Volume 532, August 2011
|Number of page(s)||6|
|Published online||14 July 2011|
Sensitivity of 1670 GHz east and west limb line profiles to (top) torus central position and (bottom) gas dispersion velocity. Top: model calculations, performed here for a radially infinitely narrow torus located at 2, 3, 4, and 6 Saturn radii (RS), confirm that the absorbing material is located near 4 RS, and not e.g. in Saturn’s main rings at <2 RS. Bottom: model calculations for several values of molecule dispersion velocity Vrms. Best fits are obtained for Vrms = 2.3 km s-1 (resp. 2.0 km s-1) for the east (resp. west) limb spectrum. Dynamically colder models with Vrms = 0.8 km s-1 or Vrms = 0.5 km s-1 (typical of plume material ejection conditions) produce too narrow absorptions.
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Additional model fits of the 1670 GHz north, center and south observations. Determination of the torus vertical scale height H. Assuming that the column density falls as N(z) = Neq e−z/H, where z is the distance from the equatorial plane, the red, green, and dark blue curves correspond to H = 0.8, 0.4, and 0.2 RS, and Neq = (2.5, 4, 8) × 1013 cm-2, respectively. The lower absorption in the northern spectrum compared to center and south indicates that RS. Test of a physical model. The light blue curves are based on the distribution of NH2O predicted from the Cassidy & Johnson (2010) model for a 0.85 × 1028 s-1 Enceladus source rate (and shown in the left panel of Fig. 3, main text). This model provides an overall good match of all H2O lines, including the sorth-south asymmetry. Although not shown here, this physical model also gives a good match of the 557 and 1113 GHz absorption, and also underestimates the 987 GHz absorption by a factor ~1.7.
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© ESO, 2011
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