HR Diagram Read Your Textbook: Foundations of Astronomy –Chapter 9, 10 Homework Problems Chapter 9 –Review Questions: 1, 4, 5, 7 –Review Problems: 1-5 –Web Inquiries: 1 Homework Problems Chapter 10 –Review Questions: 1, 2, 4, 6-8 –Review Problems: 1-4, 8 –Web Inquiries: 2

Intrinsic Brightness vs Spectral Type A.K.A. Luminosity vs Temperature HR diagram

Stars within 5 parsecs HR diagram

100 Brightest Stars HR diagram

Luminosity Function

Spectral Frequency

Luminosity Classes CLASS DESCRIPTION I Supergiants II Bright giants III Giants IV Subgiants V Main-sequence stars/dwarfs

Luminosity Classes

Spectral Luminosity Class SURFACE TEMPERATURE (K) LUMINOSITY (Lsun) RADIUS (Rsun) OBJECT K7 V MS K7 III giant K7 I supergiant

Main Sequence Masses

Using The HR Diagram Example 1: Spectroscopic Parallax Same Spectral Type –means same temperature Same Luminosity Class –means same size m-M = 5 log d - 5 Determine Distance by observing (m ), and utilizing the HR diagram to assume (M ). L/Lsun O B A F G K M

Using The HR Diagram Example 2: Size Determination Same Spectral Type –means same temperature Different Luminosity Class –means different size L = 4  R 2  T 4 M = 0, M sun = 5 L/Lsun O B A F G K M

Using The HR Diagram Example 2: Size Determination Same Spectral Type –means same temperature Different Luminosity Class –means different size L = 4  R 2  T 4 M = 0, M sun = 5 A difference in 5 magnitudes is 100x in brightness 4  R 2  T 4 =  R sun 2  T 4 R 2 = 100 R sun 2 L/Lsun O B A F G K M

Using The HR Diagram Example 2: Size Determination Same Spectral Type –means same temperature Different Luminosity Class –means different size L = 4  R 2  T 4 M = 0, M sun = 5 A difference in 5 magnitudes is 100x in brightness 4  R 2  T 4 =  R sun 2  T 4 R 2 = 100 R sun 2 Therefore, R/R sun = (100) 1/2 L/Lsun O B A F G K M

Fundamental Stellar Parameters