Issue |
A&A
Volume 369, Number 3, April III 2001
|
|
---|---|---|
Page(s) | 1009 - 1026 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20010164 | |
Published online | 15 April 2001 |
Non-LTE line formation for MgI/II: Abundances and stellar parameters*
Model atom and first results on A-type stars
1
Universitäts-Sternwarte München, Scheinerstraße 1, 81679 München, Germany
2
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85740 Garching bei München, Germany
Corresponding author: N. Przybilla, nob@usm.uni-muenchen.de
Received:
19
September
2000
Accepted:
11
January
2001
An extensive model atom for non-LTE line-formation calculations for
neutral and singly-ionized magnesium is presented, taking into account
recent improvements in the atomic data.
As a test and first application of the model, stellar parameters
and magnesium abundances are determined on the basis of
line-blanketed LTE model atmospheres for three stars:
Vega (A0 V), η Leo (A0 Ib) and HD 92207
(A0 Iae) using high and high resolution spectra at visual and near-IR
wavelengths. The ionization equilibrium of Mgi/ii
proves to be a sensible temperature indicator for early A-type
stars at all luminosities. Evidence is given that in late
A and early F-type supergiants (
K) the
determination of accurate
stellar parameters is hampered by the presence of a pressure inversion region
in the model atmospheres at line-formation depths.
The Mgi/ii lines in the observations
are reproduced simultaneously by the calculated line profiles with high
accuracy. For Vega spectral synthesis in the UV region of the Mgi/ii
resonance lines also proves excellent consistency with the results from the
visual.
The dependence of the non-LTE effects on the atmospheric
parameters is discussed with special emphasis on the supergiants
where a strong radiation field at low particle densities favours
deviations from LTE, especially in the minor ionic species of neutral magnesium.
Non-LTE corrections turn out to be small in Mgi -typically
0.3 dex -even in supergiants, but are essential for an accurate
effective temperature determination. From the Mgii spectrum, only the
features at
4481 and 7877-96 Å react sensitively to
non-LTE effects. Furthermore, the influence of microturbulence on the
statistical-equilibrium calculations is investigated. The line strengths are
found to be systematically affected.
Key words: atomic data / line: formation / stars: abundan ces, fundamental parameters, supergiants
© ESO, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.