From Prestellar Cores to Protostars: the Initial Conditions of Star Formation

o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o The last decade has witnessed significant advances in ur bservati nal understanding f the earliest stages f l w-mass star f rmati n. The advent f sensitive receivers n large radi telesc pes such as the James Clerk Maxwell Telesc pe ́ (JCMT) and Institut de Radi Astr n mie Millimetrique (IRAM) 30m telesc pe has led t the identificati n f y ung pr t stars at the beginning f the main accreti n phase (“Class 0” bjects) and has made it p ssible f r the first time t pr be the inner density structure f prec llapse c res. Class 0 bjects are characterized by str ng, centrally c ndensed dust c ntinuum emissi n at submillimeter wavelengths, very little emissi n sh rtward f 10 m, and p werful jetlike utfl ws. Direct evidence f r gravitati nal infall has been bserved in several f them. They are interpreted as accreting pr t stars that have n t yet accumulated the maj rity f their final stellar mass. In c ntrast t pr t stars, prestellar c res have flat inner density pr files, suggesting that the initial c nditi ns f r fast pr t stellar c llapse depart s metimes significantly fr m a singular is thermal sphere. In the case f n nsingular initial c nditi ns, the beginning f pr t stellar ev luti n is expected t feature a brief phase f vig r us accreti n and ejecti n, which may c incide with Class 0 bjects. In additi n, submillimeter c ntinuum imaging surveys f regi ns f multiple star f rmati n, such as Ophiuchus and Serpens, suggest a picture acc rding t which each star in an embedded cluster is built fr m a finite reserv ir f mass and the ass ciated initial mass functi n (IMF) is primarily determined at the prestellar stage f ev luti n.