Justtanont, K., Decin, L., Schöier, F. L., Maercker, M., Olofsson, H., Bujarrabal, V., et al. (2010). A HIFI preview of warm molecular gas around χ Cygni: first detection of H2O emission toward an S-type AGB star. Astron. Astrophys., 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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Hartogh, P., Jarchow, C., Lellouch, E., de Val-Borro, M., Rengel, M., Moreno, R., et al. (2010). Herschel/HIFI observations of Mars: First detection of O2 at submillimetre wavelengths and upper limits on HCl and H2O2. Astron. Astrophys., 521, L49.
Abstract: We report on an initial analysis of Herschel/HIFI observations of hydrogen chloride (HCl), hydrogen peroxide (H2O2), and molecular oxygen (O2) in the Martian atmosphere performed on 13 and 16 April 2010 (Ls ~ 77°). We derived a constant volume mixing ratio of 1400 ± 120 ppm for O2 and determined upper limits of 200 ppt for HCl and 2 ppb for H2O2. Radiative transfer model calculations indicate that the vertical profile of O2 may not be constant. Photochemical models determine the lowest values of H2O2 to be around Ls ~ 75° but overestimate the volume mixing ratio compared to our measurements.
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Decin, L., Justtanont, K., De Beck, E., Lombaert, R., de Koter, A., Waters, L. B. F. M., et al. (2010). Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen by Herschel/HIFI. Astron. Astrophys., 521, L4.
Abstract: During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the high-resolution HIFI spectrometer onboard Herschel. We report on the first detection of H216O and the rarer isotopologues H217O and H218O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of $6.6 \times 10^{-5}$, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.
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de Graauw, T., Caux, E., Guesten, R., Helmich, F., Pearson, J., Phillips, T. G., et al. (2005). The Herschel-heterodyne instrument for the far-infrared (HIFI). In Bulletin of the American Astronomical Society (1219). Bulletin of the American Astronomical Society, 37.
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Crockett, N. R., Bergin, E. A., Wang, S., Lis, D. C., Bell, T. A., Blake, G. A., et al. (2010). Herschel observations of EXtra-Ordinary Sources (HEXOS): The Terahertz spectrum of Orion KL seen at high spectral resolution. Annual Rev. Astron. Astrophys., 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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