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The near-infrared structure and spectra of the bipolar nebulae M2-9 and AFGL 2688: The role of ultraviolet pumping and shocks in molecular hydrogen excitation [ Erratum: 1995ApJ...449..397H ]
Hora, Joseph L.; Latter, William B.
AA(Inst. for Astronomy, Honolulu, HI, US), AB(Inst. for Astronomy, Honolulu, HI, US)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 437, no. 1, p. 281-295 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Bipolarity, Hydrogen, Infrared Astronomy, Infrared Imagery, Molecular Excitation, Near Infrared Radiation, Planetary Nebulae, Stellar Spectra, Pumping, Shock Wave Interaction, Ultraviolet Radiation
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High-resolution near-infrared images and moderate resolution spectra were obtained of the bipolar nebulae M2-9 and AFGL 2688. The ability to spatially and spectrally resolve the various components of the nebulae has proved to be important in determining their physical structure and characteristics. In M2-9, the lobes are found to have a double-shell structure. The inner shell is dominated by emission from hydrogen recombination lines, and the outer shell is primarily emission from H2 lines in teh 2-2.5 micron region. Analysis of H2 line ratios indicates that the H2 emission is radiatively excited. A well-resolved photodissociation region is observed in the lobes. The spectrum of the central source is dominated by H recombination lines and a strong continuum rising toward longer wavelengths consistent with a T = 795 K blackbody. Also present are lines of He I and Fe II. In contrast, the N knot and E lobe of M2-9 show little continuum emission. The N knot spectrum consists of lines of (Fe II) and hydrogen recombination lines. In AGFL 2688, the emission from the bright lobes is mainly continuum reflected from the central star. Several molecular features from C2 and CN are present. In the extreme end of the N lobe and in the E equatorial region, the emission is dominated by lines of H2 in the 2-2.5 region. The observed H2 line ratios indicate that the emission is collisionally excited, with an excitation temperature Tex approixmately = 1600 +/- 100 K.

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