Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...189.9703d&link_type=abstract
American Astronomical Society, 189th AAS Meeting, #97.03; Bulletin of the American Astronomical Society, Vol. 28, p.1401
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the results of a near-infrared spectroscopic survey of planetary nebulae at McDonald Observatory during 1986 - 1993, using a grating spectrometer based on a 1 x 32-element InSb array. Most of the observations were taken in the K-band, with resolving power R = lambda /Delta lambda = 600 in order to resolve v = 1-0 S(1) 2.121mu m H_2 from the adjacent Hei 2.113mu m line. We also simultaneously measured the strengths of Hi Br gamma and Heii 2.189mu m. The typical limiting flux in our 3.8arcsec square beam was 1 - 3 x 10(-14) erg cm(-2) s(-1) , corresponding to a limiting surface brightness of 3 x 10(-5) to 1 x 10(-4) erg cm(-2) s(-1) ster(-1) . An early result of this study was the first conclusive proof that the UV-pumping or ``fluorescence'' mechanism rather than thermal (shock) excitation was responsible for the H_2 emission in a planetary nebula, Hubble 12 (Dinerstein et al. 1988, ApJ, 327, L27). Here we report results for 15 additional nebulae, 8 of which showed detectable H_2 emission. We mapped 6 objects by stepping the aperture along E-W and/or N-W axes through the central star, at intervals separated by 3arcsec , in order to find a position which isolated the H_2 emission; observations at the central position or with large, centered beams are often contaminated by strong continuum and line emission from the central star and the ionized gas. For selected positions, we also obtained observations in the J and H bands and with a setting that included the 1-0 S(0) 2.223mu m and 2-1 S(1) 2.247mu m H_2 lines. The observed line intensity ratios range from those characteristic of ``pure fluorescence'' to values typical of thermally-excited (or thermalized fluorescent) emission, with the planetary nebula BD+30(deg) 3639 representing an intermediate case.
Crawford J. J.
Dinerstein Harriet
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