Astron. Astrophys. 347, 401-408 (1999)

1. Introduction

Radiative losses are a fundamental physical process taking place in plasmas, and their knowledge is essential to evaluate the plasma energy balance and build up models of the source.

In the past, several calculations have been performed by many authors including both continuum and line emission for an increasing number of ions: Cox & Tucker 1969 and Tucker & Koren 1971, later used by Landini & Monsignori Fossi 1975 for loop modeling; McWhirter et al. 1975 also providing analytical fits to their results, Raymond 1979, used by Rosner et al. 1978 for loop modeling, Summers & McWhirter 1979, Gaetz & Salpeter 1983, Landini & Monsignori Fossi 1990, Sutherland & Dopita 1993 and many others.

The calculation of this function requires the knowledge of a large amount of atomic data and transition probabilities for both line and continuum radiation. Each of these calculations used state-of-the-art datasets of transition probabilities, but in the last few years many new and more accurate calculations of atomic data have become available for a large number of ions of the most abundant elements. Also, these calculations evaluated level populations using the Coronal Model Approximation . The use of new transition probabilities and the evaluation of detailed atomic level population may change the radiative losses and affect the energy balance.

Recently large databases such as CHIANTI (Dere et al. 1997, Landi et al. 1999) and ADAS (Summers et al. 1996) have been created including the most accurate transition probabilities available in the literature, thus enabling a complete recalculation of the radiative losses. In the present work we have made use of the Arcetri Spectral Code (Landi & Landini 1998, described in Sect. 2) to calculate line and continuum radiation in order to evaluate the total emissivity and the radiative losses for an optically thin plasma. The results are presented in Sect. 3.

As line and continuum radiation depends on a number of parameters such as electron density, ion fractions, element abundances and atomic models, Sect. 3 also reports a critical discussion on the effects of changes in each of these parameters on the resulting radiative losses. Parametric fits are given to the resulting radiative losses curves in Sect. 4 which may help the analytical integration of theoretical models.

© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999
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