Observations of Low-Mass Protostars: Cold Envelopes and Hot Corinos

Recent years have seen substantial progresses in our understanding of solar type protostellar structure, and particularly of the chemical structure of the protostellar envelopes. On the one hand, the cold outer regions keep intact the memory of the previous pre-collapse phase, when the dust is so cold and dense that almost all molecules freeze out onto the dust grain mantles. The gas-phase chemical composition undergoes dramatic changes, the most spectacular aspect of which is the huge increase of the molecular deuteration degree, which can reach 13 orders of magnitude with respect to the elemental D/H ratio. On the other hand, in the innermost regions of the envelope - the so-called hot corinos - the grain mantles evaporate when the dust temperatures exceed 100 K, injecting into the gas phase hydrogenated molecules, such as formaldehyde and methanol. Those molecules probably undergo chemical reactions that form more complex organic molecules, which have now also been observed in low-mass hot corinos. In this contribution, I review what we have and have not recently understood concerning both the cold envelopes and the hot corinos of solar-type protostars.