Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...434..719k&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 434, no. 2, p. 719-732
Astronomy and Astrophysics
Astronomy
48
Broken Symmetry, Carbon Stars, Cosmic Dust, Density Distribution, Infrared Astronomy, Optical Polarization, Reflection Nebulae, Stellar Envelopes, Astronomical Interferometry, Astronomical Polarimetry, Coronagraphs, Infrared Imagery, Stellar Evolution
Scientific paper
We present polarimetric, coronagraphic near-infrared images of the reflection nebula surrounding the carbon star IRC +10216. These images demonstrate convincingly that the dust envelope is not spherically symmetric. In unocculted images at J (1.25 micrometers) and in occulted images at H (1.65 micrometers) and K (2.2 micrometers), the nebula appears elongated, with major axis lying at position angle approximately 20 deg. The position angle of elongation is the same as that previously determined from near-infrared speckle interferometry for the inner approximately 1 sec of the envelope. The elliptical symmetry of the J polarimetric map offers additional evidence of the axial symmetry of the envelope and indicates that the equatorial plane of IRC +10216 lies perpendicular to the major axis of the nebula. The polarization map also indicates that the source of illumination -- presumably the stellar photosphere or hot dust located very near the photosphere -- is directly detected at wavelengths as short as approximately 1 micrometers. We find that the density distribution of grains in the polar regions is roughly n varies as r-2 and estimate that the scattering dust mass within 12 sec in radius of the central star is approximately 5 x 10-6 solar masses. These results support a model in which the envelope of IRC +10216 is weakly bipolar and is viewed at an intermediate inclination angle such that we have a direct line of sight to the central star. The axisymmetric near-infrared intensity and polarization morphologies are best understood in terms of enhanced mass loss in the equatorial plane. An examination of previous near-infrared and millimeter-wave mapping observations supports this hypothesis. These observations make clear that axisymmetric structure can be well established before an intermediate-mass star leaves the asymptotic giant branch. It is possible that the dust envelope of IRC +10216 presents an early manifestation of the more profound bipolar structure that characterizes highly evolved preplanetary nebulae.
Kastner Joel H.
Weintraub David A.
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