The SVS13-A Class I chemical complexity as revealed by S-bearing species. SOLIS XIII

Abstract

Context. Recent results in astrochemistry revealed that some molecules such as interstellar complex organic species and deuterated species represent precious tools to investigate star forming regions. Sulphuretted species can also be used to follow the chemical evolution of the early stages of the Sun-like star forming process. Aims. The goal is to obtain a census of S-bearing species using interferometric images, towards SVS13-A, a Class I object associated with a hot corino rich in interstellar complex organic molecules. Methods. To this end, we used the NGC1333 SVS13-A data at3mm and 1.4mm obtained with the IRAM-NOEMA interferometer in the framework of the Large Program SOLIS. The line emission of S-bearing species has been imaged and analysed using LTE and LVG approaches. Results. We imaged the spatial distribution on ≤ 300 au scale of the line emission of SO, SO, CS, CS, CS, OCS, H2CS, H2CS, and NS. The low excitation (9 K) SO line is tracing (i) the low-velocity SVS13-A outflow and (ii) the fast (up to 100 km s away from the systemic velocity) collimated jet driven by the nearby SVS13-B Class 0 object. Conversely, the rest of the lines are confined in the inner SVS13-A region, where complex organics have been previously imaged. More specifically the non-LTE LVG analysis of SO, SO2, and H2CS indicates a hot corino origin (size in the 60-120 au range). Temperatures between 50 K and 300 K, and volume densities larger than 10 cm have been derived. The abundances of the sulphuretted are in the following ranges: 0.3–6 × 10 (CS), 7 × 10 – 1 × 10 (SO), 1–10 × 10 (SO2), a few 10 (H2CS and OCS), and 10–10 (NS). The N(NS)/N(NS) ratio is larger than 10, supporting that the NS ion is mainly formed in the extended envelope. Conclusions. The [H2CS]/[H2CO] ratio, once measured at high-spatial resolutions, increases with time (from Class 0 to Class II objects) by more than one order of magnitude (from ≤ 10 to a few 10). This suggests that [S]/[O] changes along the Sun-like star forming process. Finally, the estimate of the [S]/[H] budget in SVS13-A is 2%-17% of the Solar System value (1.8 × 10), being consistent with what was previously measured towards Class 0 objects (1%-8%). This supports that the enrichment of the sulphuretted species with respect to dark clouds keeps constant from the Class 0 to the Class I stages of low-mass star formation. The present findings stress the importance of investigating the chemistry of star forming regions using large observational surveys as well as sampling regions on a Solar System scale.