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Astron. Astrophys. 315, L313-L316 (1996)

Very small grain emission in NGC7023*

R.J. Laureijs1, J. Acosta-Pulido5,1,2, P. Ábráham6,5, U. Kinkel5,1, U. Klaas5,1, H.O. Castaneda5,1,2, L. Cornwall3,1, C. Gabriel1, I. Heinrichsen4,1, D. Lemke5, G. Pelz5,1, B. Schulz1, and H.J. Walker3

1 ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca, Apdo 50727, E-28080 Madrid, Spain
2 IAC, E-38200 La Laguna, Tenerife, Spain
3 CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
4 MPIK, Saupfercheckweg 1, D-69117, Heidelberg, Germany
5 MPIA, Königstuhl 17, D-69117, Heidelberg, Germany
6 Konkoly Observatory of the Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest, Hungary

Received 29 July 1996 / Accepted 28 August 1996

Abstract. We observed the reflection nebula NGC7023 at various positions using wide and narrow band photometry centred on the 7.7 and 11.3  img1.gifm PAH emission features and wide band photometry at 20 and 25  img1.gifm. No significant variations have been detected over the nebula in the 7.3 and 20  img1.gifm continuum relative to the total emission in the 6-15  img1.gifm range (hereafter img2.gif ). 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  img1.gifm PAH emission features show clear variations. We find that in weaker radiation fields of the nebula the 11.3 and 7.7 img1.gifm features are not the dominant emission components in the 6-15 img1.gifm range. The 11.5 img1.gifm band increases whereas the 11.3 img1.gifm emission feature decreases relative to img2.gif in the outer parts of the nebula. The effect can be explained by increased hydrogenation of PAH molecules.

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

* Based on observations made with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

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Last change: December 16, 1996
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