KSPEC Spectrum of the Planetary Nebula Hubble 12

The spectra of Hubble 12, at the core position. The wavelength positions of lines of H I, He I, and other strong lines are indicated. Note that the wavelength scales for each of the ranges are slightly different. The apparent emission features between 2.0 and 2.02 microns are due to differences in the atmospheric absorption when the reference star data were taken. This plot appears in the paper ``A Butterfly in the Making: Revealing the Near-Infrared Structure of Hubble 12'', by J. L. Hora and W. B. Latter, Astrophysical Journal v. 461, p. 288 (1996 April 10). The observations were performed on 1994 September 25 UT on the UH 2.2M telescope. The instrument was configured with a 1.0 x 6.5 arcsec slit, providing a resolving power of 700. Images were taken simultaneously with the spectral integrations using the slit-viewing detector, allowing for accurate placement and guiding. The extracted length of the slit was 2 arcsec. Alternating source and sky integrations were taken and differenced to remove sky and telescope background flux. The total on-source integration time was 150 sec.

The planetary nebula (PN) Hubble 12 (Hb 12; PN G111.8--02.8) has been notable primarily because it represents one of the clearest cases known of fluorescent molecular hydrogen (H2) emission, first determined by Dinerstein et al. (1988 ApJLett, 327, L27) and recently confirmed by Ramsay et al. (1993 MNRAS 263, 695). The observed H2 line ratios were found to closely match those calculated by Black & van Dishoeck (1987 ApJ 322, 412) for the case of pure fluorescent emission. Objects which exhibit pure fluorescent spectra have proven to be rare, since in regions with strong UV fields and densities of greater than or about 10^4 cm^{-3}, the line ratios are driven to values which are characteristic of ``collisional'' fluorescent emission (Sternberg & Dalgarno 1989 ApJ 338, 197). Shocks are common in PNe, and in most PNe observed to date in which H2 emission has been detected the H2 appears to be purely shock-excited or has a significant shock-excited contribution (e.g., Beckwith et al. 1978; Storey 1984; Latter et al. 1993; Aspin et al. 1993; Graham et al. 1993; Kastner et al. 1994; Hora & Latter 1994).

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