Download Spectral Classification

Spectral Classification
Oh Be A Fine Guy/Gal; Kiss Me
How do we Classify and why?
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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.
Example
How Atoms Produce Spectra!
.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
.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
ARTURUS in Bootes
.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
.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
.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
.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.
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Examples: Rigel, Spica
.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
http://www.sttff.net/ast/spectralclassification.html
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.
BINARY SYSTEMS
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.
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
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!