Astronomy and Astrophysics Letters dedicated to ISO

Very small grain emission in NGC7023

R.J. Laureijs - J. Acosta-Pulido - P. Ábráham - U. Kinkel - U. Klaas - H.O. Castañeda - L. Cornwall - C. Gabriel - I. Heinrichsen - D. Lemke - G. Pelz - B. Schulz - H.J. Walker


We observed the reflection nebula NGC7023 at various positions using wide and narrow band photometry centred on the 7.7 and 11.3 micron PAH emission features and wide band photometry at 20 and 25 microns. No significant variations have been detected over the nebula in the 7.3 and 20 micron continuum relative to the total emission in the 6-15 microns range (hereafter Tau).This result supports the hypothesis that most of the continuum emission in both bands come from very small grains.

In contrast, the 7.7 and 11.3 micron PAH emission features show clear variations. We find that in weaker radiation fields of the nebula the 11.3 and 7.7 micron features are not the dominant emission components in the 6-15 microns range. The 11.5 micron band increases whereas the 11.3 micron emission feature decreases relative to Tau in the outer parts of the nebula. The effect can be explained by increased hydrogenation of PAH molecules.

interstellar medium: reflection nebulae: NGC7023 - interstellar medium: dust, extinction - interstellar medium: molecules

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