Context. Massive stars play crucial roles in galactic dynamics and chemical evolution. They are the most significant sources of ionizing UV radiation, their substantial mass-loss rates and explosions inject energy and enrich their surroundings, and their dynamical interactions eject stars and alter the evolution of stellar clusters. Consequently, the study of massive stars is essential for understanding various astrophysical phenomena, including galaxy chemical evolution, interstellar medium dynamics, gamma-ray bursts, and the reionization of the Universe. Key parameters influencing the evolution of massive stars include mass, mass-loss rate, chemical composition, and rotation. The orbits of spectroscopic binaries are particularly valuable because they provide constraints on stellar masses, and when combined with complementary data (e.g., photometry or interferometry), these masses can be fully determined. Aims. The OWN Survey was started two decades ago to study Galactic O- and WN- (hence the name) type southern spectroscopic binaries. In this paper we present the final results for single-lined (SB1) spectroscopic orbits. Methods. The OWN Survey carried out a long-term spectroscopic campaign to search for radial velocity variations indicative of orbital motion in a sample of southern Galactic O- and WN-type stars with high-resolution spectrographs in Argentina and Chile. The OWN spectra were later combined with high-resolution spectra from other sources and, in some cases, photometric time series to derive orbits and disentangled spectra, from which masses were constrained or determined and spectral classifications obtained. High-resolution optical spectra of 212 massive stars were obtained during the similar to 20 years of the OWN project, and each target was observed at least three times. Results. Among the 212 stars, 144 exhibited radial-velocity variations greater than 15 km s(-1). We present a complete and coherent compilation for the 23 systems with single-lined spectroscopic orbits identified in our sample. In Paper II we will perform a similar analysis for the systems with double-lined spectroscopic orbits.
The enzymatic production of low-molecular-weight chitosan and chitooligosaccharides (COS), with broad application potential in agriculture, food, medicine, and cosmetics, has emerged as an attractive alternative to chemical chitosan depolymerization owing to its substrate specificity and environmentally benign catalytic action. However, the functional properties of available chitosanases need to be enhanced to meet the demands of industrial COS manufacturing under high temperature and substrate concentrations. In this work, we performed directed evolution on a recombinant Bacillus subtilis chitosanase to increase chitosan hydrolysis performance and thermal resistance. Three rounds of directed evolution screening (similar to 9000 clones) yielded variants MT1, MT2, and MT3 with higher specific activity, achieved through Vmax improvement and increased T-1/2 at 60 degrees C. HPLC, DLS, and MALDI-TOF results indicate differences in the hydrolysis kinetics and size distribution of COS products over reaction time, suggesting a narrower distribution and a lower average molecular weight. Molecular dynamics simulations and docking studies revealed potential modulation of chitosanase activity via changes in the opening and closing dynamics of the active-site cleft. These results suggest that future efforts targeting the cleft interface could significantly advance both the catalytic performance and the mechanistic understanding of GH46 family chitosanases.
Context. Symbiotic stars are interacting binary systems composed of a red giant transferring material to a hot compact star, typically a white dwarf. These systems are crucial for studying stellar evolution, accretion processes, mass transfer, and a variety of complex astrophysical phenomena. However, there is a significant discrepancy between the number of confirmed symbiotic stars (similar to 300) and the estimated population in the Milky Way (1.2 & times; 10(3) - 1.5 & times; 10(4)), suggesting that a large fraction remains undetected. Aims. To address this issue, we propose the identification of new symbiotic stars through the application of machine-learning techniques. Our approach combines multiband photometric data from Gaia DR3, 2MASS, and WISE, together with parallax measurements and the pseudo-equivalent width of H alpha, to effectively distinguish symbiotic candidates from other stellar populations. Methods. We trained a random forest model using a sample of 166 confirmed S-type symbiotic stars and a control sample of 1600 nonsymbiotic stars. To mitigate class imbalance and improve the classification performance, we applied the synthetic minority oversampling technique (SMOTE). The model achieved an F-1 score of 89% for the symbiotic class. Results. We applied our model to a catalog of approximately 2.5 million stars selected based on photometric colors consistent with those of S-type symbiotic stars. We identified 990 candidates in this sample with a classification probability of at least 70%. To refine the selection, we applied statistically and physically motivated cuts based on effective temperature, surface gravity, and metallicity and complemented the cuts by SkyMapper photometry. This process yielded 12 high-confidence candidates, characterized by cool temperatures, low surface gravities, solar-like metallicity, H alpha emission, luminosities ranging from moderate to high, and ultraviolet excesses consistent with the properties of S-type symbiotic systems. Conclusions. To evaluate the model performance, we applied it to a validation set of symbiotic stars recently confirmed in the literature. We recovered 92.3% of them. This result supports the effectiveness and generalizability of our classification approach.
We investigate the dynamic magnetic response of planar ferromagnetic nanostructures with wire-ring morphology using micromagnetic simulations. By systematically varying the inner ring diameter and thickness, we analyze how geometric confinement governs the accessibility of stable and metastable magnetic states and shapes the spin-wave spectra. The equilibrium configurations are found to depend strongly on the relaxation pathway, giving rise to bistability for intermediate ring diameters. Dynamic susceptibility calculations under microwave excitation reveal distinct resonance spectra associated with low- and high-energy magnetic states, which we classify in terms of two energy-evolution paths. Spatial Fourier analysis of the out-of-plane magnetization identifies wire-like, ring-localized, and hybrid spin-wave modes, whose localization and spectral complexity are controlled by geometry. Our results demonstrate that planar wire-ring nanostructures offer a versatile platform for tailoring spin-wave excitations through geometric design, with potential implications for reconfigurable magnonic and spintronic devices.
Neltuma tamarugo is a strict phreatophyte endemic to the Atacama Desert whose persistence is threatened by groundwater decline. To characterize its hydraulic strategy, we assessed stomatal conductance, leaf hydraulic conductance, and whole-plant hydraulic conductance under semi-controlled water stress, and analyzed the relationship between predawn and midday water potential under both semi-controlled and field conditions in the Llamara Salt Flat under contrasting levels of groundwater decline. Under semi-controlled conditions, stomatal closure and near-zero whole-plant hydraulic conductance occurred at very negative midday water potentials (approximately − 4.33 and − 4.49 MPa, respectively), well below the turgor loss point and leaf hydraulic P50, and close to leaf hydraulic P88. Water stress also reduced branch growth and leaf area, followed by leaf shedding. In both semi-controlled and field conditions, predawn and midday stem water potentials were strongly coupled, with slopes near unity and relatively large Hydroscape Areas, indicating predominantly anisohydric behavior. In the field, trees under severe groundwater decline showed a lower Ψtlp, suggesting some acclimation, although midday water potentials still frequently fell below the turgor loss point. These results indicate that N. tamarugo maintains function under severe water deficit through anisohydric regulation and canopy-level adjustment. However, continued groundwater decline likely reduces functional performance and increases long-term mortality risk, highlighting the need to prevent further phreatic decline in this threatened species.
