The spectral features of HD 94509 are highly unusual, adding an extreme to
the zoo of Be and shell stars. The shell dominates the spectrum, showing lines
typical for spectral types mid-A to early-F, while the presence of a late/mid
B-type central star is indicated by photospheric hydrogen line wings and helium
lines. Numerous metallic absorption lines have broad wings but taper to narrow
cores. They cannot be fit by Voigt profiles.
We aim to describe and illustrate unusual spectral features of this star, and
make rough calculations to estimate physical conditions and abundances in the
shell. Furthermore, the central star is characterized.
We assume mean conditions for the shell. An electron density estimate is made
from the Inglis-Teller formula. Excitation temperatures and column densities
for Fe I and Fe II are derived from curves of growth. The neutral H column
density is estimated from high Paschen members. The column densities are
compared with calculations made with the photoionization code Cloudy.
Atmospheric parameters of the central star are constrained employing non-LTE
spectrum synthesis.
Overall chemical abundances are close to solar. Column densities of the
dominant ions of several elements, as well as excitation temperatures and the
mean electron density are well accounted for by a simple model. Several
features, including the degree of ionization, are less well described.
HD 94509 is a Be star with a stable shell, close to the terminal-age main
sequence. The dynamical state of the shell and the unusually shaped, but
symmetric line profiles, require a separate study.Comment: 10 pages, 9 tables, 13 figures; accepted for publication by Astronomy
and Astrophysic
