Parent Star Research Articles

Effect of Some Modified Models of Gravity on the Radial Velocity of Binary Systems

For many classes of astronomical and astrophysical binary systems, long observational records of their radial velocity V, which is their directly observable quantity, are available. For exoplanets close to their parent stars, they cover several full orbital revolutions, while for wide binaries such as, e.g., the Proxima/α Centauri AB system, only relatively short orbital arcs are sampled by existing radial velocity measurements. Here, the changes ΔV induced on a binary’s radial velocity by some long-range modified models of gravity are analytically calculated. In particular, extra-potentials proportional to r−N,N=2,3 and r2 are considered; the Cosmological Constant Λ belongs to the latter group. Both the net shift per orbit and the instantaneous one are explicitly calculated for each model. The Cosmological Constant induces a shift in the radial velocity of the Proxima/α Centauri AB binary as little as ΔV≲10−7ms−1, while the present-day accuracy in measuring its radial velocity is σV≃30ms−1. The calculational scheme presented here is quite general, and can be straightforwardly extended to any other modified gravity.

The Galactic underworld: the spatial distribution of compact remnants

ABSTRACT We chart the expected Galactic distribution of neutron stars and black holes. These compact remnants of dead stars – the Galactic underworld – are found to exhibit a fundamentally different distribution and structure to the visible Galaxy. Compared to the visible Galaxy, concentration into a thin flattened disc structure is much less evident with the scale height more than tripling to 1260 ± 30 pc. This difference arises from two primary causes. First, the distribution is in part inherited from the integration over the evolving structure of the Galaxy itself (and hence the changing distribution of the parent stars). Secondly, an even larger effect arises from the natal kick received by the remnant at the event of its supernova birth. Due to this kick we find 30 per cent of remnants have sufficient kinetic energy to entirely escape the Galactic potential (40 per cent of neutron stars and 2 per cent of black holes) leading to a Galactic mass-loss integrated to the present day of $\sim 0.4{{\ \rm per\ cent}}$ of the stellar mass of the Galaxy. The black hole – neutron star fraction increases near the Galactic centre: a consequence of smaller kick velocities in the former. Our simulated remnant distribution yields probable distances of 19 and 21 pc to the nearest neutron star and black hole, respectively, while our nearest probable magnetar lies at 4.2 kpc. Although the underworld only contains of order $\sim 1{{\ \rm per\ cent}}$ of the Galaxy’s mass, observational signatures and physical traces of its population, such as microlensing, will become increasingly present in data ranging from gravitational wave detectors to high precision surveys from space missions such as Gaia.

The GAPS Programme at TNG

Context. The measurement of the spin-orbit alignment of hot Jupiters, including a range of orbital and physical properties, can provide information about the evolution of the orbits of this special class of giant planets. Aims. We aim to refine the orbital and physical parameters and determine the sky-projected planet orbital obliquity λ of five eccentric (e ≅ 0.1–0.3) transiting planetary systems: HAT-P-15, HAT-P-17, HAT-P-21, HAT-P-26, and HAT-P-29, whose parent stars have an effective temperature between 5100 K < Teff < 6200 K. Each of the systems hosts a hot Jupiter, except for HAT-P-26, which hosts a Neptune-mass planet. Methods. We observed transit events of these planets with the HARPS-N spectrograph, obtaining high-precision radial velocity measurements that allow us to measure the Rossiter–McLaughlin effect for each of the target systems. We used these new HARPS-N spectra and archival data, including those from Gaia, to better characterise the stellar atmospheric parameters. The photometric parameters for four of the hot Jupiters were recalculated using 17 new transit light curves, obtained with an array of medium-class telescopes, and data from the TESS space telescope. HATNet time-series photometric data were checked for the signatures of rotation periods of the target stars and their spin axis inclination. Results. From the analysis of the Rossiter-McLaughlin effect, we derived a sky-projected obliquity of λ = 13° ± 6°, λ = −26.3° ± 6.7°, λ = −0.7° ± 12.5°, λ = −26° ± 16°, for HAT-P-15 b, HAT-P-17 b, HAT-P-21 b, and HAT-P-29 b, respectively. Based on theoretical considerations, these small values of λ should be of primordial origin, with the possible exception of HAT-P-21. Due to the quality of the data, we were not able to fully constrain λ for HAT-P-26 b, although a prograde orbit is favoured (λ = 18° ± 49°). The stellar activity of HAT-P-21 indicates a rotation period of 15.88 ± 0.02 days, which allowed us to determine its true misalignment angle ψ = 25° ± 16°. Our new analysis of the physical parameters of the five exoplanetary systems returned values compatible with those existing in the literature. Using TESS and the available transit light curves, we reviewed the orbital ephemeris for the five systems and confirmed that the HAT-P-26 system shows transit timing variations, which may tentatively be attributed to the presence of a third body.

HORuS transmission spectroscopy and revised planetary parameters of KELT-7 b

ABSTRACT We report on the high-resolution spectroscopic observations of two planetary transits of the hot Jupiter KELT-7b (Mp = 1.28 ± 0.17MJup, Teq = 2028 K) observed with the High Optical Resolution Spectrograph (HORuS) mounted on the 10.4-m Gran Telescopio Canarias (GTC). A new set of stellar parameters are obtained for the rapidly rotating parent star from the analysis of the spectra. Using the newly derived stellar mass and radius, and the planetary transit data of the Transiting Exoplanet Survey Satellite (TESS) together with the HORuS velocities and the photometric and spectroscopic data available in the literature, we update and improve the ephemeris of KELT-7b. Our results indicate that KELT-7 has an angle λ = −10.55 ± 0.27 deg between the sky projections of the star’s spin axis and the planet’s orbital axis. By combining this angle and our newly derived stellar rotation period of 1.38 ± 0.05 d, we obtained a 3D obliquity ψ = 12.4 ± 11.7 deg (or 167.6 deg), thus reinforcing that KELT-7 is a well-aligned planetary system. We search for the presence of Hα, Li i, Na i, Mg i, and Ca ii features in the transmission spectrum of KELT-7b but we are only able to determine upper limits of 0.08–1.4 per cent on their presence after accounting for the contribution of the stellar variability to the extracted planetary spectrum. We also discuss the impact of stellar variability on the planetary data. Our results reinforce the importance of monitoring the parent star when performing high-resolution transmission spectroscopy of the planetary atmosphere in the presence of stellar activity.

Discovery of an optical cocoon tail behind the runaway HD 185806

ABSTRACT Studies on the circumstellar structures around evolved stars provide vital information on the evolution of the parent star and the properties of the local interstellar medium. In this work, we present the discovery and characterization of an optical cocoon tail behind the star HD 185806. The cocoon apex emission is puzzling, as it is detected in the infrared but shows no signal in the optical wavelength. The H α and [O iii] fluxes of the nebular structure vary from 2.7 to 8.5 × 10−12 erg s−1 cm−2 and from 0.9 to 7.0 × 10−13 erg s−1 cm−2, respectively. Through high-resolution spectroscopy, we derive the spectral type of the star, construct the position–velocity diagrams of the cocoon tail for the H α, [O iii], and [N ii] emission lines, and determine its velocity in the range of −100–40 km s−1. Furthermore, we use SED fitting and mesa evolutionary models adopting a distance of 900 pc, and classify HD 185806 as a 1.3 M⊙ star, in the transition phase between the RGB and early AGB stages. Finally, we study the morpho-kinematic structure of the cocoon tail using the astronomical software SHAPE. An ellipsoidal structure, with an inclination of ∼19° with respect to the plane of sky is found to better reproduce the observed cocoon tail of HD 185806.

The impact of two non-transiting planets and stellar activity on mass determinations for the super-Earth CoRoT-7b

ABSTRACT CoRoT-7 is an active star, whose orbiting planets and their masses have been under debate since their initial detection. In the previous studies, CoRoT-7 was found to have two planets, CoRoT-7b and CoRoT-7c with orbital periods 0.85 and 3.69 d, and a potential third planet with a period ∼9 d. The existence of the third planet has been questioned later as potentially being an activity-induced artefact. Moreover, mass of the transiting planet CoRoT-7b has been estimated to have widely different values owing to the activity level of the parent star, the consequent RV ‘jitter’, and the methods used to rectify this ambiguity. Here. we present an analysis of the HARPS archival RV (RV) data of CoRoT-7 using a new wavelength-domain technique, scalpels, to correct for the stellar activity-induced spectral line-shape changes. Simultaneous modelling of stellar activity and orbital motions, identified using the ℓ1- periodogram, shows that scalpels effectively reduce the contribution of stellar variability to the RV signal and enhance the detectability of exoplanets around active stars. Using kima nested-sampling package (Faria et al.), we modelled the system incorporating a Gaussian Process together with scalpels. The resultant posterior distributions favoured a three-planet system comprising two non-transiting planets, CoRoT-7c and CoRoT-7d with orbital periods 3.697 ± 0.005 and 8.966 ± 1.546 d, in addition to the known transiting planet. The transiting planet CoRoT-7b is found to be a rocky super-Earth with a mass of Mb = 6.06 ± 0.65M⊕. The determined masses of Mc = 13.29 ± 0.69M⊕ and Md = 17.14 ± 2.55M⊕ suggest the non-transiting planets CoRoT-7c and CoRoT-7d to be structurally similar to Uranus and Neptune.

Computed Physical Characteristics of the HD 158259 ‎Planetary System‎: ‎Semi-Major Axis‎, Orbital Period, and the ‎Triads Resonance of Successive ‎Planets

HD 158259 (or HIP 85268) is one of the members of the main sequence in G0 group stars located approximately at 88 ‎light-‎years away in the constellation Draco, discussed with respect to the solar system. HD 158259 was discovered by the ‎SOPHIE ‎échelle spectrograph using the radial velocity method. This system includes five confirmed planets orbiting HD ‎‎158259, ‎together with one unconfirmed planet. The planets orbit in a near 2/3 (or 3:2) orbital resonance. Starting from the innermost ‎pairing, the period ratios are with the period ratios ‎‎1.5757, 1.5146, 1.5296, 1.5128, and 1.4482, respectively, starting from the ‎innermost pairing. Here we theoretically investigate the HD ‎‎158259 system for the Semi-major axis, planet's mass, star ‎luminosity, ‎ inner,‎‏ ‏ ‏center, outer, and ∆(HZ) habitable zone. We account for radial ‎velocity amplitude, planet density, and ‎Laplace’s resonance, theoretically. The existing possibility of the sixth and undetected ‎planet (HD 158259 g) was also ‎investigated. The orbital period and semi-major axis of this planet, computed with 0.047726 years (17.420 ‎days) and 0.135 ‎AU respectively, with 𝑅2 = 0.9964. The radial velocity amplitude of this new and undetected planet was ‎computed to be about ‎‎1.625 km/s. The mass of planets in terms of Solar, Jupiter, and Earth have shown direct direct proportional ‎relation with an ‎approximate increase in their semi-major axis. The lowest mass is closest to the star and the highest mass is farthest from the star. We ‎compare the habitability zone to that of NASA, Kopparapu et.al, and the original Kopparapu estimate. The application of the relative mean motion ration (RMMR) for resonance in the triads of successive planets showed that the mode of RMMR is ‎approximately ‎2/3 (or 3:2) orbital resonance, with the calculated period ratios shown above. we have also calculated the planetary ‎equilibrium temperature (PET) in terms of the size, temperature, Albedo and distance planet to its parent star.‎

The Great Planetary Heist: theft and capture in star-forming regions

ABSTRACT Gravitational interactions in star-forming regions are capable of disrupting and destroying planetary systems, as well as creating new ones. In particular, a planet can be stolen, where it is directly exchanged between passing stars during an interaction; or captured, where a planet is first ejected from its birth system and is free-floating for a period of time, before being captured by a passing star. We perform sets of direct N-body simulations of young, substructured star-forming regions, and follow their evolution for 10 Myr in order to determine how many planets are stolen and captured, and their respective orbital properties. We show that in high-density star-forming regions, stolen and captured planets have distinct properties. The semimajor axis distribution of captured planets is significantly skewed to wider orbits compared to the semimajor axis distribution of stolen planets and planets that are still orbiting their parent star (preserved planets). However, the eccentricity and inclination distributions of captured and stolen planets are similar, but in turn very different to the inclination and eccentricity distributions of preserved planets. In low-density star-forming regions these differences are not as distinct but could still, in principle, be used to determine whether observed exoplanets have likely formed in situ or have been stolen or captured. We find that the initial degree of spatial and kinematic substructure in a star-forming region is as important a factor as the stellar density in determining whether a planetary system will be altered, disrupted, captured, or stolen.

Analysis of circular gratings as image plane coronagraph filters

Coronagraphy is an efficient technique for identifying and characterizing extra-solar planets orbiting in the habitable zone of their parent star. An important family of coronagraphs is based on amplitude or phase filters placed at an intermediate image plane of the optical system, spreading starlight outside of the so-called “Lyot stop” located at the exit pupil plane of the instrument. This article explores the potential of circular amplitude and phase gratings employed as image plane coronagraph filters. It presents a theoretical analysis of the simplest case of an amplitude circular grating and introduces an inversion paradigm with respect to classical Lyot coronagraph, by exchanging its image and pupil masks. Various types of circular gratings are considered and their performance is evaluated with the help of numerical simulations. The most promising solutions are presented and discussed. The main conclusion is that high attenuation ratios of the parent star are feasible, provided that the system is properly optimized with a Lyot stop especially tailored to the grating filter.

The formation of discs in the interior of AGB stars from the tidal disruption of planets and brown dwarfs

ABSTRACT A significant fraction of isolated white dwarfs host magnetic fields in excess of a MegaGauss. Observations suggest that these fields originate in interacting binary systems where the companion is destroyed thus leaving a singular, highly magnetized white dwarf. In post-main-sequence evolution, radial expansion of the parent star may cause orbiting companions to become engulfed. During the common envelope phase, as the orbital separation rapidly decreases, low-mass companions will tidally disrupt as they approach the giant’s core. We hydrodynamically simulate the tidal disruption of planets and brown dwarfs, and the subsequent accretion disc formation, in the interior of an asymptotic giant branch star. Compared to previous steady-state simulations, the resultant discs form with approximately the same mass fraction as estimated but have not yet reached steady state and are morphologically more extended in height and radius. The long-term evolution of the disc and the magnetic fields generated therein require future study.

A multi-planetary system orbiting the early-M dwarf TOI-1238

Context. The number of super-Earth and Earth-mass planet discoveries has increased significantly in the last two decades thanks to the Doppler radial velocity and planetary transit observing techniques. Either technique can detect planet candidates on its own, but the power of a combined photometric and spectroscopic analysis is unique for an insightful characterization of the planets, which in turn has repercussions for our understanding of the architecture of planetary systems and, therefore, their formation and evolution. Aims. Two transiting planet candidates with super-Earth radii around the nearby (d = 70.64 ± 0.06 pc) K7–M0 dwarf star TOI-1238 were announced by NASA’s Transiting Exoplanet Survey Satellite (TESS), which observed the field of TOI-1238 in four different sectors. We aim to validate their planetary nature using precise radial velocities taken with the CARMENES spectrograph. Methods. We obtained 55 CARMENES radial velocity measurements that span the 11 months between 9 May 2020 and 5 April 2021. For a better characterization of the parent star’s activity, we also collected contemporaneous optical photometric observations at the Joan Oró and Sierra Nevada observatories and retrieved archival photometry from the literature. We performed a combined TESS+CARMENES photometric and spectroscopic analysis by including Gaussian processes and Keplerian orbits to account for the stellar activity and planetary signals simultaneously. Results. We estimate that TOI-1238 has a rotation period of 40 ± 5 d based on photometric and spectroscopic data. The combined analysis confirms the discovery of two transiting planets, TOI-1238 b and c, with orbital periods of 0.764597−0.000011+0.000013 d and 3.294736−0.000036+0.000034 d, masses of 3.76−1.07+1.15 M⊕ and 8.32−1.88+1.90 M⊕, and radii of 1.21−0.10+0.11 R⊕ and 2.11−0.14+0.14 R⊕. They orbit their parent star at semimajor axes of 0.0137 ± 0.0004 au and 0.036 ± 0.001 au, respectively.The two planets are placed on opposite sides of the radius valley for M dwarfs and lie between the star and the inner border of TOI-1238’s habitable zone. The inner super-Earth TOI-1238 b is one of the densest ultra-short-period planets ever discovered (ρ = 11.7−3.4+4.2 g cm−3). The CARMENES data also reveal the presence of an outer, non-transiting, more massive companion with an orbital period and radial velocity amplitude of ≥600 d and ≥70 m s−1, which implies a likely mass of M ≥ 2 √(1− e2) MJup and a separation ≥1.1 au from its parent star.

Faint intermediate luminosity optical transients (ILOTs) from engulfing exoplanets on the Hertzsprung gap

ABSTRACT We follow the evolution of four observed exoplanets to the time when the respective parent star of each planet evolves off the main sequence and engulfs its planet to start a common envelope evolution (CEE), concluding that in each case this process powers an intermediate luminosity optical transient (ILOT; luminous red nova). We characterize the final thousands of days of the orbital decay towards a CEE and determine the properties of the star at the onset of the CEE. We scale the properties of the ILOT V1309 Scorpii to the properties of a planet that enters a CEE inside a star on and near the Hertzsprung gap to estimate the duration and luminosity of the expected ILOT. Based on these, we estimate that for a planet of Jupiter mass the ILOT will last for several days and reach a luminosity of several thousand solar luminosity. This type of ILOTs are less luminous than classical novae. Because of the small amount of expected dust and the small amount of energy that an accretion process on to the planet can release, such ILOTs can teach us on the merger at the onset of CEE of stellar companions. Our study adds to the variety of ILOTs that planets can power as they interact with a more massive companion.

On the solar dynamics from radio signal communication by recent solar probes

The very inquisition of the humanity always remains about its parent star of this planetary system. Scientists across the world are always egger to investigate the details of the phenomenon of the solar flares and coronal mass ejections (CMEs). There are some fundamental mysteries related to the solar coronal heating along with the acceleration of the solar wind and energetic particles. In this context we have discussed on the solar radio signal data obtained from the Parker Solar Probe (PSP) mission of National Aeronautics and Space Administration (NASA), USA in course of its journey towards the Sun and the very recent data of Solar and Heliospheric Observatory (SOHO) space probe of European Space Agency (ESA) and NASA. In this work the simultaneous and periodical analysis of the data from the SOHO and PSP will light into the delicate features of the near and far Earth observations on the solar coronal mass ejections related dynamics and that reveals some interesting facts in relation to the solar magnetic field.

Hot Jupiters accreting onto their parent stars: Effects on the stellar activity

AbstractHot Jupiters (HJs) are massive gaseous planets orbiting close to their host stars. Due to their physical characteristics and proximity to the central star, HJs are the natural laboratories to study the process of stellar‐planet interaction (SPI). Phenomena related to SPI may include the inflation and evaporation of planetary atmospheres, the formation of cometary tails and bow shocks and magnetospheric interaction between the magnetic field of the planet and that of the star. Several works suggest that some systems show enhanced stellar activity in phase with the planetary rotation period. In this work, we use a 3D magneto‐hydrodynamic model that describes a system composed by a star and a HJ and that includes the corresponding planetary and stellar winds. The aim is to investigate whether the material evaporating from the planet interacts with the stellar extended corona, and generates observable features. Our simulation shows that, in some conditions, the planetary wind expands and propagates mainly along the planetary orbit. Moreover, part of the planetary wind collides with the stellar wind and a fraction of the planet's outflow is funneled by the stellar magnetic field and hits the stellar surface. In both events, the material is heated up to temperatures of a few MK by a shock. These phenomena could manifest in the form of enhanced stellar activity at some orbital phases of the planet.

Polluted white dwarfs reveal exotic mantle rock types on exoplanets in our solar neighborhood

Prior studies have hypothesized that some polluted white dwarfs record continent-like granitic crust—which is abundant on Earth and perhaps uniquely indicative of plate tectonics. But these inferences derive from only a few elements, none of which define rock type. We thus present the first estimates of rock types on exoplanets that once orbited polluted white dwarfs—stars whose atmospheric compositions record the infall of formerly orbiting planetary objects—examining cases where Mg, Si, Ca and Fe are measured with precision. We find no evidence for continental crust, or other crust types, even after correcting for core formation. However, the silicate mantles of such exoplanets are discernable: one case is Earth like, but most are exotic in composition and mineralogy. Because these exoplanets exceed the compositional spread of >4,000 nearby main sequence stars, their unique silicate compositions are unlikely to reflect variations in parent star compositions. Instead, polluted white dwarfs reveal greater planetary variety in our solar neighborhood than currently appreciated, with consequently unique planetary accretion and differentiation paths that have no direct counterparts in our Solar System. These require new rock classification schemes, for quartz + orthopyroxene and periclase + olivine assemblages, which are proposed here.

Evolution equations of the multi-planetary problem with variable masses

AbstractWe investigated the influence of the variability of the masses of planets and the parent star on the dynamic evolution of n planetary systems, considering that the masses of bodies change isotropically with different rates. The methods of canonical perturbation theory, which developed on the basis of aperiodic motion over a quasi-conical cross section and methods of computer algebra were used. 4n evolutionary equations were obtained in analogues of Poincare elements. As an example, the evolutionary equations of the three-planet exosystem K2 − 3 were obtained explicitly, which is a system of 12 linear non-autonomous differential equations. Further, the evolutionary equations will be investigated numerically.

Significant interstellar object production by close stellar flybys

Context. Within just two years, two interstellar objects (ISOs) – 1I/‘Oumuamua and 2I/Borisov – have been discovered, the first of their kind. Large quantities of planetesimals form as a by-product of planet formation. Therefore, it seems likely that ISOs are former planetesimals that became somehow unbound from their parent star. The discoveries raise the question of the dominant ISO formation process. Aims. Here, we concentrate on planetesimals released during another star’s close flybys. Such close flybys happen most frequently during the first 10 Myr of a star’s life. Here, we quantify the amount of planetesimals released during close stellar flybys, their ejection velocity and likely composition. Methods. We numerically study the dependence of the effect of parabolic flybys on the mass ratio between the perturber and parent star, the periastron distance, inclination, and angle of periastron. Results. As expected, close prograde flybys of high-mass stars produce the most considerable amount of ISOs. Especially flybys of stars with M > 5 M⊙ on trajectories closer than 250 AU can lead to more planetesimals turning into ISOs than remaining bound to the parent star. Even strongly inclined orbits do not significantly reduce the ISO production; only retrograde flybys lead to a significantly lower ISO production. For perturbers slightly more massive than the parent star, there is a competition between ISO production and planetesimals being captured by the perturber. Whenever ISOs are produced, they leave their parent system typically with velocities in the range of 0.5–2 km s−1. This ejection velocity is distinctly different to that of ISOs produced by planet scattering (~4–8 km s−1) and those shed during the stellar post-main-sequence phase (~0.1–0.2 km s−1). Using the typical disc truncation radius in various cluster environments, we find that clusters like the Orion nebula cluster are likely to produce the equivalent of 0.85 Earth-masses of ISOs per star. In contrast, compact clusters like NGC 3603 could produce up to 50 Earth-masses of ISOs per star. Our solar-system probably produced the equivalent of 2–3 Earth masses of ISOs, which left our solar system at a mean ejection velocity of 0.7 km s−1. Conclusions. Most ISOs produced by flybys should be comet-like, similar to Borisov and unlike ‘Oumuamua. ISOs originating from compact long-lived clusters would often show a deficiency in CO. As soon as a statistically significant sample of ISOs is discovered, the combined information of their observed velocities and composition might help in constraining the dominant production process.

The future influence of six exoplanets on the envelope properties of their parent stars on the giant branches

ABSTRACT We study the evolution of six exoplanetary systems with the stellar evolutionary code Modules for Experiments in Stellar Astrophysics(mesa) and conclude that they will likely spin-up the envelope of their parent stars on the red giant branch (RGB) or later on the asymptotic giant branch (AGB) to the degree that the mass-loss process might become non-spherical. We choose six observed exoplanetary systems where the semimajor axis is $a_i \simeq 1\small{-}2 {~\rm au}$, and use the binary mode of mesa to follow the evolution of the systems. In four systems, the star engulfs the planet on the RGB, and in two systems on the AGB, and the systems enter a common envelope evolution (CEE). In two systems where the exoplanet masses are Mp ≃ 10MJ, where MJ is Jupiter mass, the planet spins up the envelope to about $10{{\ \rm per\ cent}}$ of the break-up velocity. Such envelopes are likely to have significant non-spherical mass-loss geometry. In the other four systems where Mp ≃ MJ the planet spins up the envelope to values of $1{-}2 {{\ \rm per\ cent}}$ of break-up velocity. Magnetic activity in the envelope that influences dust formation might lead to a small departure from spherical mass-loss even in these cases. In the two cases of CEE on the AGB, the planet deposits energy to the envelope that amounts to ${\gt}10{{\ \rm per\ cent}}$ of the envelope binding energy. We expect this to cause a non-spherical mass-loss that will shape an elliptical planetary nebula in each case.

ESPRESSO mass determination of TOI-263b: an extreme inhabitant of the brown dwarf desert

The TESS mission has reported a wealth of new planetary systems around bright and nearby stars amenable for detailed characterizations of planet properties and atmospheres. However, not all interesting TESS planets orbit around bright host stars. TOI-263 b is a validated ultra-short-period substellar object in a 0.56-day orbit around a faint (V = 18.97) M 3.5 dwarf star. The substellar nature of TOI-263 b was explored using multicolor photometry: a true radius of 0.87 ± 0.21 RJ was determined, establishing TOI-263 b ’s nature as somewhere between an inflated Neptune and a brown dwarf. The orbital period-radius parameter space occupied by TOI-263 b is quite unique, which prompted a further characterization of its true nature. Here, we report radial velocity measurements of TOI-263 obtained with three VLT units and the ESPRESSO spectrograph to retrieve the mass of TOI-263 b. We find that TOI-263 b is a brown dwarf with a mass of 61.6 ± 4.0 MJup. Additionally, the orbital period of the brown dwarf is found to be synchronized with the rotation period of the host star, and the system is found to be relatively active, possibly revealing a star–brown dwarf interaction. All these findings suggest that the system’s formation history might be explained via disk fragmentation and a later migration to close-in orbits. If the system is found to be unstable, TOI-263 will be an excellent target to test the migration mechanisms before the brown dwarf becomes “engulfed” by its parent star.

TEM Analyses of Unusual Presolar Silicon Carbide: Insights into the Range of Circumstellar Dust Condensation Conditions

Abstract Presolar silicon carbide (SiC) grains in meteoritic samples can help constrain circumstellar condensation processes and conditions in C-rich stars and core-collapse supernovae (CCSNe). This study presents our findings on eight presolar SiC grains from asymptotic giant branch (AGB) stars (four mainstream and one Y grain) and CCSNe (three X grains), chosen on the basis of μ-Raman spectral features that were indicative of their having unusual non-3C polytypes and/or high degrees of crystal disorder. Analytical transmission electron microscopy (TEM), which provides elemental compositional and structural information, shows evidence for complex histories for the grains. Our TEM results confirm the presence of non-3C,2H crystal domains. Minor-element heterogeneities and/or subgrains were observed in all grains analyzed for their compositions. The C/O ratios inferred for the parent stars varied from 0.98 to ≥1.03. Our data show that SiC condensation can occur under a wide range of conditions, in which environmental factors other than temperature (e.g., pressure, gas composition, heterogeneous nucleation on precondensed phases) play a significant role. Based on previous μ-Raman studies, ∼10% of SiC grains may have infrared (IR) spectral features that are influenced by crystal defects, porosity, and/or subgrains. Future sub-diffraction-limited IR measurements of complex SiC grains might shed further light on the relative contributions of each of these features to the shape and position of the characteristic IR 11 μm SiC feature and thus improve the interpretation of IR spectra of AGB stars like those that produced the presolar SiC grains.