ASTR 1P02 Lecture 1: Astro notes Lecture 1 + 2
17 Jan 2017
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Stellar formation and evolution: to find out about the star formation we need to look at the neighbourhoods of young stars. where to find the youngest stars, recall the h-r diagram. Main sequence stars (over 90% of all stars are in this group) Spectral class coolest being m, hottest being o and b. Lifetime of a star = fuel available (m[mass]) / energy output (l[luminosity]) = m/l: for main sequence stares l=m3. 5 = m/m3. 5 = 1/m3. 5. Hence, the larger the mass, the shorter the lifetime. Thus, the youngest stars are at the upper left corner of the main sequence: very luminous and very hot (o- and b- spectral class). When we view them we find that they are surrounded by clouds of gas (by mass: 75% hydrogen and 25% helium) and dust. When we can observe them at visible wavelengths (from 400nm to 700nm, 1nm = 10 9m) we call them nebulae.
