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Star Classification 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. O and B stars are uncommon but very bright; M stars are common but dim.. An easy mnemonic for remembering these is: "Oh be a fine girl, kiss me." The Sun is a as a G2V type star, a yellow dwarf and a main sequence star. Hertzsprung - Russell Diagram The Hertzsprung -Russell (H-R) Diagram is a graph that plots stars color (spectral type or surface temperature) vs. its luminosity (intrinsic brightness or absolute magnitude). On it, astronomers plot stars' color, temperature, luminosity, spectral type, and evolutionary stage. This diagram shows that there are 3 very different types of stars: • • • Most stars, including the sun, are "main sequence stars," fueled by nuclear fusion converting hydrogen into helium. For these stars, the hotter they are, the brighter. These stars are in the most stable part of their existence; this stage generally lasts for about 5 billion years. As stars begin to die, they become giants and supergiants (above the main sequence). These stars have depleted their hydrogen supply and are very old. The core contracts as the outer layers expand. These stars will eventually explode (becoming a planetary nebula or supernova, depending on their mass) and then become white dwarfs, neutron stars, or black holes (again depending on their mass). Smaller stars (like our Sun) eventually become faint white dwarfs (hot, white, dim stars) that are below the main sequence. These hot, shrinking stars have depleted their nuclear fuels and will eventually become cold, dark, black dwarfs. Spectral Classes Averag Averag Approximat e Average Star e Mass Main e Surface Radius Luminosit Typ Color (The Characteristic Examples Temperatur (The y (The Sun e Sun = s e Sun = = 1) 1) 1) O B A Blue over 25,000 K Blue 11,000 25,000 K Blue 7,500 11,000 K F Blue 6,000 - 7,500 to K White G White to 5,000 - 6,000 Yello K w K Orang 3,500 - 5,000 e to K Red M under 3,500 K Red 60 18 3.2 1.7 15 7 2.5 1.3 Singly ionized helium lines (H I) either in 104 emission or HIGHEST absorption. Strong UV continuum. 10333 Neutral helium lines (H II) in absorption. Rigel Spica 80 Hydrogen (H) lines strongest for A0 stars, decreasing for other A's. Sirius, Vega 6 Ca II absorption. Metallic lines become noticeable. Canopus, Procyon Absorption lines of neutral metallic atoms and ions (e.g. once-ionized calcium). Sun, Capella 1.2 1.1 1.1 10-1 0.8 0.3 10 Lacertra 0.9 0.4 10-2 Metallic lines, Arcturus, some blue Aldebaran continuum. 0.4 0.04 (very faint) 10-4 Some molecular Betelgeuse bands of , Antares titanium oxide. Name _________________________________________Date _________________ The Hertzsprung-Russell Diagram Student Worksheet answer the questions on the back of this page using the above HR Diagram Let’s Practice plotting some stars from the drawing above the information will come from the group copy “Star Classification” paper. Rigel, Sirius, Arcturus, Procyon, Betelgeus THE H-R DIAGRAM 1. What is the approximate surface temperature of the sun? ___________________ 2. Would the surface temperature of white dwarf stars be higher or lower than red supergiants? (Circle one of the bold words) 3. What is the color of the stars with the highest surface temperature? ___________________ What is the color of the stars with the lowest surface temperature? _____________________________________________________ 4. List the color of the stars from hottest to coldest: HOT_______________________________________________________ ______________________________________________________COLD 5. Most of the stars on the HR Diagram are classified as which type of star? ___________________________________________________________ 6. How is it possible for white dwarf stars to have lower luminosity than the sun even though the sun is cooler than white dwarfs? ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ 7. Plot the following stars. Star A = 4,000 0C and low/medium brightness Star B = 6,000 0C and high brightness Star C = 20,000 0C and low/medium brightness Star D = 6,000 0C and medium brightness Identify the type/color for each star: Star: Star A Star B Star C Star D 8. Color: Type: What is the name of our most popular star located at point D? _________________