4.1. Stark Broadening

In the field of Stark broadening, the recent book, "Principles of Plasma Spectroscopy", by Griem (1997), gives a helpful, updated compilation of the two older ones by the same author (Griem 1964, 1974). The first section deals with the Stark broadening of isolated lines which may be described using a collisional approach. The lines of hydrogen, hydrogenic ions and helium are discussed separately; these lines, which are sensitive to many - body effects, require specific treatments.

Isolated Lines

The semi - classical formalism provides a powerful tool for the rapid calculation of line widths and shifts with a mean accuracy of +/- 30 %. As a consequence, the number of transitions considered has increased rapidly. In this period for example, data for lines of C V, P IV, P V, Be III, B III, S V, Ca IX, Ca X, Si XI, Si XIII, Na X, O VII, Mg XI, Sc X, Sc XI, Ti XI, Ti XII, K VIII,K IX (Dimitrijevic & Sahal - Bréchot 1 - 10) Mn II, Mn III, Ga III, Ge III, Ge IV (Popovic & Dimitrijevic 1998), Xe II (Popovic & Dimitrijevic 1996), Ba I, Ba II(Dimitrijevic & Sahal - Bréchot 1996b), Sr I (Dimitrijevic & Sahal - Bréchot 1997), Mg I (Dimitrijevic & Sahal - Bréchot 1996a) and OI (Ben Nessib & Ben Lakhdar, 1996), have been computed. Despite the large number of tabulated results, accessible by internet at the Centre de Données de Strasbourg:

One notes also the large number of experimental determinations of line widths and/or shifts for the transitions: NII, NIII and NIV (3s - 3p and 3p - 3d, Milosavljevic and Djenize 1998), NII (463.054 nm, Djenize and Milosavljevic, 1998), Ne I (3p - 3s, 3p - 3d, Del Val et al. 1999), B III (2s - 2p, Griem et al. 1997), Na I (467 - 498 nm, Kettlitz and Oltmanns 1996), Si I (220, 250, 288 nm, Sreckovic et al. 1998), Si II (386, 385 nm, Wollschlager et al. 1997), C II, N II, O II, F II and Ne II (3s - 3p and 3p - 3p, Blagojevic et al. 1999a) Xe III (4f - 6d, 5d - 4f, 5d - 6p, 6p - 7s, 6s - 4f, Romeo y Bidegain et al. 1998), O II (3s - 3p, 3s' - 3p', 3p - 3d, 3p - 4s, Djenize et al. 1998), Ar I (425 nm, Djurovic et al. 1997), Ar II (90 spectral lines, Pellerin et al. 1997), and the study of the variation of the widths/shifts along the Be-sequence (3s - 3p, Wrubel et al. 1998), the Li- and Be- sequences (C IV, N V, O VI 3s²S - 3p²P, and B II, C III, N IV, O V 3s³S - 3p³P, Blagojevic et al. 1999b), the B-like sequence (N III, O IV, F V, 3s - 3p and 3p - 3d, Blagojevic et al. 1996).

Hydrogen Lines

In the case of the lines of hydrogen, extensive calculations have been carried out. For example, the tabulation of the Paschen lines, using the Model Microfield Method, give both the line centres and the line wings to an accuracy better than 15 % (Stehlé 1996a). Also, precise Monte Carlo calculations of the line width of the Paschen alpha line have been made by Cardenoso et al. (1997), and this method is designed for intermediate and high density plasmas. Accurate full-profile computations have been performed for the Paschen alpha, beta and Brackett alpha lines (Motapon et al. 1997) and the Lyman alpha line (Motapon 1998), using a quantum description of the collisions with ions and electrons. In the line centre, this description is limited to low-density plasmas.
At low density, the line shapes of hydrogen have a Lorentzian shape. An analytical expression for their width is given by Stehlé (1996b), together with parameters necessary for the computation of the Holtsmark intensity in the line wings.
The far wings of the hydrogen lines exhibit molecular satellite features which, in astrophysical plasmas, are attributed to the transient formation of H - H or H - H⁺ molecules. These satellites are used to determine the gravity in DA white dwarfs. Recent progress has been made by including the variation of the radiative dipole moment during the collision for the Lyman beta line (H - H⁺ satellites, Allard et al. 1998a) and for the Lyman alpha line (H - H, and H - H⁺ satellites, Allard et al. 1998b).
Two new theoretical research areas have been developed. The first concerns the study of the lines of hydrogen in the presence of magnetic fields (Günter and Könies 1999, Brillant et al. 1998). These developments may be useful in the future for the characterization of magnetic stars. The second is the study of the shift and asymmetry of the Balmer alpha, beta and gamma lines; these effects are produced by short-range interactions with the plasma charges (Günter and Könies 1997).

Helium Lines

The study of the intensity and shape of forbidden transitions in helium stopped in 1975, probably because of its intrinsic difficulty. The subject has recently been revisited by Beauchamp et al. (1997), for application to Helium rich (DB) White Dwarfs, using a static approximation for the interaction between helium and the plasma ions. They calculated the line shapes for the 2p-ns, 2s-np and 2p-nd transitions which are in the optical range. The Stark widths and shifts of allowed infrared helium lines (3p-7d, 3d-7f, 3p-9d, 3d-12f, 3p-10d) have also recently been studied theoretically by Terzi et al. (1998), in the semi-classical approximation, both in the impact and quasistatic limits.

Lines of H-like Ions

The study of lines of hydrogenic heavy ions is only important in opacity calculations for stellar interiors, or for the evaluation of the radiative forces in stellar envelopes. This requires the description of the full line, from the centre to the line wings. One may use the recent parametrization given for the lines of C, N and O by Gonzalez et al. (1998).
 

4.2. Line Broadening by Foreign Gases and Molecular Line Broadening

Introduction and Reviews

During the period 1996-9, there has again been considerable activity in the field of spectral line broadening by neutral species, both theoretically and experimentally, and much of the work has been stimulated by the need to interpret observations of the atmospheres of planets and cool stars. The proceedings of the 14th International Conference on Spectral Line Shapes (Herman 1999) include a special section on astrophysical and atmospheric applications. Valuable databases that provide information on many molecular species for spectroscopic studies of atmospheres have been further extended, see the reviews of Wenger & Champion (1998), Rothman et al. (1998) and Jacquinet-Husson et al. (1999). Szudy & Baylis (1996) have reviewed Unified Franck-Condon theory and its applications to the far wings of pressure-broadened profiles, rainbow satellites and the collisional redistribution of radiation. Gamache et al. (1998) have presented a critical review of data for the pressure broadening and shift of spectral lines of ozone.
It is not the aim of this report to be exhaustive; the papers cited have been chosen on the basis of their potential astrophysical interest. The preceding reviews contain many references, and so only papers not included in them are listed below.

Broadening of Atomic Lines

Results have been obtained for the broadening of far-wing profiles of lithium lines by helium (Behmenburg et al. 1996), and general tables for calculation of the broadening of atomic p-d, d-p, d-f, and f-d transitions by neutral hydrogen are presented by Barklem & O'Mara (1997, 1998) and Barklem et al. 1998). Results for the broadening of Na D lines by O₂, N₂, CO₂ and H₂O and Mg and Ca lines by N₂ are given by Nefedov et al. (1999) and El Ghazaly et al. (1999).

Broadening of Molecular Lines

In addition to the research described in the reviews of Wenger & Champion (1998), Rothman et al. (1998) and Jacquinet-Husson et al. (1999), the pressure broadening and shift of various molecular bands has been investigated either experimentally or theoretically and the molecules are listed below together with their perturbing atomic or molecular species. They are: H₂ - He, H₂ (Michaut et al. 1998, Joubert et al. 1999), ¹²CH₃D - He, H₂, N₂ (Boussin et al. 1999), H₂S - He, H₂, N₂, O₂ (Flatin et al. 1999, Ball et al. 1999), CO - He, Ar (Sinclair et al. 1998), CO₂ - He, Ar, CO₂, N₂, O₂ (Rodrigues et al. 1998, Vigasin 1999, Ma et al. 1999, De Rosa et al. 1999), N₂ - N₂ (Buldyreva et al. 1999), NH₃ - H₂, NH₃ (Irwin et al. 1999, Birnbaum et al. 2000), N₂O - He, N₂ (Bouanich et al. 1998), ¹⁶O₂ - ¹⁶O₂ (Schermaul & Learner 1999), ¹⁶O¹⁸O - ¹⁶O¹⁸O (Schermaul 1999) and OH - He, H₂, N₂, O₂ (Park et al. 1999).

Collision Induced Spectra

Collision-induced absorption in dense atmospheres of cool stars has been reviewed by Borysow and Jorgensen (1999). Recent publications include studies of far-infrared bands of H₂, CO₂, O₂ and liquid methane (Brodbeck et al. 1999, Gruszka & Borysow 1999, Moreau et al. 2000, Birnbaum et al. 1999), and of the fundamental band of CO broadened by N₂ (Luo et al. 1999).

Data Bases

Currently available are the following databases:
Spherical Top Data System (STDS),