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The Internal Extinction Curve of NGC 6302 and its Extraordinary Spectrum

Published online by Cambridge University Press:  05 March 2013

Brent Groves ,
Michael A. Dopita ,
Robert E. Williams  and
Chon-Trung Hua
Brent Groves
Affiliation:
Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd, Weston, ACT 2611, Australia; bgroves@mso.anu.edu.au
Michael A. Dopita
Affiliation:
Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd, Weston, ACT 2611, Australia; Michael.Dopita@anu.edu.au
Robert E. Williams
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA; wms@stsci.edu
Chon-Trung Hua
Affiliation:
Laboratorie d'Astronomie Spatiale, Marseille, France; Trung.Hua@astrsp-mrs.fr
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Abstract

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In this paper we present a new method for obtaining the optical wavelength-dependent reddening function of planetary nebulae (PN), using the nebular and stellar continuum. The data used was a spectrum of NGC 6302 obtained using the Double Beam Spectrograph on the 2.3 m telescope at Siding Springs Observatory over three nights. This resulted in a spectrum covering a wavelength range 3300–8600 Å with a large dynamical range and a mean signal to noise of >102 Å−1 in the nebular continuum. With such a high S/N the continuum can be accurately compared with a theoretical model of nebular plus stellar continuum. The nebular electron temperature and density used in the model are determined using ratios of prominent emission lines. The reddening function can then be obtained from the ratio of the theoretical and the observed continuum. In the case of NGC 6302, it is known that much of the reddening arises from dust within or around the nebula, so that any differences between the measured reddening law and the 'standard' interstellar reddening law will reflect differences in the nebular grain size distribution or composition. We find that for NGC 6302, the visible to IR extinction law is indistinguishable from 'standard' interstellar reddening, but that the UV extinction curve is much steeper than normal, suggesting that more small dust grains had been ejected into the nebula by the PN central star. We have detected the continuum from the central star and determined its Zanstra temperature to be of order 150,000 K. Finally, using the extinction law that we have determined, we present a complete dereddened line list of nearly 600 emission lines, and report on the detection of the He(2–10) and He(2–8) Raman features at λ4331 Å and λ4852 Å, and the detection of Raman scattered O VI features at λ6830 Å and λ7087 Å. We believe this to be the first detection of this process in a PN.

Keywords

planetary nebulae: individual (NGC 6302)dust, extinction

Information

Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 19 , Issue 4 , 2002 , pp. 425 - 442
Copyright
Copyright © Astronomical Society of Australia 2002

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