ASTR 1P02 Lecture : Astronomy 1PO2.docx
12 Mar 2012
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Clue: look at the surroundings of young stars. Hint: recall the h-r diagram (luminosity [l] vs. Surface temperature [t] graph for a group of stars) For the main sequence stars one has eddington"s mass-luminosity recation: Lifetime of a star = fuel available / energy output =m/l = m/m3. 5 = 1/m2. 5. Thus very hot and bright stars (those at the upper left corner of the main sequence) are the youngest stars that we could observe. Observations show that such stars are surrounded by the clouds of interstellar material (i. e. gas [hydrogen {74% by mass} helium {24% by mass} and dust] [small solid particles of rocky material and ice]) When such clouds can be seen at visual wavelengths they are called nebulae. Three basic types of nebulae: dark nebulae light from the stars opposite the observer is absorbed by the dust particles in the nebula. The observations using infrared detectors confirm that dark nebulae emit in the infrared part of the spectrum.
