AST201H1 Lecture Notes - Lecture 10: Stellar Classification

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST201H1
• Professor: Michael Reid

Document Summary

Properties of stars: what we want to know. Spectrum (light): apparent brightness, color, spectral lines. Hertzsprung-russell (h-r) diagrams are very important tools in astronomy because they reveal key relationships among the properties of stars. An h-r diagram is made by plotting stars according to their surface temperatures and luminosities. Horizontal axis: spectral type => indicates the correlation between color and lines temperature. Temperature decreases from left to right because the diagram is based on the spectral sequence obafgkm (star class) Vertical axis: luminosity (solar units lsun) => each tick mark represent a luminosity. 10 times as large as that of the prior tick mark as stellar luminosities span a wide range. Stars near the upper left are hot and luminous. Stars can also be classified by their spectral class : the strength of the hydrogen. Hot stars break molecules apart, so they don"t produce lines; lots of lines from molecules in the atmospheres of cooler stars.