# Stellar-Spectra

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```					                                  Astronomy Challenge 4
Stellar Spectra Identification

Introduction: Stars are classified by their spectral lines. Although other variables influence the
spectra of stars, temperature is the primary factor that determines the characteristics of the
spectra. The spectra of stars are classified into the following divisions O, B, A, F, G, K, M from
the highest to lowest temperature. Each of these spectral classes is divided into ten subdivisions
numbered from 0 to 9. We therefore have spectral classes such as O9 or F6. The sub divisions 0
to 9 go from higher to lower temperature; hence an A5 star has a higher temperature than an A7.

Procedure: Take a few minutes to study the “Standard Set of Spectrograms”. Note that some
lines increase in intensity with temperature, where others decrease. Hydrogen lines first increase
and then decrease in intensity with temperature. Hydrogen lines are not especially useful for
classification because of their intensity variation. The spectra in the “Standard Set of
Spectrograms” have reference spectra of iron directly below each spectrum for comparison
purposes.

The most useful lines for spectral classification are 4026 Ao (helium) for spectral classes from
O5 to B6, 3968 Ao (the K line of ionized calcium) for classes B6 to F0, and 4227 Ao (neutral
calcium) for classes from F0 to M0.

1. Take the first set of spectra. These spectra are for known stars whose names are written
on the left of the spectra; make sure that you arrange your spectra so the name is on the
left. These spectra also have a reference spectra of iron directly below for comparisons
purposes. To help get a sense of the spectral classes of these stars arrange the spectra
from the hottest to the coolest stars.

2. Now on the answer sheet write the name of each of your stars and estimate its spectral
class (both letter and number) by comparison to the standard spectra. You should note
that the “Standard Set of Spectrograms” do not contain all the of the sub divisions hence
you may have to estimate the spectral class of you star. For example if the spectrum of
your star seems to be half way between an F5 and a G0 then you would classify it as a F7
of F8. Write your classification of each of your stars on the answer sheet. After you have
completed determining the spectral classification of all of the stars in your set ask your
instructor to check you work.

3. After your instructor has reviewed your classification of the known stars in 2 above,
study the “Standard Set of Spectrograms” again. When you have sufficiently studied the
“Standard Set of Spectrograms” return both the spectra of your stars (place them
carefully in the envelop from which you obtained them) and the “Standard Set of
Spectrograms” to your instructor. Your instructor will then give you a new set of
unknown spectra. Each spectrum has a letter on it on the right end. Arrange these spectra
from the highest temperature to the lowest temperature star and list them in that order on
the answer sheet. (Note: that each set of unknown spectra is different so don’t assume
that your neighbor’s set is the same as yours).
Name __________________________________

Lab Challenge 4: Stellar Spectra Identification Answer Sheet

2. Identification of Spectral Class

Spectra Set Number ______________

Star Name                            Spectral Class

1. ___________________________           ____________

2 ___________________________            ____________

3 ___________________________            ____________

4 ___________________________            ____________

5 ___________________________            ____________

6 ___________________________            ____________

7 ___________________________            ____________

8 ___________________________            ____________

9 ___________________________            ____________

10. _________________________            ____________
Name __________________________________

Lab Challenge 4: Stellar Spectra Identification Answer Sheet

3. Ordering Spectra by Temperature

Spectra Set Number ______________

Highest Temperature                  Star Letter

________

________

________

________

________

________

________

________

________

________

________

________

Lowest Temperature

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 views: 5 posted: 9/5/2012 language: English pages: 3