Gaseous Envelope Research Articles

Optimization and mechanism of precise finishing of TC4 alloy by plasma electrolytic polishing

A plasma electrolytic polishing (PEP) technique was used to yield high-quality, precise surfaces of a TC4 alloy to ensure high reflectivity. An orthogonal experiment was carried out to investigate the multiple factors affecting the surface quality of the alloy during the polishing process. The factors that affect the surface roughness are ranked as follows based on the extent of the effect: temperature > time > voltage > depth. The surface crest and trough area decreases by an order of magnitude, and the average roughness of the alloy is reduced to approximately 1/27 of its original magnitude after PEP. The vapour gaseous envelope (VGE) ascends as the bubble expanded under the buoyant force of the electrolyte, causing the thickness of the plasma-gas layer close to the electrolyte-air interface to increase. Further, it is proposed that the mechanism of surface smoothing during the PEP process involves a combination of discontinuous discharge, electrochemical reactions, and dissolution, thereby finishing the surface of the TC4 alloy. This work provides an alternative to the surface finishing of TC4 by PEP, which is expected to be a promising technique for polishing complex structures, especially porous structures (such as 3D printed Ti, Cu, Al, Nb, Mg, and their alloys).

Spin of protoplanets generated by pebble accretion: Influences of protoplanet-induced gas flow

Context. In the pebble accretion model, protoplanets accrete millimeter-to-centimeter-sized particles (pebbles). When a protoplanet grows, a dense gas envelope forms around it. The envelope affects accretion of pebbles and, in particular, the spin angular momentum transfer at the collision to the planet. Aims. We aim to investigate the spin state of a protoplanet during the pebble accretion influenced by the gas flow in the gravitational potential of the protoplanet and how it depends on the planetary mass, the headwind speed, the distance from the host star, and the pebble size. Methods. We performed nonisothermal three-dimensional hydrodynamical simulations in a local frame to obtain the gas flow around the planet. We then numerically integrated three-dimensional orbits of pebbles under the obtained gas flow. Finally, assuming uniform spatial distribution of incoming pebbles, we calculated net spin by summing up specific angular momentum that individual pebbles transfer to the protoplanet at impacts. Results. We find that a protoplanet with the envelope acquires prograde net spin rotation regardless of the planetary mass, the pebble size, and the headwind speed of the gas. This is because accreting pebbles are dragged by the envelope that commonly has prograde rotation. As the planetary mass or orbital radius increases, the envelope is thicker and the prograde rotation is faster, resulting in faster net prograde spin. When the dimensionless thermal mass of the planet, m = RBondi/H, where RBondi and H are the Bondi radius and the disk gas scale height, is larger than a certain critical mass (m ≳ 0.3 at 0.1 au or m ≳ 0.1 at 1 au), the spin rotation exceeds the breakup one. Conclusions. The predicted spin frequency reaches the breakup one at the planetary mass miso,rot ~ 0.1 (a/1 au)−1/2 (where a is the orbital radius), suggesting that the protoplanet cannot grow beyond miso,rot. It is consistent with the Earth’s current mass and could help the formation of the Moon with a giant impact on a fast-spinning proto-Earth.

Identification of molecular clouds in emission maps: a comparison between methods in the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey

ABSTRACT The growing range of automated algorithms for the identification of molecular clouds and clumps in large observational data sets has prompted the need for the direct comparison of these procedures. However, these methods are complex and testing for biases is often problematic: only a few of them have been applied to the same data set or calibrated against a common standard. We compare the Fellwalker method, a widely used watershed algorithm, to the more recent Spectral Clustering for Interstellar Molecular Emission Segmentation (SCIMES). SCIMES overcomes sensitivity and resolution biases that plague many friends-of-friends algorithms by recasting cloud segmentation as a clustering problem. Considering the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) and the CO High-Resolution Survey (COHRS), we investigate how these two different approaches influence the final cloud decomposition. Although the two methods produce largely similar statistical results over the CHIMPS dataset, FW appears prone to oversegmentation, especially in crowded fields where gas envelopes around dense cores are identified as adjacent, distinct objects. FW catalogue also includes a number of fragmented clouds that appear as different objects in a line-of-sight projection. In addition, cross-correlating the physical properties of individual sources between catalogues is complicated by different definitions, numerical implementations, and design choices within each method, which make it very difficult to establish a one-to-one correspondence between the sources.

Can Protostellar Outflows Set Stellar Masses?

The opening angles of some protostellar outflows appear too narrow to match the expected core–star mass efficiency (SFE) = 0.3–0.5, if the outflow cavity volume traces outflow mass, with a conical shape and a maximum opening angle near 90°. However, outflow cavities with a paraboloidal shape and wider angles are more consistent with observed estimates of the SFE. This paper presents a model of infall and outflow evolution based on these properties. The initial state is a truncated singular isothermal sphere which has mass ≈ 1 M ⊙, freefall time ≈ 80 kyr, and small fractions of magnetic, rotational, and turbulent energy. The core collapses pressure free as its protostar and disk launch a paraboloidal wide-angle wind. The cavity walls expand radially and entrain envelope gas into the outflow. The model matches the SFE values when the outflow mass increases faster than the protostar mass by a factor 1–2, yielding protostar masses typical of the IMF. It matches the observed outflow angles if the outflow mass increases at nearly the same rate as the cavity volume. The predicted outflow angles are then typically ∼50° as they increase rapidly through the stage 0 duration of ∼40 kyr. They increase more slowly up to ∼110° during their stage I duration of ∼70 kyr. With these outflow rates and shapes, the model predictions appear consistent with observational estimates of the typical stellar masses, SFEs, stage durations, and outflow angles, with no need for external mechanisms of core dispersal.

FAST discovery of long tidal tails in NGC 4490/85

ABSTRACT We report the discovery of a 100 kpc H i tail in the merging galaxy pair NGC 4490/85 detected by the Five-Hundred-meter Aperture Spherical radio Telescope (FAST). The tidal tails extended in both the south and north directions, and they are much longer than that reported previously based on the VLA interferometric maps. The NGC 4490/85 is surrounded by a large gas envelope, and a starburst low-metallicity dwarf galaxy MAPS 1231+42 is found to be connected with the gas envelope, indicating that galaxy interaction trigged the intense star formation in it. Based on the fact that the metallicity in MAPS 1231+42 is one order of magnitude lower than that in the two discs of NGC 4490 and NGC 4485, we speculate that the gas near this galaxy should be primordial and could be due to gas inflow from the circumgalactic medium. We also found a collimated gas component pointing at a nearby dwarf galaxy KK 149, suggesting that this galaxy might also be interacting with the NGC 4490 pair. We discuss the possible origin of the long tidal tails and the extended gas envelope in this merging system based on the new data from FAST.

The shared evaporation history of three sub-Neptunes spanning the radius–period valley of a hyades star

ABSTRACT We model the evaporation histories of the three planets around K2-136, a K-dwarf in the Hyades open cluster with an age of 700 Myr. The star hosts three transiting planets, with radii of 1.0, 3.0, and 1.5 Earth radii, where the middle planet lies above the radius–period valley and the inner and outer planets are below. We use an XMM–Newton observation to measure the XUV radiation environment of the planets, finding that the X-ray activity of K2-136 is lower than predicted by models but typical of similar Hyades members. We estimate the internal structure of each planet, and model their evaporation histories using a range of structure and atmospheric escape formulations. While the precise X-ray irradiation history of the system may be uncertain, we exploit the fact that the three planets must have shared the same history. We find that the Earth-sized K2-136b is most likely rocky, with any primordial gaseous envelope being lost within a few Myr. The sub-Neptune, K2-136c, has an envelope contributing 1–1.7 per cent of its mass that is stable against evaporation thanks to the high mass of its rocky core, whilst the super-Earth, K2-136d, must have a mass at the upper end of the allowed range in order to retain any of its envelope. Our results are consistent with all three planets beginning as sub-Neptunes that have since been sculpted by atmospheric evaporation to their current states, stripping the envelope from planet b and removing most from planet d whilst preserving planet c above the radius-period valley.

The young mini-Neptune HD 207496b that is either a naked core or on the verge of becoming one

Aims. We report the discovery and characterisation of the transiting mini-Neptune HD 207496 b (TOI-1099) as part of a large programme that aims to characterise naked core planets.Methods. We obtained HARPS spectroscopic observations, one ground-based transit, and high-resolution imaging which we combined with the TESS photometry to confirm and characterise the TESS candidate and its host star.Results. The host star is an active early K dwarf with a mass of 0.80 ± 0.04M⊙, a radius of 0.769 ± 0.026R⊙, and aGmagnitude of 8. We found that the host star is young, ~0.52 Gyr, allowing us to gain insight into planetary evolution. We derived a planetary mass of 6.1 ± 1.6M⊕, a planetary radius of 2.25 ± 0.12R⊕, and a planetary density ofρp= 3.27−0.91+0.97g cm−3.Conclusions. From internal structure modelling of the planet, we conclude that the planet has either a water-rich envelope, a gas-rich envelope, or a mixture of both. We have performed evaporation modelling of the planet. If we assume the planet has a gas-rich envelope, we find that the planet has lost a significant fraction of its envelope and its radius has shrunk. Furthermore, we estimate it will lose all its remaining gaseous envelope in ~0.52 Gyr. Otherwise, the planet could have already lost all its primordial gas and is now a bare ocean planet. Further observations of its possible atmosphere and/or mass-loss rate would allow us to distinguish between these two hypotheses. Such observations would determine if the planet remains above the radius gap or if it will shrink and be below the gap.

Dynamical Evolution of Closely Packed Multiple Planetary Systems Subject to Atmospheric Mass Loss

A gap in exoplanets’ radius distribution has been widely attributed to the photoevaporation threshold of their progenitors’ gaseous envelope. Giant impacts can also lead to substantial mass loss. The outflowing gas endures tidal torque from the planets and their host stars. Alongside the planet–star tidal and magnetic interaction, this effect leads to planets’ orbital evolution. In multiple super-Earth systems, especially in those that are closely spaced and/or contain planets locked in mean motion resonances, modest mass loss can lead to dynamical instabilities. In order to place some constraints on the extent of planets’ mass loss, we study the evolution of a series of idealized systems of multiple planets with equal masses and a general scaled separation. We consider mass loss from one or more planets either in the conservative limit or with angular momentum loss from the system. We show that the stable preservation of idealized multiple planetary systems requires either a wide initial separation or a modest upper limit in the amount of mass loss. This constraint is stringent for the multiple planetary systems in compact and resonant chains. Perturbation due to either impulsive giant impacts between super-Earths or greater than a few percent mass loss can lead to dynamical instabilities.

Распределение плотности в газовой оболочке планеты

Purpose: Theoretical study of gas density distribution around the planet given self-gravity. Methods: Proposed in this paper equations for the planet gaseous envelope density with corresponding boundary conditions are solved analytically and numerically by Runge-Kutta method. Results: For the first time, the analysis of numerical solution of equations for all the space where the planet gravitational influence prevails - in the distance range from the planet surface till Hill radius - has been pursued using similarity method. Near the planet, the solution coincides with classical barometric formula, at intermediary distances, - with barometric formula which takes into consideration the dependence of free fall acceleration from the distance till the planet, at large distances, - with the dependence of density for singular isothermal gas sphere due to self-gravity. Practical significance: On the basis of the solution obtained, the unified picture of the planet gaseous envelope density distribution was analyzed. The results presented in the paper can be useful both for university physics professors and for the researchers involved in astrophysics.

Global N-body simulations of circumbinary planet formation around Kepler-16 and -34 analogues I: Exploring the pebble accretion scenario

ABSTRACT Numerous circumbinary planets have been discovered in surveys of transiting planets. Often, these planets are found to orbit near to the zone of dynamical instability, close to the central binary. The existence of these planets has been explained by hydrodynamical simulations that show that migrating circumbinary planets, embedded in circumbinary discs, halt at the central cavity that is formed by the central binary. Transit surveys are naturally most sensitive to finding circumbinary planets with the shortest orbital periods. The future promise of detecting longer period systems using radial-velocity searches, combined with the anticipated detection of numerous circumbinary planets by ESA’s PLATO mission, points to the need to model and understand the formation and evolution of circumbinary planets in a more general sense than has been considered before. With this goal in mind, we present a newly developed global model of circumbinary planet formation that is based on the mercury6 symplectic N-body integrator, combined with a model for the circumbinary disc and prescriptions for a range of processes involved in planet formation such as pebble accretion, gas envelope accretion, and migration. Our results show that under reasonable assumptions, the pebble accretion scenario can produce circumbinary systems that are similar to those observed, and in particular is able to produce planets akin to Kepler-16b and Kepler-34b. Comparing our results to other systems, we find that our models also adequately reproduce such systems, including multiplanet systems. Resonances between neighbouring planets are frequently obtained, whilst ejections of planets by the central binary acts as an effective source of free floating planets.

Assessing model-based carbon and oxygen abundance derivation from ultraviolet emission lines in AGNs

ABSTRACT We present an adapted version of the code HII-CHI-mistry-UV to derive chemical abundances from emission lines in the ultraviolet, for use in narrow line regions (NLR) of active galactic nuclei (AGN). We evaluate different ultraviolet emission line ratios and how different assumptions about the models, including the presence of dust grains, the shape of the incident spectral energy distribution, or the thickness of the gas envelope around the central source, may affect the final estimates as a function of the set of emission lines used. We compare our results with other published recipes for deriving abundances using the same emission lines and show that deriving the carbon-to-oxygen abundance ratio using C iii] λ 1909 Å and O iii] λ 1665 Å emission lines is a robust indicator of the metal content in AGN that is nearly independent of the model assumptions, similar to the case of star-forming regions. Moreover, we show that a prior determination of C/O allows for a much more precise determination of the total oxygen abundance using carbon UV lines, as opposed to assuming an arbitrary relationship between O/H and C/O, which can lead to non-negligible discrepancies.

Dynamical masses of two young transiting sub-Neptunes orbiting HD 63433

Context.Although the number of exoplanets reported in the literature exceeds 5000 so far, only a few dozen of them are young planets (≤900 Myr). However, a complete characterization of these young planets is key to understanding the current properties of the entire population. Hence, it is necessary to constrain the planetary formation processes and the timescales of dynamical evolution by measuring the masses of exoplanets transiting young stars.Aims.We characterize and measure the masses of two transiting planets orbiting the 400 Myr old solar-type star HD 63433, which is a member of the Ursa Major moving group.Methods.We analysed precise photometric light curves of five sectors of the TESS mission with a baseline of ~750 days and obtained ~150 precise radial velocity measurements with the visible and infrared arms of the CARMENES instrument at the Calar Alto 3.5 m telescope in two different campaigns of ~500 days. We performed a combined photometric and spectroscopic analysis to retrieve the planetary properties of two young planets. The strong stellar activity signal was modelled by Gaussian regression processes.Results.We have updated the transit parameters of HD 63433 b and c and obtained planet radii ofRpb= 2.140 ± 0.087R⊕andRpc= 2.692 ± 0.108R⊕. Our analysis allowed us to determine the dynamical mass of the outer planet with a 4σsignificance (Mpc= 15.54 ± 3.86M⊕) and set an upper limit on the mass of the inner planet at 3σ (Mpb< 21.76M⊕). According to theoretical models, both planets are expected to be sub-Neptunes, whose interiors mostly consist of silicates and water with no dominant composition of iron, and whose gas envelopes are lower than 2% in the case of HD 63433 c. The envelope is unconstrained in HD 63433 b.

TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS

Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ. Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope. Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series. Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of Mb = 20.4−2.5+2.6 M⊕ (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of Rb = 3.490−0.064+0.070 R⊕ (∼1.9%). Our mass and radius measurements imply a mean density of ρb = 2.65−0.35+0.37 g cm−3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41−0.20+0.34 M⊕ and a thickness of 1.05−0.29+0.30 R⊕. Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b.

Anatomy of rocky planets formed by rapid pebble accretion

We explore the heating and differentiation of rocky planets that grow by rapid pebble accretion. Our terrestrial planets grow outside of the ice line and initially accrete 28% water ice by mass. The accretion of water stops after the protoplanet reaches a mass of 0.01MEwhere the gas envelope becomes hot enough to sublimate the ice and transport the vapour back to the protoplanetary disc by recycling flows. The energy released by the decay of26Al melts the accreted ice to form clay (phyllosilicates), oxidized iron (FeO), and a water surface layer with ten times the mass of Earth’s modern oceans. The ocean–atmosphere system undergoes a run-away greenhouse effect after the effective accretion temperature crosses a threshold of around 300 K. The run-away greenhouse process vaporizes the water layer, thereby trapping the accretion heat and heating the surface to more than 6000 K. This causes the upper part of the mantle to melt and form a global magma ocean. Metal melt separates from silicate melt and sediments towards the bottom of the magma ocean; the gravitational energy released by the sedimentation leads to positive feedback where the beginning differentiation of the planet causes the whole mantle to melt and differentiate. All rocky planets thus naturally experience a magma ocean stage. We demonstrate that Earth’s small excess of182W (the decay product of182Hf) relative to the chondrites is consistent with such rapid core formation within 5 Myr followed by equilibration of the W reservoir in Earth’s mantle with182W-poor material from the core of a planetary-mass impactor, provided that the equilibration degree is at least 25–50%, depending on the initial Hf/W ratio. The planetary collision must have occurred at least 35 Myr after the main accretion phase of the terrestrial planets.

Probing gas kinematics towards the high-mass protostellar object G358.46−0.39

ABSTRACTWe investigated the nature of protostellar objects in G358.46−0.39 and their gas kinematics using ALMA data, with the aim of understanding the ongoing star formation activities in the region. The dust continuum map reveals multiple cores (MM1a, MM1b, MM1c, and MM2) dominated by MM1a, with no detectable free–free emission. We calculated the masses and the column densities of the various objects (MM1a, MM1b, MM1c, and MM2). A total of 33, 10, 10, and 9 molecular transitions are detected towards MM1a, MM1b, MM1c, and MM2, respectively. The differences in the number of molecular lines detected towards each of the cores support different excitation conditions at different positions. We derived the kinetic temperature ranges of MM1a, MM1b, MM1c, and MM2 to be ∼96–118, 96–114, 72–74, and 80–84 K, respectively. A highly collimated bipolar outflow traced by 12CO emission is observed to be associated with MM1a, with knots along the outflow lobes, which could be an indication of episodic ejection. The C17O emission is observed to be likely tracing a slowly rotating envelope of gas around MM1a. The velocity field map of CH3OH (22, 1 − 31, 2) emission suggests the presence of a rotating structure, possibly a disc. The physical and kinematic properties of MM1a are strong indication of a massive young stellar object, with ongoing outflow activity and accretion in its early stage of formation.

Kepler-102: Masses and Compositions for a Super-Earth and Sub-Neptune Orbiting an Active Star

Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the solar system. Kepler-102, which consists of five tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using RVs. Previous work found a high density for Kepler-102d, suggesting a composition similar to that of Mercury, while Kepler-102e was found to have a density typical of sub-Neptune size planets; however, Kepler-102 is an active star, which can interfere with RV mass measurements. To better measure the mass of these two planets, we obtained 111 new RVs using Keck/HIRES and Telescopio Nazionale Galileo/HARPS-N and modeled Kepler-102's activity using quasiperiodic Gaussian process regression. For Kepler-102d, we report a mass upper limit M d < 5.3 M ⊕ (95% confidence), a best-fit mass M d = 2.5 ± 1.4 M ⊕, and a density ρ d = 5.6 ± 3.2 g cm−3, which is consistent with a rocky composition similar in density to the Earth. For Kepler-102e we report a mass M e = 4.7 ± 1.7 M ⊕ and a density ρ e = 1.8 ± 0.7 g cm−3. These measurements suggest that Kepler-102e has a rocky core with a thick gaseous envelope comprising 2%–4% of the planet mass and 16%–50% of its radius. Our study is yet another demonstration that accounting for stellar activity in stars with clear rotation signals can yield more accurate planet masses, enabling a more realistic interpretation of planet interiors.

Compositional turbulence and layering in the gaseous envelopes of forming planets

ABSTRACT Differential settling and growth of dust grains impact the structure of the radiative envelopes of gaseous planets during formation. Sufficiently rapid dust growth can result in envelopes with substantially reduced opacities for radiation transport, thereby facilitating planet formation. We revisit the problem and establish that dust settling and grain growth also lead to outer planetary envelopes that are prone to compositional instabilities, by virtue of their inverted mean-molecular weight gradients. Under a variety of conditions, we find that the radiative envelopes of forming planets experience compositional turbulence driven by a semi-transparent version of the thermohaline instability (’fingering convection’). The standard double-diffusive thermohaline theory does not apply here and is replaced by a simplified first-principle treatment for the semitransparent regime of interest. The compositional turbulence seems efficient at mixing dust in the radiative envelopes of planets forming at super-au distances (say 5 au) from a Sun-like star, but not so at sub-au distances (say 0.2 au). We also address the possibility of compositional layering in this context. Distinct turbulent regimes for planetary envelopes growing at sub-au versus super-au distances could leave an imprint on the final planets formed.

A CHEOPS-enhanced view of the HD 3167 system

Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations.

The mass-radius relation of intermediate-mass planets outlined by hydrodynamic escape and thermal evolution

Context. Exoplanets in the mass range between Earth and Saturn show a wide spread in radius, and thus in density, for a given mass. Aims. We aim to understand to which extent the observed radius spread is affected by the specific planetary parameters at formation and by planetary atmospheric evolution. Methods. We employed planetary evolution modeling to reproduce the mass-radius (MR) distribution of the 199 planets that are detected so far whose mass and radius were measured to the ≤45% and ≤15% level, respectively, and that are less massive than 108 M⊕. We simultaneously accounted for atmospheric escape, based on the results of hydrodynamic simulations, and thermal evolution, based on planetary structure evolution models. Because high-energy stellar radiation affects atmospheric evolution, we accounted for the entire range of possible stellar rotation evolution histories. To set the planetary parameters at formation, we used analytical approximations based on formation models. Finally, we built a grid of synthetic planets with parameters reflecting those of the observed distribution. Results. The predicted radius spread reproduces the observed MR distribution well, except for two distinct groups of outliers (≈20% of the population). The first group consists of very close-in Saturn-mass planets with Jupiter-like radii for which our modeling under-predicts the radius, likely because it lacks additional (internal) heating similar to the heating that causes inflation in hot Jupiters. The second group consists of warm (~400–700 K) sub-Neptunes, which should host massive primordial hydrogen-dominated atmospheres, but instead present high densities indicative of small gaseous envelopes (&lt;1–2%). This suggests that their formation, internal structure, and evolution is different from that of atmospheric evolution through escape of hydrogen-dominated envelopes accreted onto rocky cores. The observed characteristics of low-mass planets (≤10–15 M⊕) strongly depend on the impact of atmospheric escape, and thus of the evolution of the host star's activity level, while primordial parameters are less relevant. Instead, the parameters at formation play the dominant role for more massive planets in shaping the final MR distribution. In general, the intrinsic spread in the evolution of the activity of the host stars can explain just about a quarter of the observed radius spread.

Effect of carbon and nitrogen diffusion zone on growth mechanism of boride layer produced on Q235 Steel

The purpose of this study was to indicate the effect of the presence of the carbon and nitrogen diffusion zone below the boride layers of Q235 low-carbon steel. The boride layers were produced by cathodic plasma electrolysis treatment (PET). Based on the results, the boride layer thickness on the treated samples at 260 V and 300 V varied from 10 μm to 22 μm. The XRD and GDOES analysis demonstrate that the boride layer on the treated samples mainly consists of single Fe 2 B phase, and the top loose layer mainly contain Fe 2 O 3 , Fe 3 C, Fe 4 N, and BN phases. The boride layers exhibited excellent scratch resistance compared to the bare Q235 steel. In addition, the plasma electron temperature was around 3000–4500 K, and the frequency spectra of acoustic signals were related to the voltage-time and current-time curves. At the high temperature and strong electric field, the decomposition reaction of electrolyte and the growth mechanism of the boride layers were discussed. Schematic of reactions in vapor gaseous envelope around the Q235 steel cathode during the plasma electrolysis process. • The boride layers on Q235 steel were produced by cathodic plasma electrolysis treatment. • The boride layers exhibited excellent scratch and adhesion resistance. • The OES and air acoustic spectra were measured. • Decomposition reactions of electrolyte and growth mechanism of boride layer were discussed.