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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 308699.0, MPI für Astronomie / Publikationen_mpia
Multi-aperture photometry of extended IR sources with ISOPHOT. I. The nature of extended IR emission of planetary Nebulae
Authors:Klaas, U.; Walker, H. J.; Müller, T. G.; Richards, P. J.; Schreiber, J.
Date of Publication (YYYY-MM-DD):2006
Journal Abbrev.:Astronomy and Astrophysics
Start Page:523
End Page:535
Audience:Not Specified
Abstract / Description:Context: .ISOPHOT multi-aperture photometry is an efficient method to resolve compact sources or to detect extended emission down to relatively faint levels with single detectors in the wavelength range 3 to 100 mum.<BR /> Aims: .Using ISOPHOT multi-aperture photometry and complementary ISO spectra and IR spectral energy distributions we discuss the nature of the extended IR emission of the two PNe NGC 6543 and NGC 7008.<BR /> Methods: .In the on-line appendix we describe the data reduction, calibration and interpretation methods based on a simultaneous determination of the IR source and background contributions from the on-source multi-aperture sequences. Normalized profiles enable direct comparison with point source and flat-sky references. Modelling the intensity distribution offers a quantitative method to assess source extent and angular scales of the main structures and is helpful in reconstructing the total source flux, if the source extends beyond a radius of 1 arcmin. The photometric calibration is described and typical accuracies are derived. General uncertainty, quality and reliability issues are addressed, too. Transient fitting to non-stabilised signal time series, by means of combinations of exponential functions with different time constants, improves the actual average signals and reduces their uncertainty.<BR /> Results: .The emission of NGC 6543 in the 3.6 mum band coincides with the core region of the optical nebula and is homogeneously distributed. It is comprised of 65% continuum and 35% atomic hydrogen line emission. In the 12 mum band a resolved but compact double source is surrounded by a fainter ring structure with all emission confined to the optical core region. Strong line emission of [ArIII] at 8.99 mum and in particular [SIV] at 10.51 mum shapes this spatial profile. The unresolved 60 mum emission originates from dust. It is described by a modified (emissivity index beta = 1.5) blackbody with a temperature of 85 K, suggesting that warm dust with a mass of 6.4 × 10-4 Mo is mixed with the ionised gas. The gas-to-dust mass ratio is about 220. The 25 mum emission of NGC 7008 is characterised by a FWHM of about 50´´ with an additional spot-like or ring-like enhancement at the bright rim of the optical nebula. The 60 mum emission exhibits a similar shape, but is about twice as extended. Analysis of the spectral energy distribution suggests that the 25 mum emission is associated with 120 K warm dust, while the 60 mum emission is dominated by a second dust component with 55 K. The dust mass associated with this latter component amounts to 1.2 × 10-3 Mo, significantly higher than previously derived. The gas-to-dust mass ratio is 59 which, compared to the average value of 160 for the Milky Way, hints at dust enrichment by this object.<BR />
Free Keywords:techniques: photometric; astronomical data bases: miscellaneous; infrared: ISM; planetary nebulae: individual: NGC 6543; planetary nebulae: individual: NGC 7008; methods: data analysis
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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