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Stellar theory enables us to understand the properties of stars at different stages of their evolution, and contributes to other fields of astrophysics such as galactic and exoplanet studies. Assessing the accuracy of stellar theories necessitates high precision, model-independent measurements of the properties of real stars, such as those obtainable for the components of double-lined eclipsing binaries (DLEBs), while asteroseismology offers probing power of the stellar interior if one or both components pulsate. KIC 4851217 is a DLEB containing two late A-type stars and exhibits pulsations of the |$\delta$| Scuti type. By analysing high resolution HERMES and moderate resolution ISIS spectra, jointly with Kepler and Transiting Exoplanet Survey Satellite light curves, we measured the masses, radii, and effective temperatures of the components to precisions of |$\sim$| 0.5, |$\sim$| 1.1, and |$\sim$| 1 per cent, respectively. We additionally report the discovery and characterization of a tertiary M-dwarf companion. Models of the system's spectral energy distribution agree with an age of 0.82 Gyr, with the more massive and larger secondary component near the end of the main-sequence lifetime. An examination of the pulsating component's pulsation frequencies reveals 39 pulsation multiplets that are split by the orbital frequency. For most of these, it is evident that the pulsation axes have been tilted into the orbital plane. This makes KIC 4851217 a tidally tilted pulsator (TTP). This precisely characterized |$\delta$| Scuti DLEB is an ideal candidate for advancing intermediate-mass stellar theory, contributing to our understanding of hierarchical systems as well as to the topic of TTPs. [ABSTRACT FROM AUTHOR]

To date, we have access to enormous inventories of stellar spectra that allow the extraction of atmospheric parameters and chemical abundances essential in stellar studies. However, characterizing such a large amount of data is complex and requires a good understanding of the studied object to ensure reliable and homogeneous results. In this study, we present a methodology to measure homogenously the basic atmospheric parameters and detailed chemical abundances of over 1600 thin disc main-sequence stars in the 100 pc solar neighbourhood, using APOGEE-2 infrared spectra. We employed the code tonalli to determine the atmospheric parameters using a prior on |$\log {g}$|⁠. The |$\log {g}$| prior in tonalli implies an understanding of the treated population and helps to find physically coherent answers. Our atmospheric parameters agree within the typical uncertainties (100 K in |$\mathrm{T_{eff}}$|⁠ , 0.15 dex in |$\log {g}$| and [M/H]) with previous estimations of ASPCAP and Gaia DR3. We use our temperatures to determine a new infrared colour–temperature sequence, in good agreement with previous works, that can be used for any main-sequence star. Additionally, we used the bacchus code to determine the abundances of Mg, Al, Si, Ca, and Fe in our sample. The five elements (Mg, Al, Si, Ca, Fe) studied have an abundance distribution centred around slightly subsolar values in agreement with previous results for the solar neighbourhood. The over 1600 main-sequence stars' atmospheric parameters and chemical abundances presented here are useful in follow-up studies of the solar neighbourhood or as a training set for data-driven methods. [ABSTRACT FROM AUTHOR]

Newly-developed spectrographs with increased resolving powers, particularly those covering the near-IR range, allow the characterization of more and more absorption lines in stellar spectra. This includes the identification and confirmation of absorption lines and the calibration of oscillator strengths. In this study, we provide empirical values of |${{\rm log} gf}$| based on the abundances of classical Cepheids obtained with optical spectra to establish the consistency between optical and infrared abundance results. Using time series spectra of classical Cepheids obtained with WINERED spectrograph (0.97–1.35  |$\mu$| m, R |$\sim$| 28000), we demonstrate that we can determine the stellar parameters of the observed Cepheids, including effective temperature (⁠|${T_\mathrm{eff}}$|⁠), surface gravity (⁠|${{\rm log} g}$|⁠), microturbulence (⁠|$\xi$|⁠), and metallicity (⁠|${\rm {[{\mathrm{ M}}/\mathrm{ H}]}}$|⁠). With the newly calibrated relations of line-depth ratios, we can achieve accuracy and precision comparable to optical studies, with uncertainties of |$\sim$| 90 K and 0.108 dex for |${T_\mathrm{eff}}$|⁠ , and |${{\rm log} g}$|⁠ , respectively. Finally, we created a new atlas of absorption lines, featuring precise abundance measurements of various elements found in the atmosphere of Cepheids, including neutron-capture elements whose |${{\rm log} gf}$| values have been astrophysically calibrated. [ABSTRACT FROM AUTHOR]

We identify the bright Am-type star HD 181793 to be a previously unknown eclipsing, chemically peculiar heartbeat binary, the second of its kind known. The system carries an orbital period of |$P = 11.47578275 \pm 0.00000055$| d. We use TESS photometry and LCOGT NRES radial velocity data to build a self-consistent orbital model and determine the fundamental stellar characteristics of the primary. We use a spectral separation method to unveil the secondary and measure the masses of both stars. The radial velocity amplitude of the primary, |$K_1 = 47.41\, {^ {+0.13}}_ {-0.12}$| km s−1, gives a mass |$M_1 = 1.57 \pm 0.01$|  M |$_\odot$|⁠. The secondary radial velocity amplitude |$K_2 = 84.95\, {^ {+0.12}}_ {-0.09}$| km s−1 yields a mass ratio |$q = 0.558 \pm 0.002$| and a secondary mass |$M_2 = 0.87 \pm 0.01$| M |$_\odot$|⁠. From the spectral energy distribution and Gaia parallax, we find a radius |$R_1 = 2.04 \pm 0.05$|  R |$_\odot$|⁠. The grazing transit profile and spectroscopic luminosity ratio indicate |$R_2 = 1.04\, {^ {+0.15}}_ {-0.10}$|  R |$_\odot$|⁠ , suggesting an early-K spectral type. We show that the heartbeat feature in the TESS light curve can be explained by time-varying ellipsoidal variation, driven by the orbital eccentricity of |$e = 0.3056\, {^ {+0.0024}}_ {-0.0026}$|⁠ , and relativistic beaming of the light of the primary. We find no evidence of tidally excited oscillations. [ABSTRACT FROM AUTHOR]

This is the first comprehensive study of the eclipsing binaries V527 Dra and V2846 Cyg, based on radial velocities and ground- and space-based light curves. We perform detailed modeling of these data to derive the absolute parameters and the orbital properties of the two systems. V527 Dra is found to be a semidetached, and V2846 Cyg a contact binary. Both show continual out-of-eclipse variations that can be explained by migrating dark spots of magnetic origin. We also perform the eclipse timing variation (ETV) analysis which reveals that V527 Dra has a tertiary companion whose mass (⁠|${\sim} 1 \,{\rm M}_{\odot }$|⁠) and orbital inclination (⁠|${\sim} 70^{\circ }$|⁠) are additionally constrained by radial velocities. The ETV diagram of V2846 Cyg displays a quadratic trend accompanied by a low-amplitude cyclic variation, likely due to a magnetic cycle, although further eclipse times are needed to provide a clearer explanation. Lastly, we demonstrate a correlation between the variations in spot parameters obtained via light curve modelling for individual orbital cycles and the residual ETVs, essentially confirming the assumption of magnetic activity in both systems. [ABSTRACT FROM AUTHOR]

We made a survey of the variable stars in a 13.2 × 13.2 arcmin |$^{2}$| centred on the field of the Galactic bulge cluster NGC 6558. A total of 78 variables were found in the field of the cluster. Many of these variables are included in the catalogue of variable stars in Galactic globular clusters (Clement et al. 2001), OGLE or Gaia DR3 data releases. A membership analysis based on the proper motions of Gaia DR3 revealed that many of these variables do not belong to the cluster. We employed the data from the aforementioned surveys and our own data in the VI photometric system to estimate the periods, which along with the light-curves morphology and position in a deferentially dereddened colour–magnitude diagram (CMD), help classifying the variable types. Two new member variables were found; an eclipsing binary (V18) and a semiregular SR/L (V19). In the end, we conclude that only nine variables are likely cluster members. Member variables were used to discuss the mean metallicity and distance of the parental cluster and find the average values. [ABSTRACT FROM AUTHOR]

Aims. We aim to investigate the theoretical possibility of accurately determining the helium-to-metal enrichment ratio ΔY/ΔZ from precise observations of double-lined eclipsing binary systems. Methods. Using Monte Carlo simulations, we drew synthetic binary systems with masses between 0.85 and 1.00 M⊙ from a grid of stellar models. Both stars were sampled from a grid with ΔY/ΔZ = 2.0, with a primary star at 80% of its main-sequence evolution. Subsequently, a broader grid with ΔY/ΔZ from 1.0 to 3.0 was used in the fitting process. To account for observational uncertainties, two scenarios were explored: S1, with realistic uncertainties of 100 K in temperature and 0.1 dex in [Fe/H]; and S2, with halved uncertainties. We repeated the simulation at two baseline metallicities: [Fe/H] = 0.0 and −0.3. Results. The posterior distributions of ΔY/ΔZ revealed significant biases. The distributions were severely biased towards the edge of the allowable range in the S1 error scenario. The situation only marginally improved when considering the S2 scenario. The effect is due to the impact of changing ΔY/ΔZ in the stellar effective temperature and its interplay with [Fe/H] observational error, and it is therefore not restricted to the specific fitting method. Despite the presence of these systematic discrepancies, the age of the systems were recovered unbiased with 10% precision. Conclusions. Our findings indicate that the observational uncertainty in effective temperature and metallicity significantly hinders the accurate determination of the ΔY/ΔZ parameter from main-sequence binary systems. [ABSTRACT FROM AUTHOR]

We studied eight new doubly eclipsing stellar systems. We found that they are all rare examples of quadruple systems of 2 + 2 architecture, where both inner pairs are eclipsing binaries. Until now, such a configuration had only been proven for dozens of systems on the whole sky. We enlarged this rare group of systems with four stars in the Small Magellanic Cloud (SMC) galaxy and four brighter stars on the northern sky. These analysed systems are the following: OGLE SMC-ECL-2339 (both eclipsing periods of 0.72884 days and 3.39576 days; mutual orbital period of 5.95 years); OGLE SMC-ECL-3075 (1.35890 d, 2.41587 d, 9.75 yr); OGLE SMC-ECL-4756 (0.91773 d, 2.06047 d, 4.34 yr); OGLE SMC-ECL-6093 (0.90193 d, 2.03033 d, 31.2 yr); GSC 01949-01700 (0.24058 d, 0.75834 d, 21.7 yr); ZTF J171602.61+273606.5 (0.36001 d, 4.51545 d, 19.5 yr); WISE J210935.8+390501 (0.33228 d, 3.51575 d, 1.9 yr); and V597 And (0.46770 d, 0.35250, 20.4 yr). These systems constitute a rare selection of W UMa stars among the doubly eclipsing quadruples. For all of the systems, new dedicated observations were obtained as well. V597 And is definitely the most interesting system for several reasons: (1) the system is the brightest in our sample; (2) it is a rare quintuple (2 + 2) + 1 system; and (3) it is also closest to the Sun. It yielded the predicted angular separation of the two components of 57 mas, which is probably within the detection limits for modern, high-angular-resolution techniques. [ABSTRACT FROM AUTHOR]

Context. Radio surveys of early-type stars have revealed a number of non-thermal emitters. Most of these have been shown to be binaries, where the collision between the two stellar winds is responsible for the non-thermal emission. Aims. HD 168112 is a non-thermal radio emitter, whose binary nature has only recently been confirmed spectroscopically. We obtained independent spectroscopic observations to determine its orbit, in addition to radio observations to see if the thermal or non-thermal nature of the emission changes during the periastron passage. Methods. We monitored HD 168112 spectroscopically for a 13 yr time span. From these data, we determined the orbital parameters, which we compared to the previous results in the literature. The stellar parameters of both components were determined by comparing the spectra to TLUSTY models. From the spectral index of the radio observations, we found how the nature of the emission changes as the system goes through periastron. Combining our results with other literature data allowed us to further constrain the orbital and stellar parameters. Results. We find HD 168112 to have an orbital period of P = 512.17−0.11+0.41 days, an eccentricity of e = 0.7533−0.0124+0.0053, and a mass ratio close to one. From our spectroscopic modelling, we derived the stellar parameters, but we had difficulty arriving at a spectroscopic mass ratio of one. The radio observations around periastron show only thermal emission, suggesting that most of the synchrotron photons are absorbed in the two stellar winds at that phase. Combining our data with the optical interferometry detection, we could constrain the inclination angle to i ~ 63°, and the mass of each component to ~26 M⊙. Conclusions. We have provided an independent spectroscopic confirmation of the binary nature of HD 168112. Although detected as a non-thermal radio emitter, near periastron the radio emission of this highly eccentric system is thermal and is mainly formed in the colliding-wind region. This effect will also occur in other colliding-wind binaries. [ABSTRACT FROM AUTHOR]

Context. Deep learning (DL) techniques are a promising approach among the set of methods used in the ever-challenging determination of stellar parameters in M dwarfs. In this context, transfer learning could play an important role in mitigating uncertainties in the results due to the synthetic gap (i.e. difference in feature distributions between observed and synthetic data). Aims. We propose a feature-based deep transfer learning (DTL) approach based on autoencoders to determine stellar parameters from high-resolution spectra. Using this methodology, we provide new estimations for the effective temperature, surface gravity, metallicity, and projected rotational velocity for 286 M dwarfs observed by the CARMENES survey. Methods. Using autoencoder architectures, we projected synthetic PHOENIX-ACES spectra and observed CARMENES spectra onto a new feature space of lower dimensionality in which the differences between the two domains are reduced. We used this low-dimensional new feature space as input for a convolutional neural network to obtain the stellar parameter determinations. Results. We performed an extensive analysis of our estimated stellar parameters, ranging from 3050 to 4300 K, 4.7 to 5.1 dex, and −0.53 to 0.25 dex for Teff, log 푔, and [Fe/H], respectively. Our results are broadly consistent with those of recent studies using CARMENES data, with a systematic deviation in our Teff scale towards hotter values for estimations above 3750 K. Furthermore, our methodology mitigates the deviations in metallicity found in previous DL techniques due to the synthetic gap. Conclusions. We consolidated a DTL-based methodology to determine stellar parameters in M dwarfs from synthetic spectra, with no need for high-quality measurements involved in the knowledge transfer. These results suggest the great potential of DTL to mitigate the differences in feature distributions between the observations and the PHOENIX-ACES spectra. [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]

Stellar spectral template libraries play an important role in the automated analysis of stellar spectra. Synthetic template libraries cover a very large parameter space but suffer from poor matching with observed spectra. In this study, we propose a synthetic-to-observed spectral translation (SOST) method based on generative adversarial networks. The SOST method is able to calibrate synthetic spectra by converting them to the corresponding observed spectra. We applied this method to Kurucz synthetic spectra and observed spectra data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). After that, we constructed a stellar spectral library with uniform and broad parameter distributions using the SOST-corrected Kurucz synthetic spectra. Our stellar spectral template library contains 2431 spectra spanning a parameter space of 3500–8000 K for effective temperature (Teff), 0.0–5.0 dex for surface gravity (log g), and −2.0–0.5 dex for metallicity ([Fe/H]). The spectra in the library have a resolution of R ∼ 1800 and cover the wavelength range 3900–8700 Å. In order to verify the accuracy of this template library, we used the template library and the template-matching algorithm to derive the parameters of the PASTEL database. Compared to measurements using the original synthetic template library, the accuracies of the three parameters, Teff, log g, and [Fe/H], are improved, from 140 K, 0.31 dex, and 0.21 dex to 121 K, 0.26 dex, and 0.13 dex, respectively. In addition, we re-parameterised more than six million stellar spectra released by LAMOST DR8. [ABSTRACT FROM AUTHOR]

Context. Blue supergiants (BSGs) are key objects for understanding the evolution of massive stars, which play a crucial role in the evolution of galaxies. However, discrepancies between theoretical predictions and empirical observations have opened up important questions yet to be answered. Studying statistically significant and unbiased samples of these objects can help to improve the situation. Aims. We perform a homogeneous and comprehensive quantitative spectroscopic analysis of a large sample of Galactic luminous blue stars (a majority of which are BSGs) from the IACOB spectroscopic database, providing crucial parameters to refine and improve theoretical evolutionary models. Methods. We derived the projected rotational velocity (υ sin i) and macroturbulent broadening (υmac) using IACOB-BROAD, which combines Fourier transform and line-profile fitting techniques. We compared high-quality optical spectra with state-of-the-art simulations of massive star atmospheres computed with the FASTWIND code. This comparison allowed us to derive effective temperatures (Teff), surface gravities (log 푔), microturbulences (ξ), surface abundances of silicon and helium, and to assess the relevance of stellar winds through a wind-strength parameter (log Q). Results. We provide estimates and associated uncertainties of the above-mentioned quantities for the largest sample of Galactic luminous O9 to B5 stars spectroscopically analyzed to date, comprising 527 targets. We find a clear drop in the relative number of stars at Teff ≈ 21 kK, coinciding with a scarcity of fast rotating stars below that temperature. We speculate that this feature (roughly corresponding to B2 spectral type) might be roughly delineating the location of the empirical terminal-age main sequence in the mass range between 15 and 85 M⊙. By investigating the main characteristics of the υ sin i distribution of O stars and BSGs as a function of Teff, we propose that an efficient mechanism transporting angular momentum from the stellar core to the surface might be operating along the main sequence in the high-mass domain. We find correlations between ξ,υmac and the spectroscopic luminosity 퓛 (defined as Teff4 / g). We also find that no more than 20% of the stars in our sample have atmospheres clearly enriched in helium, and suggest that the origin of this specific subsample might be in binary evolution. We do not find clear empirical evidence of an increase in the wind strength over the wind bi-stability region toward lower Teff. [ABSTRACT FROM AUTHOR]

Context. Modeling the convection process is a long-standing problem in stellar physics. To date, all ad hoc models have relied on a free parameter, α, (among others) that has no real physical justification and is therefore poorly constrained. However, a link exists between this free parameter and the entropy of the stellar adiabat. There are existing prescriptions, derived from 3D stellar atmospheric models, that treat entropy as a function of stellar atmospheric parameters (effective temperature, surface gravity, and chemical composition). This can offer sufficient constraints on α through the development of entropy-calibrated models. However, several questions have arisen as these models are increasingly used with respect to which prescription should be used and whether it ought to be used in its original form, along with the impacts of uncertainties on entropy-calibrated models. Aims. We aim to study the three existing prescriptions in detail and determine which of them demonstrate the most optimal performance and how it should be applied. Methods. We implemented the entropy-calibration method into the stellar evolution code (Cesam2k20) and performed comparisons with the Sun and the α Cen system. In addition, we used data from the CIFIST grid of 3D atmosphere models to evaluate the accuracy of the prescriptions. Results. Of the three entropy prescriptions currently available, we determined the one that has the best functional form for reproducing the entropies of the 3D models. However, the coefficients involved in this formulation must not be taken from the original paper because they were calibrated against a flawed set of entropies. We also demonstrate that the entropy obtained from this prescription should be corrected for the evolving chemical composition and for an entropy offset different between various EoS tables. This must be done following a precise procedure to ensure that the classical parameters obtained from the models are not strongly biased. Finally, we provide a data table with entropy of the adiabat of the CIFIST grid, along with the fits for these entropies. Conclusions. Thanks to a precise examination of entropy-calibrated modeling, we are able to offer our recommendations with respect to which adiabatic entropy prescription to use, how to correct it, and how to implement the method into a stellar evolution code. [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]

Context. The binary star NY Hya is a bright, detached, double-lined eclipsing system with an orbital period of just under five days with two components each nearly identical to the Sun and located in the solar neighbourhood. Aims. The objective of this study is to test and confront various stellar evolution models for solar-type stars based on accurate measurements of stellar mass and radius. Methods. We present new ground-based spectroscopic and photometric as well as high-precision space-based photometric and astrometric data from which we derive orbital as well as physical properties of the components via the method of least-squares minimisation based on a standard binary model valid for two detached components. Classic statistical techniques were invoked to test the significance of model parameters. Additional empirical evidence was compiled from the public domain; the derived system properties were compared with archival broad-band photometry data enabling a measurement of the system's spectral energy distribution that allowed an independent estimate of stellar properties. We also utilised semi-empirical calibration methods to derive atmospheric properties from Strömgren photometry and related colour indices. Results. We measured (percentages are fractional uncertainties) masses, radii, and effective temperatures of the two stars in NY Hya and found them to be MA = 1.1605 ± 0.0090 M⊙ (0.78%), RA = 1.407 ± 0.015 R⊙ (1.1%), Teff, A = 5595 ± 61 K (1.09%), MB = 1.1678 ± 0.0096 M⊙ (0.82%), RB = 1.406 ± 0.017 R⊙ (1.2%), and Teff, B = 5607 ± 61 K (1.09%). The atmospheric properties from Strömgren photometry agree well with spectroscopic results. No evidence was found for nearby companions from high-resolution imaging. A detailed analysis of space-based data revealed a small but significant eccentricity (e cos ω) of the orbit. The spectroscopic and frequency analysis on photometric time series data reveal evidence of clear photospheric activity on both components likely in the form of star spots caused by magnetic activity. Conclusions. We confronted the observed physical properties with classic and magnetic stellar evolution models. Classic models yielded both young pre-main-sequence and old main-sequence turn-off solutions with the two components at super-solar metallicities, in disagreement with observations. Based on chromospheric activity and X-ray observations, we invoke magnetic models. While magnetic fields are likely to play an important role, we still encounter problems in explaining adequately the observed properties. To reconcile the observed tensions we also considered the effects of star spots known to mimic magnetic inhibition of convection. Encouraging results were obtained, although unrealistically large spots were required on each component. Overall we conclude that NY Hya proves to be complex in nature, and requires additional follow-up work aiming at a more accurate determination of stellar effective temperature and metallicity. [ABSTRACT FROM AUTHOR]

A sample of warm, low-level semiregular variables chosen from the General Catalogue of Variable Stars is studied for their chemical compositions by analysing high-resolution optical spectra. The abundance ratios from Na/Fe to Eu/Fe displayed by these and previously analysed semiregular variables are quite similar to ratios displayed by normal red giants across the Galactic thin and thick discs and halo populations in the solar neighbourhood, suggesting from this perspective that the variables may be among the more photometrically active red giants. [ABSTRACT FROM AUTHOR]

EBLM J0608 |$-$| 59/TOI-1338/BEBOP-1 is a 12 |$^{\rm th}$| -magnitude, F9 V star in an eclipsing binary with a much fainter M dwarf companion on a wide, eccentric orbit (P  = 14.6 d). The binary is orbited by two circumbinary planets: one transiting on a 95-d orbit and one non-transiting on a 215-d orbit. We have used high-precision photometry from the TESS mission combined with direct mass measurements for the two stars published recently to measure the following model-independent radii: |$R_1 = 1.32 \pm 0.02 {\rm R}_{\odot }$|⁠ , |$R_2 = 0.309 \pm 0.004 {\rm R}_{\odot }$|⁠. Using |$R_1$| and the parallax from Gaia EDR3, we find that this star's angular diameter is |$\theta = 0.0309 \pm 0.0005$|  mas. The apparent bolometric flux of the primary star corrected for both extinction and the contribution from the M dwarf (⁠|$\lt 0.4$|  per cent) is |${\mathcal {F}}_{{\oplus },0} = (0.417\pm 0.005)\times 10^{-9}$|  erg cm |$^{-2}$|  s |$^{-1}$|⁠. Hence, this F9 V star has an effective temperature |$T_{\rm eff,1} = 6031{\rm \, K} \pm 46{\rm \, K\, (rnd.)} \pm 10 {\rm \, K\, (sys.)}$|⁠. EBLM J0608 |$-$| 59 is an ideal benchmark star that can be added to the sample of such systems we are establishing for 'end-to-end' tests of the stellar parameters measured by large-scale spectroscopic surveys. [ABSTRACT FROM AUTHOR]

In the hunt for Earth-like exoplanets, it is crucial to have reliable host star parameters, as they have a direct impact on the accuracy and precision of the inferred parameters for any discovered exoplanet. For stars with masses between 0.35 and 0.5 M⊙, an unexplained radius inflation is observed relative to typical stellar models. However, for fully convective objects with a mass below 0.35 M⊙, it is not known whether this radius inflation is present, as there are fewer objects with accurate measurements in this regime. Low-mass eclipsing binaries present a unique opportunity to determine empirical masses and radii for these low-mass stars. Here, we report on such a star, EBLM J2114−39 B. We have used HARPS and FEROS radial velocities and TESS photometry to perform a joint fit of the data and produce one of the most precise estimates of a very low mass star's parameters. Using a precise and accurate radius for the primary star using Gaia DR3 data, we determine J2114−39 to be a M 1 = 0.998 ± 0.052 M⊙ primary star hosting a fully convective secondary with mass |$M_2~=~0.0993~\pm 0.0033~\, \mathrm{M_{\odot }}$|⁠ , which lies in a poorly populated region of parameter space. With a radius |$R_2 =~0.1250~\pm 0.0016~\, \mathrm{R_{\odot }}$|⁠ , similar to TRAPPIST-1, we see no significant evidence of radius inflation in this system when compared to stellar evolution models. We speculate that stellar models in the regime where radius inflation is observed might be affected by how convective overshooting is treated. [ABSTRACT FROM AUTHOR]

The u -band magnitude is vital for determining stellar parameters and investigating specific astronomical objects. However, flux calibration in the u band for stars in the Galactic disc presents significant challenges. In this study, we introduce a comprehensive recalibration of u -band photometric magnitudes of the VPHAS+ Data Release 4, employing the stellar colour regression technique. By leveraging the expansive set of XP spectra and G BP photometry from Gaia Data Release 3, as well as the individual stellar extinction values provided by the literature, we have obtained precise model magnitudes of nearly 3 million stars. Our analysis identifies systematic magnitude offsets that exhibit a standard deviation of 0.063 mag across different observational visits, 0.022 mag between various CCDs, and 0.009 mag within pixel bins. We have implemented precise corrections for these observational visits, CCD chips, and pixel bins-dependent magnitude offsets. These corrections have led to a reduction in the standard deviation between the observed magnitudes and the model magnitudes from 0.088 to 0.065 mag, ensuring that the calibrated magnitudes are independent of stellar magnitude, colour, and extinction. The enhanced precision of these magnitudes substantially improves the quality of astrophysical research and offers substantial potential for furthering our understanding of stellar astrophysics. [ABSTRACT FROM AUTHOR]

High-contrast eclipsing binaries with low mass M-dwarf secondaries are precise benchmark stars to build empirical mass–radius relationships for fully convective low-mass (⁠|$\rm M_{\star } \lt 0.35\, M_{\odot }$|⁠) dwarf stars. The contributed light of the M-dwarf in such binaries is usually much less than one per cent at optical wavelengths. This enables the detection of circumbinary planets from precise radial velocity measurements. High-resolution cross-correlation techniques are typically used to detect exoplanet atmospheres. One key aspect of these techniques is the post-processing, which includes the removal of telluric and spectral lines of the host star. We introduce the application of such techniques to optical high-resolution spectra of the circumbinary planet-host TOI-1338/BEBOP-1, turning it effectively into a double-lined eclipsing binary. By using simulations, we further explore the impact of post-processing techniques for high-contrast systems. We detect the M-dwarf secondary with a significance of 11σ and measure absolute dynamical masses for both components. Compared to previous model-dependent mass measurements, we obtain a four times better precision. We further find that the post-processing results in negligible systematic impact on the radial velocity precision for TOI-1338/BEBOP-1 with more than |$96.6\,$|  per cent (1σ) of the M-dwarf's signal being conserved. We show that these methods can be used to robustly measure dynamical masses of high-contrast single-lined binaries providing important benchmark stars for stellar evolution particularly near the bottom of the main sequence. We also demonstrate how to retrieve the phase curve of an exoplanet with high-resolution spectroscopy using our data. [ABSTRACT FROM AUTHOR]

EC 19529−4430 was identified as a helium-rich star in the Edinburgh–Cape (EC) Survey of faint-blue objects and subsequently resolved as a metal-poor extreme helium (EHe) star in the Southern African Large Telescope (SALT) survey of chemically peculiar hot subdwarfs. This paper presents a fine analysis of the SALT high-resolution spectrum. EC 19529−4430 has |$T_{\rm eff} = 20\, 700 \pm 250$|  K, |$\log g /{\rm cm\, s^{-2}} = 3.49\pm 0.03$|⁠ , and an overall metallicity some 1.3 dex below solar; surface hydrogen is |$\approx 0.5~{{\ \rm per\ cent}}$| by number. The surface CNO ratio 1:100:8 implies that the surface consists principally of CNO-processed helium and makes EC 19529−4430 the coolest known carbon-poor and nitrogen-rich EHe star. Metal-rich analogues include V652 Her and GALEX J184559.8−413827. Kinematically, its retrograde orbit indicates membership of the Galactic halo. No pulsations were detected in TESS photometry and there is no evidence for a binary companion. EC 19529−4430 most likely formed from the merging of two helium white dwarfs, which themselves formed as a binary system some 11 Gyr ago. [ABSTRACT FROM AUTHOR]

The empirical upper limit to Red Supergiant (RSG) luminosity, known as the Humphreys-Davidson (HD) limit, has been commonly explained as being caused by the stripping of stellar envelopes by metallicity-dependent, line-driven winds. As such, the theoretical expectation is that the HD limit should be higher at lower metallicity, where weaker mass-loss rates mean that higher initial masses are required for an envelope to be stripped. In this work, we test this prediction by measuring the luminosity function of RSGs in M31 and comparing to those in the LMC and SMC. We find that $\[\log ({L_{{\rm{m}}ax}}/{L_ \odot }) = 5.53 \pm 0.03\]$ in M31 (Z ≳ Z⊙), consistent with the limit found for both the LMC (Z ∼ 0.5 Z⊙) and SMC (Z ∼ 0.25 Z⊙), while the RSG luminosity distributions in these 3 galaxies are consistent to within 1σ. We therefore find no evidence for a metallicity dependence on both the HD limit and the RSG luminosity function, and conclude that line-driven winds on the main sequence are not the cause of the HD limit. [ABSTRACT FROM AUTHOR]

Current models of stellar evolution predict that stars more massive than ∼6 M⊙ should have completely depleted all lithium (Li) in their atmospheres by the time when they reach the He core burning phase. Against this, a non-negligible number of red giants with masses ≳6 M⊙ presenting strong Li lines have recently been reported. Motivated by this finding, we have carried out a spectroscopic survey of red supergiants (RSGs) in the Perseus Arm and a selection of young open clusters in the Magellanic Clouds to assess the presence of the Li i 6708Å doublet line. Based on a sample of > 70 objects, close to one third of RSGs in the Perseus Arm display noticeable Li lines, with perhaps a trend towards a lower fraction among more luminous stars. The samples in the Magellanic Clouds are not as large, but hint at a metallicity dependence. Twenty one RSGs in 5 LMC clusters show a very high fraction of Li detection, around 40%. Conversely, 17 RSGs in 5 SMC clusters give only one secure detection. The interpretation of these observational results is not straightforward, but a mechanism for Li production seems most likely. Further characterisation work is ongoing, while theoretical studies into this matter are urgently needed. [ABSTRACT FROM AUTHOR]

Upcoming large-scale spectroscopic surveys such as WEAVE and 4MOST will provide thousands of spectra of massive stars, which need to be analysed in an efficient and homogeneous way. Studies on massive stars are usually based on samples of a few hundred objects which pushes current spectroscopic analysis tools to their limits because visual inspection is necessary to verify the spectroscopic fit. The novel spectroscopic analysis pipeline takes advantage of the statistics that large samples provide, and determines the model error to account for imperfections in stellar atmosphere codes due to simplified, wrong or missing physics. Considering observational plus model uncertainties improve spectroscopic fits. The pipeline utilises the entire spectrum rather than selected diagnostic lines allowing a wider range of temperature from B to early O stars to be analysed. A small fraction of stars like peculiar, contaminated or spectroscopic binaries require visual inspection, which are identified through their larger uncertainties. [ABSTRACT FROM AUTHOR]

An overview is provided of the scientific goals of the Magellanic Cloud component of the STScI Directors Discretionary UV initiative ULLYSES, together with the complementary spectroscopic survey XShootU (VLT/Xshooter) and other ancillary datasets. Together, ULLYSES and XShootU permit the first comprehensive, homogeneous study of wind densities and velocities in metal-poor massive stars, plus UV/optical spectroscopic libraries for population synthesis models and a large number of interstellar sight-lines towards the Magellanic Clouds. [ABSTRACT FROM AUTHOR]

Whether it be due to rapid rotation or binary interactions, deviations from spherical symmetry are common in massive stars. These deviations from spherical symmetry are known to cause non-uniform distributions of various parameters across the surface including temperature, which can drive internal mixing processes within the envelopes of these massive stars. Despite how common these 3D distortions are, they are often neglected in spectroscopic analyses. We present a new spectral analysis code called spamms (Spectroscopic PAtch Model for Massive Stars) specifically designed to analyze non-spherical systems. We discuss how the code works and discuss its assumptions. Furthermore, we demonstrate how spamms can be applied to a variety of different types of systems and we show how it can model 3D effects in a way that current analysis techniques are not able to. [ABSTRACT FROM AUTHOR]

In 2020, HR 6819 was reported to be a triple system containing the closest black hole to Earth. However, these results were contested, with an alternative explanation of a post-interaction binary suggested. Using new integral field spectroscopic and interferometric data, we have been able to determine the true nature of this exotic source. [ABSTRACT FROM AUTHOR]

We present the results obtained using spectroscopic data taken with the intermediate-resolution Multi Unit Spectroscopic Explorer (MUSE) of B and A-type supergiants and bright giants in the Sculptor Group galaxy NGC 300. For our analysis, a hybrid local thermodynamic equilibrium (LTE) line-blanketing+non-LTE method was used to improve the previously published results for the same data. In addition, we present some further applications of this work, which includes extending the flux-weighted gravity luminosity relationship (FGLR), a distance determination method for supergiants. This pioneering work opens up a new window to explore this relation, and also demonstrates the enormous potential of integral field spectroscopy (IFS) for extragalactic quantitative stellar studies. [ABSTRACT FROM AUTHOR]

In addition to being spectacular objects, very massive stars (VMS) are suspected to have a tremendous impact on their environment and on the whole cosmic evolution. The nucleosynthesis both during their advanced stages and their final explosion likely contribute greatly to the overall enrichment of the Universe. Their resulting Supernovae are candidates for the most superluminous events and their extreme conditions lead also to very important radiative and mechanical feedback effects, from local to cosmic scale. With the recent implementation of a new equation of state in the GENEC stellar evolution code, appropriate for describing the conditions in the central regions of very massive stars in the advanced phases, we present new results on VMS evolution from Population III to solar metallicity. We explore their evolution and final fate as potential (P)PISNe across the cosmic time. We compare our results to recent spectroscopic observations of VMS in the Large Magellanic Cloud (LMC). We also underline the important radiative feedback of Population III VMS during the reionization epoch and the chemical contribution of these stars at high metallicity, especially for short-lived radionuclei. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of a comprehensive study of six eclipsing binaries whose components are confirmed or suspected Am stars. By combining long-term, high-resolution Catania Astrophysical Observatory Spectropolarimeter (CAOS) spectroscopy and TESS photometry, we have been able to accurately obtain the orbital parameters of each system as well as the atmospheric parameters of its components. We performed an in-depth chemical analysis and provided chemical abundances of C, O, Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, Zr, and Ba. From the solution of the light and radial curves, we have determined the masses, radii, and temperatures with a good degree of accuracy. We observe apsidal motion in the eccentric system HD 216429, in which the Rossiter-McLaughlin effect is also noted. We inferred the age of our targets by fitting isochrones on the HR diagram and find that both components in each system are properly described with the same isochrone, which reinforces our results. Furthermore, dynamical and evolutionary masses, independently obtained, show an excellent agreement. According to the out-of-eclipse variability shown in their TESS light curves and their position on the Hertzsprung-Russell diagram, we claim that the stars HD 42954 (as δ Sct type) and HD 151604 (γ Dor) have a pulsating nature. Based on the chemical analysis, we corroborate that four of the systems studied here are formed by Am stars, while in the remaining ones (HD 126031 and HD 216429) only the primary component exhibits a peculiar composition. Additionally, the age distribution found in Am stars supports their suitability as age tracers in stellar populations. [ABSTRACT FROM AUTHOR]

Aims. We investigated the theoretical biases affecting the asteroseismic grid-based estimates of stellar mass, radius, and age in the presence of a mismatch between the heavy element mixture of observed stars and stellar models. Methods. We performed a controlled simulation adopting a stellar effective temperature, [Fe/H], an average large frequency spacing, and a frequency of maximum oscillation power as observational constraints. Synthetic stars were sampled from grids of stellar models computed with different [α/Fe] values from 0.0 to 0.4. The mass, radius, and age of these objects were then estimated by adopting a grid of models with a fixed [α/Fe] value of 0.0. The experiment was repeated assuming different sets of observational uncertainties. In the reference scenario, we adopted an uncertainty of 1.5% in seismic parameters, 50 K in effective temperature, and 0.05 dex in [Fe/H]. A higher uncertainty in the atmospheric constraints was also adopted in order to explore the impact on the precision of the observations of the estimated stellar parameters. Results. Our Monte Carlo experiment showed that estimated parameters are biased up to 3% in mass, 1.5% in radius, and 4% in age when the reference uncertainty scenario was adopted. These values correspond to 45%, 48%, and 16% of the estimated uncertainty in the stellar parameters. These non-negligible biases in mass and radius disappear when adopting larger observational uncertainties because of the possibility of the fitting algorithm exploring a wider range of possible solutions. However, in this scenario, the age is significantly biased by −8%. Finally, we verified that the stellar mass, radius, and age can be estimated with a high accuracy by adopting a grid with the incorrect value of [α/Fe] if the metallicity [Fe/H] of the target is adjusted to match the Z in the fitting grid. In this scenario, the maximum bias in the age was reduced to 1.5%. [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. Our aim in this paper is to refine the orbital and physical parameters of the HATS-2 planetary system and study transit timing variations and atmospheric composition thanks to transit observations that span more than 10 yr and that were collected using different instruments and pass-band filters. We also investigate the orbital alignment of the system by studying the anomalies in the transit light curves induced by starspots on the photosphere of the parent star. Methods. We analysed new transit events from both ground-based telescopes and NASA's TESS mission. Anomalies were detected in most of the light curves and modelled as starspots occulted by the planet during transit events. We fitted the clean and symmetric light curves with the JKTEBOP code and those affected by anomalies with the PRISM+GEMC codes to simultaneously model the photometric parameters of the transits and the position, size, and contrast of each starspot. Results. We found consistency between the values we found for the physical and orbital parameters and those from the discovery paper and ATLAS9 stellar atmospherical models. We identified different sets of consecutive starspot-crossing events that temporally occurred in less than five days. Under the hypothesis that we are dealing with the same starspots, occulted twice by the planet during two consecutive transits, we estimated the rotational period of the parent star and, in turn the projected and the true orbital obliquity of the planet. We find that the system is well aligned. We identified the possible presence of transit timing variations in the system, which can be caused by tidal orbital decay, and we derived a low-resolution transmission spectrum. [ABSTRACT FROM AUTHOR]

In recent years, a new generation of optical intensity interferometers has emerged, leveraging the existing infrastructure of Imaging Atmospheric Cherenkov Telescopes (IACTs). The MAGIC telescopes host the MAGIC-SII system (Stellar Intensity Interferometer), implemented to investigate the feasibility and potential of this technique on IACTs. After the first successful measurements in 2019, the system was upgraded and now features a real-time, dead-time-free, 4-channel, GPU-based correlator. These hardware modifications allow seamless transitions between MAGIC's standard very-high-energy gamma-ray observations and optical interferometry measurements within seconds. We establish the feasibility and potential of employing IACTs as competitive optical Intensity Interferometers with minimal hardware adjustments. The measurement of a total of 22 stellar diameters are reported, 9 corresponding to reference stars with previous comparable measurements, and 13 with no prior measurements. A prospective implementation involving telescopes from the forthcoming Cherenkov Telescope Array Observatory's Northern hemisphere array, such as the first prototype of its Large-Sized Telescopes, LST-1, is technically viable. This integration would significantly enhance the sensitivity of the current system and broaden the UV-plane coverage. This advancement would enable the system to achieve competitive sensitivity with the current generation of long-baseline optical interferometers over blue wavelengths. [ABSTRACT FROM AUTHOR]

Detailed chemical studies of F/G/K – or solar-type – stars have long been routine in stellar astrophysics, enabling studies in both Galactic chemodynamics and exoplanet demographics. However, similar understanding of the chemistry of M and late-K dwarfs – the most common stars in the Galaxy – has been greatly hampered both observationally and theoretically by the complex molecular chemistry of their atmospheres. Here, we present a new implementation of the data-driven Cannon model, modelling T eff, log  g , [Fe/H], and [Ti/Fe] trained on low–medium resolution optical spectra (4000–7000  Å) from 103 cool dwarf benchmarks. Alongside this, we also investigate the sensitivity of optical wavelengths to various atomic and molecular species using both data-driven and theoretical means via a custom grid of MARCS synthetic spectra, and make recommendations for where MARCS struggles to reproduce cool dwarf fluxes. Under leave-one-out cross-validation, our Cannon model is capable of recovering T eff, log  g , [Fe/H], and [Ti/Fe] with precisions of 1.4 per cent, |$\pm 0.04\,$|  dex, |$\pm 0.10\,$|  dex, and |$\pm 0.06\,$|  dex respectively, with the recovery of [Ti/Fe] pointing to the as-yet mostly untapped potential of exploiting the abundant – but complex – chemical information within optical spectra of cool stars. [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]

We report the discovery of a new Blue Large-Amplitude Pulsator (BLAP), SMSS J184506−300804 (SMSS-BLAP-1) in Data Release 2 of the SkyMapper Southern Sky Survey. We conduct high-cadence photometric observations in the u band to confirm a periodic modulation of the light curve. SMSS-BLAP-1 has a ∼19-min pulsation period with an amplitude of 0.2 mag in u band, and is similar to the classical BLAPs found by OGLE. From spectroscopic observations with the Wide-Field Spectrograph on the Australian National University 2.3m telescope, we confirm it as a low-gravity BLAP: best-fitting parameters from the non-LTE tlusty model are estimated as T eff = 29 020 |$^{+193}_{-34}$|  K, log g = 4.661 |$^{+0.008}_{-0.143}$| (cm s−2), and log n (He)/ n (H) = −2.722 |$^{+0.057}_{-0.074}$|  dex. However, our BLAP exhibits a very He-deficient atmosphere compared to both low- and high-gravity BLAPs, which have log n (He)/ n (H) in the range −0.41∼−2.4. [ABSTRACT FROM AUTHOR]

The Transiting Exoplanet Survey Satellite (TESS) mission has provided the community with high-precision times-series photometry for ∼2.8 million stars across the entire sky via the full frame image (FFI) light curves produced by the TESS Science Processing Operations Center (SPOC). This set of light curves is an extremely valuable resource for the discovery of transiting exoplanets and other stellar science. However, due to the sample selection, this set of light curves does not constitute a magnitude-limited sample. In order to understand the effects of this sample selection, we use Gaia Data Release 2 (DR2) and Data Release 3 (DR3) to study the properties of the stars in the TESS -SPOC FFI light-curve set, with the aim of providing vital context for further research using the sample. We report on the properties of the TESS -SPOC FFI targets in Sectors 1–55 (covering Cycles 1–4). We cross-match the TESS -SPOC FFI targets with the Gaia DR2 and DR3 catalogues of all targets brighter than Gaia magnitude 14 to understand the effects of sample selection on the overall stellar properties. This includes Gaia magnitude, parallax, radius, temperature, non-single star flags, luminosity, radial velocity, and stellar surface gravity. In total, there are ∼16.7 million Gaia targets brighter than G  = 14, which when cross-matched with the TESS -SPOC FFI targets leaves ∼2.75 million. We investigate the binarity of each TESS -SPOC FFI target and calculate the radius detection limit from two detected TESS transits that could be detected around each target. Finally, we create a comprehensive main-sequence TESS -SPOC FFI target sample that can be utilized in future studies. [ABSTRACT FROM AUTHOR]

Ultra-short period planets (USPs) have orbital periods of less than 1 d. Since their masses and radii can be determined to a higher precision than long-period planets, they are the preferred targets to determine the density of planets which constrains their composition. The K2-106 system is particularly interesting because it contains two planets of nearly identical masses. One is a high-density USP, the other is a low-density planet that has an orbital period of 13 d. Combining the Gaia DR3 results with new ESPRESSO data allows us to determine the masses and radii of the two planets more precisely than before. We find that the USP K2-106 b has a density consistent with an Earth-like composition, and K2-106 c is a low-density planet that presumably has an extended atmosphere. We measure a radius of |$\rm R_p=1.676_{-0.037}^{+0.037}$| |$\rm R_{{\oplus }}$|⁠ , a mass of |$\rm M_p=7.80_{-0.70}^{+0.71}$| M ⊕, and a density of |$\rm \rho =9.09_{-0.98}^{+0.98}$| |$\rm g\, cm^{-3}$| for K2-106 b. For K2-106 c, we derive |$R_p=2.84_{-0.08}^{+0.10}$| |$\rm R_{{\oplus }}$|⁠ , |$M_p=7.3_{-2.4}^{+2.5}$| |$\rm M_{{\oplus }}$|⁠ , and a density of |$\rm \rho = 1.72_{-0.58}^{+0.66}$| |$\rm g\, cm^{-3}$|⁠. We finally discuss the possible structures of the two planets with respect to other low-mass planets. [ABSTRACT FROM AUTHOR]

We present a statistical and multiwavelength photometric studies of young open cluster IC 1590. We identified 91 cluster members using Gaia DR3 astrometry data using ensemble-based unsupervised machine learning techniques. From Gaia EDR3 data, we estimate the best-fitting parameters for IC 1590 using the Automated Stellar Cluster Analysis package (asteca) yielding the distance d ∼ 2.87 ± 0.02 kpc, age ∼ 3.54 ± 0.05 Myr, metallicity z ∼ 0.0212 ± 0.003, binarity value of ∼ 0.558, and extinction Av ∼ 1.252 ± 0.4 mag for an Rv value of ∼ 3.322 ± 0.23. We estimate the initial mass function slope of the cluster to be α = 1.081 ± 0.112 for single stars and α = 1.490 ± 0.051 for a binary fraction of ∼ 0.558 in the mass range 1  M⊙ ≤ m (M⊙) ≤ 100  M⊙. The G -band luminosity function slope is estimated to be ∼ 0.33 ± 0.09. We use (J − H) versus (H − Ks) colour–colour diagram to identify young stellar objects (YSOs). We found that all the identified YSOs have ages ≤ 2 Myr and masses ∼ 0.35 – 5.5  M⊙. We also fit the radial surface density profile. Using the galpy , we performed orbit analysis of the cluster. The extinction map for the cluster region has been generated using the PNICER technique, and it is almost similar to the dust structure obtained from the 500  μm dust continuum emissions map of Herschel SPIRE. We finally at the end discussed the star formation scenario in the cluster region. [ABSTRACT FROM AUTHOR]

Upcoming large-scale spectroscopic surveys with e.g. WEAVE (William herschel telescope Enhanced Area Velocity Explorer) and 4MOST (4-metre Multi-Object Spectroscopic Telescope) will provide thousands of spectra of massive stars, which need to be analysed in an efficient and homogeneous way. Usually, studies of massive stars are limited to samples of a few hundred objects, which pushes current spectroscopic analysis tools to their limits because visual inspection is necessary to verify the spectroscopic fit. Often uncertainties are only estimated rather than derived and prior information cannot be incorporated without a Bayesian approach. In addition, uncertainties of stellar atmospheres and radiative transfer codes are not considered as a result of simplified, inaccurate, or incomplete/missing physics or, in short, idealized physical models. Here, we address the question of 'How to compare an idealized model of complex objects to real data?' with an empirical Bayesian approach and maximum a posteriori approximations. We focus on application to large-scale optical spectroscopic studies of complex astrophysical objects like stars. More specifically, we test and verify our methodology on samples of OB stars in 30 Doradus region of the Large Magellanic Clouds using a grid of fastwind model atmospheres. Our spectroscopic model de-idealization analysis pipeline takes advantage of the statistics that large samples provide by determining the model error to account for the idealized stellar atmosphere models, which are included into the error budget. The pipeline performs well over a wide parameter space and derives robust stellar parameters with representative uncertainties. [ABSTRACT FROM AUTHOR]

Observations of low-mass stars have frequently shown a disagreement between observed stellar radii and radii predicted by theoretical stellar structure models. This 'radius inflation' problem could have an impact on both stellar and exoplanetary science. We present the final results of our observation programme with the CHaracterising ExOPlanet Satellite (CHEOPS) to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions (EBLMs). Combined with the spectroscopic orbits of the solar-type companions, we can derive the masses, radii, and effective temperatures of 23 M-dwarf stars. We use the pycheops data analysis software to analyse their primary and secondary occultations. For all but one target, we also perform analyses with Transiting Exoplanet Survey Satellite (TESS) light curves for comparison. We have assessed the impact of starspot-induced variation on our derived parameters and account for this in our radius and effective temperature uncertainties using simulated light curves. We observe trends in inflation with both metallicity and orbital separation. We also observe a strong trend in the difference between theoretical and observational effective temperatures with metallicity. There is no such trend with orbital separation. These results are not consistent with the idea that the observed inflation in stellar radius combines with lower effective temperature to preserve the luminosity predicted by low-mass stellar models. Our EBLM systems provide high-quality and homogeneous measurements that can be used in further studies of radius inflation. [ABSTRACT FROM AUTHOR]

We infer the dynamical masses of stars across the Hertzsprung–Russell (H–R) diagram using wide binaries from the Gaia survey. Gaia 's high-precision astrometry measures the wide binaries' orbital motion, which contains the mass information. Using wide binaries as the training sample, we measure the mass of stars across the 2D H–R diagram using the combination of statistical inference and neural networks. Our results provide the dynamical mass measurements for main-sequence stars from 0.1 to 2 M⊙, unresolved binaries, and unresolved triples on the main sequence, and the mean masses of giants and white dwarfs. Two regions in the H–R diagram show interesting behaviours in mass, where one of them is pre-main-sequence stars, and the other one may be related to close compact object companions like M dwarf-white dwarf binaries. These mass measurements depend solely on Newtonian dynamics with minimal assumptions on eccentricities, providing independent constraints on stellar evolutionary models, and the occurrence rate of compact objects. [ABSTRACT FROM AUTHOR]

Detailed chemical composition of stars is of prime interest for a range of topics in modern stellar astrophysics, such as the chemical evolution of the Galaxy or the formation, composition, and structure of exoplanets. In this work, we derive the C and O abundances and update Sc, V, Mn, and Co abundances considering hyperfine structure effects and correcting for non-local thermodynamical equilibrium for a sample of 196 late-F, G-, and early-K stars with wide resolved M-dwarf companions. We accomplished this by employing the equivalent width method and high-resolution spectroscopic data. Furthermore, we investigated the distributions of [X/Fe] ratios and [C/O] as a function of metallicity ([Fe/H]) and kinematic population. The observed trends are consistent with previous findings reported in the literature. Additionally, we searched for confirmed exoplanets around our primary stars in the literature and found 24 exoplanets in 17 systems, while none of the M-dwarf companions in our sample presented confirmed exoplanets. In conclusion, our study provides homogeneous abundances from high-resolution spectra for a large sample of FGK primary stars, paving the way for further research on stellar abundances of the M secondaries and exoplanetary science. [ABSTRACT FROM AUTHOR]

Estimating precise metallicity of M dwarfs is a well-known difficult problem due to their complex spectra. In this work, we empirically calibrate the metallicity using wide binaries with a F, G, or K dwarf and a M dwarf companion. With 1308 FGK+M wide binaries well observed by LAMOST, we calibrated M dwarf's [Fe/H] by using the Stellar LAbel Machine (SLAM) model, a data-driven method based on support vector regression. The [Fe/H] labels of the training data are from FGK companions in range of [−1,0.5] dex. The T effs are based on APOGEE, spanning [3100, 4400] K. The uncertainties in SLAM estimates of [Fe/H] and T eff are ∼0.15 dex and ∼40 K, respectively, at snri >100, where snri is the signal-to-noise ratio (SNR) at i band of M dwarf spectra. We applied the trained SLAM model to determine the [Fe/H] and T eff for ∼630 000 M dwarfs with low-resolution spectra in LAMOST DR9. Compared to other literature also using FGK+M wide binaries for calibration, our [Fe/H] estimates show no bias but a scatter of ∼0.14–0.18 dex. However, the [Fe/H] compared to APOGEE shows a systematic difference of ∼0.10–0.15 dex with a scatter of ∼0.15–0.20 dex. While the T eff compared to APOGEE has a bias of 3 K with a scatter of 62 K, it is systematically higher by 180 K compared to other calibrations based on the bolometric temperature. Finally, we calculated the ζ index for 1308 M dwarf secondaries and presents a moderate correlation between ζ and [Fe/H]. [ABSTRACT FROM AUTHOR]

The kinematics, mean α-elements, and ages of the stars reveal two distinct disc populations observed in the Solar neighbourhood. Although several studies have been carried out to characterize abundances of chemical elements and kinematic identifications in these populations, there are few studies that dealt with the analysis of stellar rotation and characteristics of populations focused on low-mass stars of the F and G types. In this work, we propose a new approach to classify stellar populations from the thin and thick disc for F and G dwarf stars by relating chemical abundance and rotation (v  sin  i) of these stars in the rotational–chemical–plane (v  sin  i –[α/Fe]–[Fe/H] plot). Our results show that the two rotational-chemical sequences disentangled, high- and low-[α/Fe] components, present properties (α-enhanced, ages, kinematics, space velocity gradients, local density ratio) closely linked to the stars of the chemically and kinematically defined as thin and thick disc components. This study has an impact on calibrations that relate ages to rotation (gyro-chronology) as well as age to chemical abundances (chemochronology), as well as sheds light on the understanding of the processes of Galactic disc formation. [ABSTRACT FROM AUTHOR]

We present the results of the spectroscopic study of a chemically peculiar star HD 152564. Using medium-resolution (R  = 37 000) observations obtained with the high-resolution fibre échelle spectrograph mounted on the South African Large Telescope, we determined atmospheric parameters T eff = 11 950 ± 200 K and log  g  = 3.6 ± 0.2 dex. Abundance analysis revealed mild deficiency of the light elements and an overabundance of up to ∼2 dex of metals, with the greatest excess for silicon. With these characteristics, HD 152564 is a typical member of the silicon subgroup of Ap stars. The rotational modulation of the light curve and line profiles of HD 152564 are typical for the inhomogeneous surface distribution of elements in its atmosphere. We performed multi-element Doppler imaging of the surface of HD 152564. Abundance maps constructed for He, O, Mg, Si, and Fe revealed the concentration of these elements in a sequence of equatorial spots as well as in the circumpolar rings. The photometric maximum of the light curve coincided with the visibility of two most overabundant silicon spots. Abundances determined from the different ionization stages of Fe and Si show clear evidence for vertical stratification of these elements in the atmosphere of HD 152564. Meanwhile, the horizontal distribution of silicon reconstructed from the lines of different ionization stages and excitation energies appears to be identical with increasing average abundance deeper in atmosphere. [ABSTRACT FROM AUTHOR]

It has been suggested that small chemical anomalies observed in planet-hosting wide binary systems could be due to planet signatures, where the role of the planetary mass is still unknown. We search for a possible planet signature by analysing the T C trends in the remarkable binary system HD 196067–HD 196068. At the moment, only HD 196067 is known to host a planet that is near the brown dwarf regime. We take advantage of the strong physical similarity between both stars, which is crucial to achieving the highest possible precision in stellar parameters and elemental chemical abundances. This system gives us a unique opportunity to explore whether a possible depletion of refractories in a binary system could be inhibited by the presence of a massive planet. We performed a line-by-line chemical differential study, employing the non-solar-scaled opacities, in order to reach the highest precision in the calculations. After differentially comparing both stars, HD 196067 displays a clear deficiency in refractory elements in the T C plane, a lower iron content (0.051 dex), and also a lower Li  i content (0.14 dex) than its companion. In addition, the differential abundances reveal a T C trend. These targets represent the first cases of an abundance difference around a binary system hosting a super-Jupiter. Although we explored several scenarios to explain the chemical anomalies, none of them can be entirely ruled out. Additional monitoring of the system as well as studies of larger sample of wide binary systems hosting massive planets are needed to better understand the chemical abundance trend observed in HD 196067−68. [ABSTRACT FROM AUTHOR]

It is known from archival TESS data that the semi-detached Algol system XZ Ursae Majoris (UMa) is one of the candidate binary stars exhibiting short-period oscillations. We secured new high-resolution spectroscopic observations for the program target to better understand its binary and pulsation properties. From the echelle spectra, the radial velocities (RVs) of the eclipsing pair were derived, and the atmosphere parameters of the primary component were measured to be v Asin  i  = 80 ± 7 km s−1, T eff, A = 7940 ± 120 K, and [M/H] = −0.15 ± 0.20. The combined solution of our double-lined RVs and the TESS data provides robust physical parameters for XZ UMa with mass and radius measurement precision of better than 2%. The outside-eclipse residuals from a mean light curve in the 0.002 phase bin were used for multifrequency analyses, and we extracted 32 significant frequencies (22 in <5.0 d−1 and 10 in 39–52 d−1). The low frequencies may be mostly aliasing sidelobes, while six of the high frequencies may be pulsation signals arising from the detached primary located inside the δ Sct domain. Their periods, pulsation constants, and pulsational–orbital-period ratios indicate that the mass-accreting primary star is a δ Sct pulsator and, hence, XZ UMa is an oscillating eclipsing Algol. [ABSTRACT FROM AUTHOR]