Spectral Classification

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Spectral Classification

• Oh Be A Fine Guy/Gal Kiss Me

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How do we Classify and why?

• In astronomy, stellar classification is a
  classification of stars based initially on
  photoshperic temperatures and its associated
  spectral characteristics, and then refined in
  terms of other characteristics.
• Early stellar classification by temperatures
  posed difficulties for distant stars. Stellar
  spectroscopy offers a way to classify stars
  according to their absorption lines particular
  absorption lines can be observed only for a
  certain range of temperatures because only in
  that range are the involved atomic energy levels
  populated.

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Example
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How Atoms Produce Spectra!
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.M Stars.

• Class M is by far the most common class if we go
  by the number of stars. All the red dwarfs go in
  here and they are plentiful over 78 of stars
  are red dwarfs.
• Examples Betelgeuse, Anteres

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ANTARES In Scorpio
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Betelguese in Orion
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.K Stars.

• Class K are orangish stars which are slightly
  cooler than our Sun. Some K stars are giants and
  supergiants, such as Arcturus while others are
  main sequence stars. These make up some 13 of
  main sequence stars.
• Examples Acrturus

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ARTURUS in Bootes
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.G Stars.

• Class G stars are probably the most well known if
  only for the reason that our Sun is of this
  class. G is host to the "Yellow Evolutionary
  Void". Supergiant stars often swing between O or
  B (blue) and K or M (red). While they do this,
  they do not stay for long in the G classification
  as this is an extremely unstable place for a
  supergiant to be. These are about 8 of all main
  sequence stars.
• Examples Sun, Capella

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.F Stars.

• Class F stars are still quite powerful but they
  tend to be main sequence stars.Their color is
  white with a slight tinge of yellow. These
  represent 3.1 of all main sequence stars.
• Examples Canopus, Procyon

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Procyon
Canopus
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.A Stars.

• Class A stars are amongst the more common naked
  eye stars. As with all class A stars, they are
  white or green. Many white dwarfs are also A.
  They comprise perhaps 0.63 of all main sequence
  stars.
• Examples Vega, Sirius

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.B Stars.

• Class B stars are extremely luminous and blue.
  As O and B stars are so powerful, they live for a
  very short time. They do not stray far from the
  area in which they were formed as they don't have
  the time. They therefore tend to cluster together
  in what we call OB1 associations. and contains
  all of the constellation of Orion. They
  constitute about 0.13 of main sequence stars --
  rare, but much more common than those of class O.
  
• Examples Rigel, Spica

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.O Stars.

• Class O stars are very hot and very luminous,
  being strongly violet in color in fact, most of
  their output is in the ultraviolet range. These
  are the rarest of all main sequence stars,
  constituting as little as 1/32,000th of the
  total. O-stars shine with a power over a million
  times our Sun's output.
• Examples Epsilon Orionis

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http//www.sttff.net/ast/spectralclassification.ht
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Cepheid Variables

• Cepheid variables are stars that regularly
  pulsate in size and change in brightness. As the
  star increases in size, its brightness decreases
  then, the reverse occurs. Cepheid Variables may
  not be permanently variable the fluctuations may
  just be an unstable phase the star is going
  through. Polaris in an examples of a Cepheid.

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BINARY SYSTEMS
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Eclipsing Binary

• An eclipsing binary is two close stars that
  appear to be a single star varying in brightness.
  The variation in brightness is due to the stars
  periodically obscuring or enhancing one another.
  This binary star system is tilted (with respect
  to us) so that its orbital plane is viewed from
  its edge.

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Oh Be A Fine Guy/Gal Kiss Me
Class Temperature Star Color (visible light) Mass Radius Luminosity
O 30,000 - 60,000 K Bluish 60 15 1,400,000
B 10,000 - 30,000 K Bluish 18 7 20,000
A 7,500 - 10,000 K White bluish tinge 3.2 2.5 80
F 6,000 - 7,500 K White 1.7 1.3 6
G 5,000 - 6,000 K Yellowish white 1.1 1.1 1.2
K 3,500 - 5,000 K Yellow-orange 0.8 0.9 0.4
M 2,000 - 3,500 K Orange-red 0.3 0.4 0.04
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Thanks Annie!

• Annie Jump Cannon and many other Harvard women
  dedicated hours to this classification system and
  analyzed millions of spectral absorption plates.
  In the end their male counterparts took all the
  credit, but the real work was done by a room of
  amazing female astrophysicist, and Annie Cannon
  devised the classification we use today!