favourable forming conditions for rocky planets close in and planetesimals at large radii. In this paper we present the first resolved millimetre study of the debris disc in the 4.6 Gyr old multiplanet system 61 Vir, combining ALMA and JCMT data at 0.86 mm. We fit the data using a parametric disc model, finding that the disc of planetesimals extends from 30 AU to at least 150 AU, with a surface density distribution of millimetre sized grains with a power law slope of 0.1$^{+1.1}_{-0.8}$. We also present a numerical collisional model that can predict the evolution of the surface density of millimetre grains for a given primordial disc, finding that it does not necessarily have the same radial profile as the total mass surface density (as previous studies suggested for the optical depth), with the former being flatter. Finally, we find that if the planetesimal disc was stirred at 150 AU by an additional unseen planet, that planet should be more massive than 10 M$_{\oplus}$ and lie between 10-20 AU. Lower planet masses and semi-major axes down to 4 AU are possible for eccentricities $\gg$ 0.1., Comment: 15 pages, 10 figures, accepted for publication in MNRAS

While most of the known debris discs present cold dust at tens of AU, a few young systems exhibit hot dust analogous to the Zodiacal dust. $\eta$ Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in-situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here we present ALMA observations of $\eta$ Corvi with a resolution of 1."2 (~22au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152au and radial FWHM of 46au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4sigma detection of CO at ~ 20au. CO could be released in situ from icy planetesimals being passed in when crossing the H$_2$O or CO$_2$ ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100au, with a mass of 3-30 M$_\oplus$ and an eccentricity < 0.08. Such a planet would be able to clear its chaotic zone on a timescale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust., Comment: 22 pages, 16 figures. Accepted for publication in MNRAS

This paper considers the dynamics of scattering of planetesimals or planetary embryos by a planet on a circumstellar orbit. We classify six regions in the planet's mass versus semimajor axis parameter space according to the dominant outcome for scattered objects: ejected, accreted, remaining, escaping, Oort Cloud, depleted Oort Cloud. We use these outcomes to consider which planetary system architectures maximise the observability of specific signatures, given that signatures should be detected first around systems with optimal architectures (if such systems exist in nature). Giant impact debris is most readily detectable for 0.1-10Mearth planets at 1-5au, depending on detection method and spectral type. While A stars have putative giant impact debris at 4-6au consistent with this sweet spot, that of FGK stars is typically <<1au contrary to expectations; an absence of 1-3au giant impact debris could indicate a low frequency of terrestrial planets there. Three principles maximise cometary influx from exo-Kuiper belts: a chain of closely separated planets interior to the belt, none of which is a Jupiter-like ejector; planet masses not increasing strongly with distance (for a net inward torque on comets); ongoing replenishment of comets, possibly by embedded low-mass planets. A high Oort Cloud comet influx requires no ejector and architectures that maximise the Oort Cloud population. Cold debris disks are usually considered classical Kuiper belt analogues. Here we consider the possibility of detecting scattered disk analogues, which could be betrayed by a broad radial profile and lack of small grains, as well as spherical 100-1000au mini-Oort Clouds. Some implications for escaping planets around young stars, detached planets akin to Sedna, and the formation of super-Earths, are also discussed., Comment: 25 pages, MNRAS in press

An increasing number of observations have shown that gaseous debris discs are not an exception. However, until now we only knew of cases around A stars. Here we present the first detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with radiative transfer calculations we study the dust and CO mass distribution. We find the dust is distributed in a ring with a radius of 86.0 +- 0.4 AU and a radial width of 23.2 +- 1.0 AU. At this frequency the ring radius is smaller than in the optical, revealing grain size segregation expected due to radiation pressure. We also report on the detection of low level continuum emission beyond the main ring out to ~200 AU. We model the CO emission in the non-LTE regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging between 1.2x10^-6 Mearth and 2.9x10^-6 Mearth, depending on the gas kinetic temperature and collisional partners densities. The CO densities and location suggest a secondary origin, i.e. released from icy planetesimals in the ring. We derive a CO+CO2 cometary composition that is consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is shaping the dust distribution., Comment: Accepted for publication in MNRAS

HD 142527A is one of the most studied Herbig Ae/Be stars with a transitional disk, as it has the largest imaged gap in any protoplanetary disk: the gas is cleared from 30 to 90 AU. The HD142527 system is also unique in that it has a stellar companion with a small mass compared to the mass of the primary star. This factor of ~20 in mass ratio between the two objects makes this binary system different from any other YSO. The HD142527 system could therefore provide a valuable test bed. This low-mass stellar object may be responsible for both the gap and dust trapping observed by ALMA at longer distances. We observed this system with the NACO and GPI instruments using the aperture masking technique. Aperture masking is ideal for providing high dynamic range even at very small angular separations. We present the spectral energy distribution for HD142527A and B. Brightness of the companion is now known from the R band up to the M' band. We also followed the orbital motion of HD 142527B over a period of more than two years. The SED of the companion is compatible with a T=3000+/-100K object in addition to a 1700K blackbody environment (likely a circus-secondary disk). From evolution models, we find that it is compatible with an object of mass 0.13+/-0.03Msun, radius 0.90+/-0.15Rsun, and age $1.0^{+1.0}_{-0.75}$Myr. This age is significantly younger than the age previously estimated for HD142527A. Computations to constrain the orbital parameters found a semi major axis of $140^{+120}_{-70}$mas, an eccentricity of 0.5+/-0.2, an inclination of 125+/-15 degrees, and a position angle of the right ascending node of -5+/-40 degrees. Inclination and position angle of the ascending node are in agreement with an orbit coplanar with the inner disk, not coplanar with the outer disk. Despite its high eccentricity, it is unlikely that HD142527B is responsible for truncating the inner edge of the outer disk., Comment: published in A&A; 8 pages

The formation of planetesimals requires that primordial dust grains grow from micron- to km-sized bodies. Dust traps caused by gas pressure maxima have been proposed as regions where grains can concentrate and grow fast enough to form planetesimals, before radially migrating onto the star. We report new VLA Ka & Ku observations of the protoplanetary disk around the Herbig Ae/Be star MWC 758. The Ka image shows a compact emission region in the outer disk indicating a strong concentration of big dust grains. Tracing smaller grains, archival ALMA data in band 7 continuum shows extended disk emission with an intensity maximum to the north-west of the central star, which matches the VLA clump position. The compactness of the Ka emission is expected in the context of dust trapping, as big grains are trapped more easily than smaller grains in gas pressure maxima. We develop a non-axisymmetric parametric model inspired by a steady state vortex solution with parameters adequately selected to reproduce the observations, including the spectral energy distribution. Finally, we compare the radio continuum with SPHERE scattered light data. The ALMA continuum spatially coincides with a spiral-like feature seen in scattered light, while the VLA clump is offset from the scattered light maximum. Moreover, the ALMA map shows a decrement that matches a region devoid of scattered polarised emission. Continuum observations at a different wavelength are necessary to conclude if the VLA-ALMA difference is an opacity or a real dust segregation., Comment: Accepted for publication in ApJ