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Classification of stars (A-level only)

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Question 4

HD 10138 A and HD 10138 B are two stars that appear very close to each other when viewed from Earth.

There are two possible reasons for this:

  • they are an orbiting binary system
  • they are distant from each other and only appear in the same line of sight.

In an orbiting binary system, the difference between the apparent magnitude and the absolute magnitude for each star is similar.

The table below shows data about these two stars.

Temperature / KKKRadius of star / mmmApparent magnitude
HD 10138 A9800980098001.2×1091.2 \times 10^91.2×10911.411.411.4
HD 10138 B3100310031008.4×1098.4 \times 10^98.4×10910.110.110.1

Discuss the appearance of the two stars to an astronomer on the Earth. In your answer you should:

  • compare the colour of the stars
  • compare the brightness of the stars
  • deduce, with a calculation, whether the stars form an orbiting binary system.
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Classification of stars (A-level only) Questions

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