Bibcode
Cuesta, L.; Phillips, J. P.
Bibliographical reference
Astronomy and Astrophysics, v.326, p.831-841
Advertised on:
10
1997
Journal
Citations
2
Refereed citations
1
Description
We have acquired narrow and broad band imaging, together with high and
low resolution spectroscopy for the source IRAS 09371+1212. As a result,
we are able to show the presence of systematic colour gradients within
the interior and exterior envelopes. Whilst the interior bright lobes
are characterised by relatively high values of V-R (a regime of
reddening which also extends asymmetrically to the east), the exterior
shell possesses an annulus of lower V-R; an index which gradually
increases again to larger radii. Such trends are, in part,
characteristic of reflection nebulae, and may also indicate an evolution
in grain properties with radial displacement from the nucleus; although
gradients V-R/B-V appear inconsistent with either normal interstellar
dust or model ice grains. Spectroscopy of a narrow Hα absorption
feature has further been used to evaluate the variation of grain scatter
velocity along the source major axis. The results are inconsistent with
previous measures in indicating a substantially invariant velocity for
the southerly lobe, and a trend towards systematically increasing
velocities in the northern lobe; there is no evidence to favour
appreciable velocity decrements. In addition, we note evidence for
strongly variable line width and depth. These may be explained in terms
of a non-spherically symmetric scatter model providing grain sizes are
modest, lobe densities are broadly invariant, and there are appreciable
levels of both shell extinction and multiple and forward grain
scattering. Alternative explanations in terms of cavity outflow models
are also discussed. Finally, we note that the presumed
post-main-sequence status of this source is not necessarily inconsistent
with a high galactic latitude, and that the height of the source above
the galactic plane may be less than supposed from its observed
luminosity.