Joachim M. Bestenlehner

Despite being a powerful tool, the synthesis of stellar population models requires many ingredients, all of them involving assumptions and uncertainties. In particular the libraries of stellar spectra are crucial ingredients. In this work we present a new empirical spectral library, that will push the limits for modeling young, low metallicity stellar systems.

Digital competency is now core to chemical engineering practice, yet the extent and coherence of digitalisation skills provision across undergraduate curricula remain uneven. This study maps qualitatively and qualitatively digital learning outcomes across undergraduate chemical engineering programmes at the University of Sheffield, against a digital skills framework (data analysis, process simulation, process automation & control, reproducible workflows, programming, data governance). In recent years, digital skills education within chemical engineering education has advanced considerably, driven by the broader industrial shift toward Industry 4.0 and reinforced by the global challenges. Academic institutions have begun to integrate digitalisation-related content more deliberately within syllabus, in alignment with degree programme accreditation requirements and industry needs. Beyond introductory spreadsheet manipulation and basic programming, many courses are now embedding more advanced digital capabilities, including data engineering, scientific programming, process analytics, and optimisation techniques. Results of this study reveal a scaffolded digital pathway, where students are exposed gradually through core taught content and applied knowledge activities to a variety of digital tools across their years of study in a by-design approach at earlier years that becomes organic later on. From limited exposure and credit correlation in Year 1, students complete Year 4 having at least quadrupled their exposure to digital tools, with higher credits awarded to “digital” in the case of particular elective modules or research projects. This study offers a methodology and a worked example for chemical engineering programmes seeking measurable uplift in Industry 4.0 readiness and impact on chemical engineering graduate outcomes.

Context . Hot massive stars lose mass through radiation-driven winds, producing significant chemical, radiative, and mechanical feedback in the surrounding environment. The properties of these winds play a crucial role in determining the star’s evolutionary path. Considering the physics of radiation-driven winds, the wind properties should depend on the metal content of the stellar atmosphere. Therefore, studying the wind properties of massive stars in different metallicities (Z) provides a sanity check on prescriptions that are widely used in evolutionary calculations. Aims . We first aim to obtain the stellar and wind properties of a sample of late-O and B supergiants in the Small Magellanic Cloud (SMC). Using these properties, we aim to quantify the dependence of wind properties on metallicity by comparing them with those of a Large Magellanic Cloud (LMC) counterpart study, which has a similar sample and data, and employed the same modelling techniques used in this study. Methods . Spectroscopic modelling of UV and optical data from ULLYSES and XShootU was performed using the radiative transfer code CMFGEN. We also employed an updated Bayesian inference method similar to BONNSAI to explore the evolutionary history of our sample. Results . We derived the stellar and wind properties of 20 late-O and B supergiants. We derived the following metallicity-dependent recipe for wind momentum: log D _mom = (1.64 − 0.75 log Z/Z _⊙ ) log ( L _bol /10 ⁶ L _⊙ ) + 1.38 log Z/Z _⊙ + 29.17, which is applicable for 5.4 ≤ log L _bol / L _⊙ ≤ 6.1 and 14 ≤ T _eff /kK ≤ 32. Conclusions . We find a significant dependence of the wind momentum on the metallicity, which is largely due to the mass-loss rates. We do not find any evidence of a discontinuity in either the mass-loss rate or the ratio of the terminal wind velocity to the escape velocity, v _∞ / v _esc , between 25 and 21 kK, which could be attributed to the bi-stability jump, although when taking into account the effect of luminosity in the transformed mass-loss rate, the behaviour appears to be different. Stellar parameters are consistent across different methods and radiative transfer codes, whereas mass-loss rates differ significantly with our values being generally lower. We find a discrepancy between the evolutionary and spectroscopic masses in 40% of our sample, with the evolutionary mass usually being systematically higher. The mass-loss rates of blue supergiants are far too low to strip the stellar envelope and the subsequent formation of classical Wolf-Rayet (WR) stars, leading to the conclusion that luminous blue variable eruptions or binary interactions are necessary to explain characteristics of the WR population in the SMC.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

The Binarity at LOw Metallicity (BLOeM) survey is an ESO large programme designed to obtain multi-epoch spectroscopy for 929 massive stars in the Small Magellanic Cloud (SMC). It will provide binary fractions and orbital configurations of binary systems and search for dormant black hole binary candidates (OB+BH). We present projected rotational velocities ( v sin i ) of all sources, and, using the multiplicity properties presented in previous papers, we derive the v sin i distributions of apparent single stars, single-lined spectroscopic (SB1) binaries, and SB2 systems. We identify a locus in the Hertzsprung-Russell diagram where rotational velocities decrease significantly; we interpret this feature as broadly corresponding to the terminal-age main sequence. The main-sequence cohort is distinguished by a broad range of v sin i values, but with a strong peak in the distribution in the range 30–60 km s ⁻¹ , which is close to the resolution limit of ∼30 km s ⁻¹ , indicating the presence of many upper limits. Sources in this low v sin i peak are distributed throughout the main sequence and are also present in the SB1 sample, though less prominent than in the single-star distribution. A preliminary analysis of the lowest v sin i cohort, which includes SB1 systems, implies that roughly one-third may be nitrogen rich, and we speculate that this cohort is a mix of pristine single stars, long-period binaries, and merger products. The SB2 systems appear to be mostly short-period binaries in synchronous rotation, and their v sin i estimates are distributed around a mean value of ∼140 km s ⁻¹ . Higher v sin i sources are also present in the single and SB1 systems, all of which have a tail to higher v sin i values. This is consistent with tidal and mass-transfer effects. The supergiants, with a few exceptions, have low v sin i , and the bulk of these systems is essentially unresolved at the current spectral resolution (∼30 km s ⁻¹ ).

Context Massive stars (>8 M_⊙) play an important role in galactic evolution at all cosmic ages. A deeper understanding of the behaviour of mass loss in low metallicity environments is therefore required. This behaviour largely determines the path of a massive star throughout its life, and its final fate. A better understanding would allow us to predict the evolution of massive stars in the early Universe better. Aims We investigated the theoretical bi-stability jump, which predicts an increase in the mass-loss rates below T_eff ≈25–21 kK. We further constrained the photospheric and wind parameters of a sample of late-O and B supergiants in the Large Magellanic Cloud. Methods We used the 1D non-local thermal equilibrium radiative transfer model CMFGEN in a grid-based approach and a fine-tuned spectroscopic fitting procedure that allowed us to determine the stellar and wind parameters of each star. We applied this method to ultra-violet data from the ULLYSES programme and to complementary optical data from the XShootU collaboration. We also used evolutionary models to obtain the evolutionary masses, and we compared them to the spectroscopic masses we derived. Results We derived physical parameters and wind properties of 16 late-O and B supergiants that span a wide temperature range of T_eff ≈12–30 kK, surface gravity range of log (g/cm s⁻²) ≈1.8–3.1, and mass-loss rate range of Ṁ ˙≈ 10^−7.6−10^−5.7 M_⊙ yr⁻¹. We also compared our results to previous studies that attempted to investigate the metallicity dependence of the wind properties. Conclusions The photospheric and wind properties we derived are consistent with those of multiple previous studies. The evolutionary and spectroscopic masses for most of our sample are consistent within the uncertainties. Our results do not reproduce a bi-stability jump in any temperature range, but rather a monotonic decrease in the mass-loss rate at lower temperatures. We obtain a relation of the wind terminal velocity to effective temperature for supergiants in the Large Magellanic Cloud of ν_∞/km s⁻¹ = 0.076(±0.011)T_eff/K − 884(±260). The mass-loss rates we derived disagree with the mass-loss rates predicted by any of the numerical recipes. This is also the case for the ratio of the terminal wind velocity to the escape velocity ν_∞/ν_esc, and we derived the relation ν_∞/ν_esc = 4.1(±0.8) log (T_eff/K) −16.3(± 3.5). The wind parameters depend on the metallicity, based on a comparison with a previous study of the Small Magellanic Cloud, and the modified wind momentum-luminosity relation is log D_mom^LMC = 1.39(±0.54)log(L_bol/L_⊙) + 20.4(±3.0).

Context. Mass loss governs the evolution of massive stars and shapes the stellar surroundings. To quantify the impact of the stellar winds, we need to know the exact mass-loss rates; however, empirical constraints on the rates are hampered by limited knowledge of their small-scale wind structure, also referred to as ‘wind clumping’. Aims. We aim to improve empirical constraints on the mass loss of massive stars by investigating the clumping properties of their winds, in particular, the relation between stellar parameters and wind structure. Methods. We analysed the optical and ultraviolet spectra of 25 O-type giants and supergiants in the Large Magellanic Cloud, using the model atmosphere code FASTWIND and a genetic algorithm. We derived the stellar and wind parameters, including detailed clumping properties, such as the amount of clumping, the density of the interclump medium, velocity–porosity of the medium, and wind turbulence. Results. We obtained stellar and wind parameters for 24 of our sample stars and found that the winds are highly clumped, with an average clumping factor of 〈f_cl〉 = 33 14, an interclump density factor of 〈f_ic〉 = 0.2 0.1, and moderate-to-strong velocity-porosity effects of 〈f_vel〉 = 0.6 0.2. The scatter around the average values of the wind-structure parameters is large. With the exception of a significant, positive correlation between the interclump density factor and mass loss, we find no dependence of clumping parameters on the mass-loss rate or stellar properties. Conclusions. In the luminosity range we investigate here, the empirical and theoretical mass-loss rates both have a scatter of about 0.5 dex (or a factor 3). Within this uncertainty, the empirical rates and theoretical predictions are in agreement. The origin of the scatter of the empirically inferred mass-loss rates requires further investigation. It is possible that our description of wind clumping is still not sufficient to capture effects of the structured wind, which could contribute to the scatter.