What kind of stars are found here?

A star in this region of the Hertzsprung-Russell diagram has a temperature of roughly 29,000 Kelvin (29,000 K), a luminosity 20 times less than that of the Sun (0.05 × L), and a radius one hundred times smaller than the Sun (R = 0.01 × R). This star lies along the narrow band where white dwarf stars are found. The high temperature indicates that this star is the end-product of a recent nova of a low-mass star (an older star would have had more time to cool, and to move down the white dwarf sequence to lower luminosities and cooler temperatures).

Try to read the values of L, T, and R for yourself from the diagram. Do you estimate values for the luminosity, temperature, and size of the star similar to those listed above?

We can use the Stephan-Boltzmann Law to relate the temperature (T), size (R), and luminosity (L) of a star to each other. Measuring L, R, and T in solar units, we say that:

Let us say that the temperature of the star is exactly 28,900 K. We know that the temperature of the Sun is 5,800 K, so we can convert the temperature of the star into solar units. This is just a way of asking How hot is the star relative to the Sun? (If the star is six as hot as the Sun, for example, T = 6 × T. If the star is six times cooler as the Sun, T = 0.166 × T.)

This star is five times hotter than the Sun. Now assume that the radius of the star is exactly 0.0103 × R. (We don't need to convert this radius to solar units, as we are already using them.) The final step is to calculate the luminosity L, from T and R.

We estimated a value of L = 0.05 L from the diagram, for stars found in this area – so we did a reasonable job!