The Arcetri Spectral Code - E.Landi and M.Landini (2002)
The Arcetri Spectral Code (Landi and Landini 2002)
allows to evaluate the spectrum of continuum and line radiation emitted by hot
and optically thin plasmas in the spectral range 1-2000 Angstrom.
The Code is composed by a large database of atomic data and transition probabilities for
calculating spectral line emissivities and a suite of fortran
programs able to evaluate free-free, free-bound and two-photon continuum radiation.
Continuum programs
The continuum programs and data are described in more detail
in Landini and Monsignori Fossi (1990). The continuum approximations come from:
- Free-free continuum: Kato (1976). The Code computation includes H
and He only. The mean Gaunt factor is evaluated following Karzas and Latter (1961).
- Free-bound continuum: Kato (1976). Free-bound continuum is evaluated
for all ions up to Z=30; recombinations to the ground levels only are considered.
- Two-photon continuum: Tucker and Koren (1971). Only H-like ions (up to
Z=30) are considered.
Line emissivity
Line emissivities are calculated according to the formula:
Nj(X+m) N(X+m) N(X) N(H) Aij
Emissivity = ------- x ------- x ----- x ----- x ---- x (Ei - Ef) erg cm3 s-1
N(X+m) N(X) N(H) Ne Ne
(a) (b) (c) (d) (e) (f)
where
- a: Level population relative to ions' total population;
- b: Ion fraction (assuming ionization equilibrium);
- c: Element abundance relative to hydrogen;
- d: Hydrogen abundance relative to free electron density Ne. The
assumed value is 0.8;
- e: Aij=Einstein coefficient for spontaneous radiative decay;
- f: Energy of each emitted photon.
The element abundances from Feldman 1992 have been adopted.
The ionization equilibrium ion fractions come from Mazzotta et al. (1998);
elements are included up to Z=30.
Emission line database
The Arcetri Spectral Code calculates spectral line emissivities by solving the equations of
statistical equilibrium for level population (term a of the above equation)
for all the ions included in the present version.
The calculation of level populations requires a huge amount of atomic data and radiative and
collisional transition probabilities. The data are taken from the CHIANTI database (Dere et al.
1997, Landi et al. 1999, Dere et al. 2001). CHIANTI is a database consisting of critically
evaluated atomic data and transition probabilities necessary to analyze spectral observations
of optically thin plasmas.
Only some transitions, not yet
included in the CHIANTI database, are still treated with the
Coronal Model Approximation using the equations in Landini and Monsignori-Fossi (1990).
As the atomic data and transition probabilities are taken from intermediate coupling
calculations, they allow the calculation of line emissivities for each component of a
multiplet separately.
References
- Dere, K.P., Landi, E., Mason, H.E., Monsignori-Fossi, B.C., Young, P.R., 1997, A&ASS, 125, 149
- Dere, K.P., Landi, E., Young, P.R., Del Zanna, G., 2001, ApJS, 134, 331
- Karzas, W.J., Latter, R., 1961, ApJSS, 6, 167
- Kato, T., 1976, ApJSS, 30, 397
- Landi, E., Landini, M., 2002, A&A, 384, 1124
- Landi, E., Landini, M., Dere, K.P., Young, P.R., 1999, A&ASS, 135, 339
- Landini, M., Monsignori-Fossi, B.C., 1990, A&ASS, 82, 229
- Landini, M., Monsignori-Fossi, B.C., 1991, A&ASS, 91, 183
- Tucker, W.H., Koren, M., 1971, ApJ, 168, 283
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