The chemical evolution of protoplanetary discs is not fully understood, several factors influence the final distribution of disc material. One such factor are inward drifting and evaporating pebbles that enrich the inner disc with vapour. In particular, it is first enriched with water vapour, resulting in a low C/O ratio, before carbon-rich gas from the outer disc is transported inwards elevating the C/O ratio again. However, it is unclear how internal photoevaporation, which carries away gas and opens gaps that block inward drifting pebbles, affects the chemical composition of the disc. We aim to study these effects in discs around solar-like stars, where we especially focus on the C/O ratio and the water content. The simulations are carried out using a semi-analytical 1D disc model. Our code chemcomp includes viscous evolution and heating, pebble growth and drift, pebble evaporation and condensation, and a simple chemical partitioning model. We show that internal photoevaporation plays a major role in the (chemical) evolution of protoplanetary discs: As it opens a gap, inward drifting pebbles are stopped and cannot contribute to the volatile content any more. In addition, gas from the outer disc is carried away by photoevaporative winds. Consequently, the C/O ratio in the inner disc is low. In contrast, gaps opened by giant planets allow the gas to pass, resulting in an elevated C/O ratio, similar to viscous discs without internal photoevaporation. This will enable us to distinguish observationally between these two scenarios when measuring the C/O ratio, implying that we can infer the cause of gap structures in disc observations. In the case of a photoevaporative disc, we additionally find an elevated water content in the inner disc as the water vapour and ice undergo a cycle of evaporation/re-condensation, preventing its inward accretion onto the star.
Protoplanetary disks are dispersed by viscous evolution and photoevaporation in a few million years; in the interim small, sub-micron sized dust grains must grow and form planets. The time-varying abundance of small grains in an evolving disk directly affects gas heating by far-ultraviolet photons, while dust evolution affects photoevaporation by changing the disk opacity and resulting penetration of FUV photons in the disk. Photoevaporative flows, in turn, selectively carry small dust grains leaving the larger particles---which decouple from the gas---behind in the disk. We study these effect…
We investigate the influence of photoevaporation of protoplanetary discs on the final distribution of exoplanets semi-major axis distances. We model giant planet migration in viscous discs affected by photoevaporation driven by either pure EUV or soft X-ray radiation (XEUV). We show that the final exoplanet distributions are strongly dependant on the choice of the photoevaporation model. In particular, we find that XEUV is more efficient than pure EUV radiation at parking planets at approximately 1-2 AU distance from their central star, hence roughly reproducing the observed peak in the exopla…
The streaming instability is often invoked as solution to the fragmentation and drift barriers in planetesimal formation, catalyzing the aggregation of dust on kyr timescales 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. …
Circumstellar discs with large dust depleted cavities and vigorous accretion onto the central star are often considered signposts for (multiple) giant planet formation. In this letter we show that X-ray photoevaporation operating in discs with modest (factors 3-10) gas-phase depletion of Carbon and Oxygen at large radii (> 15 AU) yield the inner radius and accretion rates for most of the observed discs, without the need to invoke giant planet formation. We present one-dimensional viscous evolution models of discs affected by X-ray photoevaporation assuming moderate gas-phase depletion of Carbo…
Planet-forming disc evolution is not independent of the star formation and feedback process in giant molecular clouds. In particular, OB stars emit UV radiation that heats and disperses discs in a process called 'external photoevaporation'. This process is understood to be the dominant environmental influence acting on planet-forming discs in typical star forming regions. Our best studied discs are nearby, in sparse stellar groups where external photoevaporation is less effective. However the majority of discs are expected to reside in much stronger UV environments. Understanding external phot…
Protoplanetary discs are complex dynamical systems where several processes may lead to the formation of ring-like structures and planets. These discs are flared following a profile where the vertical scale height increases with radius. In this work, we investigate the role of this disc flaring geometry on the formation of rings and holes. We combine a flattening law change with X-ray and FUV photoevaporative winds. We have used a semi-analytical 1D viscous α approach, presenting the evolution of the disc mass and mass rate in a grid of representative systems. Our results show that changing the…
We propose a new hypothesis for the origin of protoplanetary discs with large inner holes (or gaps), so-called transition discs. Our gas disc model takes into account layered accretion, in which poorly-ionized low-viscosity dead zones are sandwiched by high-viscosity surface layers, and photoevaporative winds induced by X-rays from the central stars. We find that a gap opens at a radius outside a dead zone, if the mass loss rate due to photoevaporative winds exceeds the mass accretion rate in the dead zone region. Since the dead zone survives even after the gap opens, mass accretion onto the c…
We assess the potential of planet formation instigating the early formation of a photoevaporation driven gap, up to radii larger than typical for photoevaporation alone. For our investigation we make use of hydrodynamics models of photoevaporating discs with a giant planet embedded. We find that, by reducing the mass accretion flow onto the star, discs that form giant planets will be dispersed at earlier times than discs without planets by X-ray photoevaporation. By clearing the portion of the disc inner of the planet orbital radius, planet formation induced photoevaporation (PIPE) is able to …
Gas giants' early ($\lesssim 5$ 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 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…
Protoplanetary discs are the site of star and planet formation, and their evolution and consequent dispersal deeply affect the formation of planetary systems. In the standard scenario they evolve on timescales ~Myr due to the viscous transport of angular momentum. The analytical self-similar solution for their evolution predicts also specific disc isochrones in the accretion rate - disc mass plane. However, photoevaporation by radiation emitted by the central star is likely to dominate the gas disc dispersal of the innermost region, introducing another (shorter) timescale for this process. In …
Many theoretical studies have shown that external photoevaporation from massive stars can severely truncate, or destroy altogether, the gaseous protoplanetary discs around young stars. In tandem, several observational studies report a correlation between the mass of a protoplanetary disc and its distance to massive ionising stars in star-forming regions, and cite external photoevaporation by the massive stars as the origin of this correlation. We present N-body simulations of the dynamical evolution of star-forming regions and determine the mass-loss in protoplanetary discs from external photo…
The discovery of giant planets in wide orbits represents a major challenge for planet formation theory. In the standard core accretion paradigm planets are expected to form at radial distances $\lesssim 20$ au in order to form massive cores (with masses $\gtrsim 10~\textrm{M}_{\oplus}$) able to trigger the gaseous runaway growth before the dissipation of the disc. This has encouraged authors to find modifications of the standard scenario as well as alternative theories like the formation of planets by gravitational instabilities in the disc to explain the existence of giant planets in wide orb…
Photoevaporation of protoplanetary discs by high energy radiation from the central young stellar object is currently the favourite model to explain the sudden dispersal of discs from the inside out. While several theoretical works have provided a detailed pictured of this process, the direct observational validation is still lacking. Emission lines produced in these slow moving protoplanetary disc winds may bear the imprint of the wind structure and thus provide a potential diagnostic of the underlying dispersal process. In this paper we primarily focus on the collisionally excited neutral oxy…
The Kepler transit survey with follow-up spectroscopic observations has discovered numerous super-Earth sized planets and revealed intriguing features of their sizes, orbital periods, and their relations between adjacent planets. For the first time, we investigate the size evolution of planets via both giant impacts and photoevaporation to compare with these observed features. We calculate the size of a protoplanet, which is the sum of its core and envelope sizes, by analytical models. $N$-body simulations are performed to evolve planet sizes during the giant impact phase with envelope strippi…
Protoplanetary discs form and evolve in a wide variety of stellar environments and are accordingly exposed to a wide range of ambient far ultraviolet (FUV) field strengths. Strong FUV fields are known to drive vigorous gaseous flows from the outer disc. In this paper we conduct the first systematic exploration of the evolution of the solid component of discs subject to external photoevaporation. We find that the main effect of photoevaporation is to reduce the reservoir of dust at large radii and this leads to more efficient subsequent depletion of the disc dust due to radial drift. Efficient …
We model the radiatively driven flow from IM Lup -- a large protoplanetary disc expected to be irradiated by only a weak external radiation field (at least 10$^4$ times lower than the UV field irradiating the Orion Nebula Cluster proplyds). We find that material at large radii ($>400$AU) in this disc is sufficiently weakly gravitationally bound that significant mass loss can be induced. Given the estimated values of the disc mass and accretion rate, the viscous timescale is long ($\sim10$Myr) so the main evolutionary behaviour for the first Myr of the disc's lifetime is truncation of the disc …
The photoevaporation of protoplanetary discs by nearby massive stars present in their birth cluster plays a vital role in their evolution. Previous modelling assumes that the disc behaves like a classical Keplerian accretion disc out to a radius where the photoevaporative outflow is launched. There is then an abrupt change in the angular velocity profile, and the outflow is modelled by forcing the fluid parcels to conserve their specific angular momenta. Instead, we model externally photoevaporating discs using the slim disc formalism. The slim disc approach self consistently includes the adve…
The strong X-ray irradiation from young solar-type stars may play a crucial role in the thermodynamics and chemistry of circumstellar discs, driving their evolution in the last stages of disc dispersal as well as shaping the atmospheres of newborn planets. In this paper we study the influence of stellar mass on circumstellar disc mass-loss rates due to X-ray irradiation, extending our previous study of the mass-loss rate's dependence on the X-ray luminosity and spectrum hardness. We focus on stars with masses between 0.1 and 1 Solar mass, which are the main target of current and future mission…
We have performed hydrodynamic and radiative transfer calculations of a photoevaporating disc around a Herbig Ae/Be star to determine the evolution and observational impact of dust entrained in the wind. We find that the wind selectively entrains grains of different sizes at different radii resulting in a dust population that varies spatially and increases with height above the disc at radii > 10 AU. This variable grain population results in a 'wingnut' morphology to the dust density distribution. We calculate images of this dust distribution at NIR wavelengths that also show a wingnut morphol…
The so-called transition discs provide an important tool to probe various mechanisms that might influence the evolution of protoplanetary discs and therefore the formation of planetary systems. One of these mechanisms is photoevaporation due to energetic radiation from the central star, which can in principal explain the occurrence of discs with inner cavities like transition discs. Current models, however, fail to reproduce a subset of the observed transition discs, namely objects with large measured cavities and vigorous accretion. For these objects the presence of (multiple) giant planets i…
We study the utility of the [OI] 6300$\mathring{\mathrm A}$ forbidden line for identifying and interpreting externally driven photoevaporative winds in different environments and at a range of distances. Thermally excited [OI] 6300$\mathring{\mathrm A}$ is a well known tracer of inner disc winds, so any external contribution needs to be distinguishable. In external winds, the line is not thermally excited and instead results from the dissociation of OH and we study how the line luminosity resulting from that process scales with the disc/environmental parameters. We find that the line luminosit…
High energy radiation from a planet host star can have strong influence on the final habitability of a system through several mechanisms. In this context we have constructed a catalogue containing the X-ray luminosities, as well as basic stellar and planetary properties of all known stars hosting giant planets (> 0.1 Mjup) that have been observed by the Chandra X-ray Observatory, XMM-Newton and/or ROSAT. Specifically in this paper we present a first application of this catalogue to search for a possible imprint of X-ray photoevaporation of planet-forming discs on the present-day orbital distri…
A tension between dust and gas radii: the role of substructures and external photoevaporation in protoplanetary disks
Ludwig-Maximilians-Universität München（慕尼黑大学）；Università degli Studi di Milano（米兰大学）；European Southern Observatory（欧洲南方天文台）；INAF, Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；University of Chicago（芝加哥大学）
Most stars form and spend their early life in regions of enhanced stellar density. Therefore the evolution of protoplanetary discs (PPDs) hosted by such stars are subject to the influence of other members of the cluster. Physically, PPDs might be truncated either by photoevaporation due to ultraviolet flux from massive stars, or tidal truncation due to close stellar encounters. Here we aim to compare the two effects in real cluster environments. In this vein we first review the properties of well studied stellar clusters with a focus on stellar number density, which largely dictates the degree…
The EUV/X-ray photoevaporation and core-powered mass-loss models are both capable of reproducing the bimodality in the sizes of small, close-in exoplanets observed by the \textit{Kepler} space mission, often referred to as the "radius gap". However, it is unclear which of these two mechanisms dominates the atmospheric mass-loss which is likely sculpting the radius gap. In this work, we propose a new method of differentiating between the two models, which relies on analysing the radius gap in 3D parameter space. Using models for both mechanisms, and by performing synthetic transit surveys we pr…
The formation of planets within a disc must operate within the time frame of disc dispersal, it is thus crucial to establish what is the dominant process that disperses the gaseous component of discs around young stars. Planet formation itself as well as photoevaporation by energetic radiation from the central young stellar object have been proposed as plausible dispersal mechanisms. [abridged]. In this paper we use the different metallicity dependance of X-ray photoevaporation and planet formation to discriminate between these two processes. We study the effects of metallicity, Z, on the disp…
Photoevaporation of planet forming discs by high energy radiation from the central star is potentially a crucial mechanism for disc evolution and it may play an important role in the formation and evolution of planetary system. We present here a new generation of X-ray photoevaporation models for solar-type stars, based on a new set of hydrodynamical simulations, which account for stellar irradiation via a new, significantly improved, parameterisation of gas temperatures, based on detailed photoionisation and radiation transfer calculations. This is the first of a series of papers aiming at pr…
Young solar-type stars are known to be strong X-ray emitters and their X-ray spectra have been widely studied. X-rays from the central star may play a crucial role in the thermodynamics and chemistry of the circumstellar material as well as in the atmospheric evolution of young planets. In this paper we present model spectra based on spectral parameters derived from the observations of young stars in the Orion Nebula Cluster from the Chandra Orion Ultradeep Project (COUP). The spectra are then used to calculate new photoevaporation prescriptions that can be used in disc and planet population s…
The nature and rate of (viscous) angular momentum transport in protoplanetary discs (PPDs) has important consequences for the formation process of planetary systems. While accretion rates onto the central star yield constraints on such transport in the inner regions of a PPD, empirical constraints on viscous spreading in the outer regions remain challenging to obtain. Here we demonstrate a novel method to probe the angular momentum transport at the outer edge of the disc. This method applies to PPDs that have lost a significant fraction of their mass due to thermal winds driven by UV irradiati…
Numerical models have shown that disc dispersal via internal photoevaporation driven by the host star can successfully reproduce the observed pile-up of warm Jupiters near 1-2 au. However, since a range of different mechanisms have been proposed to cause the same feature, clear observational diagnostics of disc dispersal leaving an imprint in the observed distribution of giant planets could help to constrain the dominant mechanisms. We aim to assess the impact of disc dispersal via X-ray driven-photoevaporation (XPE) onto giant planet separations in order to provide theoretical constraints on …
We study the evolution and final dispersal of protoplanetary discs that evolve under the action of internal and external photoevaporation, and different degrees of viscous transport. We identify five distinct dispersal pathways, which are i) very long lived discs ($>20\,$Myr), ii) inside-out dispersal where internal photoevaporation dominates and opens inner holes, iii) outside-in dispersal where external photoevaporation dominates through disc truncation and two intermediate regimes characterised by lingering material in the inner disc with the outer disc dispersed predominantly by either int…
The Galactic Centre is known to have undergone a recent star formation episode a few Myrs ago, which likely produced many T Tauri stars hosting circumstellar discs. It has been suggested that these discs may be the compact and dusty ionized sources identified as ``G-clouds''. Given the Galactic Centre's hostile environment, we study the possible evolutionary pathways these discs experience. We compute new external photoevaporation models applicable to discs in the Galactic Centre that account for the sub-sonic launching of the wind and absorption of UV photons by dust. Using evolutionary disc …
High resolution spectra of typical wind diagnostics ([OI] 6300 Å and other forbidden emission lines) can often be decomposed into multiple components: high-velocity components with blueshifts up to several 100 km/s are usually attributed to fast jets, while narrow (NLVC) and broad (BLVC) low-velocity components are believed to trace slower disc winds. Under the assumption that the line-broadening is dominated by Keplerian rotation, several studies have found that the BLVCs should trace gas launched between 0.05 and 0.5 au and correlations between the properties of BLVCs and NLVCs have been int…
We present an open access grid of 3930 calculations of externally evaporating protoplanetary discs. This spans a range of disc sizes (1-400AU), disc masses, UV field strengths (10-10$^4$G$_0$) and stellar masses (0.05-1.9M$_\odot$). The grid is publicly available for download, and offers a means of cheaply including external photoevaporation in disc evolutionary calculations. It can also be queried using an online tool for quick estimates of instantaneous mass loss rates (e.g for convenient evaluation of real observed systems). The `FRIED' grid itself illustrates that for discs around stars $\…
We present models of giant planet migration in evolving protoplanetary discs. We show that disc clearing by EUV photoevaporation can have a strong effect on the distribution of giant planet semi-major axes. During disc clearing planet migration is slowed or accelerated in the region where photoevaporation opens a gap in the disc, resulting in "deserts" where few giant planets are found and corresponding "pile-ups" at smaller and larger radii. However, the precise locations and sizes of these features are strong functions of the efficiency of planetary accretion, and therefore also strongly dep…
The dearth of planets with sizes around 1.8 $\mathrm{R_\oplus}$ is a key demographic feature discovered by the $Kepler$ mission. Two theories have emerged as potential explanations for this valley: photoevaporation and core-powered mass-loss. However, Rogers et al. (2021) shows that differentiating between the two theories is possible using the three-dimensional parameter space of planet radius, incident flux, and stellar mass. We use homogeneously-derived stellar and planetary parameters to measure the $Kepler$ exoplanet radius gap in this three-dimensional space. We compute the slope of the …
We explore how measurements of protoplanetary disc masses and accretion rates provided by surveys of star forming regions can be analysed via the dimensionless accretion parameter, which we define as the product of the accretion rate and stellar age divided by the disc mass. By extending and generalising the study of Jones et al (2012), we demonstrate that this parameter should be less than or of order unity for a wide range of evolutionary scenarios, rising above unity only during the final stages of outside in clearing by external photoevaporation. We use this result to assess the reliabilit…
We couple star cluster formation and feedback simulations of a Carina-like star forming region with 1D disc evolutionary models to study the impact of external photoevaporation on disc populations in massive star forming regions. To investigate the effect of shielding of young stellar objects by star forming material, we track the FUV field history at each star in the cluster with two methods: i) Monte Carlo radiative transfer accounting for the shielding of stars from the FUV by the star forming cloud ii) Geometric dilution of the radiation from other stars which ignores shielding effects. We…
The formation of gas giant planets must occur during the first few Myr of a star's lifetime, when the protoplanetary disc still contains sufficient gas to be accreted onto the planetary core. The majority of protoplanetary discs are exposed to strong ultraviolet irradiation from nearby massive stars, which drives winds and depletes the mass budget for planet formation. It remains unclear to what degree external photoevaporation affects the formation of massive planets. In this work, we present a simple one dimensional model for the growth and migration of a massive planet under the influence o…
Many stars form in regions of enhanced stellar density, wherein the influence of stellar neighbours can have a strong influence on a protoplanetary disc (PPD) population. In particular, far ultraviolet (FUV) flux from massive stars drives thermal winds from the outer edge of PPDs, accelerating disc destruction. In this work, we present a novel technique for constraining the dynamical history of a star forming environment using PPD properties in a strongly FUV irradiated environment. Applying recent models for FUV induced mass loss rates to the PPD population of Cygnus OB2, we constrain how lon…
