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Astronomy 1020-H Stellar Astronomy Spring_2014 Day-23
Course Announcements • SmartworksChapters 13: Due Fri. 3/21 • Smartworks Chapters 14: Due Fri. 3/28 • APSU Research and Creativity Forum April 11-12, 2014 • Abstracts are due: 4:30pm Fri., March 21 • Dark Night – Wed. 3/26 at the Observatory • Dark Night – Mon. 3/31 at the Observatory
Spectroscopic ParallaxLecture Tutorial pg. 45 • Work with a partner! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you both agree on and write complete thoughts into your LT. • If you get stuck or are not sure of your answer, ask another group.
Star Clusters • We’ll come to these, but star clusters are the key to understanding stellar populations. • Same age. • Same chemical composition. • Same distance.
Concept Quiz—The Main Sequence Which of the following statements about the main sequence is not true? • Hotter stars are more massive. • More massive stars are more luminous. • Hotter stars are more luminous. • Most main sequence stars are more luminous than the Sun.
Not all stars are on the main sequence. • Remember Stefan-Boltzmann. • Some stars are cool but very luminous: giants or supergiants. • Some have low luminosity but are very hot: white dwarfs. • Different luminosity classes.
Different temperature stars have different habitable zones: regions where life as we know it could be supported. • Water must be able to exist as liquid. • So far, only a few planets have been found in the habitable zones of their stars.
PROCESS OF SCIENCE • Understanding the meaning behind stellar data took decades, and the contributions of dozens of people, all working toward a common goal.
The Sun is the Largest Object in the Solar System • The Sun contains more than 99.85% of the total mass of the solar system • If you put all the planets in the solar system, they would not fill up the volume of the Sun • 110 Earths or 10 Jupiters fit across the diameter of the Sun How big is the Sun?
How Do You Describe a Stable, Main Sequence Star? • 4 Structure Equations: • dM/dr = 4pr2r • dP/dr = GMr/r2 • dT/dr = -3krL/64pr2sT3(rad) • dT/dr = 0.4(T/P)dP/dr(conv) • dL/dr = 4pr2re • 4 Auxiliary Equations: • P = pkT/mmH (IGL) • P = krg (AGL) • k = k0Z(1 + X)pT-3.5(opacity) • e = e0X1X2rTn (Energy gen.) • n = ~4 (pp); ~20 (CNO)
How Do You Describe a Stable, Main Sequence Star? • Loosely: • A self-gravitating sphere of mostly Hydrogen (74%) and Helium (24%) in hydrostatic equilibrium with the inward gravitational force balanced by an outward radiation pressure, powered by Hydrogen fusion in the core.
Structure of the Sun • We only see the outer layers of the Sun. • Physics tells us about the interior. • Key idea: hydrostatic equilibrium. • At each point there’s a balance: • Outward pressure = inward force of gravity. • Rate of energy emitted = rate produced in the core. • Density, temperature, pressure increase towards the center.
We only see the outer layers of the Sun. • Physics tells us about the interior. • The Sun must be in balance to have existed in a constant state for billions of years.
At each point in the Sun there is balance: • Hydrostatic equilibrium: outward pressure = inward force of gravity. • Solar energy production must equal what is radiated away.