Astron. Astrophys. 326, 831-841 (1997)

Dust scattering and kinematics
within the envelope of IRAS 09371+1212

J.P. Phillipsand L. Cuesta <sup>1, 2

1</sup> Instituto Nacional de Astrofisica, Optica y Electronica, A. Postal 51 y 216 Pue., Puebla, Mexico
² Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain

Received 24 April 1996 / Accepted 18 February 1997

Abstract

We have acquired narrow and broad band imaging, together with high and low resolution spectroscopy for the source IRAS 09371+1212. As a result, we are able to show the presence of systematic colour gradients within the interior and exterior envelopes. Whilst the interior bright lobes are characterised by relatively high values of (a regime of reddening which also extends asymmetrically to the east), the exterior shell possesses an annulus of lower ; an index which gradually increases again to larger radii. Such trends are, in part, characteristic of reflection nebulae, and may also indicate an evolution in grain properties with radial displacement from the nucleus; although gradients appear inconsistent with either normal interstellar dust or model ice grains.

Spectroscopy of a narrow absorption feature has further been used to evaluate the variation of grain scatter velocity along the source major axis. The results are inconsistent with previous measures in indicating a substantially invariant velocity for the southerly lobe, and a trend towards systematically increasing velocities in the northern lobe; there is no evidence to favour appreciable velocity decrements. In addition, we note evidence for strongly variable line width and depth. These may be explained in terms of a non-spherically symmetric scatter model providing grain sizes are modest, lobe densities are broadly invariant, and there are appreciable levels of both shell extinction and multiple and forward grain scattering. Alternative explanations in terms of cavity outflow models are also discussed.

Finally, we note that the presumed post-main-sequence status of this source is not necessarily inconsistent with a high galactic latitude, and that the height of the source above the galactic plane may be less than supposed from its observed luminosity.

Key words: dust extinction -- jets and outflows -- kinematics and dynamics -- reflection nebulae -- planetary nebulae: Frosty Leo

Send offprint requests to: J.P. Phillips

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Contents

• 1. Introduction
• 2. Observations
• 3. Variations in colour index
• 4. Variation of velocity through the envelope
• 5. Outflow scatter models
  • 5.1. Grain scattering model
  • 5.2. Cavity outflow models
• 6. Evolutionary status
• 7. Conclusions
• References

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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