The sulfur depletion problem: upper limits on the H2S2, HS·2, and S2 gas-phase abundances toward the low-mass warm core IRAS 16293-2422R. Martín-Doménech, I. Jiménez-Serra, G. M. Muñoz Caro, H. S. P. Müller, A. Occhiogrosso, L. Testi, P. M. Woods and S. VitiA&A, 585 (2016) A112DOI: https://doi.org/10.1051/0004-6361/201526271