Subdwarf Stars - Cool Subdwarfs

Cool Subdwarfs

Like ordinary main-sequence stars, cool subdwarfs (of spectral types G to M) produce their energy from hydrogen fusion. The explanation of their underluminosity lies in their low metallicity: these stars are unenriched in elements heavier than helium. The lower metallicity decreases the opacity of their outer layers and decreases the radiation pressure, resulting in a smaller, hotter star for a given mass. This lower opacity also allows them to emit a higher percentage of ultraviolet light for the same spectral type relative to a Population I star, a feature known as the ultraviolet excess. Usually members of the Milky Way's halo, they frequently have high space velocities relative to the Sun.

Subclasses of cool subdwarfs are as following:

  • cool subdwarf: Example: SSSPM J1930-4311 (sdM7)
  • extreme subdwarf: Example: APMPM J0559-2903 (esdM7)

Read more about this topic:  Subdwarf Stars

Famous quotes containing the word cool:

    While yet it is cold January, and snow and ice are thick and solid, the prudent landlord comes from the village to get ice to cool his summer drink; impressively, even pathetically, wise, to foresee the heat and thirst of July now in January,—wearing a thick coat and mittens! when so many things are not provided for. It may be that he lays up no treasures in this world which will cool his summer drink in the next.
    Henry David Thoreau (1817–1862)