Astronomy and Astrophysics – Astronomy
Scientific paper
May 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...498..267s&link_type=abstract
Astrophysical Journal v.498, p.267
Astronomy and Astrophysics
Astronomy
29
Infrared: Ism: Lines And Bands, Ism: Kinematics And Dynamics, Ism: Molecules, Ism: Planetary Nebulae: Individual Alphanumeric: Bd +30 Degrees 3639
Scientific paper
High spatial and spectral resolution spectra of the near-infrared H2 emission from the planetary nebula BD +30 deg3639 are presented. A 7" x 13" portion of the nebula was mapped at a resolution of 6000 in the v = 1-0 S(1) emission line of molecular hydrogen, revealing the morphology and kinematics of the H2 emission. These spectra show large velocity shifts in the H2 line across the nebula. Comparison with single-dish CO observations show significant velocity differences between the peaks of H2 emission and CO emission. Such differences are unexpected for a photodissociation region (PDR), since PDRs are supposed to form in the surface of the cold gas (as is the case for NGC 7027). A single long-slit spectrum which includes the peak of the H2 emission and covers the entire K band at a resolution of 1000 is analyzed. Fourteen molecular hydrogen emission lines are detected in a 2" x 0."5 region covering the bright northeastern H2 lobe. The line ratios indicate that the H2 emission is radiatively excited, but that the gas density is large enough (n >~ 104.5-105 cm-3) for collisions to thermalize the lowest vibrational states. The measured ratio of ortho-hydrogen to para-hydrogen is 2.51 +/- 0.22, slightly smaller than the equilibrium value of 3. Spatial variations of the v = 2-1 vibrational temperature and the v = 1 ortho/para ratio are consistent with a decrease in the relative proportion of collisional excitation as distance from the central star increases.
Armus Lee
Knop Rob A.
Larkin James E.
Matthews Keith
Shupe Dave L.
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