The SVS13-A Class I chemical complexity as revealed by S-bearing
  species. SOLIS XIII
  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: We used data at
3mm and 1.4mm obtained with IRAM-NOEMA in the framework of the Large Program
SOLIS. Results: We imaged the spatial distribution of the line emission of
32SO, 34SO, C32}S, C34S, C33S, OCS, H2C32S, H2C34S, and NS. The low excitation
(9 K) 32SO line is tracing the fast collimated jet driven by the nearby
SVS13-B. Conversely, the rest of the lines are confined in the inner SVS13-A
region, where complex organics have been previously imaged. The non-LTE LVG
analysis of SO, SO2, and H2CS indicates a hot corino origin (60-120 au).
Temperatures between 50 K and 300 K, and volume densities larger than 10^5 cm-3
have been derived. The abundances are in the following ranges: 0.3-6 10^-6
(CS), 7 10^-9} - 1 10^-7 (SO), 1-10 10^-7 (SO2), a few 10^-10 (H2CS and OCS),
and 10^{-10} - 10^{-9}(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 increases with time (from Class 0 to Class
II objects) by more than one order of magnitude. This suggests that [S]/[O]
changes along the Sun-like star forming process. The estimate of the [S]/[H]
budget in SVS13-A is 2%-17% of the Solar System value (1.8 10^-5), 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.
