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The life and time of stars

The life and time of stars . Stellar formation, Stellar evolution, Stellar structure and Theoretical stars . Luminosity, Brightness and H-R diagrams . Very useful parameter in measuring and comparing stars. Luminosity/intrinsic luminosity Total power radiated(W)

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The life and time of stars

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  1. The life and time of stars Stellar formation, Stellar evolution, Stellar structure and Theoretical stars T.May, A. QI, S. Bashforth, J.Bello

  2. Luminosity, Brightness and H-R diagrams • Very useful parameter in measuring and comparing stars. • Luminosity/intrinsic luminosity Total power radiated(W) • Also apparent brightness, b, power crossing unit area at the Earth perpendicular to the path of light. • b • Colour is related to intrinsic luminosity and therefore mass. • Standardized brightness of each star. T.May, A. QI, S. Bashforth, J.Bello

  3. Stellar nurseries • Interstellar clouds mostly contain Hydrogen. • Higher density regions form clouds, this is where stars form. • Much of H is in molecular form. • kinetic energy of the gas pressure = potential energy of gravitational force. • The cloud undergoes gravitational collapse. • The mass is called Jeans Mass. • Cloud breaks down become stellar embryo. T.May, A. QI, S. Bashforth, J.Bello

  4. Protostars • A large mass that forms by contraction out of the gas of a molecular cloud in the interstellar medium. • During collapse density of cloud increases towards the centre. • At 2000K H2 dissociates. • After a certain density the material if transparent to allow energy to escape. • Convection within the star and radiation from the exterior allows for further contraction. • This continues until it is hot enough for pressure to support gravitational collapse. T.May, A. QI, S. Bashforth, J.Bello

  5. Observations • Early stages of a stars life cycle can be seen in infrared. • Observed in near-IR extinction maps • Can only be directly observed in our own galaxy. • Distant galaxies, detection is through spectral signature. • MWC 349-estimated at 1000 years old • VLA 1623- First class 0 Protostars, yet to accumulate majority of mass. T.May, A. QI, S. Bashforth, J.Bello

  6. Role of mass in the life cycle of the star • Different masses of stars form via different mechanisms. • Low-mass star formation, is due to gravitational collapse of rotating density enhancements within molecular clouds. • Massive stars emit large quantities of radiation which push against infalling material. T.May, A. QI, S. Bashforth, J.Bello

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