Planet Engulfment Research Articles

Detailed Abundances of the Planet-hosting TOI-1173 A/B System: Possible Evidence of Planet Engulfment in a Very Wide Binary

Over the last decade, studies of large samples of binary systems have identified chemical anomalies and shown that they might be attributed to planet formation or planet engulfment. However, both scenarios have primarily been tested in pairs without known exoplanets. In this work, we explore these scenarios in the newly detected planet-hosting wide binary TOI-1173 A/B (projected separation ∼11,400 au), using high-resolution MAROON-X and ARCES spectra. We determined photospheric stellar parameters both by fitting stellar models and via the spectroscopic equilibrium approach. Both analyses agree and suggest that they are cool main-sequence stars located in the thin disk. A line-by-line differential analysis between the components (B−A) displays an abundance pattern in the condensation temperature plane, where the planet-hosting star TOI-1173 A is enhanced in refractory elements such as iron by more than 0.05 dex. This suggests the engulfment of ∼18 M ⊕ of rocky material in star A. Our hypothesis is supported by the dynamics of the system (detailed in our companion paper), which suggest that the super-Neptune TOI-1173 A b might have been delivered to its current short period (∼7 days) through circularization and von Zeipel–Lidov–Kozai mechanisms, thereby triggering the engulfment of inner rocky exoplanets.

The true nature of HE 0057-5959, the most metal-poor, Li-rich star

The Li-rich stars are a class of rare objects with a surface lithium abundance, A(Li), that exceeds that of other stars in the same evolutionary stage. The origin of these stars is still debated, and valuable routes to look at include the Cameron-Fowler mechanism, a mass-transfer process in a binary system, or the engulfment of rocky planets or brown dwarfs. Metal-poor ([Fe/H]<−1 dex) stars are only a small fraction of the entire population of Li-rich stars. We observed the metal-poor ([Fe/H]=−3.95±0.11 dex) giant star HE 0057–5959 with MIKE at the Magellan Telescope, deriving A(Li)NLTE=+2.09±0.07 dex. Such an Li abundance is significantly higher, by about 1 dex, than that of other stars at the same evolutionary stage. A previous analysis of the same target suggested that its high A(Li) reflects an ongoing first-dredge-up process. We revised the nature of HE 0057-5959 by comparing its stellar parameters and A(Li) with appropriate stellar evolution models describing Li depletion due to the deepening of the convective envelope. This comparison rules out that HE 0057-5959 is caught during its first dredge-up, the latter having already ended according to the parameters of this star. Its A(Li), remarkably higher than the typical lithium plateau drawn by similar giant stars, demonstrates that HE 0057-5959 joins the class of the rare metal-poor, Li-rich stars. HE 0057-5959 is the most metal-poor, Li-rich star discovered so far. We considered different scenarios to explain this star also comparing it with the other metal-poor, Li-rich stars. No internal mixing able to activate the Cameron-Fowler mechanism is known for metal-poor stars at this evolutionary stage. The engulfment of planets is also disfavoured because such metal-poor stars should not host planets. Finally, HE 0057-5959 is one of the most Na-rich among the Li-rich stars, and we found that a strong excess of Na abundance is common to all three Li-rich stars with [Fe/H]<–3 dex. This finding could support the scenario of mass transfer from a massive companion star (able to simultaneously produce large amounts of both elements) in a binary system, even if we found no evidence of radial velocity variations.

Revealing the Fate of Exoplanet Systems: Asteroseismic Identification of Host Star in the Red Clump or Red Giant Branch

Determining the evolutionary stage of stars is crucial for understanding the evolution of exoplanetary systems. In this context, red giant branch (RGB) and red clump (RC) stars, which formed at stages in the later evolution of stars situated before and after the helium flash, harbor critical clues to unveiling the evolution of planets. The first step in revealing these clues is to confirm the evolutionary stage of the host stars through asteroseismology. However, up to now, host stars confirmed to be RGB or RC stars are extremely rare. In this investigation, we present a comprehensive asteroseismic analysis of two evolved stars, HD 120084 and HD 29399, known to harbor exoplanets, using data from the Transiting Exoplanet Survey Satellite. We have discovered for the first time that HD 120084 is an RC star in the helium-core-burning phase, and confirmed that HD 29399 is an RGB star in the hydrogen-shell burning phase. Through the precise measurement of asteroseismic parameters such as νmax , Δν, and ΔΠ1, we have determined the evolutionary states of these stars and derived their fundamental stellar parameters. The significance of this study lies in the application of automated techniques to measure asymptotic period spacings in red giants, which provides critical insights into the evolutionary outcomes of exoplanet systems. We demonstrate that asteroseismology is a potent tool for probing the internal structures of stars, thereby offering a window into the past and future dynamics of planetary orbits. The presence of a long-period giant planet orbiting HD 120084, in particular, raises intriguing questions about the potential engulfment of inner planets during the host star’s expansion, a hypothesis that warrants further investigation.

An Earth-sized Planet on the Verge of Tidal Disruption

TOI-6255 b (GJ 4256) is an Earth-sized planet (1.079 ± 0.065 R ⊕) with an orbital period of only 5.7 hr. With the newly commissioned Keck Planet Finder and CARMENES spectrographs, we determine the planet’s mass to be 1.44 ± 0.14 M ⊕. The planet is just outside the Roche limit, with P orb/P Roche = 1.13 ± 0.10. The strong tidal force likely deforms the planet into a triaxial ellipsoid with a long axis that is ∼10% longer than the short axis. Assuming a reduced stellar tidal quality factor Q⋆′≈107 , we predict that tidal orbital decay will cause TOI-6255 to reach the Roche limit in roughly 400 Myr. Such tidal disruptions may produce the possible signatures of planet engulfment that have been seen on stars with anomalously high refractory elemental abundances compared to their conatal binary companions. TOI-6255 b is also a favorable target for searching for star–planet magnetic interactions, which might cause interior melting and hasten orbital decay. TOI-6255 b is a top target (with an Emission Spectroscopy Metric of about 24) for phase-curve observations with the James Webb Space Telescope.

At least one in a dozen stars shows evidence of planetary ingestion.

Stellar chemical compositions can be altered by ingestion of planetary material1,2 and/or planet formation, which removes refractory material from the protostellar disk3,4. These 'planet signatures' appear as correlations between elemental abundance differences and the dust condensation temperature3,5,6. Detecting these planet signatures, however, is challenging owing to unknown occurrence rates, small amplitudes and heterogeneous star samples with large differences in stellar ages7,8. Therefore, stars born together (that is, co-natal) with identical compositions can facilitate the detection of planet signatures. Although previous spectroscopic studies have been limited to a small number of binary stars9-13, the Gaia satellite14 provides opportunities for detecting stellar chemical signatures of planets among co-moving pairs of stars confirmed to be co-natal15,16. Here we report high-precision chemical abundances for a homogeneous sample of ninety-one co-natal pairs of stars with a well defined selection function and identify at least seven instances of planetary ingestion, corresponding to an occurrence rate of eight per cent. An independent Bayesian indicator is deployed, which can effectively disentangle the planet signatures from other factors, such as random abundance variation and atomic diffusion17. Our study provides evidence of planet signatures and facilitates a deeper understanding of the star-planet-chemistry connection by providing observational constraints on the mechanisms of planet engulfment, formation and evolution.

A long-term study of the magnetic field and activity in the M giant RZ Ari

Aims. We present a detailed long-term study of the single M6 III giant RZ Ari to obtain direct and simultaneous measurements of the magnetic field, activity indicators, and radial velocity in order to infer the origin of its activity. We study its magnetic activity in the context of stellar evolution, and for this purpose, we also refined its evolutionary status and Li abundance. In general, for the M giants, little is known about the properties of the magnetic activity and its causes. RZ Ari possess the strongest surface magnetic field of the known Zeeman-detected M giants and is bright enough to allow a deep study of its surface magnetic structure. The results are expected to shed light on the activity mechanism in these stars. Methods. We used the spectropolarimeter Narval at the Télescope Bernard Lyot (Observatoire du Pic du Midi, France) to obtain a series of Stokes I and Stokes V profiles for RZ Ari. Using the least-squares deconvolution technique, we were able to detect the Zeeman signature of the magnetic field. We measured its longitudinal component by means of the averaged Stokes V and Stokes I profiles. In addition, we also applied Zeeman-Doppler imaging (ZDI) to search for the rotation period of the star, and we constructed a tentative magnetic map. It is the first magnetic map for a star that evolved at the tip of red giant branch (RGB) or even on the asymptotic giant branch (AGB). The spectra also allowed us to monitor chromospheric emission lines, which are well-known indicators of stellar magnetic activity. From the observations obtained between September 2010 and August 2019, we studied the variability of the magnetic field of RZ Ari. We also redetermined the initial mass and evolutionary status of this star based on current stellar evolutionary tracks and on the angular diameter measured from CHARA interferometry. Results. Our results point to an initial mass of 1.5 M⊙ so that this giant is more likely an early-AGB star, but a lotaction at the tip of the RGB is not completely excluded. With a v sin i of 6.0 ±0.5 km s−1, the upper limit for the rotation period is found to be 909 days. On the basis of our dataset and AAVSO photometric data, we determined periods longer than 1100 days for the magnetic field and photometric variability, and 704 days for the spectral line activity indicators. The rotation period determined on the basis of the Stokes V profiles variability is 530 days. A similar period of 544 days is also found for the photometric data. When we take this rotation period and the convective turnover time into account, an effective action of an α-ω-type dynamo seems to be unlikely, but other types of dynamo could be operating there. The star appears to lie outside the two magnetic strips on the giant branches, where the α-ω-type dynamo is expected to operate effectively, and it also has a much higher lithium content than the evolutionary model predicts. These facts suggest that a planet engulfment could speed up its rotation and trigger dynamo-driven magnetic activity. On the other hand, the period of more than 1100 days cannot be explained by rotational modulation and could be explained by the lifetime of large convective structures. The absence of linear polarization at the time the magnetic field was detected, however, suggests that a local dynamo probably does not contribute significantly to the magnetic field, at least for that time interval.

Planet-driven scatterings of planetesimals into a star: probability, time-scale, and applications

ABSTRACT A planetary system can undergo multiple episodes of intense dynamical activities throughout its life, resulting in the production of star-grazing planetesimals (or exocomets) and pollution of the host star. Such activity is especially pronounced when giant planets interact with other small bodies during the system’s evolution. However, due to the chaotic nature of the dynamics, it is difficult to determine the properties of the perturbing planet(s) from the observed planetesimal-disruption activities. In this study, we examine the outcomes of planetesimal-planet scatterings in a general setting. We focus on one-planet systems, and determine the likelihood and time-scale of planetesimal disruption by the host star as a function of the planet properties. We obtain a new analytical expression for the minimum distance a scattering body can reach, extending previous results by considering finite planet eccentricity and non-zero planetesimal mass. Through N-body simulations, we derive the distribution of minimum distances and the likelihood and time-scales of three possible outcomes of planetesimal-planet scatterings: collision with the planet, ejection, and disruption by the star. For planetesimals with negligible mass, we identify four defining dimensionless parameters (the planet eccentricity, planet-to-star mass ratio, planet radius to semimajor axis ratio, and the stellar disruption radius to planet semimajor axis ratio) that enable us to scale the problem and generalize our findings to a wide range of orbital configurations. Using these results, we explore three applications: falling evaporating bodies in the β Pictoris system, white dwarf pollution due to planetesimal disruption and planet engulfment by main-sequence stars.

Metrics for Optimizing Searches for Tidally Decaying Exoplanets

Tidal interactions between short-period exoplanets and their host stars drive orbital decay and have likely led to engulfment of planets by their stars. Precise transit timing surveys, with baselines now spanning decades for some planets, are directly detecting orbital decay for a handful of planets, with corroboration for planetary engulfment coming from independent lines of evidence. More than that, recent observations have perhaps even caught the moment of engulfment for one unfortunate planet. These portentous signs bolster prospects for ongoing surveys, but optimizing such a survey requires considering the astrophysical parameters that give rise to robust timing constraints and large tidal decay rates, as well as how best to schedule observations conducted over many years. The large number of possible targets means it is not feasible to continually observe all planets that might exhibit detectable tidal decay. In this study, we explore astrophysical and observational properties for a short-period exoplanet system that can maximize the likelihood for observing tidally driven transit timing variations. We consider several fiducial observational strategies and real exoplanet systems reported to exhibit decay. We show that moderately frequent (a few transits per year) observations may suffice to detect tidal decay within just a few years. Tidally driven timing variations take time to grow to detectable levels, so we estimate how long that growth takes as a function of timing uncertainties and tidal decay rate and provide thresholds for deciding that tidal decay has been detected.

An alternative formation scenario for uranium-rich giants: engulfing an Earth-like planet

ABSTRACT The actinides, such as the uranium (U) element, are typically synthesized through the rapid neutron-capture process (r-process), which can occur in core-collapse supernovae or double neutron star mergers. There exist nine r-process giant stars exhibiting conspicuous U abundances, commonly referred to as U-rich giants. However, the origins of these U-rich giants remain ambiguous. We propose an alternative formation scenario for these U-rich giants whereby a red giant (RG) engulfs an Earth-like planet. To approximate the process of an RG engulfing an Earth-like planet, we employ an accretion model wherein the RG assimilates materials from said planet. Our findings demonstrate that this engulfment event can considerably enhance the presence of heavy elements originating from Earth-like planets on the surfaces of very metal-poor stars (Z = 0.00001), while its impact on solar-metallicity stars is comparatively modest. Importantly, the structural and evolutionary properties of both very metal-poor and solar-metallicity stars remain largely unaffected. Notably, our engulfment model effectively accounts for the observed U abundances in known U-rich giants. Furthermore, the evolutionary trajectories of U abundances on the surfaces of RGs subsequent to the engulfment of Earth-like planets encompass all known U-rich giants. Therefore, it is plausible that U-rich giants are formed when an RG engulfs an Earth-like planet.

WIYN Open Cluster Study 89. M48 (NGC 2548) 2: Lithium Abundances in the 420 Myr Open Cluster M48 from Giants through K Dwarfs* * The WIYN Observatory is a joint facility of the University of Wisconsin−Madison, Indiana University, the National Optical Astronomy Observatory, and the University of Missouri. † †WIYN Open Cluster Study, Mathieu ().

We consider WIYN/Hydra spectra of 329 photometric candidate members of the 420 Myr old open cluster M48 and report lithium detections or upper limits for 234 members and likely members. The 171 single members define a number of notable Li-mass trends, some delineated even more clearly than in Hyades/Praesepe: the giants are consistent with subgiant Li dilution and prior MS Li depletion due to rotational mixing. A dwarfs (8600–7700 K) have upper limits higher than the presumed initial cluster Li abundance. Two of five late A dwarfs (7700–7200 K) are Li-rich, possibly due to diffusion, planetesimal accretion, and/or engulfment of hydrogen-poor planets. Early F dwarfs already show evidence of Li depletion seen in older clusters. The Li–T eff trends of the Li Dip (6675–6200 K), Li Plateau (6200–6000 K), and G and K dwarfs (6000–4000 K) are very clearly delineated and are intermediate to those of the 120 Myr old Pleiades and 650 Myr old Hyades/Praesepe, which suggests a sequence of Li depletion with age. The cool side of the Li Dip is especially well defined with little scatter. The Li–T eff trend is very tight in the Li Plateau and early G dwarfs, but scatter increases gradually for cooler dwarfs. These patterns support and constrain models of the universally dominant Li depletion mechanism for FGK dwarfs, namely rotational mixing due to angular momentum loss; we discuss how diffusion and gravity-wave-driven mixing may also play roles. For late G/K dwarfs, faster rotators show higher Li than slower rotators, and we discuss possible connections between angular momentum loss and Li depletion.

Giant Planet Engulfment by Evolved Giant Stars: Light Curves, Asteroseismology, and Survivability

About ten percent of Sun-like (1–2 M ⊙) stars will engulf a 1–10 M J planet as they expand during the red giant branch (RGB) or asymptotic giant branch (AGB) phase of their evolution. Once engulfed, these planets experience a strong drag force in the star’s convective envelope and spiral inward, depositing energy and angular momentum. For these mass ratios, the inspiral takes ∼10–102 yr (∼102–103 orbits); the planet undergoes tidal disruption at a radius of ∼1 R ⊙. We use the Modules for Experiments in Stellar Astrophysics (MESA) software instrument to track the stellar response to the energy deposition while simultaneously evolving the planetary orbit. For RGB stars, as well as AGB stars with M p ≲ 5 M J planets, the star responds quasi-statically but still brightens measurably on a timescale of years. In addition, asteroseismic indicators, such as the frequency spacing or rotational splitting, differ before and after engulfment. For AGB stars, engulfment of an M p ≳ 5 M J planet drives supersonic expansion of the envelope, causing a bright, red, dusty eruption similar to a “luminous red nova.” Based on the peak luminosity, color, duration, and expected rate of these events, we suggest that engulfment events on the AGB could be a significant fraction of low-luminosity red novae in the Galaxy. We do not find conditions where the envelope is ejected prior to the planet’s tidal disruption, complicating the interpretation of short-period giant planets orbiting white dwarfs as survivors of common envelope evolution.

Planet engulfment detections are rare according to observations and stellar modelling

ABSTRACTDynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere abundance pattern will reflect accretion of rocky material from planets. Multistar systems are excellent environments to search for such abundance trends because stellar companions form from the same natal gas cloud and are thus expected to share primordial chemical compositions to within 0.03–0.05 dex. Abundance measurements have occasionally yielded rocky enhancements, but a few observations targeted known planetary systems. To address this gap, we carried out a Keck-HIRES survey of 36 multistar systems, where at least one star is a known planet host. We found that only HAT-P-4 exhibits an abundance pattern suggestive of engulfment but is more likely primordial based on its large projected separation (30 000 ± 140 au) that exceeds typical turbulence scales in molecular clouds. To understand the lack of engulfment detections among our systems, we quantified the strength and duration of refractory enrichments in stellar photospheres using mesa stellar models. We found that observable signatures from 10 M⊕ engulfment events last for ∼90 Myr in 1 M⊙ stars. Signatures are largest and longest lived for 1.1–1.2 M⊙ stars, but are no longer observable ∼2 Gyr post-engulfment. This indicates that engulfment will rarely be detected in systems that are several Gyr old.

Occurrence rate of hot Jupiters orbiting red giant stars

Context. Hot Jupiters form an enigmatic class of object whose formation pathways are not yet clear. Determining their occurrence rates as a function of orbit, planet and stellar mass, and system age can be an important ingredient for understanding how they form. To date, various hot Jupiters have been discovered orbiting red giant stars, and deriving their incidence would be highly interesting. Aims. In this study our aim is to determine the number of hot Jupiters in a well-defined sample of red giants, estimate their occurrence rate, and compare it with that for A-, F-, and G-type stars. Methods. A sample of 14474 red giant stars, with estimated radii between 2 and 5 R⊙, was selected using Gaia to coincide with observations by the NASA TESS mission. Subsequently, the TESS light curves were searched for transits from hot Jupiters. The detection efficiency was determined using injected signals, and the results further corrected for the geometric transit probability to estimate the occurrence rate. Results. Three previously confirmed hot Jupiters were found in the TESS data, in addition to one other TESS object of interest, and two M-dwarf companions. This results in an occurrence rate of 0.37−0.09+0.29%. Due to the still large uncertainties, this cannot be distinguished from that of A-, F-, and G-type stars. We argue that it is unlikely that planet engulfment in expanding red giants plays an important role in this sample.

Evidence of extra mixing in field giants as traced by the lithium and carbon isotope ratio

Context.Although not predicted by standard stellar evolution, the surface abundance of light elements, such as lithium (Li), carbon, and nitrogen, changes during the red giant branch (RGB) as a result of extra mixing. This is usually associated with thermohaline mixing acting after the RGB bump. Peculiar Li-enriched RGB stars might also be related to either enhanced mixing or pollution from external sources.Aims.We measure the Li abundance and carbon isotopic ratio12C/13C in a sample of 166 field red giants with −0.3 ≤ [Fe/H] ≤ 0.2, targeted by the EXPRESS radial velocity program to analyze the effects of extra mixing.Methods.We measured the abundances with spectral synthesis using high-quality spectra. Multiple-epoch observations needed for exoplanet detection were used to decrease the effects of telluric contamination in12C/13C measurements.Results.Due to the prevalence of upper limits, the Li abundance pattern is complicated to interpret, but the comparison between RGB and core He-burning giants shows effects of mixing consistent with thermohaline. The most Li-enriched giant in the sample, classified as a RGB star close to the RGB bump, has low12C/13C. Given that the12C/13C should not be affected by planet engulfment, this does not seem to be the source of the high Li. There is a decreasing correlation between mass and12C/13C in the RGB and an increasing correlation in the horizontal branch, which, once again, is consistent with thermohaline mixing. Our data also show a correlation between12C/13C and [Fe/H]. There is no evident impact of binarity either on Li or on12C/13C.Conclusions.Our sample shows behavior consistent with additional mixing acting after the RGB bump. The12C/13C adds new clues which can be used to describe extra mixing, and it could well be the best tool to study mixing in giants. Additional measurements of12C/13C in field stars would greatly improve our ability to compare data with models and understand mixing mechanisms.

Planet engulfment signatures in twin stars

ABSTRACT Planet engulfment can be inferred from enhancement of refractory elements in the photosphere of the engulfing star following accretion of rocky planetary material. Such refractory enrichments are subject to stellar interior mixing processes, namely thermohaline mixing induced by an inverse mean-molecular-weight gradient between the convective envelope and radiative core. Using mesa stellar models, we quantified the strength and duration of engulfment signatures following planet engulfment. We found that thermohaline mixing dominates during the first ∼5–45 Myr post-engulfment, weakening signatures by a factor of ∼2 before giving way to depletion via gravitational settling on longer time-scales. Solar metallicity stars in the 0.5–1.2 M⊙ mass range have observable signature time-scales of ∼1 Myr–8 Gyr, depending on the engulfing star mass and amount of material engulfed. Early type stars exhibit larger initial refractory enhancements but more rapid depletion. Solar-like stars (M = 0.9–1.1 M⊙) maintain observable signatures (>0.05 dex) over time-scales of ∼20 Myr–1.7 Gyr for nominal 10 M⊕ engulfment events, with longer-lived signatures occurring for low-metallicity and/or hotter stars (1 M⊙, ∼2–3 Gyr). Engulfment events occurring well after the zero-age main sequence produce larger signals due to suppression of thermohaline mixing by gravitational settling of helium (1 M⊙, ∼1.5 Gyr). These results indicate that it may be difficult to observe engulfment signatures in solar-like stars that are several Gyr old.

Detecting weak beryllium lines with CUBES

Beryllium is a light element with one single stable isotope, 9Be, which is a pure product of cosmic-ray spallation in the interstellar medium. Beryllium abundances in late-type stars can be used in studies about evolutionary mixing, Galactic chemical evolution, planet engulfment, and the formation of globular clusters. Some of these uses of Be abundances figure among the science cases of the Cassegrain U-Band Efficient Spectrograph (CUBES), a new near-UV low- and medium-resolution spectrograph under development for the Very Large Telescope. Here, we report on a study about beryllium abundances in extremely metal-poor stars in the context of the phase A of CUBES. Our motivation is to understand the limits for the detection of weak lines in extremely metal-poor stars of low Be abundances. We analyze simulated CUBES observations, performed in medium-resolution mode, based on synthetic spectra for four mock stars with [Fe/H] \leq -3.0. We find that detecting the Be lines is possible in certain cases, but is very challenging and requires high signal-to-noise ratio. Depending on the atmospheric parameters of the target stars, and if signal-to-noise per pixel of about 400 can be achieved, it should be possible to detect Be abundances between log(Be/H) = -13.1 and -13.6, with a typical uncertainty of \pm 0.15 dex. Using CUBES, the required data for such studies can be obtained for stars that are fainter by two magnitudes with respect to what is possible with current instrumentation.

Detailed Abundances of Planet-hosting Open Clusters. The Praesepe (Beehive) Cluster*

Abstract It is not yet fully understood how planet formation affects the properties of host stars, in or out of a cluster; however, abundance trends can help us understand this process. We present a detailed chemical abundance analysis of six stars in Praesepe, a planet-hosting open cluster. Pr0201 is known to host a close-in (period of 4.4 days) giant planet (mass of 0.54 M J), while the other five cluster members in our sample (Pr0133, Pr0081, Pr0208, Pr0051, and Pr0076) have no detected planets according to measurements of radial velocity. Using high-resolution echelle spectra with high signal-to-noise ratio obtained with Keck/HIRES and a novel approach to measurements of equivalent width (XSpect-EW), we derived abundances of up to 20 elements spanning a range of condensation temperatures (T C). We find a mean cluster metallicity of [Fe/H] = +0.21 ± 0.02 dex, in agreement with most previous determinations. We find most of our elements show an [X/Fe] scatter of ∼0.02–0.03 dex and conclude that our stellar sample is chemically homogeneous. The T C slope for the cluster mean abundances is consistent with zero and none of the stars in our sample exhibit individually a statistically significant T C slope. Using a planet engulfment model, we find that the planet host, Pr0201, shows no evidence of significant enrichment in its refractory elements when compared to the cluster mean that would be consistent with a planetary accretion scenario.

Chemical evidence for planetary ingestion in a quarter of Sun-like stars

Stellar members of binary systems are formed from the same material, therefore they should be chemically identical. However, recent high-precision studies have unveiled chemical differences between the two members of binary pairs composed by Sun-like stars. The very existence of these chemically inhomogeneous binaries represents one of the most contradictory examples in stellar astrophysics and source of tension between theory and observations. It is still unclear whether the abundance variations are the result of chemical inhomogeneities in the protostellar gas clouds or instead if they are due to planet engulfment events occurred after the stellar formation. While the former scenario would undermine the belief that the chemical makeup of a star provides the fossil information of the environment where it formed, a key assumption made by several studies of our Galaxy, the second scenario would shed light on the possible evolutionary paths of planetary systems. Here, we perform a statistical study on 107 binary systems composed by Sun-like stars to provide - for the first time - unambiguous evidence in favour of the planet engulfment scenario. We also establish that planet engulfment events occur in stars similar to our own Sun with a probability ranging between 20 and 35$\%$. This implies that a significant fraction of planetary systems undergo very dynamical evolutionary paths that can critically modify their architectures, unlike our Solar System which has preserved its planets on nearly circular orbits. This study also opens to the possibility of using chemical abundances of stars to identify which ones are the most likely to host analogues of the calm Solar System.

3D NLTE spectral line formation of lithium in late-type stars.

Accurately known stellar lithium abundances may be used to shed light on a variety of astrophysical phenomena such as big bang nucleosynthesis, radial migration, ages of stars and stellar clusters, and planet engulfment events. We present a grid of synthetic lithium spectra that are computed in non-local thermodynamic equilibrium (NLTE) across the stagger grid of three-dimensional (3D) hydrodynamic stellar atmosphere models. This grid covers three Li lines at 610.4, 670.8, and 812.6 nm for stellar parameters representative of FGK-type dwarfs and giants, spanning T eff = 4000-7000 K, log g = 1.5-5.0, [Formula: see text]-0.5, and A(Li) = -0.5-4.0. We find that our abundance corrections are up to 0.15 dex more negative than in previous work, due to a previously overlooked NLTE effect of blocking of UV lithium lines by background opacities, which has important implications for a wide range of science cases. We derive a new 3D NLTE solar abundance of A(Li) = 0.96±0.05, which is 0.09 dex lower than the commonly used value. We make our grids of synthetic spectra and abundance corrections publicly available through the breidablik package. This package includes methods for accurately interpolating our grid to arbitrary stellar parameters through methods based on Kriging (Gaussian process regression) for line profiles, and multilayer perceptrons (a class of fully connected feedforward neural networks) for NLTE corrections and 3D NLTE abundances from equivalent widths, achieving interpolation errors of the order of 0.01 dex.

The influence of planetary engulfment on stellar rotation in metal-poor main-sequence stars

Context. The method of gyrochronology relates the age of its star to its rotation period. However, recent evidence of deviations from gyrochronology relations has been reported in the literature. Aims. We study the influence of tidal interaction between a star and its companion on the rotation velocity of the star to explain peculiar stellar rotation velocities. Methods. We followed the interaction of a star and its planet using a comprehensive numerical framework that combines tidal friction, magnetic braking, planet migration, and detailed stellar evolution models from the GARSTEC grid. We focus on close-in companions from 1 to 20 MJup orbiting low-mass (0.8 − 1 M⊙) main-sequence stars with a broad metallicity of [Fe/H] = − 1 up to solar. Results. Our simulations suggest that the dynamical interaction between a star and its companion can have different outcomes that depend on the initial semi-major axis and the mass of the planet, as well as on the mass and metallicity of its host star. In most cases, especially in the case of planet engulfment, we find a catastrophic increase in stellar rotation velocity from 1 kms−1 to over 40 kms−1 while the star is still on the main-sequence. The main prediction of our model is that low-mass main-sequence stars with abnormal rotation velocities should be more common at low-metallicity, as lower [Fe/H] favours faster planet engulfment, based on the assumption that the occurrence rate of close-in massive planets is similar at all metallicities. Conclusions. Our scenario explains peculiar rotation velocities of low-mass main-sequence stars by the tidal interaction between the star and its companion. Current observational samples are too narrow and incomplete, and, thus, they are not sufficient for our model to be tested.