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Crockett NR, Bergin EA, Wang S, Lis DC, Bell TA, Blake GA, et al. Herschel observations of EXtra-Ordinary Sources (HEXOS): The Terahertz spectrum of Orion KL seen at high spectral resolution. Annual Rev. Astron. Astrophys.. 2010;521:L21 (1 to 5).
Abstract: We present the first high spectral resolution observations of Orion KL in the frequency ranges 1573.4–1702.8 GHz (band 6b) and 1788.4–1906.8 GHz (band 7b) obtained using the HIFI instrument on board the Herschel Space Observatory. We characterize the main emission lines found in the spectrum, which primarily arise from a range of components associated with Orion KL including the hot core, but also see widespread emission from components associated with molecular outflows traced by H2O, SO2, and OH. We find that the density of observed emission lines is significantly diminished in these bands compared to lower frequency Herschel/HIFI bands.
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Loenen AF, van der Werf PP, Güsten R, Meijerink R, Israel FP, Requena-Torres MA, et al. Excitation of the molecular gas in the nuclear region of M 82. Astron. Astrophys.. 2010;521:L2.
Abstract: We present high-resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M 82. Six 12CO lines, 2 13CO lines and 4 fine-structure lines have been detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures, and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n = 103.5 cm-3) clouds, with column densities of NH = 1021.5 cm-2 and a relatively low UV radiation field (G0 = 102). The remaining gas is predominantly found in clouds with higher densities (n = 105 cm-3) and radiation fields (G0 = 102.75), but somewhat lower column densities (NH = 1021.2 cm-2). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n = 106 cm-3) and UV field (G0 = 103.25). These results show the strength of multi-component modelling for interpretating the integrated properties of galaxies.
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Justtanont K, Decin L, Schöier FL, Maercker M, Olofsson H, Bujarrabal V, et al. A HIFI preview of warm molecular gas around χ Cygni: first detection of H2O emission toward an S-type AGB star. Astron. Astrophys.. 2010;521:L6.
Abstract: Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the S-type AGB star χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ Cyg.
Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been performed to derive the temperature, density, and velocity structure of the circumstellar envelope.
Results. We report the first detection of circumstellar H2O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters for the circumstellar envelope, we modelled both the ortho- and para-H2O lines. Our modelling results are consistent with the velocity structure expected for a dust-driven wind. The derived total H2O abundance (relative to H2) is (1.1±0.2) × 10-5, much lower than that in O-rich stars. The derived ortho-to-para ratio of 2.1±0.6 is close to the high-temperature equilibrium limit, consistent with H2O being formed in the photosphere.
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