4 research outputs found
Neutral material around the B[e] supergiant star LHA 115-S 65: An outflowing disk or a detached Keplerian rotating disk?
B[e] supergiants are surrounded by large amounts of hydrogen neutral
material, traced by the emission in the optical [OI] lines. This neutral
material is most plausibly located within their dense, cool circumstellar
disks, which are formed from the (probably non-spherically symmetric) wind
material released by the star. Neither the formation mechanism nor the
resulting structure and internal kinematics of these disks (or disk-like
outflows) are well known. However, rapid rotation, lifting the material from
the equatorial surface region, seems to play a fundamental role. The B[e]
supergiant LHA 115-S 65 (S65) in the SMC is one of the two most rapidly
rotating B[e] stars known. Its almost edge-on orientation allows a detailed
kinematical study of its optically thin forbidden emission lines. With a focus
on the [OI] lines, we test the two plausible disk scenarios: the outflowing and
the Keplerian rotating disk. Based on high- and low-resolution optical spectra,
we investigate the density and temperature structure in those disk regions that
are traced by the [OI] emission to constrain the disk sizes and mass fluxes
needed to explain the observed [OI] line luminosities. In addition, we compute
the emerging line profiles expected for either an outflowing disk or a
Keplerian rotating disk, which can directly be compared to the observed
profiles. Both disk scenarios deliver reasonably good fits to the line
luminosities and profiles of the [OI] lines. Nevertheless, the Keplerian disk
model seems to be the more realistic one, because it also agrees with the
kinematics derived from the large number of additional lines in the spectrum.
As additional support for the presence of a high-density, gaseous disk, the
spectrum shows two very intense and clearly double-peaked [CaII] lines. We
discuss a possible disk-formation mechanism, and similarities between S65 and
the group of LBVs.Comment: 13 pages, 12 figures, accepted for publication in A&