Issue |
A&A
Volume 394, Number 2, November I 2002
|
|
---|---|---|
Page(s) | 707 - 715 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20021217 | |
Published online | 15 October 2002 |
Theoretical study of the collisional depolarization
and of the Hanle effect in the Na I D
line
observed on the solar limb
Laboratoire d'Étude du Rayonnement et de la Matière en Astrophysique, CNRS FRE 2460 – LERMA, Observatoire de Paris, Section de Meudon, 92195 Meudon, France
Corresponding authors: V. Bommier, V.Bommier@obspm.fr b.kerkeni@ucl.ac.uk
Received:
31
May
2002
Accepted:
31
July
2002
In recent years, Landi Degl'Innocenti ([CITE],
[CITE]) has proposed a model of the polarization spectrum of
the D lines observed near the solar limb, based on lower
level polarization effects. By so doing, he obtains a remarkable
agreement between his model and the observations, so that he comes to
a conclusion about a paradox, because the existence of lower level
polarization is incompatible with a magnetic field strength higher
than 10 mGauss (except vertical), and with possible depolarizing
collision effects. In the present paper, we investigate the
depolarizing collision effects (collisions with neutral hydrogen) by
using the collisional rates computed with ab-initio and quantum
chemistry methods by Kerkeni ([CITE]; see also Kerkeni et al. [CITE], and Kerkeni [CITE]). We
solve the statistical equilibrium equations for the atomic density
matrix, taking into account these depolarizing collisions. We
investigate the effect of a weak magnetic field (Hanle effect). Our
results indicate that the lower levels should be completely
depolarized by the collisions at the depth where the
D
lines are formed. Furthermore, large values of the lower level
alignment such as those introduced by Landi Degl'Innocenti in his
model to get a good theoretical fit of the observations, seem to us
unlikely, as our computations confirm. Thus, as the agreement between
the model by Landi Degl'Innocenti and the observations is however very
convincing, the paradox is confirmed, reinforced and increased by our
results.
Key words: Sun: atmosphere / Sun: magnetic fields / atomic data / atomic processes / line: formation / polarization
© ESO, 2002
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.