Astrophysical applications

In stellar astronomy, spectroscopic studies are indirectly revealing the structure deep down in stars where one could not see otherwise. An internal structure shows up in the emergent radiation spectrum both kinematically and through abundance anomalies. The solution of the solar corona line problem in 1942 may serve as a typical example of astrophysical applications of atomic spectroscopy [256]. 

There are numerous needs for precise atomic data, particularly in the ultraviolet region, in heavy and highly ionized systems. These data include energy levels, wavelengths of electronic transitions, their oscillator strengths and transition probabilities, lifetimes of excited states, line shapes, etc. [278]. 

Astrophysicists enumerate a large number of present problems in astrophysics, in which atomic data are used or are needed. They ask about what is known and what can be measured or calculated at the moment and with what precision. Some groups successfully combine the production and use of atomic data [279]. 

Over the past decades we have witnessed the explosive growth of astro-physical spectroscopic observations in both the ultraviolet and infrared 

Taking advantage of advances in computational atomic and plasma physics and of the availability of powerful supercomputers, a collaborative effort - the international Opacity Project - has been made to compute accurate atomic data required for opacity calculations. The work includes computation of energy levels, oscillator strengths, photoionization cross-sections and parameters for pressure broadening of spectral lines. Several 

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Among a number of indirect methods which have been suggested for nuclear astrophysics applications the Trojan Horse Method (THM) is particularly suitable in the case of (p,a), (n,a),(n,p) reactions. In the following we will not discuss in details the method, so we refer to [3] for further details. 

Measurements of collision-induced spectra reflect certain details about intermolecular interactions. If analyzed with care, such information will enhance knowledge of molecular interactions. Furthermore, for specific applications, laboratory measurements of collision-induced spectra taken at a few fixed temperatures must be interpolated, often even extrapolated to the temperatures of interest. We will, therefore, discuss the tools available for analysis and further use of laboratory measurements, for example, for astrophysical applications. 

At high temperatures, vibrational states must also be included in the partition sum above. The nuclear weights are gj for hydrogen we have, for example, gj = 1 for even j, and gj = 3 for odd j. However, we mention that in low-temperature laboratory measurements as well as in astrophysical applications, para-H2 and ortho-H2 abundances may actually differ from the proportions characteristic of thermal equilibrium (Eq. 6.53). In such a case, at any fixed temperature T, one may account for non-equilibrium proportions by assuming gj values so that the ratio go/gi reflects the actual para to ortho abundance ratio. Positive frequencies correspond to absorption, but the spectral function g(co T) is also defined for negative frequencies which correspond to emission. We note that the product V g a> T) actually does not depend on V because of the reciprocal F-dependence of Pt, Eq. 6.52. 

The significance of collision-induced absorption for the planetary sciences is well established (Chapter 7) reviews and updates appeared in recent years [115, 165, 166, 169-173]. Numerous efforts are known to model experimental and theoretical spectra of the various hydrogen bands for the astrophysical applications [170, 174-181]. More recently, important applications of colhsional absorption in astrophysics were discovered in the cool and extremely dense stellar atmospheres of white dwarf stars [14, 43, 182-184], at temperatures from roughly 3000 to 6000 K. Under such conditions, large populations of vibra-tionally excited H2 molecules exist and collision-induced absorption extends well into the visible region of the spectrum and beyond. Numerous hot bands, high H2 overtone bands, and H2 rotovibrational sum and difference spectral bands due to simultaneous transitions that were never measured in the laboratory must be expected. Ab initio calculations of the collisional absorption processes in the dense atmospheres of such stars have yet to be provided so that the actual stellar emission spectra may be obtained more accurately than presently known. 

S. J. Adelman and W. L. Wiese (eds). Astrophysical Applications of Powerful New Databases, Astronomical Society of the Pacific Conference Series Volume 78, Book Crafters, Inc., San Francisco, 1995. 

Data for almost all dust materials of interest for protoplanetary disks and for more general astrophysical applications have been determined by laboratory work. Tables for e or for n and k can be obtained from the Jena-St. Petersburg database.2... 

A major review of electron-impact excitation rates is being performed under the sponsorship of the Data Center at the Joint Institute for Laboratory Astrophysics. Application to the atmosphere see... 

A linear algebraic system of rate equations for the fast species results, which can be solved a priori. Hence a strongly reduced (in the number of species to be treated) system is obtained. This concept originates from astrophysical applications and from Laser physics. It is in some instances also referred to as collisional-radiative approximation , for the fast species, lumped species concept , bundle-n method or intrinsic low dimensional manifold (ILDM) method in the literature. We refer to [9,12,13] for further references on this. 

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