Bibcode
DOI
Cuesta, L.; Phillips, J. P.
Bibliographical reference
The Astronomical Journal, Volume 119, Issue 1, pp. 335-341.
Advertised on:
1
2000
Citations
7
Refereed citations
6
Description
We have acquired narrowband imaging of NGC 2346 in the transitions H I
λ6563 and λ4861 and [O III] λ5007. As a result, we
are able to evaluate the variation of both excitation and extinction
over the projected central parts of the nebular shell. Extinction
appears to be surprisingly uniform, and there is (in particular) little
evidence for the reddening asymmetries proposed in previous analyses.
Cusplike enhancements in Av at the periphery of the source
are attributed to a layer of extincting material at the limits of the H
II region, implying a value of major-axis reddening
ΔAv<0.5 mag. Similar extinctions are also deduced
from an analysis of infrared and millimeter-wavelength observations. It
is unclear what proportion of this reddening may be attributed to the
molecular belt, although it seems likely that this feature contributes
~0.3 mag of extinction in the northern lobe and explains the north-south
asymmetries noted in optical images. Given that levels of local
extinction are quite modest, it seems likely that the larger part of the
observed reddening (Av~2 mag) arises from intervening
interstellar material, a conclusion that is again at variance with
previous analyses. Such a presumption would explain the relative
uniformity in extinction over the face of the nebula, and similarity
between distances estimated from extinction and those determined through
alternative analyses. If this is accepted, however, then it follows that
prior estimates of central star extinction must be greatly in error. One
possible origin for this error is noted from Hubble Space Telescope
imagery in [N II] λ6584, where it is clear that a secondary star
is located close to the presumed A-type central star, a component that
was not allowed for in previous analyses. It is unclear whether this
star is physically associated with the core binary system.