Variable stars across the observational HR diagram - IOPscience
HR Diagram
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Transcript of HR Diagram
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 TypeA.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
4000 0.1 0.7 K7 V MS 4000 20 10 K7 III giant 4000 3000 100 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 = 4R2T4 M = 0, Msun = 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 = 4R2T4 M = 0, Msun = 5
A difference in 5 magnitudes is 100x in brightness4R2T4 = 100 4Rsun
2T4 R2 = 100 Rsun
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 = 4R2T4 M = 0, Msun = 5
A difference in 5 magnitudes is 100x in brightness4R2T4 = 100 4Rsun
2T4 R2 = 100 Rsun
2 Therefore, R/Rsun = (100)1/2
L/Lsun
O B A F G K M
Fundamental Stellar Parameters