## 5. Analysis of the continuum flux distributionAll of the low-resolution spectra of Cet were obtained in a trailed mode and therefore cannot be calibrated in absolute units. For the same reason, the observational material cannot be used to investigate the UV light curves during the pulsation cycle. We therefore analysed the phase-averaged observations. For this purpose, we constructed the mean energy flux distribution by co-adding all of the low-resolution images for a given camera. We first filtered short and long wavelength images by a five-point filter with least-squares weights and fitted them, in the sense of the minimum least-square deviations, to SWP 29811 and LWP 9636 images, respectively. As one can see from Table 2, there are 8 low-resolution SWP images symmetrically distributed over pulsating phases. In particular, 3 images (SWP 29807, 29808 and 29811) were taken at , whereas another 3 images (SWP 29809, 29813 and 29814) at . The remaining two observations were obtained at (SWP 29810) and (SWP 29812), respectively. We therefore calculated the mean spectrum, assuming the same weights for all the low-resolution SWP images. In the case of the low-resolution LWP images taken at = 0.1901, 0.4960, 0.5565 and 0.8625, we first derived the mean spectrum from observations at = 0.4960 and 0.5565, and then calculated the arithmetic mean spectrum for this camera. These observational data are supplemented by the ground-based observations from 3300 Å to 6050 Å made by Schild et al. (1971). Thus the analysed energy flux distribution of Cet contains UV and visual observations in the form of three pieces of the spectrum corresponding to wavelength regions 1200 - 1950 Å, 1900 - 3200 Å and 3300 - 6050 Å, respectively. Next, the observed flux distribution was dereddened by means of the
mean extinction curve given by Savage & Mathis (1979). As the
first approach, we adopted the extinction curve corresponding to E(
) = 1.7 E(
) =
. The last equality corresponds to E(
) =
shown in Table 1. Having dereddened flux
distribution, we searched for the best fit of the theoretical flux to
the observed one, in the least-squares sense, by adjusting log
and log
Similar analysis was made for the high-resolution images of
Cet. Also in this case, only relative
energy flux distributions can be studied, but now due to the small
aperture used, with the exception of the LWP 6341 image. The carefully
reprocessed images were pre-filtered by a 121-point running mean
filter reducing the spectral resolution to about 5 Å, comparable
with the low-resolution IUE observations. These spectra (cf. Table 2)
were obtained with a time step of about 30 min and are well
distributed over the pulsating phase. The mean spectrum was therefore
calculated with the same weights for all images. No important
discrepancy was found between the two sets of data for the continuum
flux distribution, although using high-resolution images and assuming
E(
) =
the best fit solution exists for slightly
different parameters of log
= 4.378 and log Now, we examined how well the phase-averaged energy flux
distribution represents the steady state model. For this purpose,
theoretical fluxes generated for a nonadiabatic model of
Cet (cf. Sect. 2.2) at pulsating phases
( © European Southern Observatory (ESO) 1997 Online publication: October 15, 1997 |