Lydia Sonia Cidale

Context. Radiation-driven winds in B-type stars play a key role in the evolution of stars, yet the hydrodynamical structure of the winds remains uncertain, particularly in evolved objects. While the classical fast solution of the modified Castor, Abbot and Klein (m–CAK) theory is widely adopted, it does not always reproduce the optical wind diagnostics of B-type giants and supergiants. Aims. We investigated the applicability of the classical fast and the δ -slow hydrodynamical solutions to B-type stellar winds through a homogeneous spectroscopic analysis based on optical diagnostics. Methods. We analysed 50 Galactic B-type spectra spanning luminosity classes I to V using mid- and high-resolution optical spectra from the IACOB, ESO-UVES, and CASLEO datasets. Synthetic spectra were taken from the ISOSCELES grid, which combines hydrodynamical wind models computed with H YDWIND and non-local thermodynamic equilibrium (NLTE) radiative transfer using F ASTWIND . Stellar and wind parameters were derived via a multi-line χ ² fitting procedure using hydrogen, helium, and silicon lines. Results. We find evidence for a statistical preference for different hydrodynamical regimes across luminosity classes within the adopted modelling framework. A large fraction of B-type supergiants (∼96%) and giants (∼88%) are better reproduced by models based on the δ -slow hydrodynamical solution, characterised by higher ionisation parameters, lower terminal velocities ( v _∞ ≲ 300 km s ⁻¹ ), and denser outflows. In contrast, most dwarfs and subgiants (∼88%) in the sample are more frequently consistent with the classical fast solution, with a higher v _∞ and a lower Ṁ . This behaviour suggests a dichotomy between luminosity classes, which is further supported by systematic trends of δ , Ṁ , and v _∞ with effective temperature. Conclusions. These results suggest that the δ -slow solution may provide a viable and physically motivated framework for modelling the optical spectra of evolved B-type stars, whereas fast solutions remain adequate for less evolved objects. However, given that optical diagnostics have limited sensitivity to the outer wind regions, these conclusions should be regarded as indicative only. By employing hydrodynamically motivated wind structures rather than prescribed velocity laws, the ISOSCELES grid offers a consistent basis for interpreting optical wind diagnostics. It motivates future combined multiwavelength studies to constrain B-type stellar winds further.

Context. The physical properties of O-type supergiant stars remain largely unexplored. By analysing their light variations, we can sometimes unravel underlying physical phenomena, such as binarity, stellar pulsations, and rotation modes, as well as discover previously unobserved or unexplored phenomena in these types of stars. Aims. This study aims to analyse the TESS light curves of three O-type supergiant stars to identify periodic signatures and gain deeper insights into their internal dynamics and structure. Our primary goal is to search for the presence of rotational modulation and possible evidence of Rossby waves. Methods. A period search was performed on photometric data of three supergiant O-type stars using the generalised Lomb-Scargle periodogram and the weighted wavelet Z-transform together, leveraging the advantages of each method. We explored phase diagrams and searched for rotational splitting. If the observed wave frequencies were consistent with the dispersion relation of global Rossby waves, we identified them as potential signatures of this mechanism. We used a graphical method to compare the observed and predicted frequencies. Results. The three analysed supergiant stars (HD 188001, HD 192639, and HD 159952) exhibit a comparable set of frequencies. We classify most of the observed frequencies as g -mode oscillations (either ℓ = 1 or ℓ = 2), in agreement with the evolutionary state of the objects. In all cases, we find evidence of rotational modulation. The remaining oscillation patterns may be consistent with Rossby ( r ) modes, including both tesseral and sectoral configurations. The angle of inclination of the rotation axis was estimated using stellar parameters available in the literature, together with the rotational period derived in this work. We also discuss a possible connection between the observed low-frequency waves and the red-noise component commonly observed in the periodogram of photometric time series of massive supergiants. Conclusions. Our results provide evidence of g -mode oscillations modulated by rotation. In addition, we find that Rossby waves may be excited in rotating O-type supergiants, which suggests that these large-scale inertial oscillations could play a role in the observed low-frequency variability of such stars. A comprehensive theoretical treatment addressing the development of pulsations in rotating stars lies beyond the scope of the present work and is deferred to future studies. Further investigation would provide insight into the star’s surface flows, rotation, and angular momentum transport.

Context. Massive stars continuously enrich the surrounding interstellar medium by supplying it with stellar material driven by their powerful winds. B supergiant stars (BSGs) in particular are a type of massive star characterized by strong winds and notable photometric and spectroscopic variability. Aims. We aim to conduct a pilot study of the optical spectroscopic variability of the BSG HD 75149 between 2004 and 2025. Its extended temporal baseline and pronounced variability amplitude make it particularly well suited for investigating the physical origin of the observed short-term variability within a consistent hydrodynamical and radiative-transfer framework. Methods. We analyzed 25 nightly averaged optical spectra obtained with different instruments and telescopes, some of them with observations over several consecutive days. We measured the radial velocities (RVs) and equivalent widths (EWs) of 17 spectral lines (H, He I , Si III , N II , Mg II , C II ). We modeled the H α emission, absorption, and P-Cygni profiles using the ISOSCELES grid and the δ -slow hydrodynamic regime. Results. H α shows variability in intervals of a few days, including P-Cygni changes, while metal lines show small RV amplitudes, consistent with pulsating oscillations. The largest variation in the mass-loss rate corresponds to an increase of a factor of 1.8 within four days. In contrast, the terminal velocity remains barely affected during the same time interval. Conclusions. The pronounced variation observed in hydrogen lines, in contrast with the variability of other lines, suggests that it is due to mass-loss rate episodes driven by a slow wind occurring on a timescale comparable to photometric variations. We found no evidence of a close binary companion in the sample used, but we cannot completely exclude the possibility of a wide or low-inclination companion.

Context. Radiation-driven winds of massive stars can be described within the modified Castor-Abbott-Klein theory, which parametrises the radiation force through three key quantities: α , δ , and k . Different combinations of these parameters, together with rotation, result in three types of stationary solutions, namely fast (or classical), δ -slow, and Ω-slow solutions. Aims. The primary objective of this work is to model radiation-driven winds inside the gap region between the fast and δ -slow regimes, where stationary solutions have proven elusive. We computed synthetic line profiles of H I , He I , and Si IV to illustrate the morphology of different wind regimes. Methods. We employed the time-dependent hydrodynamic code ZEUS-3D, capable of obtaining stationary solutions by progressing through an initial solution. Then, we computed the line profiles solving the transfer equation for an expanding atmosphere, assuming spherical symmetry in the comoving frame, under non-local thermodynamic equilibrium conditions. Results. We find new stationary solutions in the gap region, alongside their corresponding line profiles for a typical B supergiant star model. In this model, the new solutions are stable, and some present a kink in the velocity profile at a fixed distance from the star, depending on the δ value. Perturbations in the wind ionisation may trigger transitions between different hydrodynamic regimes and offer a plausible explanation for structured and variable winds. A systematic investigation of these effects will be the subject of future work. Furthermore, we investigated the resulting line profiles from different hydrodynamic solutions and compared them with those predicted by a velocity profile given by a β -law using the same global wind parameters.

The post-main-sequence evolution of massive stars involves phases of intense, often eruptive mass loss, including the B[e] supergiant phase. These hot stars are surrounded by cool, dense circumstellar disks that host complex chemistry, producing both molecules and dust. Understanding the mass-loss history of B[e] supergiants is essential for constraining stellar evolution models, particularly regarding their final stages. Near-infrared CO band emission serves as a key tracer of disk dynamics, typically arising from the inner edge of the molecular disk or ring. However, the oxygen-rich environments of these stars also favor the presence of other molecules that trace regions complementary to those probed by CO. In this work, we present high-resolution near-infrared spectra of the Small Magellanic Cloud B[e] supergiant LHA 115-S 18. Our analysis reveals rotationally broadened CO emission consistent with a Keplerian molecular ring, alongside strong hydrogen wind features in both H and K bands and numerous metallic emission lines. Notably, we report the first detection of hot water vapor emission in a B[e] supergiant. This finding indicates the existence of extended cool and dense regions in a harsh environment. A radial velocity offset between molecular and Pfund line emission further supports a binary system, with the molecular gas potentially being circumbinary. The discovery of hot H ₂ O around the B[e] supergiant star LHA 115-S 18 challenges classical models on the evolution and chemistry of massive binary stars and provides critical insight into mass-loss processes and molecular enrichment of the interstellar medium.

Context . Massive O-type stars lose a significant fraction of their mass through radiation-driven winds, a process that critically shapes their evolution and feedback into the interstellar medium. Accurate predictions of mass-loss rates ( Ṁ ) are essential for models of stellar structure and population synthesis. Aims . We computed wind parameters for O-type stars using a self-consistent approach that couples the hydrodynamics of the wind with detailed calculations of the line acceleration. This approach follows the theory of radiation-driven stellar winds and, thus, allows us to derive mass-loss rate distributions for different atomic configurations of the stellar flux. Methods . We used the TLUSTY code for stellar atmosphere models to compute tailored non-local thermodynamic equilibrium models; these models served as input radiation fields for the calculation of the force multiplier factor and the line-force parameters, for which we used the LOCUS code. These line-force parameters were then iteratively coupled with the HYDWIND code to solve the wind hydrodynamics. The procedure was repeated until convergence and applied across a grid of stellar parameters for three chemical configurations. Results . We obtain self-consistent wind parameters for a broad set of O-type stellar models. The results show a systematic decrease in mass-loss rates with the inclusion of more elements in the radiation field, which is attributed to a strong effect on the UV region of the spectral energy distribution. As more elements are included, resulting in a larger number of spectral lines, the contribution from the UV diminishes, leading to lower mass-loss rates. We fitted three theoretical prescriptions for Ṁ using a Bayesian approach; this yielded Pearson correlation values greater than 0.92 for all three model grids. It also allowed for the estimation of the wind momentum-luminosity relationships for each of the grids, yielding results similar to those based on observations of O-type stars.

Context . Binary systems with circumbinary molecular and dust rings are of great interest because they provide insights into the dynamics and evolution of stellar systems and the chemistry of the surrounding material. Aims . We aim to elucidate the nature of the B[e] binary system HD 327083 and constrain its orbital parameters and evolutionary status as well as the physical properties of its circumstellar and circumbinary envelopes. Methods . We present multi-epoch high-spectral resolution optical and near-infrared observations acquired at various observatories combined with VLTI/MIDI observations and ASAS-3 photometry. The data were analysed to obtain the orbital parameters, study individual members of the system, and derive the properties of the atomic and molecular gas and the dusty components of the complex environment of HD 327083. Results . We improved the orbital solution of HD 327083 and derived a period of P = 107.699 ± 0.005 d. Most optical lines display variations in shape and intensity when folded with the orbital motion. We assigned F6 II-III and B1 spectral types respectively to the cool and hot stellar components. A ring of molecular gas revolves around the system, and its appearance varies with the orbital phase. The MIDI flux distribution shows a silicate band in absorption at 9.7 µm. The interferometric data also indicate that the dust distribution has an elliptical shape, with its inner edge varying with orbital phase between 12.5 AU and 44 AU. Conclusions . We conclude that the B[e] binary system HD 327083 comprises a B-type massive accreting star and an F-type companion filling over 60% of its Roche lobe. The F-type companion is evolving towards the red supergiant stage. The deformed shape of the F-type star causes a broad minimum in the light curve. The hot companion (26 000 K, log g = 3.0) is hidden by a compact disc and shows a bi-polar outflow. The entire binary system presents an O-rich environment. It is surrounded by warm CO and SiO molecular rings, which are enclosed by an elliptical dust structure. All these components were formed by the evolved donor star during its evolution towards the red supergiant phase.

Context. The post-main-sequence evolution of massive stars remains poorly understood, particularly in the case of blue supergiants. As key drivers of the dynamical and chemical evolution of galaxies, massive stars warrant detailed investigation during this complex evolutionary stage. Hot supergiants exhibit pronounced photometric and spectroscopic variability, typically in the form of quasi-periodic rather than strictly periodic variations. Aims. We investigated the variability patterns of the evolved B-type star ρ Leo to determine its properties, identify the underlying physical processes, and constrain its evolutionary stage. We combined extensive long-term datasets of spectroscopic and photometric observations from various sources. These include data from the TESS and Kepler space telescopes, as well as observations from the 1.5 m telescope in Estonia. Methods. We analysed the data using the generalized Lomb–Scargle periodogram, the Lomb–Scargle periodogram with pre-whitening, and the weighted wavelet Z-transform. To determine the fundamental parameters of ρ Leo, we fitted synthetic line profiles computed with the F AST W IND code to the HARPS spectrum. We used the ZPEKTR code to infer the stellar rotation inclination angle. Results. The He I 6678.151 Å line profile exhibits significant changes in radial velocity and, consequently, in its moment values. We identify a set of periods and harmonics ranging from ∼0.8 to ∼35 days. Some periods remain nearly constant, while others appear and disappear from one observing season to another. A comparison of spectroscopic and photometric data, along with the shape of the phase curves, helps to constrain the nature of several periods. In particular, the ∼11-day period is attributed to stellar rotation, while the ∼17-day period is associated with radial pulsations. Conclusions. Despite their quasi-periodic nature, most periods are observable across multiple observing seasons. Based on the fairly wide range of detected periods, ρ Leo is likely on the blue loop of its evolution, following the red supergiant stage.

The Observatorio Astronómico de La Plata from the Facultad de Ciencias Astronómicas y Geofísicas (FCAG) of the Universidad Nacional de La Plata (UNLP) is one of the oldest observatories in South America. It has an enormous collection of observations, including thousands of spectroscopic and photographic glass plates. These observations were taken between the 1900s and the 1980s by renowned Argentine astronomers and constitute unique and unpublished records. Since 2019, the Recovery of Historical Observational Work (ReTrOH, for its initials in Spanish) project has begun digitizing the 15,000+ samples of the spectroscopic plate collection. The digitization process for each plate is a complex, error-prone, multi-stage procedure requiring several person-hours. Consequently, a multidisciplinary team of astronomers and computer scientists was formed to develop the first system capable of assisting the user in this process. This system, designated PlateUNLP , employs signal processing algorithms and computer vision models to accelerate the process, reduce error rates, and standardizes data formats and processes. A key feature of PlateUNLP is its ability to automatically detect and record each spectrum recorded on the plates, along with the corresponding metadata, thus minimizing the need for user intervention. The developed system is publicly available under an open source license. Furthermore, while the system was developed with the ReTrOH project’s requirements in mind, it could be adapted and used to assist with the digitization of thousands of other plates available around the world. PlateUNLP is therefore a first step toward making possible and practical the recovery of historical astronomical observations. Digitizing and exploiting these observations can provide a unique window into the past of our universe.

Context . Massive stars play a fundamental role in galactic evolution through their strong stellar winds, chemical enrichment, and feedback mechanisms. Accurate modelling of their atmospheres and winds is critical for understanding their physical properties and evolutionary pathways. Traditional spectroscopic analyses often rely on the β -law approximation for wind-velocity profiles, which may not capture the complexity of observed phenomena. Aims . This study aims to introduce and validate the grId of Stellar atmOSphere and hydrodynamiC modELs for massivE Stars (ISOSCELES), a grid-based framework for the quantitative spectroscopic analysis of massive stars. The project leverages hydrodynamic wind solutions derived from the m-CAK theory, including both fast and δ -slow solutions, to improve the accuracy of derived stellar and wind parameters. Methods . We constructed a comprehensive grid of models based on hydrodynamic wind solutions from the HYDWIND code and synthetic spectral line profiles generated by the FASTWIND code. The grid spans a broad parameter space covering OBA-type stars with solar metallicity. A semi-automatic fitting procedure was developed to analyse key spectral lines and derive the stellar and wind parameters. Results . Applying ISOSCELES to six stars demonstrates its ability to reproduce observed spectral profiles with high fidelity. The δ- slow solution proved effective for two early-type B supergiants. The grid also highlights the difference of using the β -law in modelling stellar winds compared with the m-CAK wind solutions. Conclusions . The ISOSCELES database represents a step forward in quantitatively analysing massive stars, offering an alternative to the β -law approximation. Future work will address the inclusion of UV lines and metallicity effects to further refine its applicability across diverse stellar populations.