Lecture: Stars
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The document discusses how to measure and classify stars based on their luminosity, apparent brightness, temperature, and spectra. Luminosity measures a star's total energy output independent of distance, while apparent brightness depends on distance and is measured via photometry. To determine luminosity, both apparent brightness and distance must be measured. A star's temperature determines its color, from hot blue stars over 25,000 K to cool red stars under 3,500 K. Stars are classified into seven main categories - O, B, A, F, G, K, and M - based on their spectra and temperature, which indicate the elements present.
Lecture: Stars
- 2. HOW BRIGHT IS A STAR? Luminosity - is the rate at which a star radiates energy into space. Apparent Brightness - is the rate at which a star's radiated energy reaches an observer on Earth.
- 3. Luminosity - Measures the Total Energy Output by the star in Watts - Distance Independent Apparent Brightness - Measures how bright the star appears to be as seen from a distance. - Depends on the distance to the star.
- 4. Measuring Apparent Brightness Photometry - The process of measuring the apparent brightness of objects. Two ways to express apparent brightness: Stellar Magnitudes Absolute Fluxes (energy per second per area)
- 5. Measuring Luminosity To measure the Luminosity of a star you need 2 measurements: the Apparent Brightness (flux) measured via photometry, and the Distance to the star measured in some way
- 6. TEMPERATURE AND COLOR - Stars are dense hot balls of gas so their spectra similar to that of a perfect thermal radiator, which produces a smooth continuous spectrum. -Therefore, the color of stars depends on their temperature--hotter stars are bluer and cooler stars are redder.
- 7. - Hot stars have temperatures around 60,000 K while cold stars have temperatures around 3,000 K. Ways to measure stars color and temperature: B-V color index Wien's Law and Temperature
- 9. CLASSIFICATION OF STARS - Stars are classified by their spectra (the elements that they absorb) and their temperature. - There are seven main types of stars. - In order of decreasing temperature, O, B, A, F, G, K, and M.
- 10. 1. O – BLUE - over 25,000 K - Singly ionized helium lines (H I) either in emission or absorption. Strong UV continuum. - 10 Lacertra 2. B – BLUE - 11,000 - 25,000 K - Neutral helium lines (H II) in absorption. -Rigel Spica
- 11. 3. A – BLUE -7,500 - 11,000 K - Hydrogen (H) lines strongest for A0 stars, decreasing for other A's. - Sirius and Vega 4. F – BLUE to WHITE - 6,000 - 7,500 K -Ca II absorption. Metallic lines become noticeable. -Canopus, Procyon
- 12. 5. G – WHITE to YELLOW -5,000- 6000K - Absorption lines of neutral metallic atoms and ions (e.g. once-ionized calcium). - Sun and Capella 6. K – ORANGE to RED - 3,500 - 5000K -Metallic lines, some blue continuum. -Arcturus, Aldebaran
- 13. 7. M – RED -under 3,500 K - Some molecular bands of titanium oxide. - Betelgeuse, Antares
- 14. THANK YOU!!
- 15. REFERENCES: http://www.astronomynotes.com/starprop/s5.htm http://docs.kde.org/ http://www.enchantedlearning.com/subjects/astronomy/stars/index.shtml Introduction to Stars, Galaxies, & the Universe Astronomy 162: Professor Barbara Ryden