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Spectra
| Term | Definition |
|---|---|
| Magnitude | refers to the apparent brightness of a star and is not a fundamental property of the star. However, the greater the flux, the smaller and more negative the apparent magnitude. |
| Second law of thermodynamics | Heat flows from hot objects to cold objects -or , in other words, hot objects radiate more energy into space than colder ones |
| Blackbody Radiators | Radiate EM ration into space at all wavelengths irrespective of size, shape or composition |
| Max Planck BB equation | His equation describes the energy flux of BB at a specific wavelength for a specified temperature |
| Temperature | temperature is a measure of heat energy |
| The Kelvin Scale Equation | T(Kelvin) = T(Centigrade) + 273 |
| Wiens Law(temperature of any star anywhere in the universe) | lamdamaxT = 2.8977 x 10^-3. Where lamdamax in meters, T in Kelvin |
| 3 types of Spectra | Continuous(blackbody) spectra, Emission spectra, Absorption Spectra |
| Continuous(Blackbody) spectra | Hot solids, liquids of dense gases. EM radiation produced at all wavelengths |
| Emission Spectra | Hot, low density gas. EM radiation at very specific wavelengths. Hot interstellar gas clouds produce such spectra. |
| Absorption Spectra | Produced when light from a continuous spectrum is viewed through a lower density, lower temperature gas. Absorption lines are seen at very specific wavelengths. Stars produce absorption line spectra. |
| Spectra type graphs | D4 |
| Stellar absorption Lines | Absorption line spectra produced by a blackbody radiator surrounded by a lower temperature gas envelope |
| Photosphere | Cool, low density envelope where the absorption lines form. |
| Emission Lines | In general, emission lines are associated with hot low density gases. |
| Three processes are at work in Emission lines | 1.High temperature-many high energy collisions. 2.Collisions between atoms places them in an excited state. 3.Between repeat collisions an excited atom releases a photon which carries away their excitation energy and produces emission line |
| Photon | Burst or packet of EM radiation with energy (E = hf) |
| Spectral analysis | Each species of atom has a unique set of absorption/ emission lines |
| Spectral Classification | Classify stars according to their spectral lines(key idea is to use 'strength' of hydrogen lines) |
| The spectral classification scheme | OB AF G KM |
| OB | >30,000(O) 10-30,000(B) hottest and most luminous stars (Blue) |
| AF | 7500-10,000(A)6000-7500(F) Strongest hydrogen lines(blue-white) |
| G | 5000-6000 (G)Sun = G2 star(yellow) |
| KM | 3500-5000(K) <3500(M)Coolest and least luminous stars (red) |
Created by:
davidvachon1
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