Issue |
A&A
Volume 460, Number 3, December IV 2006
|
|
---|---|---|
Page(s) | 821 - 829 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20065160 | |
Published online | 12 September 2006 |
Fe II emission lines in Be stars
I. Empirical diagnostic of physical conditions in the circumstellar discs
1
Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque sn, (1900) La Plata, Argentina e-mail: mlaura@fcaglp.fcaglp.unlp.edu.ar
2
Instituto de Astrofísica de La Plata (CONICET-UNLP), Paseo del Bosque sn, (1900) La Plata, Argentina
3
Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Bd. Arago, 75014 Paris, France
4
Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
5
GEPI, UMR 8111 du CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France
Received:
8
March
2006
Accepted:
22
June
2006
Aims.The Fe ii emission lines formed in the circumstellar envelopes (CE) of classical Be stars are studied in order to determine whether they are optically thin or optically thick. We also aim at deriving both average Fe ii line excitation temperatures and the extent of their formation region in the CE.
Methods.We simultaneously observed several series of Fe ii emission lines
in the Å wavelength interval and the first
members of the hydrogen Balmer series of 18 southern classical Be stars. The
optical depth regime that controls the formation of the observed Fe ii
lines and the physical parameters of their CE formation region were studied
using the empirical self-aborption-curve (SAC) method.
Results.Our calculations give an average value of for the
optical depth of the studied Fe ii lines, which implies that these
lines are optically thick in the CE of Be stars. Qualitative indications
that Fe ii emission lines should be formed in circumstellar regions
close to the central star are inferred from the correlations between Fe ii emission line widths and
. The application of the SAC method
to Fe ii emission lines confirms this result, which gives
for the extension of the line-forming region. The
proximity of the line-forming region to the central star is also supported by
the behavior of the source function of Fe ii lines, which rapidly
decreases with radii. This prevents the lines from being formed over extended
regions and/or far from the star. Finally, the correlations of the central
depression in the Balmer emission lines with
are consistent with
the flattened geometrical shapes of CEs.
Key words: stars: emission-line, Be / stars: circumstellar matter / line: profiles / line: formation
© ESO, 2006
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