The Emission-Line Universe by Jordi Cepa

By Jordi Cepa

This e-book provides lectures by means of prestigious researchers and skilled observers from the eighteenth iciness institution of the Canary Islands Astrophysics Institute (IAC), dedicated to emission strains and the astrophysical gadgets that produce them. It exhibits how emission strains in numerous wavelengths, from ultraviolet to close infrared, promises crucial info on realizing the formation and evolution of astrophysical gadgets, from the 1st stars to things in our Galaxy. It comprises useful tutorials for information relief, making this a really helpful reference for researchers and graduate scholars.

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1) Shocks generate compression and thus high gas densities. (2) This compression locally reduces the ionization parameter, and thus enhances the low-ionization emission lines such as [O ii], [N ii], [S ii] and [O i]. (3) Shock heating produces very high temperatures (of the order of millions of Kelvins), which lead to collisional ionization and the production of such ions as O3+ and He++ . (4) This high-temperature gas emits X-rays, which contribute to the ionization in front of the shock and behind it.

How will one test the validity of a model? Finally, one must evaluate the result of the investigation. Was the goal achieved? If not, what does this imply? In fact, this aspect is often overlooked; nevertheless, it is potentially very instructive and is an incentive for progress in the field. In the following we present some commented examples. 4 Abundance derivation by tailored model fitting The general procedure would be something like the following sequences. (1) Define the input parameters: the characteristics of the ionizing radiation field (luminosity, spectral energy distribution); the density distribution of the nebular gas; the chemical composition of the nebular gas; the distance.

However, it is true that, in order to explain observed emission-line ratios, the possible contribution of shock heating to photoionization must be examined. The effects of shocks that leave a signature on emission-line spectra in photoionized nebulae can be summarized as follows. (1) Shocks generate compression and thus high gas densities. (2) This compression locally reduces the ionization parameter, and thus enhances the low-ionization emission lines such as [O ii], [N ii], [S ii] and [O i]. (3) Shock heating produces very high temperatures (of the order of millions of Kelvins), which lead to collisional ionization and the production of such ions as O3+ and He++ .

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