Spectral classification of stars

An important topic in Astrophysics.. checkout and make use of it friends!!

1. SHOBANA.N.S QUEEN MARY’S COLLEGE FOR WOMEN SPECTRAL CLASSIFICATION OF STAR 1

2. Questions : What is a spectra? What is an absorption spectrum ? Can we see what stars are made up of ? Can we measure how hot they are ? 2

3. What is a spectra? 3

4. Absorption spectrum 4

5. For the other two questions the answer is : Yes we can !!! Using spectral classification of the stars. 5

6. STAR CLASSIFICATION Surface temperature of the star is associated with specific spectral classification. T he spectral classification includes 7 main types:   O ,  B ,  A ,  F ,  G ,  K ,  M . 6

7. This is called “Morgan-Keenan spectral classification” The classes, listed from hottest to coldest Class Temperature Star Color O 30,000 – 60,000 °K Blue B 10,000 – 30,000 °K Blue A   7,500  - 10,000 °K White F   6,000  -  7,500 °K White   (yellowish) G   5,000  -  6,000 °K Yellow (like the Sun) K   3,500  -  5,000 °K Orange M   2,000  -  3,500 °K Red 7

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9. Notice that hottest stars are blue, while coldest stars are red. 9

10. Naos (in the constellation Puppis) These have prominent ionized and neutral helium lines and only weak hydrogen lines. Class O stars emit most of their radiation in ultra-violet. Class O stars 10

11. Class  B  stars Class  B  stars are again very luminous Rigel (in the great constellation Orion) is a prominent B class blue supergiant. Their spectra have neutral helium and moderate hydrogen lines.  11

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13. Class  A  stars Class  A  stars are amongst the more common naked eye stars. Deneb in Cygnus is another very powerful star. Sirius , that appears the brightest star as seen from Earth, is also an A class star. As with all class A stars, they are white. Many white dwarfs are also A. They have strong hydrogen lines and also ionized metals. 13

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16. Class  F  stars Class  F  stars are still quite powerful.. Fomalhaut in Pisces Australis. Their spectra is characterized by the weaker hydrogen lines and ionized metals, their color is white with a slight tinge of yellow . 16

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18. Class  G  stars Class  G  stars are probably the most well known for the reason that our Sun is of this class. They have even weaker hydrogen lines than F and have neutral helium lines but along with the ionized metals, they have neutral metals. 18

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20. Class  K STARS Class  K  are orange stars which are slightly cooler than our Sun. Some K stars are giants and supergiants , such as Arcturus , while others like Alpha Centauri B are smaller.  They have extremely weak hydrogen lines, if they are present at all, and mostly neutral metals. 20

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22. CLASS M STARS Class  M  is the most common class by the number of stars. All red dwarfs, such Proxima Centauri, the closest star to our Solar System The spectrum of an M star shows lines belonging to molecules and neutral metals but hydrogen is usually absent. Titanium oxide can be strong in M stars. 22

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24. M stars may be dwarf stars or supergiant stars, and A stars can be white dwarfs or white giants as well.  This can be understood through the Hertzsprung -Russell diagram, that is very important in astrophysics and relates temperature and spectral classification of stars with their luminosity and size. A number of other spectral types have been taken into use for rare types of stars: these are W, L, T, S, and C (that includes R and N). 24

25. Hertzsprung-Russell diagram 25

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27. THANK YOU !!!! 27