Name __________________________ Date _____________ Block ____ E.2: Stellar Radiation and Stellar Types E.2.1- State that fusion is the main energy source of stars Students should know that the basic process is one in which hydrogen is converted into helium. They do not need to know about the fusion of elements with higher proton numbers. E.2.2 - Explain that, in a stable star (for example, our Sun), there is an equilibrium between radiation pressure and gravitational pressure. “H” is Fuel How does our sun work? Fusion of hydrogen into _____________ that provides the energy, for our sun Happens on the inside of the sun (Yes, there are different layers) Produces _____________ that leave the sun and travel to Earth The proton-proton chain This is the same reaction discussed in Topic 7. Each complete chain reaction produces __________________. Remember you need 4 H to end up with one He See simplified equation: Star Stability Gravity pulls inward So much the sun should collapse. Nuclear explosions push ______________ These two have to balance out to be at pressure ________________ Ex. Balloon. Rubber is like gravity Air is like the ________________ If the temp changes the inside pressure will change and won’t be stable E.2.3 - Define the luminosity of a star. E.2.4 - Define apparent brightness and state how it is measured. Luminosity _________________ measurements give us information about the temperature, size and chemical composition of a star. Luminosity(L) is the total amount of ____________ emitted by the star per second. Unit is watt (same as power) Depends on the ________________ Ex. Two stars have same temp, the bigger one will give out more energy Sun’s luminosity of 3.839 x 1026W Apparent brightness(b) Some stars appear brighter than others. Brightness depends on: 1 a. How much energy is radiated (_______________) b. How ________________ away it is located Apparent brightness(b) is the amount of energy per _______________received per unit area. Unit is W/m2 b= d is distant to the star E.2.5 - Apply the Stefan–Boltzmann law to compare the luminosities of different stars. E.2.6 - State Wien’s (displacement) law and apply it to explain the connection between the color and temperature of stars. Black Body Radiation Black bodies absorb all ________________ of light and reflect none. It also is a perfect emitter of radiation. If temp is increased the energy available is increased. Means the ________________ can gain more energy and move into higher energy levels Means more photons released, and their average energy is ____________________. E = hf, Higher energy means higher frequency/shorter wavelength Stefan-Boltzmann Each peek represents the__________________(apparent brightness) of radiation at different wavelengths. Total intensity is the area under the curve. Power per unit area = σ = 5.6 x 10-8 W/m2K4 (Stefan-Boltzmann constant) If a star has a surface area A and temperature T then the total power emitted (luminosity), L is given by: L= Wien Displacement Law As the temperature increases, the peak wavelength is _________________ Relationship between peak wavelength and temp is Wien displacement law: λmax = (2.90 x 10-3km) / T Example The maximum in the black body spectrum of the light emitted from the sun is at 480 nm. Given that the Sun’s radius is 7.0 x 108m, calculate the temperature of the sun, the power emitted per square meter, and the luminosity. Answer: 6000K, 7.3 x 107 W/m2, 4.5 x 1026 W 2 E.2.7 - Explain how atomic spectra may be used to deduce chemical and physical data for stars. Students must have a qualitative appreciation of the Doppler effect as applied to light, including the terms red-shift and blue-shift. E.2.8 - Describe the overall classification system of spectral classes. Students need to refer only to the principal spectra classes (OBAFGKM). Stellar Spectra Remember: Electrons only exist in certain energy levels When excited only produce specific wavelengths. (Emission Spectrum) When white light passes through same gas these wavelengths are absorbed. (Absorption spectrum) Stars emit a continuous spectrum of EM Peak intensity depends on the temp. As this EM pass through the outer layer of the star, some is absorbed. The absorption spectrum of a star tells us what elements are present because of the missing lines. Stellar Spectra The absorption spectra also helps us to calculate the temperature of the gas. Hot gas Most electrons are already in higher energy levels Meaning they can’t make the biggest jump See “Energy Levels” diagram Means the higher energy photons will not be absorbed. Means a weak absorption line Which can let us find the temp E.2.8 - Describe the overall classification system of spectral classes. Students need to refer only to the principal spectra classes (OBAFGKM). Spectral Classification of Stars The spectrum of a star is related to it’s temp and chemical composition. Also the color. The peak points to it’s color Oh Be A Fine Girl Kiss Me Doppler Shift As objects move, the wave lengths they produce is either pushed together or spread apart. Called doppler effect. Applies to all waves including light from stars. Red shift – longer λ – star moving away Blue shift – shorter λ – star moving closer Class O B A F G K M Temperature 30k - 60k 10k - 30k 7.5k - 10k 6k - 7.5k 5k - 6k 3.5k - 5k 2k - 3k Color Blue Blue-White White Yellow-White Yellow Orange Red 3 Hamper Practice Exercises for topics E2 4 E2 Stellar Radiation and Stellar Types http://www.youtube.com/watch?v=ugorpmBkPE&list=PL7FD7F1082F45C268&index=3&safety_mode=true&persi st_safety_mode=1 http://www.youtube.com/watch?v=jltK_KaVGs&list=PL7FD7F1082F45C268&safety_mode=true&persis t_safety_mode=1 http://www.youtube.com/watch?v=VSd7A4rswbg&list=PL7FD7F1082F45C268&safety_ mode=true&persist_safety_mode=1 E.2.1 State that fusion is the main energy source of stars. http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html The fusion process in a young star (made mainly of Hydrogen) is. In the fusion process, when the 4 H nuclei are converted into a He nucleus a small amount of mass is lost as energy. Eg/ Mass of 4 H nuclei = 6.693 x 10-27kg Mass of 1 He nuclei = 6.645 x 10-27kg. What is the difference in their masses? The mass is released as energy. The energy is given by E = mc 2.For each fusion reaction the energy released is what? This seems like a small amount of energy but now work out the energy released by 1kg of hydrogen atoms undergoing fusion. (Hint: use percentages) This is ~ burning 2 x 107kg of coal. If the luminosity (power output) of the sun is 3.9 x 10 26W, work out how much Hydrogen the sun 'burns' each second, and how much the equivalent in coal would be. If the mass of the Sun is 2 x 1030kg, how many years can the sun burn for? What factors affect the lifetime of a star? E.2.2 Explain that, in a stable star (for example, our Sun), there is an equilibrium between radiation pressure and gravitational pressure. What is the value lf the equalized pressure and radiation of our sun? E.2.3 Define the luminosity of a star. E.2.4 Define apparent brightness and state how it is measured. http://physics.uoregon.edu/~soper/Light/luminosity.ht ml 5 1. What two factors affect how bright a star appears in our night sky? 2. What is the formula for luminosity? 3. What is apparent magnitude? What is absolute magnitude? How are they “scaled”? A Past IB Paper Question The distance of Sirius A from the Sun, calculated from its parallax is 8.7 light years. One light year equals 9.46 x 1015m. a) Explain the term parallax by sketching and labelling a suitable diagram. b) If the distance from the Earth to the Sun is 1.5 x 1011m, calculate the parallax of Sirius A. c) Explain what is meant by the luminosity of a star. d) The luminosity of Sirius A is 8.17 x 1027W. Calculate the brightness of Sirius A as measured by an observer on Earth. E.2.5 Apply the Stefan-Boltzmann law to compare the luminosities of different stars. E.2.6 State Wien’s (displacement) law and apply it to explain the connection between the color and temperature of stars. http://hyperphysics.phy-astr.gsu.edu/hbase/wien.html#c1 -Pg 756-757 Example 1 & 2 (Giancoli) -Do pg 782 #5 1. Why do we call some stars red, some blue and others white? 2. How do we know what temperature a star is to be able to place it in the right place on the HR Diagram. E.2.7 Explain how atomic spectra may be used to deduce chemical and physical data for stars. E.2.8 Describe the overall classification system of spectral classes. http://en.wikipedia.org/wiki/Stellar_classification http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/staspe.html 1. Explain how atomic spectra may be used to deduce chemical and physical data for stars. 2. What is the doppler effect? 3. What is the difference between a red shift and blue shift? 4. Describe the overall classification system of spectral classes. 5. What is the classification of stars based on? E.2.9 Describe the different types of stars? Students need to refer only to single and binary stars, Cepheids, red giants, red supergiants and white dwarts. Knowledge of different types of Cepheids is not required. E.2.10 Discuss the characteristics of spectroscopic and eclipsing binary stars. E.2.11 Identify the general regions of star types on a Hertzsprung-Russell(HR) diagrams. Plot an HR (Absolute Magnitude versus temperature) diagram for the local stars Answer the questions: 2a Do you see any patterns in the distribution of points on Plot B? 2b Why are the values of m and M different for the same stars? (Absolute magnitude (M) is a brightness quantity corrected for distance from the Earth. It is the apparent magnitude (m) a star would have if it were 32.6 light-years from the Earth.) 2c How many stars are more luminous than the sun and how many are less luminous in the local star group? 2d Is this a true statement? “As the intrinsic brightness increases, so does the temperature.” 6 Star Sun AlphaCentaruiC AlphaCentaruiA AlphaCentaruiB Barnard'sStar Wolf359 BD+36 コ 2147 Luyten726-8A Luyten726-8B SiriusA SiriusB Ross154 Ross248 epsilonEridani Ross128 61CygnusA EIndi BD+43?44A BD+43?44B Luyten789-6A Luyten789-6B ProcyonA ProcyonB BD+59?1915A BD+59?1915B Apparent Temperature Absolute Magnitude (K) magnitude -26.8 4.8 5770 11 15.8 2600 0 4.4 5800 1.4 5.8 4000 9.5 13.2 2600 13.5 16.8 2400 7.5 10.5 2700 12.6 15.4 2500 13 15.8 2400 -1.4 1.4 9500 8.4 8.4 28000 10.4 13.3 2650 12.3 14.7 2500 3.7 6.1 4500 11.1 13.5 2600 5.2 7.5 4000 4.7 7 4000 8.1 10.3 2950 11.1 13.2 2700 12.3 14.9 2500 12.3 15.9 2200 0.4 2.7 6500 10.7 13 7000 8.9 11.1 2650 9.7 11.9 2600 7
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