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Time: 16 hours
Level: Intermediate
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 Introduction Resource- We can study the individual properties of individual stars, such as photospheric temperature, luminosity, radius, composition and mass. If we wish to understand more about stars and obtain some insight...
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| | 1 The Hertzsprung-Russell diagram
- 1.1 Constructing the H–R diagram Resource
- Three properties which are suitable for comparing stars are temperature, luminosity and radius. However, we don't need all three.
- 1.2 The main classes of stars Resource
- The main classes of stars are shown in Figure 5.
- 1.3 How can we explain the distribution of stars on the H–R diagram? Resource
- Here is a possible explanation for the concentration of stars into certain regions on the H–R diagram. It is based on the reasonable assumptions that:
- 1.4 Stellar masses and stellar evolution Resource
- Measured masses range from about 0.08M⊙ to about 50M⊙, a large range, with the Sun again showing up as an average sort of star. At the upper end we have some true monsters, but even at the lower end we...
- 1.5 Star clusters and stellar evolution Resource
- Detailed observations of star clusters suggest that they occur because the stars in them form at about the same time. Moreover, the compositions of the stars are similar. Isolated stars (including isolated...
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| | 2 Observing through the interstellar medium
- 2.1 Introduction Resource
- In all the analysis of stellar properties discussed so far we have made an implicit assumption – that light emitted by a star is not changed between its emission and its arrival outside the Earth's atmosphere,...
- 2.2 Interstellar space is not empty Resource
- The difference between the apparent brightness of a star (as measured by its apparent magnitude), and its luminosity (represented by its absolute magnitude) is defined by the distance of the star. We can...
- 2.3 The effect of interstellar gas Resource
- You have seen that the ISM has been studied through the radiation that the gas and dust absorb, emit and scatter. Figure 15 summarizes the differences between these three phenomena.
- 2.4 The effect of interstellar dust Resource
- Let's now consider the dust. Photoexcitation (by absorption of photons) and collisional excitation (by atoms/molecules) occur in the atoms and molecules that constitute the surface of a dust grain. Much...
- 2.5 Using stars to probe the interstellar medium Resource
- The effects of interstellar material on starlight can be used to probe the properties of the interstellar medium itself. A few examples are:
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- The H–R diagram Resource
- The Hertzsprung-Russell (H–R) diagram displays the photospheric temperatures and luminosities of the stars. The corresponding radii are obtained from Equation A. The H–R diagram is a very useful aid to...
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- Questions Resource
- In what ways, if any, does the distance to a star influence its position on an H–R diagram?
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| | References and Acknowledgements | |
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