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# IUPUI AST 105 - Classifying Stars

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AST 105 1st Edition Lecture 3Outline of Previous Lecture (Lecture 7 on 2/3)Topic: StarsI. Local Stars a. Proxima Centauri b. Parallax c. ΘII. Temperatures of Starsa. Surface temp. of distant stars b. Two methods to find i. Photomomy ii. Spectroscopy III. Classifying Stars Outline of Current Lecture (Lecture 8 on 2/5)I. Spectral Classesa. Remember by: Officially, Bill Always Felt Guilty Kissing Monica II. Stellar Massa. Binary Star Systemb. Kepler’s 2nd and 3rd Laws Classifying Stars- Stars were classified by their color (“early on/back in time”)- Color is tied to surface temp.- Direct relation between surface temp and sizeSpectral ClassesSpectral Class Dom. Color Surface temp. ExampleO Violet 30,000-50,000 MintakaB Blue 11,000-30,000 RigelA White-blue 7500-11,000 Sirius These 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.F Yellow-white 5,900-7,500 CanopusG Yellow 5,000-5,900 SunK Orange 3,900-5,00 Ancturius H Red 2,500-3,900 Antares- Easy way to remember: OBAFGKMo Officially, Bill always felt guilty kissing Monica.- Hottest stars are “O” and coolest stars are “M”- Subclasses using digits  0-9 0hottest 9coolest - Thus, an 03 star is hotter than an 08 star Stellar Mass- We obtain mass using the binary star system - Binary star system  2 stars in close proximity orbiting each other over ½ the stars you see are really binary (appears as a single star, but really not) we use Kepler’s Laws mass of star A plus mass of star B must equal a3 divided by p2- Kepler’s 3rd law Mass of our sun = 1 solar mass Mx = mass of star x  a = distance between centers in AU (semi-major axis) p = orbital period (in years) MA + MB = a3 / p2 Q: is there a way we can find the masses individually?A: yes Via K2L and K3L as well as below formulas r a + rb = a r A x MA = rB x MB (Kepler’s 2nd Law)

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