AST222H1 Lecture Notes - Lecture 29: Red-Giant Branch, Distance Modulus, Cosmic Distance Ladder
14 Mar 2019
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Parallax is a good method for measuring direct distances. Will know l (the real luminosity) and absolute magnitude when we are familiar with local neighbourhood stars. Can figure out stars similar stars from absolute magnitude. Figure out distance modulus and distance d = (10pc)10(m-m)/5 after finding observed m . There is extinction as m is less than if only the distance effect (d = (10pc)10(m-m-a)/5) Can see cepheids from far distances so good idea to use, have strong relationship with luminosity and period (rr lyrae relationship is not as strong) Some hertzpsrung-russell diagram stars pulsate and are not stable. Pulsation period of their oscillation is a function of their mean density (indirect function of luminosity) So, can find a relation between a period, calculating luminosity (use local parallaxes) from this and then the photometric distance. When cannot use parallaxes, use cepheids to measure (measure periods, measure a few weeks with light over time scale)
