2025/10/09 by Prasanta Gorai, Gorai, Prasanta, Maryam Saberi +5
Physics and Astronomy · #Astrochemistry #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Asymptotic giant branch #Carbon star #Emission spectrum #Excitation #Excitation temperature #FOS: Physical sciences #Line (geometry) #Solar and Stellar Astrophysics (astro-ph.SR) #Stars #Stellar, planetary, and galactic studies #Sulfur
paper · doi:10.48550/arxiv.2510.08069
openalex publication_date 2025/10/09 · openalex created_date 2025/10/11 · openalex updated_date 2026/07/28
Sulfur and its isotopic ratios play a crucial role in understanding astrophysical environments, providing insights into nucleosynthesis, ISM processes, star formation, planetary evolution, and galactic chemistry. We investigate the distribution of sulfur bearing species \rmSO2, \rm34SO2, SO, and \rm34SO towards five oxygen rich Asymptotic Giant Branch (AGB) stars (o Ceti, R Dor, W Hya, R Leo, and EP Aqr), along with their excitation temperatures, column densities, and isotopic ratios. Using ALMA Band 6,7,8 data and CASSIS, we detect these species and estimate excitation temperature and column density via the rotational diagram and MCMC methods under LTE. Line imaging of various transitions is used to infer spatial distributions. The excitation temperatures of \rmSO2 range from ∼200-600 K with column densities of \rm1-7×1016 cm-2, while \rm34SO2 shows comparable or slightly lower values and about an order of magnitude lower column densities. The \rm32S/34S ratios for R Dor and W Hya are near solar, slightly higher for o Ceti, and lower for EP Aqr and R Leo. Most detected lines exhibit centralized emission: high excitation \rmSO2 traces compact hot gas in inner CSEs, whereas low-excitation lines trace more extended structures. Morphological differences, irregular emission in o Ceti, circular in R Leo and W Hya, clumpy in R Dor, and unresolved in EP Aqr may arise from variations in physical conditions, multiplicity, outflows, rotation, desorption processes, UV or cosmic ray effects, or observational resolution. Overall, the centralized SO and \rmSO2 emissions support previous findings for low mass-loss rate AGB stars, and the \rm32S/34S ratios likely reflect natal cloud composition, with deviations linked to metallicity or excitation conditions.