1	Astro 1050 Fri. Oct. 11, 2002 Today: Chapter 8, Properties of Stars Please bring calculators to class Astronomy New Articles
2	How to recognize patterns in data What patterns matter for people – and how do we recognize them? Weight and Height are easy to measure Knowing how they are related gives insight into health A given weight tends to go with a given height Weight either very high or very low compared to trend ARE important Plot weight vs. height and look for deviations from simple line Example of cars from the book Note “main sequence” of cars Weight plotted backwards Just make main sequence a line which goes down rather than up Points off main sequence are “unusual” cars
3	Stars: Patterns of L, T, R The Hertzsprung-Russsell (H-R) diagram Plot L vs. backwards T. (We can find R given L and T)
4	How are L, T, and R related? L = area ´sT⁴ = 4 p R² sT⁴ Stars can be intrinsically bright because of either large R or large T Use ratio equations to simplify above equation (Note book’s symbol for Sun is circle with dot inside) Example: Assume T is different but size is same A star is ~ 2 ´ as hot as sun, expect L is 2⁴= 16 times as bright M star is ~1/2 as hot as sun, expect L is 2^-4= 1/16 as bright B star is ~ 4 ´ as hot as sun, expect L is 4⁴= 256 times as bright Example: Assume T same but size is different If you have a G star 4 ´ as large as sun, expect L would be 4²=16 times as bright
5	L, T, R, and the H-R diagram L = 4 p R² sT⁴ The main sequence consists very roughly of similar size stars The giants, supergiants, and white dwarfs are much larger or smaller
6	Lines of constant R in the H-R diagram
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8	Different “types” of H-R diagrams
9	Luminosity Classes
10	Spectra of Different Luminosity Classes
11	Spectroscopic “Parallax”
12	What fundamental property of a star varies along the main sequence?
13	Masses of Binary stars
14	Masses of Binary stars
15	Masses of Binary stars
16	Measuring a and P of binaries Two types of binary stars Visual binaries: See separate stars a large, P long Can’t directly measure component of a along line of sight Spectroscopic binaries: See Doppler shifts in spectra a small, P short Can’t directly measure component of a in plane of sky If star is visual and spectroscopic binary get get full set of information and then get M
17	Masses and the HR Diagram Main Sequence position: M: 0.5 M_Sun G: 1 M_Sun B: 40 M_sun Luminosity Class Must be controlled by something else
18	The Mass-Luminosity Relationship L = M^3.5
19	Eclipsing Binary Stars System seen “edge-on” Stars pass in front of each other Brightness drops when either is hidden Used to measure: size of stars (relative to orbit) relative “surface brightness” area hidden is same for both eclipses drop bigger when hotter star hidden tells us system is edge on useful for spectroscopic binaries