Spectral classification of stars
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Transcript of Spectral classification of stars
SHOBANA.N.S
QUEEN MARY’S COLLEGE FOR WOMEN1
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 ?
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For the other two questions the answer is :
Yes we can !!! Using spectral classification of the stars.
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Surface temperature of the star is associated with specific spectral classification.
The spectral classification includes 7 main types:
O, B, A, F, G, K, M.
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This is called “Morgan-Keenan spectral classification”
The classes, listed from hottest to coldestClass 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 Red7
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Notice that hottest stars are blue, while coldest stars are red.
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Naos (in the constellation Puppis)
These have prominent ionized andneutral helium lines and only weakhydrogen lines.
Class O stars emit most of theirradiation in ultra-violet.
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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Hertzsprung-Russell diagram
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