AST 2002 Lecture Notes - Lecture 12: Orbital Period, Main Sequence, Orbital Velocity
Document Summary
Brightness of as star depends on both distance and luminosity. Amount of power a star radiates (energy per second) watts. Every object emits thermal radiation with a spectrum that depends on its temperature. Hotter objects emit more light per unit area at all frequency. Level of ionization also reveals a stars temperature. Absorption lies in a star"s spectrum tells us its ionization level. Visual binary- we can directly observe the orbital motion of the stars. Spectroscopic binary- we determine the orbit by measuring doppler shifts. Need two out of three observable to measure mass orbital period(p) The mass of a normal star, determines its luminosity and spectral type. The core tem of a higher mass star needs to be higher in order to balance gravity. A higher core temperature boosts the fusion rate, leading to greater luminosity. Life expectancy of 10msun star: ten times as much fuel, uses it 10^4 times as fast.
