Sulfur gas-phase abundance in dense cores

The abundance of volatile sulfur in dense clouds is long-standing problem studies the physics and chemistry star-forming regions. Sulfur an important species because its low ionization potential may possibly make it charge carrier. observed sulfur-bearing gas-phase represent only a minor fraction cosmic abundance, which has been interpreted as signature depletion into ices at surface dust grains. However, atomic sulfur, could be main carrier, cannot directly cold cores. We present measurements nitrogen sulfide (NS) radical toward four cores performed with IRAM-30m telescope. Analytical chemical considerations models over wide parameter space show that NS:N2H+ ratio provides direct constraint on sulfur. Toward early-type cores, we find $n(\rm S)/n_{\rm H}$ close, or even equal, to 14$\times 10^{-6}$, demonstrating not depleted atomic, agreement models. More chemically evolved by factors up 100 their densest parts. In L1544, shown increase increasing density. Future observations are needed discover solid-phase carrier initial steps collapse pre-stellar high regime also need explored from dynamical perspectives.