HR Diagram Read Your Textbook Foundations of Astronomy

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

Luminosity Classes

Spectral Luminosity Class SURFACE 4000 TEMPERATURE (K) 0. 1 20 3000 LUMINOSITY (Lsun) 0. 7 10 100 RADIUS (Rsun) OBJECT K 7 V MS K 7 III giant K 7 I supergiant

Main Sequence Masses

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

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

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

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

Fundamental Stellar Parameters