MidInfrared Images of NGC 7027 and BD 303639

1
Mid-Infrared Images of NGC 7027 and
BD30º3639 Kevin Volk and Sun Kwok (University of
Calgary)
Introduction The discovery of large infrared
excess in the planetary nebula (PN) NGC 7027
(Gillett et al. 1967) has led to the suggestion
that the dust components in PNs represent the
remnants of the circumstellar dust envelopes of
their asymptotic giant branch (AGB) progenitors,
and should be widely present in PNs (Kwok 1982).
This was confirmed by IRAS observations where
dust emission in the far infrared was found in
most PNs (Pottasch et al. 1984). A number of
carbon-rich PNs are found to show strong emission
features due to various stretching and bending
modes of aromatic hydrocarbon bonds (AHB, Duley
and Williams 1981, Allamandolla et al. 1989).
Comparisons between ISO spectra of evolved carbon
stars, proto-planetary nebulae (PPNs), and PNs
have shown that the AHB features develop late in
the PPN phase (Kwok et al. 1999). In order to
test the formation history of this carbonaceous
component, it would be desirable to image the
spatial distributions of the dust components.
The Gemini Telescopes, optimzed for infrared
observations with adaptive optics capabilities,
offer the unique opportunity for such
observations. Observations The carbon-rich
planetary nebulae NGC 7027 and BD30º3639 were
imaged with the OSCIR mid-infrared camera at
Gemini North Telescope on the night of July 10th,
2001. The camera has a field of view of 11
square with a scale of 0.089 per pixel. Images
were made in the N-band atmospheric window (N,
10.3, 11.7, 12.5 ?m narrow-band filters) and in
the Q-band window with a 20.8 ?m filter. From
images of Vega, we estimated that the resolution
was 0.39 FWHM in the N-band filters.
Left (clockwise from upper left) 10.3, 11.7,
12.5, and 20.8 ?m images of BD30º3639. Top
5-point mosaic image at 11.7 ?m. The colour bars
show the intensity scale in Jy/arcsec2.
Left (clockwise from upper left) 10.3, 11.7,
12.5, and 20.8 ?m images of NGC 7027. Top
5-point mosaic image at N. The colour bars show
the intensity scale in Jy/arcsec2.
Results Since both nebulae show strong AHB
emissions, it is possible to locate the emission
regions of the 11.3 ?m AHB feature by subtracting
the (scaled) adjacent continuum image from the
11.7 ?m image. A comparison between the ISO
spectrum and the OSCIR profiles shows that the
11.3 ?m feature fits in almost entirely within
the 11.7 ?m filter and the continuum can be well
approximated by the 10.3 ?m filter for
BD30º3639. For NGC 7027 the 12.5 ?m filter is
used for the continuum, since the 12.8 ?m NeII
line is weak while the 10.5 ?m SIV line is
strong.
Discussion Since the 10.5 ?m SIV line lies in
the 10.3 ?m filter window, the 10.3-continuum
image (shown below) therefore traces the
distribution of the ionized gas. When this image
is compared to the 11.7-continuum image, we can
see that the AHB emitting region clearly lies
outside of the ionized region.
BD30º3639
NGC 7027
NGC 7027
In the above Figures, the upper images are the
continuum subtracted feature emission maps (AHBs
in the left two panels, SIV 10.5 ?m at right).
In the lower images, the continuum maps (shown
as contours) are overlaid on the subtracted
images.
References Allamandolla, L.J., Tielens,
A.G.G.M., Barker, J.R. 1989, ApJS, 71,
733 Duley, W.W., Williams, D.A. 1981, MNRAS,
196, 269 Gillett, F.C., Low, F.J., Stein, W.A.
1967, ApJ, 149, L97 Kwok, S. 1982, ApJ, 258,
280 Kwok, S., Volk, K., Hrivnak, B.J. 1999,
AA, 350, L35 Pottasch, S.R. et al. 1984, AA,
138, 10 Russell, R.W., Soifer, B.T., Willner,
S.P. 1977, ApJ, 217, L149