Berlin 2001 – wissenschaftliches Programm
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AMPD: EPS AMPD
AMPD 9: Sitzung 9
AMPD 9.2: Vortrag
Freitag, 6. April 2001, 10:55–11:20, H105
How Atomic Spectroscopy can Advance Astrophysics — •Sveneric Johansson1 and Vladilen Letokhov2 — 1Department of Physics, Lund University, Lund, Sweden — 2Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Russia
Our knowledge about the stars in the Galaxy and about other galaxies in the Universe is based on our interpretation of radiation from outer space – the spatial distribution in form of images and the frequency distribution in form of spectra. Besides blackbody radiation most objects show line spectra in emission or absorption or a combination of the two. The radiating medium consists, in general, of free atoms and ions and for cool material also of molecules.
In this paper we will discuss atomic species and focus on their emission lines, as these often present challenging problems in astrophysical spectra. In general, the models predict quite well the observed absorption spectra of stars, whereas the emission line objects of lower density (e.g. outer stellar atmospheres, planetary nebulae, stellar ejecta (blobs), symbiotic stars, etc.) need the line identifications before they can be properly modelled.
The energy input to these low–density plasmas is provided by the blackbody radiation from one or more nearby stars, ionizing the plasma. Two excitation mechanisms are generally supposed to generate the emission lines in low–density plasmas: recombination and collisional excitation. We will discuss other radiative processes inside the nebula that
• affects the ionization balance
• explains the presence of strong emission lines
• explains lines with anomalous brightness and intensity ratios
The bottom line is that trapped hydrogen and helium radiation might have a great impact on
the ionization and excitation balance and the formation of the emission line spectrum.