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Astron. Astrophys. 345, 925-935 (1999)

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2. Observations

Our first set of observations of R Cas, made on 5 August 1996 (hereafter Observations I) during Revolution 263 of the ISO mission, have been reported elsewhere (Truong-Bach et al. 1998, henceforth Paper I). This date corresponds to a stellar phase of 0.5, at minimum stellar luminosity. The spectrum is rather noisy. A second set of observations were obtained on 6 June 1997 (hereafter Observations II) during Revolution 568, using the same grating LWS01 AOT apparatus and procedure. This date corresponds to a stellar phase of 0.2, when the luminosity was decreasing to its mean value. The total on-target time was 2417 sec for Observations II. As for Observations I, the spectral resolution element is 0.3 µm in second order (SW1-SW5; [FORMULA] [FORMULA] 93 µm) and 0.6 µm in first order (LW1-LW5; [FORMULA] [FORMULA] 80 µm) and the spectra were sampled at 1/4 of the resolution element. In order to form a complete spectrum from 43-197 µm, the sub-spectra from the ten LWS detectors were rescaled to give the same flux in regions of overlap. In almost all cases the fluxes were changed by less than 20%.

The merged LWS spectrum, which are continuum subtracted and labelled with some H2O transitions, are illustrated in Figs. 1-2. The H2O measured line fluxes for LWS are presented in Tables 1 and 2 with an estimated uncertainty [FORMULA] 40% which increases toward shorter wavelengths. Note that the present Table 1 for Observations I revises and completes that given previously (see Paper I). The FIR emission from R Cas was about 40% stronger in Observations II than in Observations I.

[FIGURE] Fig. 1. LWS Observations I (see Table 1 for line fluxes): continuum-subtracted spectrum of R Cas. Our model spectrum is displayed offset for clarity. Units: µm and 10-15 W m-2 µm-1. For this and subsequent Figures, the model spectrum was produced by convolving the predicted total line fluxes with the appropriate spectral resolution element for the observations

[FIGURE] Fig. 2. LWS Observations II (see Table 2 for line fluxes): continuum-subtracted spectrum of R Cas. Our model spectrum is displayed offset for clarity. Units: µm and 10-15 W m-2 µm-1


[TABLE]

Table 1. Observations I: calculated ([FORMULA] and [FORMULA] for [FORMULA] =3.8[FORMULA][FORMULA] cm and 3[FORMULA][FORMULA] cm respectively, see text) and observed ([FORMULA]) H2O line fluxes, for R Cas



[TABLE]

Table 2. Observations II: calculated ([FORMULA] and [FORMULA] for [FORMULA] =3.8[FORMULA][FORMULA] cm and 3[FORMULA][FORMULA] cm respectively, see text) and observed ([FORMULA]) H2O line fluxes for R Cas



[TABLE]

Table 2. (Continued)


A third set of observations were made during Revolution 564 (on 2 June 1997, hereafter Observations III), using the grating SWS06 AOT. The total on-target time was 1718 sec. The SWS nominal resolution is [FORMULA] 0.03 µm in the range 29-45 µm; however, because of rebinning in data-reduction, the model spectrum was convolved to a resolution lower ([FORMULA] 0.08 µm) to reproduce the observed linewidths. To judge the SWS data quality, we plot in Fig. 3 the SWS forward and backward scans with their estimated average continuum superimposed with a set of model H2O lines for identification. Because of low s/n and blending, the averaged line fluxes (Table 3) can be uncertain by a factor of [FORMULA] 2.

[FIGURE] Fig. 3. SWS Observations III: observed forward (solid ) and backward (dashed ) spectra; an H2O model line spectrum is plotted with the average continuum for line identification. Units: µm and [FORMULA] W m-2 µm-1


[TABLE]

Table 3. Observations III: calculated ([FORMULA] and [FORMULA] for [FORMULA] =3.8[FORMULA][FORMULA] cm and 3[FORMULA][FORMULA] cm respectively, see text) and observed H2O line fluxes from R Cas


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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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