Near-infrared polarimetry and modelling of the dusty young planetary nebula IRAS 19306+1407 |
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| Authors: | K T E Lowe T M Gledhill |
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| Institution: | Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB |
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| Abstract: | We present near-infrared polarimetric images of the dusty circumstellar envelope (CSE) of IRAS 19306+1407, acquired at the United Kingdom Infrared Telescope (UKIRT) using the UKIRT 1–5 μm Imager Spectrometer (UIST) in conjunction with the half-waveplate module IRPOL2. We present additional 450- and 850-μm photometry data obtained with the Submillimetre Common-User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT), as well as archived Hubble Space Telescope ( HST ) F606W - and F814W -filter images. The CSE structure in polarized flux at J and K bands shows an elongation north of north-east and south of south-west with two bright scattering shoulders north-west and south-east. These features are not perpendicular to each other and could signify a recent 'twist' in the outflow axis. We model the CSE using an axisymmetric light scattering ( als ) code to investigate the polarization produced by the CSE, and an axisymmetric radiation transport ( dart ) code to fit the spectral energy distribution. A good fit was achieved with the als and dart models using silicate grains, 0.1–0.4 μm with a power-law size distribution of a −3.5, and an axisymmetric shell geometry with an equator-to-pole ratio of 7:1. The spectral type of the central star is determined to be B1 i supporting previous suggestions that the object is an early planetary nebula. We have constrained the CSE and interstellar extinction as 2.0 and 4.2 mag, respectively, and have estimated a distance of 2.7 kpc. At this distance, the stellar luminosity is ∼4500 L⊙ and the mass of the CSE is ∼0.2 M⊙. We also determine that the mass loss lasted for ∼5300 yr with a mass-loss rate of ∼3.4 × 10−5 M⊙ yr−1. |
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| Keywords: | techniques: polarimetric stars: AGB and post-AGB circumstellar matter stars: individual: IRAS 19306+1407 stars: mass-loss infrared: stars |
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