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GSU ASTR 1020 - Surveying the Stars, Pt 2

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ASTR 1020 1st Edition Lecture 8 Outline of Last Lecture I. Surveying the StarsA. PropertiesB. DistancesC. LuminositiesD. TemperatureOutline of Current Lecture I. Surveying the Stars, pt 2A. PropertiesB. RadiiC. MassD. Binary Star SystemsE. DiagramF. Cosmic Distance ScaleCurrent LectureI. Surveying the Stars, pt 2A. Properties- Distances- Luminosities- Temperatures- Radii- MassesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.B. Radii- Angular radius and distance give radius.- Most stars are pin-points, but we are starting to measure their sizes using interferometry;C. Mass- Many stars are in binary pairs; measurement of their orbital motion allows determination of the masses of the stars.- Kepler’s Third Law:(M1 + M2) P2=a3where M1 and M2 are the masses (MSUN),P is the period (years), anda is the separation or “semi-major axis” (AU)D. Binary Star Systems• Visual Binary- Orbital motion can be measured directly• Eclipsing Binary- Combine light curve and Doppler shift curve: + radii, temperatures system inclination, masses• Spectroscopic Binary- Motion detected by Doppler ShiftsE. Diagram- Hertzsprung-Russell diagram plots the luminosity and temperature of stars- Most stars occupy the main sequence where stars create energy by H fusion (like the Sun).o Higher mass stars have larger luminosities and shorter lives-L= 4 π r2x σ T4- For given T, stars with higher L have larger radii: giants and supergiants.o Older stars where core H fusion done- For given T, stars with lower L have lower radii: white dwarfs. o Very old stars, all nuclear fusion complete.- Full spectral classification includes spectral type and luminosity classI - supergiantII - bright giantIII - giantIV - subgiantV - main sequenceF. Cosmic Distance Scale- Distance from “spectroscopic parallax”1. Measure the star’s apparent magnitude m and spectral classification2. Use spectral classification to estimate luminosity (absolute magnitude M) from HRD3. Apply inverse-square law to find distanceMagnitude version: m – M = 5 log d -

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