Solar and Stellar Spectra

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Solar and Stellar Spectra

 Introduction

The brightest star in our sky is the Sun. Absorption lines in the solar spectrum were first noticed by an English astronomer in 1802 but it was a German physicist, Joseph von Fraunhofer, who first measured and cataloged over 600 of them about 10 years later. These lines are now known as the Fraunhofer lines,

In the 1800’s scientists did not know that these lines were chemical in origin. The letters used by Fraunhofer to identify the lines have no relation to chemical symbols nor to the symbols used to designate the spectral types of stars. Today’s astronomers use some of the designations simply for convenience and ease in identifying lines.

Now we know that each absorption line is caused by a transition of an electron between energy levels in an atom. Each element has a distinct pattern of absorption lines. Once the pattern of the lines of a particular element have been observed in the laboratory, it is possible to determine whether those elements exist elsewhere in the universe simply by pattern matching the absorption lines.

In Part A we will observe and analyze emission lines in a laboratory setting.

In Part B you will work with the solar spectrum between approximately 390 and 660 nm (3900 – 660 Angstroms) and identify some of the strongest Fraunhofer lines.

In Part C you will observe and analyze actual spectra from stars and use that to best-fit and identify stellar types.

Part A: Laboratory Spectra: Observing Emission Spectra (10 pts)

There are four glass tubes each with a gaseous form of a different element. Turn on the power supply to send energy into the tubes from the top and bottoms.

Use a diffraction grating to split the incident light into its color components.

Accurately draw the number and position (by color) of the lines.

Predict which of the spectra in the slide show most closely matches. Write down the correct element.

 

Drawing Spectra

Red

 

Element 1:

Orange Yellow Green Blue Violet

 

Red

 

Element 2:

Orange Yellow Green Blue Violet

 

Red

 

Element 3:

Orange Yellow Green Blue Violet

 

Red

 

Element 4:

Orange Yellow Green Blue Violet

 

Part B: Solar Spectrum (33 pts)

We will use the solar spectrum found at:

http://www.columbia.edu/~vjd1/Solar%20Spectrum%20Ex.html

  1. Using Tables 1 and 2, and the image at the web site above, identify the elements that we detect in the upper atmosphere of the Sun using absorption lines in the spectrum,
  2. Note that lines “A” and “B” are signatures of the oxygen in the Earth’s atmosphere. The other “known” lines are not terrestrial in origin.
  3. Determine the location of each of the unknown lines and compare the wavelengths to the list of lines in Table 3 (below). ­­­

        Table 3: Identification of Unknown Lines

Line Wavelength (nm) Element Name
G    
a    
b1    
b2    
c    
d    
e    
f    
g    
h    

 

  1. Draw the arrangement of the different parts of the experiment to see bright line emission spectra. Indicate the direction of the light and label the equipment.

DESCRIBE THE ARRANGEMENT                                                            DRAW HERE

  1. The energy hits the gas from the side.
  2. The gas glows in specific wavelengths.
  3. The light from the gas goes thru

a diffraction grating.

  1. We see a emission (bright line) spectrum.

 

 

  1. Describe and draw the arrangement for seeing an absorption (darkline) spectrum. Same expectations as above.

 

 

 

 

 

 

 

 

 

 

 

 

 

Part C: Stellar Spectra (67 pts)

 

  1. Go to SCOPE at       http://scope.pari.edu/index.php

 

  1. Read the “Welcome to SCOPE” HOME page. Click on the hyperlink to “The Science.” Read the titles of the sections available and think of returning here if you want to learn more.

 

  1. Return to the HOME page and click on the hyperlink “To Take Part.” Read “How to Take Part.”

 

  1. Near the bottom find the section titled “Get Some Classification Experience” and read the directions. Complete Tables 4 and 5 while following directions.

 

 

Table 4: Get Some Classification Experience

Example My Best Match Catalogued Spectral Type Notes
first      
second      
third      
“Here are several more to practice on:”
fourth      
fifth      
sixth      

 

Table 5: Classifying to the Next Level

Example My Best Match Catalogued Spectral Type Notes
B type star      
M type star      

 

Classifying Stars

  1. Register and Log In to SCOPE. From the HOME page, choose CLASSIFY and go to “Classify a Star.” Let’s look at a new program star in “Case-16292.”
  2. When were these images taken?

 

  1. When you click on “Get Additional Information About This Plate” what do you learn?

 

 

  1. Click on the name of that plate “Case-16292_AL” and observe the stellar spectrum on the upper left of this plate

 

Table 6: My first star

Plate Star My Best Match Notes
Case-16292_AL HD 188400  

 

 

 

 

  1. Click on the next collection of plates, CTIO-12307.
  2. When were these images taken?

 

  1. When you click on “Get Additional Information About This Plate” what do you learn?

 

 

  1. Classify 12 more stars on a variety of plates and complete Table 7

 

Table 7: My classification of stars

Plate Star My Best Match Notes
       
       
       
       
       
       
       
       
       
       
       
       

 

  1. Count the number and calculate the percent of your stars that fit in each class and complete Table 8 below:

 

Table 8: Distribution of my 12 stars above

Spectral Type O B A F G K M
Number of Stars              
Percent of Stars              

 

Table 9: Distribution of 115 randomly picked SCOPE stars

Table 10: Nearby Stars                                               Table 11: Bright Stars


Star Distance (Pc) Spectral Type
Proxima Centauri 1.31 M5 V
Alpha Centauri 1.35 G2 V
Barnard’s Star 1.81 M5 V
Wolf 359 2.35 M8 V
Lalande 21185 2.52 M2 V
Sirius A 2.65 A1 V
Sirius B 2.65 B1
Luyten 726-8 2.72 M5.5 V
Ross 154 2.90 M4.5 V
Ross 248 3.14 M6 V
Eridani 3.31 K2 V
61 Cygni 3.38 K5 V
Procyon 3.51 F5 IV
Procyon B 3.51 A2
GJ 440 4.60 F8

Pc stands for parsec. I parsec equals 3.2616 light years, 206, 265 AUs, or almost 19.2 trillion miles.

 

Star Apparent magnitude Spectral Type
Sirius A -1.47 A1 V
Canopus -0.72 F0 I
Alpha Centauri 0.01 G2 V
Arcturus -0.06 K2 III
Vega 0.04 A0 V
Capella 0.05 G0 III
Rigel 0.14 B8 I
Procyon 0.37 F5 IV
Betelguese 0.41 M2 I
Achernar 0.51 B5 V
Beta Centuari 0.61 B1 III
Altair 0.77 A7 IV
Alpha Crucis 0.77 B1 IV
Aldebaran 0.86 K5 III
Spica 0.91 B1 V
Antares 0.92 M1 I
Pollux 1.16 K0 III
Formalhaut 1.15 A3 V
Deneb 1.26 A2 I


 

  1. Use Tables 10 and 11 above to determine the number and calculate the percent of brightest and nearby stars fit in each class and complete Table 12,

 

   Table 12: Distribution of nearby and bright stars

Spectral Type O B A F G K M
Number of Stars              
Percent of Stars              

 

  1. You now have four different groups of stars, a) your chosen dozen SCOPE stars, b) 115 random SCOPE stars, c) the 15 nearby stars and d) the 19 bright stars. All of those stars are in our galaxy. Question: What percent of the stars in our galaxy are in each stellar classification?

Write an evidence-based conclusion: