Stars form from clouds of gas and dust in the interstellar medium. How the tenuous interstellar gas becomes a relatively dense star, and how a new star interacts with its environment, are currently lively and active fields of astronomical research. Since the ubiquitous cosmic dust makes the gas in denser clouds opaque to visual radiation, the main way that we can probe regions of star formation is by detecting radio emissions from molecules that are formed in the gas during the collapse. About 130 different molecular species have been detected in interstellar clouds. Most of these molecular species are formed in a variety of gas phase reactions, but some species depend on surface reactions for their formation. Understanding these chemical routes helps us to describe in detail the physical conditions in the gas during the collapse that leads to star formation and in the interaction of the new star with the cloud in which it was formed. We give three examples of such interactions: (i) Wedescribehowtheinteractionofanewly-formedhotstarinteractswiththemate- rial close to the star but which was not incorporated in it. We show that the molecules that can be seen in such situations were until recently frozen-out as ices on the sur- faces of dust grains. (ii) Many young stars have outflows in the form of well-collimated high-velocity jets that impact on nearby interstellar gas to create shocked regions. We show that these shocked regions illuminate and modify the chemistry of those regions. The charac- teristic chemistry arising enables us to describe the nature of the jet/cloud interaction in detail. (iii) Stellar jets widen into general outflows that encounter clumps of denser gas. The outflow from a massive star usually ionised. The interaction between such an outflow and a pre-existing clump creates a characteristic interface chemistry. We describe recent observations that appear to be the first detection of such an interface in a region in which massive stars are forming.
Chemistry and dust in star-forming regions of space
2006
Abstract
Stars form from clouds of gas and dust in the interstellar medium. How the tenuous interstellar gas becomes a relatively dense star, and how a new star interacts with its environment, are currently lively and active fields of astronomical research. Since the ubiquitous cosmic dust makes the gas in denser clouds opaque to visual radiation, the main way that we can probe regions of star formation is by detecting radio emissions from molecules that are formed in the gas during the collapse. About 130 different molecular species have been detected in interstellar clouds. Most of these molecular species are formed in a variety of gas phase reactions, but some species depend on surface reactions for their formation. Understanding these chemical routes helps us to describe in detail the physical conditions in the gas during the collapse that leads to star formation and in the interaction of the new star with the cloud in which it was formed. We give three examples of such interactions: (i) Wedescribehowtheinteractionofanewly-formedhotstarinteractswiththemate- rial close to the star but which was not incorporated in it. We show that the molecules that can be seen in such situations were until recently frozen-out as ices on the sur- faces of dust grains. (ii) Many young stars have outflows in the form of well-collimated high-velocity jets that impact on nearby interstellar gas to create shocked regions. We show that these shocked regions illuminate and modify the chemistry of those regions. The charac- teristic chemistry arising enables us to describe the nature of the jet/cloud interaction in detail. (iii) Stellar jets widen into general outflows that encounter clumps of denser gas. The outflow from a massive star usually ionised. The interaction between such an outflow and a pre-existing clump creates a characteristic interface chemistry. We describe recent observations that appear to be the first detection of such an interface in a region in which massive stars are forming.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
