Herzprung-Russell diagram

Herzprung and Russell independently analysed the spectral types, luminosities and temperatures to produce the Herzprung-Russell diagram. 

The hottest stars have absorption features in the photosphere associated with lighter elements, some in highly ionised states, but the lower temperature stars have a more diverse atomic composition the coolest stars show molecular emission spectra. This suggests an evolution of stars that involves the formation of heavier elements and ultimately molecules. 

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Figure 4.3 Herzprung-Russell diagram. (A colour reproduction of this figure can be seen in the colour section.) (Reproduced by permission of D.Padgett (IPAC/Caltech), W.Brandner (IPAC), K.Stapelfeldt (JPL) and NASA)...

Birth lines The track of stars as they evolve from red giants onto the main sequence of the Herzprung-Russell diagram. 

Herzprung-Russell diagram A graphical plot of stellar intensity versus photosphere temperature showing that observed stars fall into classes main sequence, red giants, supergiants and white dwarfs. 

Main sequence star The majority of stars, 92 per cent, that fall on the leading diagonal of the Herzprung-Russell diagram. 

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