NLTE ionization equilibrium of Nd II and Nd III in cool A and Ap stars
Abstract
The kinetic equilibrium of Nd II -Nd III in the atmospheres of A-type stars is investigated for the first time with a model atom containing 1651 levels of Nd II, 607 levels of Nd III, and the ground state of Nd, IV. NLTE leads to an overionization of Nd II resulting in weakening the Nd II lines at mild neodymium overabundances relative to the solar Nd abundance ([Nd/H] < 2.5) and produces the opposite effect at the higher [Nd/H] values. NLTE abundance corrections grow with effective temperature and reach ∼0.6 dex at Teff = 9500 K. The Nd III lines are strengthened compared with LTE. NLTE abundance corrections range between -0.3 dex and -0.2 dex for Teff between 7500 K and 9500 K. Therefore NLTE effects may explain ionization discrepancies up to 0.8 - 0.9 dex, derived with the LTE approach.
- Publication:
-
The A-Star Puzzle
- Pub Date:
- December 2004
- DOI:
- 10.1017/S1743921304004703
- Bibcode:
- 2004IAUS..224..315M
- Keywords:
-
- Atomic data;
- line: formation;
- stars: chemically peculiar;
- stars: abundances