PX282 - B3 - spectral lines and classes

• from spectral lines, subdivisions are formed: $G0\to G9(hot\to cold)$

• the sun is a $G2$ star

• there is also a 'luminosity class', divided according to the width of spectral lines

• high gravity changes the width as high pressure causes pressure broadening

• this gives information about the radius of the star as small radius means high pressure, and therefore, wider lines

• they are labelled with roman numerals as follows:

  • $I\to IV:$ giants
  • $V:$ main sequence (dwarfs)
  • $VI:$ sub-dwarfs
  • $D:$ white dwarfs

• eg: $AOV$(dwarf), $AOI$ (giant)

image: chandra x-ray observatory