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The document discusses how astronomers classify and analyze stars using the Hertzsprung-Russell (HR) diagram. The HR diagram plots stars' luminosity versus temperature and reveals patterns like more luminous stars being hotter. Key properties of stars like their lifetimes and masses can be estimated from their position on the HR diagram. Understanding the HR diagram is important for learning about stellar interiors, evolution, and properties.
![Classification（分类）
Weight[kg]
Height[m]
•Weight: 80kg
•Height: 1.6m
•Fat…](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-2-320.jpg)
![Classification（分类）
Weight[kg]
Height[m]
•Weight: 80kg
•Height: 1.6m
•Fat…](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-3-320.jpg)
![Classification（分类）
Weight[kg]
Height[m]
•Weight: 80kg
•Height: 1.6m
•Fat…
•Weight: 80kg
•Height: 1.85m
•Muscle](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-4-320.jpg)
![Classification（分类）
Weight[kg]
Height[m]
•Weight: 80kg
•Height: 1.6m
•Fat…
•Weight: 80kg
•Height: 1.85m
•Muscle](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-5-320.jpg)
![Classification（分类）
Weight[kg]
Height[m]
•Weight: 80kg
•Height: 1.6m
•Fat…
•Weight: 80kg
•Height: 1.85m
•Muscle
•Although they are same weight, but they are
different.](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-6-320.jpg)
![Classification（分类）
Weight[kg]
Height[m]
•Weight: 80kg
•Height: 1.6m
•Fat…
•Weight: 80kg
•Height: 1.85m
•Muscle
•Although they are same weight, but they are
different.
•Classification is important to understand properties (human, and also stars)](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-7-320.jpg)
![Extending the cosmic distance scale
m − M = 5 log10 (
d[pc]
10pc )
•You remember how to measure distance to
stars by using following relation
•We can also evaluate the distance to stars if we
know the luminosity of stars ( ) and apparent
brightness .
L
b
b =
L
4πR2
•If we use the spectral type (or temperature) of
the star, we can estimate the luminosity from
HR diagram..
L](https://image.slidesharecdn.com/lecture14-230410102316-07b1e2ef/85/lecture14-35-320.jpg)
lecture14
- 1. Introduction to modern astronomy14 島袋隼⼠(Hayato Shimabukuro)（云南⼤学、 SWIFAR） ©GETTYIMAGES
- 4. Classification（分类） Weight[kg] Height[m] •Weight: 80kg •Height: 1.6m •Fat… •Weight: 80kg •Height: 1.85m •Muscle
- 5. Classification（分类） Weight[kg] Height[m] •Weight: 80kg •Height: 1.6m •Fat… •Weight: 80kg •Height: 1.85m •Muscle
- 6. Classification（分类） Weight[kg] Height[m] •Weight: 80kg •Height: 1.6m •Fat… •Weight: 80kg •Height: 1.85m •Muscle •Although they are same weight, but they are different.
- 7. Classification（分类） Weight[kg] Height[m] •Weight: 80kg •Height: 1.6m •Fat… •Weight: 80kg •Height: 1.85m •Muscle •Although they are same weight, but they are different. •Classification is important to understand properties (human, and also stars)
- 8. Classification of stars •Stars also have each properties •How do we classify stars? •What are important properties of stars?
- 9. Classification of stars •Stars also have each properties •How do we classify stars? •What are important properties of stars?
- 10. Classification of stars •Stars also have each properties •How do we classify stars? •What are important properties of stars? We usually focus on temperature and luminosity（光度） of stars
- 16. HR diagram HR diagram of well-known stars •Instead of temperature, we can also use spectrum classification. Or T = 4600 K ( 1 0.92(B − V) + 1.7 + 1 0.92(B − V) + 0.62 ) . •We can also use color index instead of temperature
- 17. HR diagram •If we plot more and more stars, we can find a relationship between luminosity and temperature. Higher temperature Larger luminosity
- 18. HR diagram •If we plot more and more stars, we can find a relationship between luminosity and temperature. Higher temperature Larger luminosity Red Giant （红巨星） Main sequence （主序） White dwarf （⽩矮星）
- 19. HR diagram •If we plot more and more stars, we can find a relationship between luminosity and temperature. Higher temperature Larger luminosity
- 20. HR diagram •If we plot more and more stars, we can find a relationship between luminosity and temperature. Higher temperature Larger luminosity
- 21. HR diagram •If we plot more and more stars, we can find a relationship between luminosity and temperature. Higher temperature Larger luminosity
- 22. HR diagram •If we plot more and more stars, we can find a relationship between luminosity and temperature. Higher temperature Larger luminosity
- 23. HR diagram •What can we know from HR diagram?? L = 4πσR2 T4
- 24. HR diagram •What can we know from HR diagram?? •The temperature of main sequence star is ranged from 3’000K to 30’000K. L = 4πσR2 T4
- 25. HR diagram •What can we know from HR diagram?? •The temperature of main sequence star is ranged from 3’000K to 30’000K. •The main sequence stars with higher temperature(Bluer stars) tend to be larger luminosity. Luminosity ∝ (Radius)2 × (Temperature)4 (Remember ) F ∝ σT4 L = 4πσR2 T4
- 26. HR diagram •What can we know from HR diagram?? •The temperature of main sequence star is ranged from 3’000K to 30’000K. •The main sequence stars with higher temperature(Bluer stars) tend to be larger luminosity. Luminosity ∝ (Radius)2 × (Temperature)4 (Remember ) F ∝ σT4 L = 4πσR2 T4
- 27. HR diagram •What can we know from HR diagram?? •The temperature of main sequence star is ranged from 3’000K to 30’000K. •The main sequence stars with higher temperature(Bluer stars) tend to be larger luminosity. Luminosity ∝ (Radius)2 × (Temperature)4 (Remember ) F ∝ σT4 •Bluer luminous stars are called “Blue giant” L = 4πσR2 T4
- 28. HR diagram •What can we know from HR diagram?? •The temperature of main sequence star is ranged from 3’000K to 30’000K. •The main sequence stars with higher temperature(Bluer stars) tend to be larger luminosity. Luminosity ∝ (Radius)2 × (Temperature)4 (Remember ) F ∝ σT4 •Bluer luminous stars are called “Blue giant” •Redder faint stars are called “Red dwarf” L = 4πσR2 T4
- 29. HR diagram •What can we know from HR diagram??
- 30. HR diagram •What can we know from HR diagram?? •The temperature of red giant stars are low compared with main sequence stars which have same luminosity.
- 31. HR diagram •What can we know from HR diagram?? •The temperature of red giant stars are low compared with main sequence stars which have same luminosity.
- 32. HR diagram •What can we know from HR diagram?? •The temperature of red giant stars are low compared with main sequence stars which have same luminosity. •The luminosity of white dwarf stars is smaller than main sequence stars, but they have high temperature.
- 33. HR diagram •What can we know from HR diagram?? •The temperature of red giant stars are low compared with main sequence stars which have same luminosity. •The luminosity of white dwarf stars is smaller than main sequence stars, but they have high temperature.
- 34. HR diagram •What can we know from HR diagram?? •The temperature of red giant stars are low compared with main sequence stars which have same luminosity. •The luminosity of white dwarf stars is smaller than main sequence stars, but they have high temperature. •As you can see, HR diagram tells us the properties of stars. We can also learn stellar interior and evolution from HR diagram.
- 35. Extending the cosmic distance scale m − M = 5 log10 ( d[pc] 10pc ) •You remember how to measure distance to stars by using following relation •We can also evaluate the distance to stars if we know the luminosity of stars ( ) and apparent brightness . L b b = L 4πR2 •If we use the spectral type (or temperature) of the star, we can estimate the luminosity from HR diagram.. L
- 36. Luminosity class •Astronomers developed a system for classifying stars called “Luminosity class”. Class Description Ia Bright supergiants Ib Supergiants II Bright giants III Giants IV Subgiants V Main sequence stars and dwarfs Luminous
- 37. Stellar masses •HR diagram apparently provides relation between temperature and luminosity of stars. •But, remember that the mass is also important property of stars. Where does HR diagram include the information of mass? •Astronomers checked the mass of stars on the main sequence and found that lower temperature stars have smaller mass. Low mass stars are cool and faint. Massive stars are hot and bright. But, why?? > it is related how stars form
- 38. Mass determination How can we determine the mass of stars? •We know roughly 50% of stars are binary（双星） •Two stars are in orbital motion around the center of mass <latexit sha1_base64="IwZJQ8OYZJRAckwK9Rj60k5vMFE=">AAAB+HicbVDLTgIxFO3gC/HBqEs3jcTEFZlBjS6Jblyi4ZXAQDqlAw2dtmk7JjjhS9y40Bi3foo7/8YCs1DwJDc5Oefe3HtPKBnVxvO+ndza+sbmVn67sLO7t190Dw6bWiQKkwYWTKh2iDRhlJOGoYaRtlQExSEjrXB8O/Nbj0RpKnjdTCQJYjTkNKIYGSv13WK9V4FdqYQ0Aj70zvtuySt7c8BV4mekBDLU+u5XdyBwEhNuMENad3xPmiBFylDMyLTQTTSRCI/RkHQs5SgmOkjnh0/hqVUGMBLKFjdwrv6eSFGs9SQObWeMzEgvezPxP6+TmOg6SCmXiSEcLxZFCYP2yVkKcEAVwYZNLEFYUXsrxCOkEDY2q4INwV9+eZU0K2X/suzdX5SqN1kceXAMTsAZ8MEVqII7UAMNgEECnsEreHOenBfn3flYtOacbOYI/IHz+QNw+ZJM</latexit> T2 / R3 Do you remember Kepler’s third law? •I skip the detail, but we can determine the mass of stars when we apply Kepler’s third law to binary.
- 39. Initial mass function •Initial mass function(IMF) describes initial distribution of masses for stars during star formation. •The number of massive stars is small and the number of less massive stars is large. 多 少
- 40. Mass and other stellar properties 少 多
- 41. Mass and other stellar properties •The mass-radius relation on main sequence stars. Massive stars are larger •The mass-luminosity relation on main sequence stars. Massive stars are brighter
- 42. Mass and other stellar properties •We would like to evaluate lifetime of stars. How long can stars burn?? •Because stars burn by nuclear fusion process, we can estimate a main sequence star’s lifetime by dividing the amount of fuel available (the mass of star) by the rate at which the fuel is being consumed (the star’s luminosity) stellar lifetime ∝ stellar mass stellar luminosity . ∝ 1 (stellar mass) 3 . stellar luminosity ∝ (stellar mass)4 Larger mass or brighter stars die earlier!
- 43. Mass and other stellar properties Let’s calculate the lifetime of Proxima Centauri! •The lifetime of the sun is roughly year (100亿年) 1010 •The mass of Proxima Centauri is roughly 0.12 (solar mass) M⊙ stellar lifetime ∝ stellar mass stellar luminosity . ∝ 1 (stellar mass) 3 . What is the lifetime of Proxima Centauri?
- 44. Mass and other stellar properties Let’s calculate the lifetime of Proxima Centauri! •The lifetime of the sun is roughly year (100亿年) 1010 •The mass of Proxima Centauri is roughly 0.12 (solar mass) M⊙ stellar lifetime ∝ stellar mass stellar luminosity . ∝ 1 (stellar mass) 3 . What is the lifetime of Proxima Centauri? (Answer)
- 45. Summary • HR diagram provides us the relation between luminosity and temperature of stars. • HR diagram tells us properties of stars. • Let’s understand how to read HR diagram.