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Chapter 12
Chapter 12

... They emit line radiation (hot, low pressure gas) but in size they are much smaller than the emission nebulae (HII regions) ...
Where planets are formed: Protoplanetary disk evolution and planet
Where planets are formed: Protoplanetary disk evolution and planet

... Nebula  distance from supernova < 0.3 pc  N>1000 • The Solar System survived the supernova explosion  distance from the supernova > 0.1 pc Solar System properties require the Sun formed in the outer region of an intermediate massive cluster, with few thousand members, necessary to provide the req ...
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... 1. A neutron star, containing a little more than _________ solar mass, compressed to a radius of about __________, can be left as a remnant after a type ______ supernova explosion. A neutron star’s density is so high that physicists calculate that this material is stable only as a __________________ ...
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ASTR 1101-001 Spring 2008 - Louisiana State University
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CASPEC Observations of the Most Metal-Deficient Main
CASPEC Observations of the Most Metal-Deficient Main

... does not lie in an obscured region, and (2) it does not illuminate fairly bright nebulosity in its immediate vicinity. Moreover, N82 is too bright to be a Herbig AelBe star. Strom et al. (1972) give a list of 12 Galactic stars of this type with known distances. If we place these stars in the SMC, th ...
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H II region



An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived blue stars forged in these regions emit copious amounts of ultraviolet light that ionize the surrounding gas. H II regions—sometimes several hundred light-years across—are often associated with giant molecular clouds. The first known H II region was the Orion Nebula, which was discovered in 1610 by Nicolas-Claude Fabri de Peiresc.H II regions are named for the large amount of ionised atomic hydrogen they contain, referred to as H II, pronounced H-two by astronomers (an H I region being neutral atomic hydrogen, and H2 being molecular hydrogen). Such regions have extremely diverse shapes, because the distribution of the stars and gas inside them is irregular. They often appear clumpy and filamentary, sometimes showing bizarre shapes such as the Horsehead Nebula. H II regions may give birth to thousands of stars over a period of several million years. In the end, supernova explosions and strong stellar winds from the most massive stars in the resulting star cluster will disperse the gases of the H II region, leaving behind a cluster of birthed stars such as the Pleiades.H II regions can be seen to considerable distances in the universe, and the study of extragalactic H II regions is important in determining the distance and chemical composition of other galaxies. Spiral and irregular galaxies contain many H II regions, while elliptical galaxies are almost devoid of them. In the spiral galaxies, including the Milky Way, H II regions are concentrated in the spiral arms, while in the irregular galaxies they are distributed chaotically. Some galaxies contain huge H II regions, which may contain tens of thousands of stars. Examples include the 30 Doradus region in the Large Magellanic Cloud and NGC 604 in the Triangulum Galaxy.
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