Lab 8
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California State University, Fullerton *
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Course
MISC
Subject
Astronomy
Date
Apr 3, 2024
Type
Pages
6
Uploaded by DrTreeFish36
Sloan Digital Sky Survey Stellar Spectra Lab
Spectra of Stars (small intro) http://cas.sdss.org/dr7/en/proj/basic/spectraltypes/stellarspectra.asp Phase I: Exploration Part A Open the example spectra in the file SDSS Stellar Spectrum Examples.pdf
1.
What is plotted against what in a spectrum?
2.
What is the unit of length used to measure the wavelength of light in SDSS spectra?
3.
What unit measures the peak of the continuum (labeled the “continuum peak” in the
example)?
4.
The second page (
SDSS Stellar Spectrum Examples.pdf) includes a plot that zooms into
the area of 6563 Angstroms. Is more light detected from the star at 6563 Angstroms or
6520 Angstroms?
5.
The feature in the zoomed area is called an “absorption line”. What is likely being
absorbed in an absorption line?
Wavelength versus intenstiy
The unit of length used to measure the wavelength of light in SDSS spectra is meters.
More light is detected from the star at 6563 Angstroms.
The unit measure for the peak of the continuum is Angstroms. The light is being absorbed in an absorption line.
Phase I: Exploration Part B Open the SDSS / SkyServer http://cas.sdss.org/dr7/en/proj/basic/spectraltypes/studentclasses.asp Navigate to the Exploring Spectra page. For this portion of the lab you may use either the spectra linked from the table online, or the spectra in the SDSS Stellar Spectra Panels 1-14.pdf
file. 6.
What do you notice about the spectra? What are the most important features they all have
in common?
7.
What differences do you notice among the spectra? How do the continuum peak and the
absorption lines change among the 14 spectra?
8.
A star’s color is primarily the ratio of the blue light to the red light in its spectrum. Stars
that shine with more light at short wavelengths than at long wavelengths look blue
—
such
as the star in the example spectrum from Part A. Can you see a relationship between
these
star's color and their spectra?
There’s no right answer for this part—I’m just curious. If you can’t see a relationship
then appreciate how the applications of hj
science
in the rest of the lab will make it clear.
I notice the colors of the star coincide with their wavelengths as high Angstroms can indicate orange colors and vice versa. They do not have much in common besides having light be recorded. The differences I notice among the spectra are that some stars have continuum peaks at low Angstroms (e.g Star 1, 3, 4, 7) while others stars have their continuum peaks at high Angstroms (e.g Star 2). Some continuum peaks are in the middle of the spectrum (e.g Star 12 &13). Some stars do not have a continuum peaks, instead having many prominent absorption lines (e.g Star 5, 9, 11, 14). For stars with continuum peaks, theres usually only 1-2 prominent absorption lines.
Yes, I can see a relationship between these star's colors and their spectra because short wavelengths equal low Angstroms, while long wavelengths equal high Angstroms.
Phase II: Origin of spectral lines http://cas.sdss.org/dr7/en/proj/advanced/spectraltypes/energylevels.asp Read the explanation of the atomic energy levels, down to the table listing the first five energy levels of hydrogen. 9.
Calculate the energy of the photons absorbed in the 6563 Angstrom line from Phase I.
a.
First convert the wavelength from Angstroms to meters so we can use the
equation from the online lab.
b.
Use the equation E = hc/
λ
to calculate the energy of the photons at that
wavelength.
10.
Which pair of the first five energy levels of hydrogen have a difference in energy that
matches the energy of photons that are absorbed in the 6563 Angstrom line?
11.
Recall, from the webpage, what happens when electrons absorb light. Since the 6563
Angstrom feature is an absorption line, do the electrons in hydrogen atoms creating this
line gain or lose energy?
gain or lose
12.
For Hydrogen to absorb light at 6563 Angstroms, which energy level do electrons in
Hydrogen start in, and which energy level to do they finish in?
13.
Find the lines labeled Hβ, Hγ, and Hδ in the example spectrum (or any of the spectra). Do
the wavelengths of these lines correspond to more or less energetic transitions than the
line at 6563 Angstroms (which is known as the Hα line)?
6.563e-7 meters
1.8891467 eV
Energy level 2 and 3 Gain
They start in energy level 3 and finish in 4. They correspond to more energetic transitions than the line at 6563.
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Phase III: Stellar Classification
Open the file SDSS Stellar Spectra 1-7.pdf
http://cas.sdss.org/dr7/en/proj/basic/spectraltypes/lines.asp 14.
Measure the strength of the Hα absorption line in each of the seven stars. The strength of
the line is literally how much light is absorbed. To measure the strength of a line, color in
the area between a line connecting the triangle centers and the actual spectrum in the
zoomed in view, and then count the number of grid squares filled. The number of filled
grid squares is a measure of the line strength.
15. Rank the stars by writing each star number in the appropriate place in the second column
of the table below.
Line Strength
Star Number
Spectral Class
Strongest line (greatest line area) A ↓
B ↓
F ↓
G ↓
K ↓
M Weakest line (least line area) O Originally, astronomers classified those stars with the strongest hydrogen lines as 'A' stars, stars with the next strongest lines as 'B' stars, the next strongest 'C' and so on. Eventually, they realized that some letters were unnecessary, and dropped them from the classification system. The letter assigned to a star is called its Spectral Class
. 2
6
3
7
1
5
4
Phase IV
: Classifying by Temperature
http://cas.sdss.org/dr7/en/proj/basic/spectraltypes/temperature.asp 16. Which is hotter: a star whose continuum peaks at 5000 Ångstroms or a star whose
continuum peaks at 6000 Ångstroms?
17. Rank the stars according to peak wavelength of each star's thermal continuum, using the
table below. Estimate where you think the star ranks if the peak is not shown on the
graph.
Wavelength
Star Number
Longest peak wavelength ↓
↓
↓
↓
↓
Shortest peak wavelength 18.
Rank the seven stars in order of temperature using the table below. Fill in both the star’s
number and its spectral class.
Temperature
Star Number
Spectral Class
Hottest ↓
↓
↓
↓
↓
Coolest 19. Summarize your results in the table below: in the first row list the spectral types in order
of decreasing Hα line strength, and in the second row in order of decreasing temperature.
The star whose continuum peaks at 5000 Angstroms is hotter. 5
1
7
3
6
4
2
2
4
6
3
7
1
5
A
O
B
F
G
K
M
Strongest Hα Line
Weakest Hα Line
Hottest Temperature
Coolest Temperature
20. Are these two classification schemes the same?
21. Which class of stars is the hottest?
22. Which class of stars is the coolest?
23.
Which class of stars has the strongest Hα line?
24.
Which classes of stars have the weakest Hα lines?
25. The accepted ordering for spectral classes among astronomers is OBAFGKM. You may
have learned the classes with the phrase "Only bad art features Godzilla killing Mothra."
Why do the classes appear in this order?
Stop at Temperature and Line Strength 2
4
6
3
7
1
5
A
O
B
F
G
K
M
No, these two classifications schemes are not the same.
Class A of stars is the hottest.
Class M of stars is the coolest.
Class A has the strongest Hα line.
Class M has the weakest Hα lines.
The classes are ranked by hottest to lowest, therefore resulting in that ordering.
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