Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aj....119..335p&link_type=abstract
The Astronomical Journal, Volume 119, Issue 1, pp. 335-341.
Astronomy and Astrophysics
Astronomy
4
Key Words: Ism: Dust, Extinction, Ism: Jets And Outflows, Ism: Kinematics And Dynamics, Ism: Planetary Nebulae: Individual: Ngc Number: Ngc 2346
Scientific paper
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.
Cuesta Luis
Phillips J. P.
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