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…

[Continue reading]

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…

[Continue reading]

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…

[Continue reading]

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,…

[Continue reading]

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…

[Continue reading]

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…

[Continue reading]

Alpha and Triple Alpha Reaction

stellar magnitude

Triple Alpha Reactions At a temperature above two alpha particles (Helium nuclei) fuse to form a nucleus. This Be nuclei is very unstable and almost decays back to two in seconds. However high density and…

[Continue reading]

Solar Neutrino Problem

solar-neutrino-problem

Until today, the solar neutrino detected by the experiment are much less than prediction in theory and this is called as solar neutrino problem. The PP chain is most important energy source in stars with…

[Continue reading]