Discovery of Far-Infrared Pure Rotational Transitions of CH+ in NGC 7027
Abstract
We report the discovery of the rotational spectrum of CH+ in the Infrared Space Observatory Long Wavelength Spectrometer (LWS) spectrum of the planetary nebula NGC 7027. The identification relies on a 1996 reanalysis of the LWS spectrum by Liu et al. and on new LWS data. The strong line at 179.62 μm (coinciding with the 212-101 transition of water vapor) and the lines at 119.90 and 90.03 μm (reported as unidentified by Liu et al.), whose frequencies are in the harmonic relation 2 : 3:4, are shown to arise from the J = 2-1, 3-2, and 4-3 rotational transitions of CH+. This identification is strengthened by the new LWS spectra of NGC 7027, which clearly show the next two rotational lines of CH+ at 72.140 and 60.247 μm. This is the first time that the pure rotational spectrum of CH+ has been observed. This discovery opens the possibility of probing the densest and warmest zones of photodissociation regions. We derive a rotational temperature for the CH+ lines of 150 +/- 20 K and a CH+/CO abundance ratio of 2-6 × 10-4.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the Principal Investigator countries: France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA.- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1997
- DOI:
- 10.1086/310729
- Bibcode:
- 1997ApJ...483L..65C
- Keywords:
-
- ISM: PLANETARY NEBULAE: INDIVIDUAL NGC NUMBER: NGC 7027;
- INFRARED: ISM: LINES AND BANDS;
- ISM: Planetary Nebulae: Individual: NGC Number: NGC 7027;
- Infrared: ISM: Lines and Bands