Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...389..347l&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 389, April 10, 1992, p. 347-356. Research supported by NSERC.
Astronomy and Astrophysics
Astronomy
34
Infrared Astronomy, Infrared Sources (Astronomy), Planetary Nebulae, Protoplanets, Stellar Evolution, Asymptotic Giant Branch Stars, Emission Spectra, Hydrogen, Infrared Imagery, Molecular Collisions, Near Infrared Radiation
Scientific paper
Near-IR images and spectroscopy of the bipolar protoplanetary nebula AFGL 618 are presented. Emission from molecular hydrogen is detected in the 0.90-1.34-micron spectrum. A visual extinction of 3.4 +4.0/-2.0 mag to the H2-emitting region is derived from molecular hydrogen line ratios. Models of collisionally excited and fluorescent H2 emission are compared with the data: the near-IR H2 spectrum is found to be dominated by emission from collisionally excited molecules at Tex of about 2000 K, but a component of fluorescent emission is also present. It is shown that this type of near-IR spectrum is an excellent tool for discriminating relatively low levels of fluorescent H2 emission from a strong collisionally excited component. Images in the H- and K-bandpasses are analyzed using models which assume single scattering of photons from the central objects. The models indicate that the bipolar axis is inclined to the plane of the sky by about 45 deg. The emission in the H- and K-bands is found to be consistent with single scattering of photons by dust with a distribution such that the dust density increases with increasing stellar latitude and is nearly zero at the poles.
Black John Harry
Kelly Douglas M.
Latter William B.
Maloney Philip R.
Rieke George H.
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