Extreme Deuteration and Hot Corinos: The Earliest Chemical Signatures of Low-Mass Star Formation

Low-mass protostars form from condensations inside molecular clouds when gravity overwhelms thermal and magnetic supporting forces. The first phases of the formation of a solartype star are characterized by dramatic changes not only in the physical structure but also in the chemical composition. Since Protostars and Planets IV (e.g., Langer et al., 2000), exciting new developments have occurred in our understanding of the processes driving this chemical evolution. These developments include two new discoveries: (1) extremely enhanced molecular deuteration, which is caused by the freeze-out of heavy-element-bearing molecules onto grain mantles during the prestellar core and Class 0 source phases; and (2) hot corinos, which are warm and dense regions at the center of Class 0 source envelopes and which are characterized by a multitude of complex organic molecules. In this chapter we will review these two new topics, and will show how they contribute to our understanding of the first phases of solar-type stars.