wolf rayet stars

supernova

Wolf Rayet Stars (discovered by C. Wolf and G. Royet in 1867) are very hot stars (T > 70,000 K). The spectra of WR stars have no absorption (dark) lines. It shows a broad emission…

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Interstellar Medium

Interstellar Medium

The medium between the stars is called interstellar medium. It consists of extremely dilute mixture of gases (neutral, ionized etc) dusts, cosmic rays and magnetic fields. The chemical composition if interstellar medium is about 90%…

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The Yerkes spectral classification

Yerkes spectral classification

The Harvard classification only takes into account the effect of the temperature on the spectrum. It is found that two stars with the same effective temperature may have widely different luminosities. Thus for a more…

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HR Diagram

HR Diagram

E. Hertzsprung and H. Norris Russell studied the relation between the absolute magnitude (or luminosity) and spectral types (or surface temperature) of stars. The diagram showing these two variables is known as HR diagram. This…

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Harvard Spectral Classification

Harvard Spectral Classification

The Harvard Spectral Classification is based on the absorption lines (i.e. bark lines) in the stellar spectrum, that are sensitive to the stellar temperature, rather than to gravity or luminosity. The important lines are H-lines,…

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Stellar Spectra

SunSpectrum

The spectra of stars are classified on the basis of the strength of the spectral lines. In 1666 Newton claimed to observe solar spectrum but no details can be found. In 1814 Spectroscopy began when…

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Carbon, Oxygen and Silicon Burning

Dynamical time scale

Carbon Burning After helium burning is completed at the core and temperature reaches up to carbon burning starts:   Oxygen Burning Oxygen is consumed at slightly higher temperatures in the reactions   Silicon Burning After…

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