Hot Molecular Cores and High-Mass Star Formation.pdf

a r X i v : a s t r o - p h / 0 3 0 9 1 5 2 v 1 4 S e p 2 0 0 3 Star Formation at High Angular Resolution ASP Conference Series, Vol. S-221, 2003 R. Jayawardhana, M.G. Burton, T.L. Bourke Hot Molecular Cores and High-Mass Star Formation F.F.S. van der Tak Max-Planck-Institut fu?r Radioastronomie, Auf dem Hu?gel 69, 53121 Bonn, Germany Abstract. This review covers hot cores in the context of high-mass star formation. After giving an overview of chemical processes and diversity during high-mass star formation, it reviews the ‘warm envelope’ phase which probably precedes the formation of hot cores. Some recent deter- minations of the cosmic-ray ionization rate are discussed, as well as recent evidence for hot cores around low-mass stars. Routes for future hot core research are outlined. 1. Introduction Named after the Orion Hot Core, hot molecular cores are small (d ～ 0.1 pc) pockets of warm ( ～ 100 K) dense ( ～ 106 cm?3) molecular gas, which show very rich submillimeter spectra. This definition includes both internally and externally heated clumps near stars of all masses, but the focus of this review is on the case of internal heating by young high-mass stars, which form the majority of known hot cores. This review only outlines basic properties of hot cores with an emphasis on recent developments. Recent reviews on the chemistry of star-forming regions, including hot cores, have been given by van Dishoeck van der Tak (2000) and Langer et al. (2000); high-mass star formation is discussed by Kurtz et al. (2000), Churchwell (2002) and Garay (this volume). 2. The embedded phase of high-mass star formation Stars of masses 8 M⊙ spend a significant fraction of their lifetime, 10%, embedded in their natal molecular clouds. This embedded phase can be sub- divided into four observationally different groups of objects: (1) The initial conditions of high-mass star formation should be large mass reservoirs which are local temperature minima and density maxima. Candidate