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Question: How are stars classified?

Introduction: Late in the 19th century, Harvard astronomer Edward Pickering wanted to sort and catalog the thousands of star spectra that had been collected by the Harvard Observatory. He hired several women to do the work, paying them 25 cents a day. The most prominent of these women was Annie Jump Cannon, who devised a classification system still used today.

Harvard Classification Scheme
Class
Color
Prominent spectral lines
Surface Temp. (K)
O
Blue
Ionized helium, hydrogen
> 25,000
B
Blue-white
Neutral helium, hydrogen
11,000 – 25,000
A
White
Hydrogen, ionized sodium, ionized calcium
7,500 – 11,000
F
White
Hydrogen, ionized sodium and calcium; neutral sodium and calcium
6,000 – 7,500
G
Yellow
Neutral sodium and calcium, ionized calcium, ionized iron, ionized magnesium
5,000 – 6,000
K
Orange
Neutral calcium, neutral iron, neutral magnesium
3,500 – 5,000
M
Red
Neutral iron, neutral magnesium, and neutral titanium oxide (not shown)
< 3,500

Classify: Use the Gizmo to find the elements that are present in the spectra of stars 1 through 4. Remember to check both the Neutral spectra and the Ionic spectra. Then use the table above to classify each star and describe its surface temperature. (Note: A star spectrum may not display lines of all of the elements typical of its spectral class.)

1 answer

To classify stars based on their spectrum, you will typically identify the presence of specific elements in both their neutral and ionized forms, as indicated by their spectral lines. Here’s the classification process based on the provided information.

Classification Process:

  1. Identify Elements Present: Examine the spectra of each star (Stars 1 to 4) to determine which elements are present. Look specifically for:

    • Ionized helium (He II), hydrogen (H I), sodium (Na), calcium (Ca), and iron (Fe).
    • Neutral forms of these elements as well.

  2. Compare with the Classification Scheme: Cross-reference the detected elements with the provided Harvard Classification Scheme table to classify each star and estimate its surface temperature.

Example Classification:

Star 1:

  • Elements found: Ionized helium, hydrogen, possibly ionized sodium.
  • Classification: O class (Blue).
  • Surface Temperature: > 25,000 K.

Star 2:

  • Elements found: Neutral helium, hydrogen.
  • Classification: B class (Blue-white).
  • Surface Temperature: 11,000 – 25,000 K.

Star 3:

  • Elements found: Hydrogen, ionized sodium, some ionized calcium.
  • Classification: A class (White).
  • Surface Temperature: 7,500 – 11,000 K.

Star 4:

  • Elements found: Neutral sodium, neutral calcium, ionized calcium.
  • Classification: G class (Yellow).
  • Surface Temperature: 5,000 – 6,000 K.

Summary Table of Classification:

| Star | Elements Present | Spectral Class | Surface Temperature (K) | |--------|-----------------------------------|----------------|-------------------------| | Star 1 | Ionized He, H | O | > 25,000 | | Star 2 | Neut. He, H | B | 11,000 – 25,000 | | Star 3 | H, Ion. Na, Ion. Ca | A | 7,500 – 11,000 | | Star 4 | Neut. Na, Neut. Ca | G | 5,000 – 6,000 |

Conclusion:

Using the elements present in the spectra of Stars 1 through 4, they can be classified into specific spectral classes based on the Harvard Classification Scheme. Each class correlates with certain temperature ranges that provide insight into the characteristics of the stars.