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The high-precision measurements of exoplanet transit light curves that are now available contain information about the planet properties, their orbital parameters, and stellar limb darkening (LD). Recent 3D magnetohydrodynamical (MHD) simulations of stellar atmospheres have shown that LD depends on the photospheric magnetic field, and hence its precise determination can be used to estimate the field strength. Among existing LD laws, the uses of the simplest ones may lead to biased inferences, whereas the uses of complex laws typically lead to a large degeneracy among the LD parameters. We have developed a novel approach in which we use a complex LD model but with second derivative regularization during the fitting process. Regularization controls the complexity of the model appropriately and reduces the degeneracy among LD parameters, thus resulting in precise inferences. The tests on simulated data suggest that our inferences are not only precise but also accurate. This technique is used to re-analyse 43 transit light curves measured by the NASA Kepler and Transiting Exoplanet Survey Satellite missions. Comparisons of our LD inferences with the corresponding literature values show good agreement, while the precisions of our measurements are better by up to a factor of 2. We find that 1D non-magnetic model atmospheres fail to reproduce the observations while 3D MHD simulations are qualitatively consistent. The LD measurements, together with MHD simulations, confirm that Kepler-17, WASP-18, and KELT-24 have relatively high magnetic fields (⁠|$\gt 200$| G). This study paves the way for estimating the stellar surface magnetic field using the LD measurements. [ABSTRACT FROM AUTHOR]

Based on the high resolution and high signal-to-noise spectra, we derived the chemical abundances of 20 elements for 20 barium (Ba-) stars. For the first time, the detailed abundances of four sample stars, namely HD 92482, HD 150430, HD 151101, and HD 177304 have been analysed. Additionally, Ba element abundance has been measured using high-resolution spectra for the first time in six of the other 16 sample stars. Based on the [s/Fe] ratios, the Ba-unknown star HD 115927 can be classified as a strong Ba-star, while the Ba-likely star HD 160538 can be categorized into a mild Ba-star. Consequently, our sample comprises three strong and 17 mild Ba-stars. The light odd-Z metal elements and Fe-peak elements exhibit near-solar abundances. The [ |$\alpha$| /Fe] ratios demonstrate decreasing trends with increasing metallicity. Moreover, the abundances of neutron-capture (n-capture) elements show significant enhancements in different degrees. Using a threshold of the signed distances to the solar rapid-process (r-process) abundance pattern |$d_{\rm s}$| = 0.6, we find that all of our sample stars are normal Ba-stars, indicating that the enhancements of slow-process (s-process) elements should be attributed to material transfer from their companions. We compare the observed n-capture patterns of sample stars with the FRUITY models, and estimate the mass of the Thermally-Pulsing Asymptotic Giant Branch stars that previously contaminated the Ba-stars. The models with low masses can successfully explain the observations. From a kinematic point of view, we note that most of our sample stars are linked with the thin disc, while HD 130255 may be associated with the thick disc. [ABSTRACT FROM AUTHOR]

Context. Carbon, nitrogen, and oxygen are the most abundant elements throughout the universe, after hydrogen and helium. Studying these elements in low-metallicity stars can provide crucial information on the chemical composition in the early Galaxy and possible internal mixing processes that can alter the surface composition of the stars. Aims. This work aims to investigate the chemical abundance patterns for CNO elements and Li in a homogeneously analyzed sample of 52 metal-poor halo giant stars. From these results, we have been able to determine whether internal mixing processes have taken place in these stars. Methods. We used high-resolution spectra with a high signal-to-noise ratio (S/N) to carry out a spectral synthesis to derive detailed C, N, O, and Li abundances for a sample of stars with metallicities in the range of −3.58 ≤ [Fe/H] ≤ −1.79 dex. Our study was based on the assumption of one-dimensional (1D) local thermodynamic equilibrium (LTE) atmospheres. Results. Based on carbon and nitrogen abundances, we investigated the deep mixing taking place within stars along the red giant branch (RGB). The individual abundances of carbon decrease towards the upper RGB while nitrogen shows an increasing trend, indicating that carbon has been converted into nitrogen. No signatures of ON-cycle processed material were found for the stars in our sample. We computed a set of galactic chemical evolution (GCE) models, implementing different sets of massive star yields, both with and without including the effects of stellar rotation on nucleosynthesis. We confirm that stellar rotation is necessary to explain the highest [N/Fe] and [N/O] ratios observed in unmixed halo stars. The predicted level of N enhancement varies sensibly in dependence of the specific set of yields that are adopted. For stars with stellar parameters similar to those of our sample, heavy elements such as Sr, Y, and Zr appear to have unchanged abundances despite the stellar evolution mixing processes. Conclusions. The unmixed RGB stars provide very useful constraints on chemical evolution models of the Galaxy. As they are more luminous than unevolved (main sequence and turnoff) stars, they also allow for stars to be probed at greater distances. The stellar CN-cycle clearly changes the atmospheric abundances of the lighter elements, but no changes were detected with respect to the heavy elements. [ABSTRACT FROM AUTHOR]

Context. We present results of high-resolution spectroscopic observations of detached eclipsing binaries (DEBs) with total eclipses, for which UVES spectra were obtained during the phase of totality. These observations serve as a key way to determine the age and initial metallicity of the systems and to verify evolutionary phases of their components and distances. Aims. With the additional, independent information concerning the effective temperature and metallicity of one of the components, we aim to estimate the precise ages of the studied binaries and show the usefulness of totality spectra. The second goal was to provide precise orbital and physical stellar parameters of the components of systems in question. Methods. Using the VLT/UVES, we obtained high-resolution spectra of 11 DEBs during their total-eclipse phase. Atmospheric parameters of then-visible (larger) components were obtained with iSpec. With additional spectroscopy from the Comprehensive Research with Échelles on the Most interesting Eclipsing binaries (CRÉME) project, public archives, and literature, we obtained radial-velocity (RV) measurements, from which orbital parameters were calculated. Photometric time-series observations from TESS and ASAS were modelled with the JKTEBOP code, and, combined with RV-based results, they allowed us to obtain physical parameters for nine double-lined systems from our sample. All the available data were used to constrain the ages with our own approach, utilising MESA isochrones. Reddening-free, isochrone-based distances were also estimated and confronted with Gaia Data Release 3 (GDR3) results. Results. We show that single spectroscopic observations taken during a total eclipse can break the age-metallicity degeneracy and allow for the precise determination of the age of a DEB. With high-quality spectroscopic and photometric data, we are able to reach a 5−10% level of uncertainty (e.g. 724−24+52 Myr). Even for single-lined DEBs, where absolute masses are not possible to obtain, the spectroscopic analysis of one of the components allows one to put strong constraints on the properties of both stars. For some cases, we noted inconsistencies between isochrone-based and GDR3 distances. For one binary, which could not be fitted with a single isochrone (RZ Eri), we suggest a new explanation. [ABSTRACT FROM AUTHOR]

High-resolution spectrographs open a detailed window onto the atmospheres of stars and planets. As the number of systems observed with different instruments grows, it is crucial to develop a standard in analyzing spectral time series of exoplanet transits and occultations, for the benefit of reproducibility. Here, we introduce the ANTARESS workflow, a set of methods aimed at processing high-resolution spectroscopy datasets in a robust way and extracting accurate exoplanetary and stellar spectra. While a fast preliminary analysis can be run on order-merged 1D spectra and cross-correlation functions (CCFs), the workflow was optimally designed for extracted 2D echelle spectra to remain close to the original detector counts, limit the spectral resampling, and propagate the correlated noise. Input data from multiple instruments and epochs were corrected for relevant environmental and instrumental effects, processed homogeneously, and analyzed independently or jointly. In this first paper, we show how planet-occulted stellar spectra extracted along the transit chord and cleaned from planetary contamination provide a direct comparison with theoretical stellar models and enable a spectral and spatial mapping of the photosphere. We illustrate this application of the workflow to archival ESPRESSO data, using the Rossiter-McLaughlin effect Revolutions (RMR) technique to confirm the spin-orbit alignment of HD 209458b and unveil biases in WASP-76b's published orbital architecture. Because the workflow is modular and its concepts are general, it can support new methods and be extended to additional spectrographs to find a range of applications beyond the proposed scope. In a companion paper, we will present how planet-occulted spectra can be processed further to extract and analyze planetary spectra decontaminated from the star, providing clean and direct measurements of atmospheric properties. [ABSTRACT FROM AUTHOR]

New hot line lists for five isotopologues of N |$_2$| O called TYM are presented, for the parent |$^{14}$| N |$_2$| |$^{16}$| O and 4 singly substituted species |$^{14}$| N |$_2$| |$^{17}$| O, |$^{14}$| N |$_2$| |$^{18}$| O, |$^{14}$| N |$^{15}$| N |$^{16}$| O and |$^{15}$| N |$^{14}$| N |$^{16}$| O. The line lists have been computed with the variational program TROVE (Theoretical ROVibrational Energies) using a new empirical potential energy surface (PES) and an accurate ab initio dipole moment surface of N |$_2$| O Ames-1. The PES was obtained by fitting to experimentally derived energies of N |$_2$| O compiled using the well established measured active rotation vibration energy levels (MARVEL) procedure. Here we also introduce an 'artificial symmetry group' |$C_{n \text{s}}(\text{AEM})$| for an efficient construction of rotation-vibrational basis set of a linear non-symmetric triatomic molecule of the XYZ type. The line lists cover the rotational excitations up to |$J=160$| and the wavenumber range up to 20000 cm |$^{-1}$|⁠. MARVEL energies are also used to improve predicted line positions resulting in excellent agreement with the available experimental spectra, as demonstrated. An extensive comparison with existing line lists for N |$_2$| O HITRAN, HITEMP, NOSL-296, NOSD-1000, and Ames-296K is provided. The TYM line lists are freely accessible from www.exomol.com. [ABSTRACT FROM AUTHOR]

Magnetars are neutron stars that host huge, complex magnetic fields which require supporting currents to flow along the closed field lines. This makes magnetar atmospheres different from those of passively cooling neutron stars because of the heat deposited by back-flowing charges impinging on the star surface layers. This particle bombardment is expected to imprint the spectral and, even more, the polarization properties of the emitted thermal radiation. We present solutions for the radiative transfer problem for bombarded plane-parallel atmospheres in the high magnetic field regime. The temperature profile is assumed a priori, and selected in such a way to reflect the varying rate of energy deposition in the slab (from the impinging currents and/or from the cooling crust). We find that thermal X-ray emission powered entirely by the energy released in the atmosphere by the magnetospheric back bombardment is linearly polarized and X-mode dominated, but its polarization degree is significantly reduced (down to 10 per cent–50 per cent) when compared with that expected from a standard atmosphere heated only from the cooling crust below. By increasing the fraction of heat flowing in from the crust the polarization degree of the emergent radiation increases, first at higher energies (⁠|${\sim} 10\ \mathrm{keV}$|⁠) and then in the entire soft X-ray band. We use our models inside a ray-tracing code to derive the expected emission properties as measured by a distant observer and compare our results with recent IXPE observations of magnetar sources. [ABSTRACT FROM AUTHOR]

The radial velocity (RV) method of exoplanet detection requires mitigation of nuisance signals arising from stellar activity. Using analytic cool and facular spot models, we explore the use of central line moments (CLMs) for recovering and monitoring rotation induced RV variability. Different spot distribution patterns, photosphere-spot contrast ratios, and the presence or absence of the convective blueshift lead to differences in CLM signals between M and G dwarfs. Harmonics of the rotation period are often recovered with the highest power in standard periodogram analyses. By contrast, we show the true stellar rotation may be more reliably recovered with string length minimization. For solar minimum activity levels, recovery of the stellar rotation signal from CLMs is found to require unfeasibly high signal-to-noise observations. The stellar rotation period can be recovered at solar maximum activity levels from CLMs for reasonable cross-correlation function (CCF) signal-to-noise ratios >1000–5000. The CLMs can be used to recover and monitor stellar activity through their mutual correlations and correlations with RV and bisector inverse span. The skewness of a CCF, a measure of asymmetry, is described by the third CLM, |$M_3$|⁠. Our noise-free simulations indicate the linear RV versus |$M_3$| correlation is up to 10 per cent higher than the RV versus bisector inverse span correlation. We find a corresponding ∼5 per cent increase in linear correlation for CARMENES observations of the M star, AU Mic. We also assess the effectiveness of the time derivative of the second CLM, |$M_2$|⁠ , for monitoring stellar activity. [ABSTRACT FROM AUTHOR]

A theoretical line list for |$^{15}$| NH |$_3$| CoYuTe-15 is presented based on the empirical potential energy and ab initio dipole moments surfaces developed and used for the production of the ExoMol line list CoYuTe for |$^{14}$| NH |$_3$|⁠. The ro-vibrational energy levels and wavefunctions are computed using the variational program trove. The line list ranges up to 10 000 cm |$^{-1}$| (⁠|$\lambda \ge 1$| μ m) and contains 929 795 249 transitions between 1 269 961 states with |$J\le 30$|⁠. The line list should be applicable for temperatures up to |$\sim$| 1000 K. To improve the accuracy of the line positions, a set of experimentally derived energy levels of |$^{15}$| NH |$_3$| is produced using the marvel (Measured Active Rotation Vibration Energy Level) procedure. To this end, 37 experimental sources of the line positions of |$^{15}$| NH |$_3$| available in the literature are collected, combined, and systematized to produce a self-consistent spectroscopic network of 21 095 |$^{15}$| NH |$_3$| transitions covering 40 vibrational bands ranging up to 6818 cm |$^{-1}$| and resulting in 2777 energy term values. These marvel energies are then used to replace the theoretical values in the CoYuTe-15 line list and also complemented by pseudo- marvel energies obtained by an isotopologue extrapolation using the previously reported marvel energies of the |$^{14}$| NH |$_3$| parent isotopologue of ammonia. A list of 53 856 high-resolution transitions between marvel states and theoretical intensities is provided in the HITRAN format. Comparison with the recent experimental spectra of |$^{15}$| NH |$_3$| illustrate the potential of the line list for detections and as an efficient assistant in spectroscopic assignments. The line list is available from www.exomol.com. [ABSTRACT FROM AUTHOR]

Context. Large spectroscopic surveys of individual massive stars, such as ULLYSES and XShootU, provide observational data for hundreds of massive stars. Their analysis requires large numbers of synthetic spectra so that stellar parameters can be determined. In addition, libraries of massive stars' spectra are needed to produce population synthesis models able to reproduce the observed spectra of unresolved young stellar populations, such as those revealed by the James Webb Space Telescope (JWST) in the early Universe. Aims. Our main goal is to provide an extensive library of synthetic spectra and spectral energy distributions of OB stars at metallicities of the Magellanic Clouds. This library will offer a wealth of spectrophotometric information, making it readily applicable to a variety of astrophysical problems. Methods. We used the CMFGEN code to calculate 606 NLTE, line-blanketed, expanding atmosphere models using a comprehensive set of atomic data. An overall metallicity of 1/2 Z⊙ and 1/5 Z⊙ was adopted for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), respectively. We produced high-resolution spectra from 30 Å to 3 µm for stars on the Main Sequence and slightly beyond. Results. We provide spectral energy distributions, normalized synthetic spectra, ionizing fluxes, and photometry in various bands: Johnson UBV, Cousins RI, Bessel JHK, selected wide JWST filters, Gaia, and LSST ugrizy filters. For each of these filters, we compute bolometric corrections for all synthetic spectra and calibrations as a function of effective temperature. Conclusions. All of our synthetic spectra are publicly available through the POLLUX database, aiming to expedite multiwavelength analyses of massive stars in low metallicity environments. [ABSTRACT FROM AUTHOR]

Context. Despite mounting evidence that extreme red supergiants (RSGs) undergo episodic mass-loss events, their role in RSG evolution remains uncertain. Critical questions remain unanswered, such as whether or not these events can strip the star, and their timescale and frequency. Aims. This study delves into [W60] B90, one of the most luminous and extreme RSGs in the Large Magellanic Cloud (LMC), with our aim being to search for evidence of episodic mass loss. Our discovery of a bar-like nebular structure at 1 pc, which is reminiscent of the bar around Betelgeuse, raised the question of whether [W60] B90 also has a bow shock, motivating the present study. Methods. We collected and analyzed proper motion data from Gaia, as well as new multi-epoch spectroscopic and imaging data, and archival time-series photometry in the optical and mid-infrared (MIR). We used MARCS models to derive the physical properties of the star from the spectra. Results. We find [W60] B90 to be a walkaway star, with a supersonic peculiar velocity in the direction of the bar. We detect shocked emission between the bar and the star, based on the [S II]/Hα > 0.4 criterion, providing strong evidence for a bow shock. The 30 yr optical light curve reveals semi-regular variability, showing three similar dimming events with ΔV ~ 1 mag, a recurrence of ~12 yr, and a rise time of 400 days. We find the MIR light curve to vary by 0.51 mag and 0.37 mag in the WISE1 and WISE2 bands, respectively, and by 0.42 mag and 0.25 mag during the last dimming event. During this event, optical spectroscopy reveals spectral variability (M3 I to M4 I), a correlation between the Teff and the brightness, increased extinction, and, after the minimum, spectral features incompatible with the models. We also find a difference of >300 K between the Teff measured from the TiO bands in the optical and the atomic lines from our J-band spectroscopy. Conclusions. [W60] B90 is a more massive analog of Betelgeuse in the LMC and therefore the first single extragalactic RSG with a suspected bow shock. Its high luminosity of log(L/L⊙) = 5.32 dex, mass-loss rate, and MIR variability compared to other RSGs in the LMC indicate that it is in an unstable evolutionary state, undergoing episodes of mass loss. Investigating other luminous and extreme RSGs in low-metallicity environments using both archival photometry and spectroscopy is crucial to understanding the mechanism driving episodic mass loss in extreme RSGs in light of the Humphreys-Davidson limit and the "RSG problem". [ABSTRACT FROM AUTHOR]

Aims. Obtaining accurate derivations of stellar atmospheric parameters is crucial in the fields of stellar and exoplanet characterization. We present the upgraded version of our computational tool ODUSSEAS with a new reference scale applied to derive Teff and [Fe/H] values for M dwarfs. Methods. The new reference dataset of ODUSSEAS consists of Teff values based on interferometry, and [Fe/H] values derived by applying updated values for the parallaxes. These reference parameters are related to the pseudo-equivalent widths (EWs) of more than 4000 stellar absorption lines. The machine learning Python "scikit learn" package creates models to determine the stellar parameters for subsequent analysis. Results. We determined Teff and [Fe/H] values for 82 planet-host stars in SWEET-Cat. We demonstrate that our new version of ODUSSEAS is capable of determining the parameters with a greater accuracy than the original by comparing our results to other methods in literature. We also compared our parameters for the same stars by measuring their spectra obtained from several instruments, showing the consistency of our determinations with standard deviation of 30 K and 0.03 dex. Finally, we examined the correlation among planetary mass and stellar metallicity, confirming prior evidence indicating that massive planets mainly form around metal-rich stars in the case of M dwarfs as well. [ABSTRACT FROM AUTHOR]

Context. The study of exoplanets at different evolutionary stages can shed light on their formation, migration, and evolution. The determination of exoplanet properties depends on the properties of their host stars. It is therefore important to characterise the host stars for accurate knowledge on their planets. Aims. Our final goal is to derive, in a homogeneous and accurate way, the stellar atmospheric parameters and elemental abundances of ten young TESS (Transiting Exoplanet Survey Satellite) transiting planet-hosting GK stars followed up with the HARPS-N (High Accuracy Radial velocity Planet Searcher for the Northern hemisphere) at TNG (Telescopio Nazionale Galileo) spectrograph within the Global Architecture of Planetary Systems (GAPS) programme. Methods. We derived stellar kinematic properties, atmospheric parameters, and abundances of 18 elements. Depending on stellar parameters and chemical elements, we used methods based on line equivalent widths and spectral synthesis. Lithium line measurements were used as approximate age estimations. We exploited chemical abundances and their ratios to derive information on planetary composition. Results. Elemental abundances and kinematic properties are consistent with the nearby Galactic thin disk. All targets show C/O<0.8 and 1.0

Context. The outcome of the formation of massive stars is an important anchor point in the formation and evolution process of these stars. It provides insight into the physics of the assembly process, and sets the conditions for stellar evolution. For massive stars, the outcome of formation is rarely observed because the processes involved unfold deep down in highly extincted molecular clouds. Aims. We characterize a population of highly reddened stars in the very young massive star-forming region M17. The group of 18 O4.5 to B9 stars constitutes one of the best samples of almost zero-age main-sequence (ZAMS) high- and intermediate-mass stars. Their properties allow us to identify the empirical location of the ZAMS of massive stars, and the rotation and mass-loss rate of stars close to or at the onset of core-hydrogen burning. Methods. We performed quantitative spectroscopic modeling of a uniform set of over 100 spectral features in optical VLT/X-shooter spectra using the nonlocal thermal equilibrium stellar atmosphere code FASTWIND and a fitting approach based on a genetic algorithm, KIWI-GA. The spectral energy distributions of photometric observations were used to determine the line-of-sight extinction. From a comparison of their positions in the Hertzsprung-Russell diagram with MIST evolutionary tracks, we inferred the stellar masses and ages. Results. We find an age of 0.4−0.2+0.6 Myr for our sample, however we also identify a strong relation between the age and the mass of the stars. All sources are highly reddened, with AV ranging from 3.6 to 10.6 mag. The sample can be subdivided into two groups. Stars more massive than 10 M⊙ have reached the ZAMS. Their projected ZAMS spin rate distribution extends to 0.3 of the critical velocity; their mass-loss rates agree with those of other main-sequence O and early-B stars. Stars with a mass in the range 3 < M/M⊙ < 7 are still on the pre-main sequence (PMS), and some of them have circumstellar disks. Evolving their υ sin i to the ZAMS assuming angular momentum conservation yields values up to ~0.6 υcrit. For PMS stars without disks, we find tentative mass-loss rates up to 10−8.5 M⊙ yr−1. The total-to-selective extinction RV is higher for PMS stars with disks than for the remainder of the sample. Conclusions. We constrain the empirical location of the ZAMS for massive (10 < M/M⊙ < 50) stars and find it to agree with its location in MIST evolutionary tracks. The ZAMS rotation rates for intermediate-mass stars are twice as high as for massive stars, suggesting that the angular momentum gain processes differ between the two groups. The relation between the age and mass of the stars suggests a lag in the formation of more massive stars relative to lower mass stars. Taking the derived mass-loss rates at face value, stellar winds are already initiated in the PMS phase. The PMS-star winds are found to be substantially more powerful than indicated by predictions for line-driven outflows. [ABSTRACT FROM AUTHOR]

Multiple populations (MPs) in globular clusters (GCs) are stars that are distinct for their abundances of light elements. The MPs can be directly separated by measuring abundances of C, N, O, Na, Al, and Mg with spectroscopy or indirectly from photometric sequences created by the impact of different chemistry on band passes of particular filters, such as the HST pseudo-colours in the ultraviolet. An attempt to link HST pseudo-colour maps (PCMs) and spectroscopy was made by Marino et al. (2019, MNRAS, 487, 3815), using abundances mostly from our FLAMES survey. However, we found that an incomplete census of stars in common was used in their population tagging. We corrected the situation by building our own PCMs and matching them with our abundances in 20 GCs, plus two GCs from other sources, doubling the sample with spectroscopic abundances available. We found that the pseudo-colour (magF275W − 2 × magF336W + magF438) does not have a monotonic trend with Na abundances, enhanced by proton-capture reactions in MPs. Moreover, on average about 16% of stars with spectroscopic Na abundances show a discrepant tagging of MPs with respect to the HST photometry. Stars with second generation (SG) chemistry are mistaken for first generation (FG) objects according to HST photometry and vice versa. In general, photometric indices tend to overestimate the fraction of FG stars, in particular in low mass GCs. We offer a simple explanation for these findings. Finally, we publish all our PCMs (with more than 31 800 stars in 22 GCs) with star ID and coordinates; this is done to ensure easy verification and reproduction, as should be the case in scientific papers. [ABSTRACT FROM AUTHOR]

Context. The complex dynamics of asymptotic giant branch (AGB) stars and the resulting stellar winds have a significant impact on the measurements of stellar parameters and amplify their uncertainties. Three-dimensional (3D) radiative hydrodynamic (RHD) simulations of convection suggest that convection-related structures at the surface of AGB star affect the photocentre displacement and the parallax uncertainty measured by Gaia. Aims. We explore the impact of the convection on the photocentre variability and aim to establish analytical laws between the photo-centre displacement and stellar parameters to retrieve such parameters from the parallax uncertainty. Methods. We used a selection of 31 RHD simulations with CO5BOLD and the post-processing radiative transfer code OPTIM3D to compute intensity maps in the Gaia G band [320–1050 nm]. From these maps, we calculated the photocentre position and temporal fluctuations. We then compared the synthetic standard deviation to the parallax uncertainty of a sample of 53 Mira stars observed with Gaia. Results. The simulations show a displacement of the photocentre across the surface ranging from 4 to 13% of the corresponding stellar radius, in agreement with previous studies. We provide an analytical law relating the pulsation period of the simulations and the photocentre displacement as well as the pulsation period and stellar parameters. By combining these laws, we retrieve the surface gravity, the effective temperature, and the radius for the stars in our sample. Conclusions. Our analysis highlights an original procedure to retrieve stellar parameters by using both state-of-the-art 3D numerical simulations of AGB stellar convection and parallax observations of AGB stars. This will help us refine our understanding of these giants. [ABSTRACT FROM AUTHOR]

Context. In this paper we present a grid of self-consistent 1D model atmospheres of cool stars, sub-stellar objects, and exoplanets in the effective temperature range 300-3000 K, including cloud formation, chemical non-equilibrium effects, and stellar irradiation. Aims. The new grid extends the classical MARCS model atmosphere grid from 2008 towards lower effective temperatures and a broader range of object types. Methods. The new model atmosphere computations, MSG, are based on a combination of three well-tested codes, the classical MARCS 1D atmospheres, the StaticWeather cloud formation code, and the GGchem chemical equilibrium code. The combined code has been updated with new and more complete molecular and atomic opacities, cloud formation, and advanced chemical equilibrium calculations, and we also added new numerical methods at low temperatures to allow for a more robust convergence. Results. The coupling between the MARCS radiative transfer and GGchem chemical equilibrium computations has effectively made it possible to reach convergence based on the electron pressure for warmer models and gas pressure for cooler models, enabling self-consistent modelling of stellar, sub-stellar, and exoplanetary objects in a very wide range of effective temperatures. We will make new cloud-free and non-irradiated models for solar metallicity and a selected variety of other chemical compositions immediately available from our home page (https://cels.nbi.ku.dk). Illustrative examples of cloudy and irradiated models as well as models based on non-equilibrium chemistry are also presented, and we will describe these in more detail and make them available upon completion at the same place for a larger range of parameter space. Conclusions. For solar metallicity models, the new additional molecular opacities only affect the structure of models cooler than Teff = 2500 K, and the effect becomes substantial for models below Teff ~1500 K. Atomic line opacities are important for models warmer than ~3000 K. The line profile of the molecular opacities may have a larger effect on the model structure than previously anticipated, particularly in the uppermost layers at low gas pressure. The qualitative changes in the relative abundances of TiO, H2O, CH4, NH3, and other molecules in our models follow the observationally defined M, L, T (and Y) sequences, but they also reveal more complex and depth-dependent abundance changes and therefore a spectral classification depending on more parameters. The self-consistent coupling to StaticWeather cloud computations allows for detailed comparison between nucleation and observed relative dimming of different spectral bands, with advanced applications for new identification methods of potential exoplanetary biology. [ABSTRACT FROM AUTHOR]

In the present paper we consider the full nonlocal thermodynamic equilibrium (non-LTE) radiation transfer problem. This formalism allows us to account for deviation from equilibrium distribution of both the radiation field and the massive particles. In the present study, two-level atoms with broadened upper level represent the massive particles. In the absence of velocity-changing collisions, we demonstrate the analytic equivalence of the full non-LTE source function with the corresponding standard non-LTE partial frequency redistribution (PFR) model. We present an iterative method based on operator splitting techniques that can be used to numerically solve the problem at hand. We benchmark it against the standard non-LTE transfer problem for a two-level atom with PFR. We illustrate the deviation of the velocity distribution function of excited atoms from the equilibrium distribution. We also discuss the dependence of the emission profile and the velocity distribution function on elastic collisions and velocity-changing collisions. [ABSTRACT FROM AUTHOR]

Context. The nature of mass-loss in massive stars is one of the most important and difficult to constrain processes in the evolution of massive stars. The largest observational uncertainties are related to the influence of metallicity and wind structure with optically thick clumps. Aims. We aim to constrain the wind parameters of sample of 18 O-type stars in the LMC, through analysis with stellar atmosphere and wind models including the effects of optically thick clumping. This will allow us to determine the most accurate spectroscopic mass-loss and wind structure properties of massive stars at sub-solar metallicity to date. This will allow us to gain insight into the impact of metallicity on massive stellar winds. Methods. Combining high signal to noise (S/N) ratio observations in the ultraviolet and optical wavelength ranges gives us access to diagnostics of multiple different ongoing physical processes in the stellar wind. We produce synthetic spectra using the stellar atmosphere modelling code FASTWIND, and reproduce the observed spectra using a genetic algorithm based fitting technique to optimise the input parameters. Results. We empirically constrain 15 physical parameters associated with the stellar and wind properties of O-type stars from the dwarf, giant and supergiant luminosity classes. These include temperature, surface gravity, surface abundances, rotation, macroturbulence and wind parameters. Conclusions. We find, on average, mass-loss rates a factor of 4–5 lower than those from theoretical predictions commonly used in stellar-evolution calculations, but in good agreement with more recent theoretical predictions. In the 'weak-wind' regime we find massloss rates orders of magnitude below any theoretical predictions. We find a positive correlation of clumping factors with effective temperature with an average fcl = 14 ± 8 for the full sample. It is clear that there is a difference in the porosity of the wind in velocity space, and interclump density, above and below a temperature of roughly 38 kK. Above 38 kK an average 46 ± 24% of the wind velocity span is covered by clumps and the interclump density is 10–30% of the mean wind. Below an effective temperature of roughly 38 kK there must be additional light leakage for supergiants. For dwarf stars at low temperatures there is a statistical preference for very low clump velocity spans, however it is unclear if this can be physically motivated as there are no clearly observable wind signatures in UV diagnostics. [ABSTRACT FROM AUTHOR]

A theoretical line list for |$^{15}$| NH |$_3$| CoYuTe-15 is presented based on the empirical potential energy and ab initio dipole moments surfaces developed and used for the production of the ExoMol line list CoYuTe for |$^{14}$| NH |$_3$|⁠. The ro-vibrational energy levels and wavefunctions are computed using the variational program trove. The line list ranges up to 10 000 cm |$^{-1}$| (⁠|$\lambda \ge 1$| μ m) and contains 929 795 249 transitions between 1 269 961 states with |$J\le 30$|⁠. The line list should be applicable for temperatures up to |$\sim$| 1000 K. To improve the accuracy of the line positions, a set of experimentally derived energy levels of |$^{15}$| NH |$_3$| is produced using the marvel (Measured Active Rotation Vibration Energy Level) procedure. To this end, 37 experimental sources of the line positions of |$^{15}$| NH |$_3$| available in the literature are collected, combined, and systematized to produce a self-consistent spectroscopic network of 21 095 |$^{15}$| NH |$_3$| transitions covering 40 vibrational bands ranging up to 6818 cm |$^{-1}$| and resulting in 2777 energy term values. These marvel energies are then used to replace the theoretical values in the CoYuTe-15 line list and also complemented by pseudo- marvel energies obtained by an isotopologue extrapolation using the previously reported marvel energies of the |$^{14}$| NH |$_3$| parent isotopologue of ammonia. A list of 53 856 high-resolution transitions between marvel states and theoretical intensities is provided in the HITRAN format. Comparison with the recent experimental spectra of |$^{15}$| NH |$_3$| illustrate the potential of the line list for detections and as an efficient assistant in spectroscopic assignments. The line list is available from www.exomol.com. [ABSTRACT FROM AUTHOR]

We report results from 8 h of JWST /MIRI low resolution spectroscopic (LRS) monitoring directly followed by 7 h of JWST /NIRSpec prism spectroscopic monitoring of the benchmark binary brown dwarf WISE 1049AB, the closest, brightest brown dwarfs known. We find water, methane, and CO absorption features in both components, including the 3.3  μ m methane absorption feature and a tentative detection of small grain (⁠|$\lt $| 1 μ m) silicate absorption at |$\gt $| 8.5 μ m in WISE 1049A. Both components vary significantly (⁠|$\gt 1~{{\rm per\ cent}}$|⁠), with WISE 1049B displaying larger variations than WISE 1049A. Using K -means clustering, we find three main transition points in wavelength for both components of the binary: (1) change in behaviour at |$\sim$| 2.3 μ m coincident with a CO absorption bandhead, (2) change in behaviour at 4.2 μ m, close to the CO fundamental band at |$\lambda \gt $|  4.4 µm, and (3) change in behaviour at 8.3–8.5 µm, potentially corresponding to silicate absorption. We interpret the light curves observed with both NIRSpec and MIRI as likely stemming from (1) a deep pressure level driving the double-peaked variability seen in WISE 1049B at wavelengths |$\lt $| 2.3 and |$\gt $| 8.5 µm, (2) an intermediate pressure level shaping the light-curve morphology between 2.3 and 4.2 µm, and (3) a higher altitude pressure level producing single-peaked and plateaued light-curve behaviour between 4.2 and 8.5 µm. [ABSTRACT FROM AUTHOR]

Excess chromospheric emissions within deep photospheric lines are effective proxies of stellar magnetism for FGK stars. This emission decays with stellar age and is a potential determinant of this important stellar quantity. We report absolutely calibrated H  |$\alpha$| chromospheric fluxes for 511 solar-type stars in a wide interval of precisely determined masses, [Fe/H], ages, and evolution states from high S/N, moderately high |$-$| resolution spectra. The comparison of H  |$\alpha$| and H + K chromospheric fluxes reveals a metallicity bias (absent from H  |$\alpha$|⁠) affecting Ca  ii H + K fluxes thereby metal-rich stars with deep line profiles mimic low chromospheric flux levels, and vice versa for metal-poor stars. This bias blurs the age–activity relation, precluding age determinations for old, inactive stars unless mass and [Fe/H] are calibrated into the relation. The H + K lines being the most widely studied tool to quantify magnetic activity in FGK stars, care should be exercised in its use whenever wide ranges of mass and [Fe/H] are involved. The H  |$\alpha$| age–activity–mass–metallicity calibration appears to be in line with the theoretical expectation that (other parameters being equal) more massive stars possess narrower convective zones and are less active than less massive stars, while more metal-rich stars have deeper convective zones and appear more active than metal-poorer stars. If regarded statistically in tandem with other age diagnostics, H  |$\alpha$| chromospheric fluxes may be suitable to constrain ages for FGK stars with acceptable precision. [ABSTRACT FROM AUTHOR]

We present a new magnetic-atmosphere model code for obtaining synthetic spectral fluxes of hydrogen-rich magnetic white dwarfs. To date, observed spectra have been analyzed with models that neglect the magnetic field's effects on the atomic populations. In this work, we incorporate state-of-art theory in the evaluation of numerical densities of atoms, free electrons, and ions in local thermodynamical equilibrium under the action of a magnetic field. The energy distribution of atoms is rigorously evaluated for arbitrary field strength. This energy pattern includes going from tightly bound states to metastable or truly bound, highly excited states embedded in the continuum, that is, over the first Landau level. Finite nuclear mass effects and the coupling between the internal atomic structure and the motion of the atom across the magnetic field are also considered. Synthetic fluxes are generated with integrations of numerical solutions of polarized radiative transfer over the visible stellar disk using a spherical t-design method. The atmosphere code is tested with observations from the Sloan Digital Sky Survey for a group of known magnetic white dwarfs. Physical stellar parameters are obtained from least-squares fits to the observed energy distribution and compared with results of previous works. We show that the use of zerofield ionization equilibrium in spectral analyses can lead to underestimated effective temperatures for highly magnetic white dwarfs. [ABSTRACT FROM AUTHOR]

The precise measurement of stellar abundances plays a pivotal role in providing constraints on the chemical evolution of the Galaxy. However, before spectral lines can be employed as reliable abundance indicators, particularly for challenging elements such as helium, they must undergo thorough scrutiny. Galactic open clusters, representing well-defined single stellar populations, offer an ideal setting for unfolding the information stored in the helium spectral line feature. In this study, we characterise the profile and strength of the helium transition at around 10 830 Å (He 10 830) in nine giant stars in the Galactic open cluster Stock 2. To remove the influence of weak blending lines near the helium feature, we calibrated their oscillator strengths (log 푔f) by employing corresponding abundances obtained from simultaneously observed optical spectra. Our observations reveal that the He 10 830 in all the targets is observed in absorption, with line strengths categorised into two groups. Three stars exhibit strong absorption, including a discernible secondary component, while the remaining stars exhibit weaker absorption. The lines are in symmetry and align with or near their rest wavelengths, suggesting a stable upper chromosphere without a significant systematic mass motion. We find a correlation between the He 10 830 strength and the Ca II log R′HK index, with a slope similar to that reported in previous studies on dwarf stars. This correlation underscores the necessity of accounting for the stellar chromosphere structure when employing He 10 830 as a probe for the stellar helium abundance. The procedure of measuring the He 10 830 we developed in this study is applicable not only to other Galactic open clusters but also to field stars, and we plan to use it to map the helium abundance across various types of stars in the future. [ABSTRACT FROM AUTHOR]

Most Galactic globular clusters (GCs) harbour multiple populations of stars (MPs) that are composed of at least two generations: the first generation is characterised by a standard α-enhanced metal mixture, as observed in field halo stars of the Milky Way, and the second generation displays an anti-correlated CN–ONa chemical abundance pattern in combination with an enhanced helium fraction. Adequate collections of stellar spectra are needed to characterize the effect of these changes in the stellar abundance on the integrated light of GCs. We present a grid of synthetic stellar spectra to cover the atmospheric parameters relevant to old stellar populations at four subsolar metallicities and two abundance patterns that are representative of the first and second generations of stars in GCs. The integrated spectra of the populations were computed using our stellar grid and empirical stellar populations, namely, colour-magnitude diagrams from the literature for Galactic GCs. The spectra range from 290 to 1000 nm, where we measured the effect on several spectrophotometric indices due to the surface abundance variations attributed to MPs. We find non-negligible effects of the MPs on the spectroscopic indices that are sensitive to C, N, Ca, or Na, and on the Balmer indices; we also describe how MPs modify specific regions in the near-UV and near-IR that can be measured with narrow or medium photometric passbands. The effects vary with metallicity. A number of these changes remain detectable even when we account for the stochastic fluctuations due to the finite nature of the stellar population cluster. [ABSTRACT FROM AUTHOR]

We present a quantitative spectral analysis of the extreme nitrogen-enhanced supergiant HD 93840 (BN1 Ib) at an intermediate galactic latitude. Based on an optical high-resolution spectrum and complementary ultraviolet and infrared (spectro-)photometry, in addition to Gaia data, we carried out a full characterisation of the star's properties. We used both hydrostatic and unified (photosphere+wind) model atmospheres that account for deviations from local thermodynamic equilibrium. A highly unusual surface CNO-mixing signature and a marked stellar overluminosity compared to the mass imply a binary channel for the star's past evolution. The kinematics shows that it has reached its current position above the Galactic plane as a runaway star, likely ejected by the supernova explosion of its former companion star. Its current bulk composition, with a notably increased mean molecular weight due to core He- and progressed shell H-burning, suggests an advanced evolutionary stage. It is poised to yield a rare core-collapse supernova of a blue supergiant about ten OB star population scale heights above the Galactic disk relatively soon, contributing to the metal enrichment of the circumgalactic medium. [ABSTRACT FROM AUTHOR]

The discrepancy between the observed and the predicted radii in low-mass stars is a well-known and yet to be resolved problem. Although various theoretical approaches have been developed since the first appearance of the problem, there is still no satisfactory mechanism or model which could successfully reproduce observed radii. The stellar magnetic field is among proposed resolutions but has not been investigated comprehensively for detached eclipsing binary stars. In this study, we present analysis of seven low-mass Kepler eclipsing binaries, KIC 4484356, KIC 4678171, KIC 5300878, KIC 6147573, KIC 8543278, KIC 9762519, and KIC 9821078. We investigate the average amplitude of the rotational modulation signal observed at out-of-eclipse phases, which could be used as the proxy for the strength of the stellar magnetic field, and possible discrepancies between observed and theoretically calculated radii of the components of the target systems. Our findings indicate radius discrepancy for both components of KIC 4678171 and KIC 9821078. Moreover, secondary components of KIC 9762519 and KIC 8543278 appear to have quite inflated radii. However, results from this limited sample do not indicate any correlation between average amplitude of the rotation modulation signal and observed radius discrepancies. [ABSTRACT FROM AUTHOR]

Auroral emission lines result from the interaction between magnetic field and stellar wind, offering valuable insights into physical properties and processes occurring within magnetospheres of celestial bodies. While extensively studied in planetary and exoplanetary atmospheres, in ultracool dwarfs, and as radio emission from early-type stars, the presence of specific auroral emission lines in hot star spectra remains unexplored. In this study, we utilized tlusty code to simulate the auroral lines, while modelling the effect of the interaction between stellar wind and magnetosphere through X-ray irradiation. Utilizing high-resolution synthetic spectra generated from model atmospheres, we identified potential candidate lines indicative of auroral emission, which were absent in non-irradiated spectra. Emission lines in synthetic spectra were present primarily in the infrared domain. The most prominent line generated by irradiation was He  ii 69458 Å, which appeared in all our model atmospheres with effective temperatures ranging from 15 kK to 30 kK. We also calculated the minimum irradiation required to detect emission in this most prominent line. The presence of emission lines was interpreted by considering changes in the population of different excited states of given atoms. Besides the appearance of infrared emission lines, high-energy irradiation causes infrared excess. To complement our simulations, we also searched for auroral lines in Far Ultraviolet Spectroscopic Explorer (FUSE) observations, which are deposited in the Multimission Archive at Space Telescope catalogue. The comparison of observed spectra with synthetic spectra did not identify any possible candidate emission lines in FUSE spectra. [ABSTRACT FROM AUTHOR]

A new molecular line list covering wavelengths λ > 1  μ m (the 0–10 000 cm−1 range) for the main isotopologue of carbonyl sulphide 16O12C32S is presented. The OCS line list, named OYT8, contains almost 2.5 billion transitions between 2.4 million rotation-vibration energy levels with the total angular momentum up to J  = 223. It is suitable for high-temperature environments up to T  = 2000 K. Line list calculations were performed with the variational nuclear motion code trove in conjunction with a highly accurate, empirically refined potential energy surface and a newly computed ab initio dipole moment surface of OCS. The OYT8 line list is adapted for high-resolution applications by replacing computed energy levels with empirically derived values of OCS where available. Comparisons of the OYT8 line list with other OCS line lists and spectra yields excellent agreement for both strong and weak spectroscopic bands. The increased coverage of the OYT8 line list and the many new spectral features that are available will greatly facilitate the future observation of OCS on exoplanets. Carbonyl sulphide joins a growing number of sulphur-bearing molecules available from the ExoMol database. The OYT8 line list along with the associated temperature- and pressure-dependent molecular opacities can be downloaded from www.exomol.com and the CDS astronomical database. [ABSTRACT FROM AUTHOR]

Heavy metal subdwarfs are a class of hot subdwarfs with very high abundances of heavy elements, typically around 10 000 times solar. They include stars, which are strongly enhanced in either lead or zirconium, as well as other elements. Vertical stratification of the enhanced elements, where the element is concentrated in a thin layer of the atmosphere, has been proposed as a mechanism to explain the apparent high abundances. This paper explores the effects of the vertical stratification of lead on the theoretical spectra of hot subdwarfs. The concentration of lead in different regions of the model atmosphere is found to affect individual lines in a broadly wavelength-dependent manner, with the potential for lines to display modified profiles depending on the location of lead enhancement in the atmosphere. This wavelength dependence highlights the importance of observations in both the optical and the UV for determining whether stratification is present in real stars. [ABSTRACT FROM AUTHOR]

Context. Determination of solar magnetic fields with a spatial resolution set by the diffraction limit of a telescope is difficult because the time required to measure the Stokes vector with sufficient signal-to-noise ratio is long compared to the solar evolution timescale. This difficulty becomes greater with increasing telescope size as the photon flux per diffraction-limited resolution element remains constant but the evolution timescale decreases linearly with the diffraction-limited resolution. Aims. We aim to improve magnetic field reconstruction at the diffraction limit without averaging the observations in time or space, and without applying noise filtering. Methods. The magnetic field vector tends to evolve more slowly than the temperature, velocity, or microturbulence. We exploit this by adding temporal regularisation terms for the magnetic field to the linear least-squares fitting used in the weak-field approximation, as well as to the Levenberg-Marquardt algorithm used in inversions. The other model parameters are allowed to change in time without constraints. We infer the chromospheric magnetic field from Ca II 854.2 nm observations using the weak field approximation and the photospheric magnetic field from Fe I 617.3 nm observations, both with and without temporal regularisation. Results. Temporal regularisation reduces the noise in the reconstructed maps of the magnetic field and provides a better coherency in time in both the weak-field approximation and Milne-Eddington inversions. Conclusions. Temporal regularisation markedly improves magnetic field determination from spatially and temporally resolved observations. [ABSTRACT FROM AUTHOR]

Context. Estimating the physical states of the surfaces of fast-rotating stars is challenging due to several intrinsic processes, which include radiative flux inhomogeneities on the photosphere induced by rotation and circumstellar signatures in their spectra. The analysis of their spectra ultimately requires the use of synthetic grids of spectra accounting for all these physical processes. Aims. In this paper, we present the 'von ZeiPEl's code for gravity darKening specTRal synthesis' (ZPEKTR) code, which is designed to perform the spectral synthesis of fast-rotating stars, accounting for gravity darkening, limb-darkening effects in the continuum and geometrical deformation induced by fast rotation. Methods. We consider colatitudinal temperature and surface-gravity variations, assuming both the classical prescription developed by von Zeipel and the new formulation by Espinosa-Lara. The code runs either with a rectangular or a triangular mesh on the stellar surface. We compare the temperature and gravitational distribution as a function of the stellar latitude arising from both models. Results. The line profiles of He I 4388, 4471, 4922, and 6678 Å produced with both formalisms are compared at three different rotation rates and illustrate differences in shape and central intensity. We also illustrate the fittings of 31 line spectra of classical Be stars averaged from the Be Stars Observation Survey (BeSOS) database and make a comparison among their apparent physical parameters and ages determined from plane-parallel non-local thermodynamical equilibrium (non-LTE) models and parameters determined from classical von Zeipel models, finding a displacement of more evolved objects towards the zero-age main sequence. We also compare the distributions of projected rotation velocities of these objects obtained with and without the inclusion of gravity-darkening effects with ZPEKTR. Conclusions. We observe a shift of the histogram of rotation velocities calculated accounting for effects of gravity darkening concerning rotation velocities obtained through the fittings with classical plane-parallel non-LTE models. We show that models that do not account for gravity darkening can underestimate the rotation velocity, because the stellar latitudes that contribute the higher velocities are those in the equator with the least radiative flux. We envisage near-future improvements to the code, such as the inclusion of differential rotation and treatment of tidal forces in binary stellar systems. [ABSTRACT FROM AUTHOR]

Aims. A series of high-precision calculations for the electronic structure of MgH have been reported in the past two decades; however, most of them d not include the core-valence correlation and still exhibit distinct differences. Furthermore, the latest high-precision results have not been applied to the studies of photodissociation dynamics. The primary motivations of this paper are to calculate a more precise electronic structure of MgH consering a core-valence correlation and to prove the photodissociation cross-sections. Methods. The electronic structure of MgH is investigated by multi-reference configuration interaction calculations with Davson correction (MRCI+Q). We performed two different sets of calculations to investigate the core-valence correlation and, as a result, obtained accurate potential energy curves (PECs) and transition dipole moments (TDMs). An extrapolation procedure was also employed to eliminate the error of basis set. Then, the photodissociation cross-sections were calculated using high-precision PECs and TDMs. Results. The PECs and TDMs of the five lowest doublet electronic states, X2Σ+, B′2Σ+, E2Σ+, A2Π, and C2Π, are obtained from calculations including core-valence correlation, termed as CV-MRCI, while PECs of the ten lowest doublet states and three quartet states are also obtained from NCV-MRCI calculations without core-valence correlation. The spectroscopic constants and band oscillator strengths are also proved with high precision levels. The equilibrium Re and vertical excitation energy Te are only 0.1% different from the measurements. Based on the CV-MRCI results, the rovibrationally resolved photodissociation cross-sections for transitions from X2Σ+ to the other four states, as well as the total local thermodynamic equilibrium cross-sections for temperatures up to 10000 K, are calculated. [ABSTRACT FROM AUTHOR]

Over the last two decades there have been considerable advances in modelling the spectra of massive stars and supernovae (SNe). Despite this progress, there are still numerous uncertainties that affect the accuracy of models. For massive stars, convection, instabilities, clumping, and our inability to model stellar winds self-consistently likely introduce systematic errors into our analyses. For SNe, and particularly for core-collapse SNe, departures from spherical symmetry strongly affect observed spectra and need to be taken into account. There are also issues with clumping, and mixing processes (both in the progenitor and the SN explosion) that need to be resolved. For both massive stars and SNe, the accuracy and availability of atomic data continues to be an ongoing issue influencing analyses. [ABSTRACT FROM AUTHOR]

The core of the cluster R136 in the Large Magellanic Cloud hosts the most massive stars known. The high mass-loss rates of these stars strongly impact their surroundings, as well as the evolution of the stars themselves. To quantify this impact accurate mass-loss rates are needed, however, uncertainty about the degree of inhomogeneity of the winds ('wind clumping'), makes mass-loss measurements uncertain. We combine optical and ultraviolet HST/STIS spectroscopy of 56 stars in the core of R136 in order to put constraints on the wind structure, improving the accuracy of the mass-loss rate measurements. We find that the winds are highly clumped, and use our measured mass-loss rates to test theoretical predictions. Furthermore we find, for the first time, tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped than those with lower mass-loss rates. [ABSTRACT FROM AUTHOR]

Adequate stellar atmosphere models are prerequisite to derive robust stellar parameters from spectroscopic analyses. I will briefly review recent results obtained with the Potdam Wolf-Rayet (PoWR) model atmosphere code, which is applicable to all types of hot stars. Using multi-wavelength observations including the UV, we analyzed large samples of massive stars at various metallicities, gaining important insights on their cosmic role and the feedback to their environment. A recent extension of PoWR allows to compose the model atmosphere from two zones. A rapidly rotating star, e.g., might possess a cooler equatorial region with a slow wind, and two polar cones with higher photospheric temperature and fast wind. For two examples of rapidly rotating O-type stars, we demonstrate that such model can reproduce wind-line profiles which otherwise would stay inconsistent. Fast rotation, which prevails in particular at low metallicities, thus might bias empirically derived parameters, having implications for feedback as well as for angular-momentum losses of SN and GRB progenitors. [ABSTRACT FROM AUTHOR]

Line-driven stellar winds are ubiquitous among hot massive stars. In some cases they can become so strong, that the whole star is cloaked by an optically thick wind. The strong outflow gives rise to large emission lines, defining the class of so-called Wolf-Rayet (WR) stars. While being major players in the evolution of massive stars, the formation of heavy black holes, and the distribution of elements, the occurrence and nature of WR winds is still quite enigmatic. A promising instrument towards a better theoretical understanding are stellar atmospheres allowing for a consistent inclusion of the hydrodynamics. By coupling stellar and wind parameters and the inclusion of a detailed non-LTE radiative transfer, they allow us to go beneath the observable layers and study the onset of WR-type winds. Establishing larger sets of models, we were able to make ground-breaking progress by identifying trends with mass and metallicity that deviate significantly from present empirical descriptions. Our modelling efforts reveal a complex picture for WR-type winds with strong, non-linear dependencies. Besides covering metallicity and mass, we further identify surface hydrogen as an important ingredient to retain WR-type mass loss at lower metallicity. Here, we present a summary of recent insights on the nature and onset of WR-type winds in massive stars including the consequences for stellar evolution, remaining open questions, and current efforts to overcome them. [ABSTRACT FROM AUTHOR]

The magnetic field in the O9.7 V star HD 54879 has been monitored for almost a decade. Spectropolarimetric observations reveal a rather strong mean longitudinal magnetic field that varies with a period of about 7.41 years. Observations in the Hα$$ \alpha $$ line show a variation with the same period, while the Hβ$$ \beta $$ line shows only little variation. Assuming the periodic variation to be caused by a slow rotation and a dipolar magnetic field, we find a magnetic field strength of ≥$$ \ge $$2 kG at the magnetic poles. With the relatively low mass loss rate of 10−9M⊙$$ {10}^{-9}{M}_{\odot } $$ year−1, this star is a case of extremely strong magnetic confinement. Both theoretical arguments and numerical simulations indicate the presence of an extended disk of increased gas density in the equatorial plane of the magnetic field, where gas from the line‐driven stellar wind is trapped. This disk is likely to be the origin of the observed Hα$$ \alpha $$ emission, which peaks together with the strongest line‐of‐sight magnetic field. The profile of the Hα$$ \alpha $$ line is resolved in several components and shows a remarkable variability with the rotation period. [ABSTRACT FROM AUTHOR]

Yellow hypergiants (YHGs) are massive stars that are commonly interpreted to be in a post-red supergiant evolutionary state. These objects can undergo outbursts on time-scales of decades, which are suspected to be due to instabilities in the envelope. To test this conjecture, the stability of envelope models for YHGs with respect to infinitesimal, radial perturbations is investigated. Violent strange mode instabilities with growth rates in the dynamical regime are identified if the luminosity-to-mass ratio exceeds ≈104 in solar units. For the observed parameters of YHGs, we thus predict instability. The strange mode instabilities persist over the entire range of effective temperatures from red to blue supergiants. Due to short thermal time-scales and dominant radiation pressure in the envelopes of YHGs, a non-adiabatic stability analysis is mandatory and an adiabatic analysis being the basis of the common perception is irrelevant. Contrary to the prevailing opinion, the models considered here do not exhibit any adiabatic instability. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of the detailed chemical abundances for a sample of 11 metal-poor, very metal-poor, and extremely metal-poor stars ([Fe/H] = −1.65 to [Fe/H]  = −3.0) as part of the HESP-GOMPA (Galactic survey Of Metal Poor stArs) survey. The abundance determinations encompass a range of elements, including C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, and Ba, with a subset of the brighter objects allowing for the measurement of additional key elements. Notably, the abundance analysis of a relatively bright highly r -process-enhanced (r -II) star (SDSS J0019+3141) exhibits a predominantly main r -process signature and variations in the lighter r -process elements. Moreover, successful measurements of thorium in this star facilitate stellar age determinations. We find a consistent odd–even nucleosynthesis pattern in these stars, aligning with expectations for their respective metallicity levels, thus implicating Type II supernovae as potential progenitors. From the interplay between the light and heavy r -process elements, we infer a diminishing relative production of light r -process elements with increasing Type II supernova contributions, challenging the notion that Type II supernovae are the primary source of these light r -process elements in the early Milky Way. A chemodynamical analysis based on Gaia astrometric data and our derived abundances indicates that all but one of our program stars are likely to be of accreted origin. Additionally, our examination of α-poor stars underscores the occurrence of an early accretion event from a satellite on a prograde orbit, similar to that of the Galactic disc. [ABSTRACT FROM AUTHOR]

With JWST slated to gain high-fidelity time-dependent data on brown dwarf atmospheres, it is highly anticipated to do the same for directly imaged, sub-Jupiter exoplanets. With this new capability, the need for a full three-dimensional (3D) understanding to explain spectral features and their time dependence is becoming a vital aspect for consideration. To examine the atmospheric properties of directly imaged sub-Jupiter exoplanets, we use the 3D Exo-FMS general circulation model to simulate a metal-enhanced generic young sub-Jupiter object. We couple Exo-FMS to a kinetic chemistry scheme, a tracer-based cloud formation scheme and a spectral radiative-transfer model to take into account the chemical and cloud feedback on the atmospheric thermochemical and dynamical properties. Our results show a highly complex feedback between clouds and chemistry on to the 3D temperature structure of the atmosphere, bringing about latitudinal differences and inducing time-dependent stormy features at photospheric pressures. This suggests a strong connection and feedback between the spatial cloud coverage and chemical composition of the atmosphere, with the temperature changes and dynamical motions induced by cloud opacity and triggered convection feedback driving chemical species behaviour. In addition, we also produce synthetic latitude-dependent and time-dependent spectra of our model to investigate atmospheric variability and periodicity in commonly used photometric bands. Overall, our efforts put the included physics in 3D simulations of exoplanets on par with contemporary 1D radiative-convective equilibrium modelling. [ABSTRACT FROM AUTHOR]

We present the first theoretical line profile calculations of the ultraviolet spectral lines of carbon perturbed by helium using a semiclassical collision approach and high-quality ab initio potentials and electronic transition dipole moments. The temperature range is from 5000 to 8000 K. These results are important for astrophysical modelling of spectra in atmospheres of white dwarf stars showing atomic carbon in an helium atmosphere. Beyond the conventional symmetrical Lorentzian core at low He density, these lines exhibit a blue asymmetric behaviour. This blue asymmetry is a consequence of low maxima in the corresponding C–He potential energy difference curves at short internuclear distances. The collisional profiles are carefully examined and their perturber density dependence allow to understand the various line shapes of the observed carbon spectral lines in helium-rich white dwarf photosphere where the He perturber densities reach several 1021 cm−3. [ABSTRACT FROM AUTHOR]

Over the past several decades, conventional spectral analysis techniques of polluted white dwarfs have become powerful tools to learn about the geology and chemistry of extrasolar bodies. Despite their proven capabilities and extensive legacy of scientific discoveries, these techniques are, however, still limited by their manual, time-intensive, and iterative nature. As a result, they are susceptible to human errors and are difficult to scale up to population-wide studies of metal pollution. This paper seeks to address this problem by presenting cecilia , the first machine learning (ML)-powered spectral modelling code designed to measure the metal abundances of intermediate-temperature (10 000 ≤ T eff ≤ 20 000 K), Helium-rich polluted white dwarfs. Trained with more than 22 000 randomly drawn atmosphere models and stellar parameters, our pipeline aims to overcome the limitations of classical methods by replacing the generation of synthetic spectra from computationally expensive codes and uniformly spaced model grids, with a fast, automated, and efficient neural-network-based interpolator. More specifically, cecilia combines state-of-the-art atmosphere models, powerful artificial intelligence tools, and robust statistical techniques to rapidly generate synthetic spectra of polluted white dwarfs in high-dimensional space, and enable accurate (≲0.1 dex) and simultaneous measurements of 14 stellar parameters – including 11 elemental abundances – from real spectroscopic observations. As massively multiplexed astronomical surveys begin scientific operations, cecilia 's performance has the potential to unlock large-scale studies of extrasolar geochemistry and propel the field of white dwarf science into the era of Big Data. In doing so, we aspire to uncover new statistical insights that were previously impractical with traditional white dwarf characterization techniques. [ABSTRACT FROM AUTHOR]

Evolved cool stars of various masses are major cosmic engines, delivering substantial mechanical and radiative feedback to the interstellar medium through strong stellar winds and supernova ejecta. These stars play a pivotal role in enriching the interstellar medium with vital chemical elements that constitute the essential building blocks for the formation of subsequent generations of stars, planets, and potentially even life. Within the complex tapestry of processes occurring in the atmospheres of these cool and luminous stars, convection takes center stage. Convection is a non-local, complex phenomenon marked by non-linear interactions across diverse length scales within a multi-dimensional framework. For these particular stars, characterized by their considerable luminosities and extensive scale heights, convection transitions to a global scale. This transition is facilitated by the transmission of radiative energy through the non-uniform outer layers of their atmospheres. To have a full understanding of this phenomenon, the application of global comprehensive 3D radiation-hydrodynamics simulations of stellar convection is of paramount importance. We present two state-of-the-art numerical codes: CO5BOLD and Athena++. Furthermore, we provide a view on their applications as: pivotal roles in enabling a comprehensive investigation into the dynamic processes linked to convection; and critical tools for accurately modeling the emissions produced during shock breakouts in Type II-P supernovae. [ABSTRACT FROM AUTHOR]

We provide in this work Stark broadening data (widths and shifts) for 120 ultraviolet spectral lines of Ni  v ion. Our calculations are performed using the semiclassical perturbation method. For energy levels and oscillator strength calculations, we use the multiconfiguration Hatree–Fock approach. Stark shifts and widths are calculated for collisions with electrons and with the positive ions: H+, He+, and He++, allowing us to take into account the important perturbers in stellar atmospheres. We compare our Stark widths with estimations obtained using the Cowley formula. Our electron impact Stark widths are also fitted with temperature using a logarithmic formula. Finally, our obtained Stark widths are used to investigate the influence of Stark broadening in the atmospheric conditions of hot DA white dwarfs. Despite the importance of ultraviolet lines of Ni  v ion for modelling white dwarf atmospheres and also for investigations of variation of fundamental constants with gravitational potential, we did not find Stark broadening data previously calculated or measured for Ni  v ion. The objective of this work is to give the missed data. [ABSTRACT FROM AUTHOR]

Magnetars, the most strongly magnetized neutron stars, are among the most promising targets for X-ray polarimetry. Imaging X-ray Polarimetry Explorer (IXPE), the first satellite devoted to exploring the sky in polarized X-rays, has observed four magnetars to date. A proper interpretation of IXPE results requires the development of new atmospheric models that can take into proper account the effects of the magnetized vacuum on par with those of the plasma. Here we investigate the effects of mode conversion at the vacuum resonance on the polarization properties of magnetar emission by computing plane-parallel atmospheric models under varying conditions of magnetic field strength/orientation, effective temperature, and allowing for either complete or partial adiabatic mode conversion. Complete mode conversion results in a switch of the dominant polarization mode, from the extraordinary (X) to the ordinary (O) one, below an energy that decreases with increasing magnetic field strength, occurring at |$\approx 0.5\, \mathrm{keV}$| for a magnetic field strength of |$B=10^{14}\, \mathrm{G}$|⁠. Partial adiabatic mode conversion results in a reduced polarization degree when compared with a standard plasma atmosphere. No dominant mode switch occurs for |$B=10^{14}\, \mathrm{G}$|⁠ , while there are two switches for lower fields of |$B=3\times 10^{13}\, \mathrm{G}$|⁠. Finally, by incorporating our models in a ray-tracing code, we computed the expected polarization signal at infinity for different emitting regions on the star surface and for different viewing geometries. The observability of quantum electrodynamics signatures with IXPE and with future soft X-ray polarimeters as Rocket Experiment Demonstration of a Soft X-ray Polarimeter is discussed. [ABSTRACT FROM AUTHOR]

The MM ro-vibrational line list for methane (12CH4) is presented; MM covers wavelengths λ > 0.83 μm (wavenumbers up to 12 000 cm−1) and contains over 50 billion transitions between 9155 208 states with total angular momentum J ≤ 60. MM was generated through solution of the nuclear motion Schrödinger equation using variational program trove for an empirically derived potential energy surface (PES) and a new high-level ab initio dipole moment surface. The PES was constructed by fitting the ro-vibrational energies of CH4 to a set of highly accurate, experimentally derived energies. Molecular states are classified using the Td (M) symmetry group and are fully assigned with rotation and vibration quantum numbers. The MM line list is adapted to high-resolution applications by replacing the calculated ro-vibrational energies with the experimentally derived values where available, namely for 23 208 states with J ≤ 27 below 9986 cm−1. Doing so leads to over 1000 000 experimentally derived CH4 lines compared to approximately |$330\, 000$| lines of 12CH4 in the HITRAN data base. The MM line list is shown to be more complete than the recent HITEMP methane line list. Methane spectra computed using MM across a broad range of temperatures and wavenumbers show excellent agreement with experiment. The MM line list supersedes the previous ExoMol methane line lists 10to10 and 30to10 both in terms of accuracy and coverage. Together with the pre-computed ExoMolOP molecular atmospheric opacity tables, it is now the recommended CH4 data set in the ExoMol data base (www.exomol.com). [ABSTRACT FROM AUTHOR]

The MM ro-vibrational line list for methane (12CH4) is presented; MM covers wavelengths λ > 0.83 μm (wavenumbers up to 12 000 cm−1) and contains over 50 billion transitions between 9155 208 states with total angular momentum J ≤ 60. MM was generated through solution of the nuclear motion Schrödinger equation using variational program trove for an empirically derived potential energy surface (PES) and a new high-level ab initio dipole moment surface. The PES was constructed by fitting the ro-vibrational energies of CH4 to a set of highly accurate, experimentally derived energies. Molecular states are classified using the Td (M) symmetry group and are fully assigned with rotation and vibration quantum numbers. The MM line list is adapted to high-resolution applications by replacing the calculated ro-vibrational energies with the experimentally derived values where available, namely for 23 208 states with J ≤ 27 below 9986 cm−1. Doing so leads to over 1000 000 experimentally derived CH4 lines compared to approximately |$330\, 000$| lines of 12CH4 in the HITRAN data base. The MM line list is shown to be more complete than the recent HITEMP methane line list. Methane spectra computed using MM across a broad range of temperatures and wavenumbers show excellent agreement with experiment. The MM line list supersedes the previous ExoMol methane line lists 10to10 and 30to10 both in terms of accuracy and coverage. Together with the pre-computed ExoMolOP molecular atmospheric opacity tables, it is now the recommended CH4 data set in the ExoMol data base (www.exomol.com). [ABSTRACT FROM AUTHOR]

Variations in chemical abundances with evolutionary phase have been identified among stars in globular and open clusters with a wide range of metallicities. In the metal-poor clusters, these variations compare well with predictions from stellar structure and evolution models considering the internal diffusive motions of atoms and ions, collectively known as atomic diffusion, when moderated by an additional mixing process with a fine-tuned efficiency. We present here an investigation of these effects in the Galactic globular cluster NGC 6121 (M4) ([Fe/H] = −1.13) through a detailed chemical abundance analysis of 86 stars using high-resolution ESO Very Large Telescope (VLT) Fibre Large Array Multi Element Spectrograph (FLAMES) spectroscopy. The stars range from the main-sequence turnoff point (TOP) to the red giant branch (RGB) just above the bump. We identify C-N-O and Mg-Al-Si abundance anticorrelations, and confirm the presence of a bimodal population differing by 1 dex in nitrogen abundance. The composition of the second-generation stars imply pollution from both massive (20–40  |$\rm M_{\odot }$|⁠) and asymptotic giant branch stars. We find evolutionary variations in chemical abundances between the TOP and RGB, which are robust to uncertainties in stellar parameters and modelling assumptions. The variations are weak, but match predictions well when employing efficient additional mixing. Without correcting for Galactic production of lithium, we derive an initial lithium abundance 2.63 ± 0.10, which is marginally lower than the predicted primordial big-bang nucleosynthesis value. [ABSTRACT FROM AUTHOR]