Results

We demonstrate the method for a variety of simulated cases similar to those encountered in existing spectra. Cases of interest include weak absorption lines located in the vicinity of stronger lines, isolated weak lines in relatively noisy spectra, and severely blended, strong saturated lines. Since most of the objects in our program were obtained with the FOS (including the 2 00 25 slit, the 1 0 circular, and the 4 3 aperture), we have used LSFs appropriate for these apertures for our simulations. Fig. 1 shows a simulated Mg II doublet with a high

velocity component approximately 1.5 diodes (375 km s) away from the main absorption. The line parameters used are cm, km s, and cm, km s. The top left panel illustrates the input spectrum. The top right panel shows the input spectrum after convolution with the LSF of the 2 00 25 slit and the G270H grating. Gaussian noise of the order of 8%is also added. The rest of the panels illustrate each one of the three methods. The GOF panel shows the restoration produced by a straight goodness of fit (GOF) criterion, without the Pixon algorithm. For all figures, the LSF used is illustrated at the bottom of the Pixon panel. Fig. 2

shows the same components, but separated only by approximately one diode element (200 km s). The residuals with respect to the original input spectrum are plotted on top of each restored spectrum.

Table 1 contains a summary of the 3 methods examined here, for the different spectra. Overall the Pixon Based Image Restoration Method reproduces the original with higher accuracy and with fewer spurious features.

Figs. 3, 4, and 5 show examples of restored FOS

spectra towards PKS 2251+11, 3C273, and 3C286, respectively. For all three figures, the top left panel illustrates the original spectrum and the continuum used for the normalization, the top right the normalized spectrum, and the rest of the panels each method respectively. The residuals are plotted above the restored spectra.

A high velocity Mg II component associated with the Magellanic Stream was identified in the original spectrum, towards PKS 2251+11, by Bahcall et al. (1993) and Savage et al. (1993). The feature is clearly seen in the restored spectra. The 3C273 results from Fig. 4 can be compared with the higher resolution GHRS observations of 3C273 (Brandt et al. 1993, Savage et al. 1993), obtained with the G270M grating, through the Large Science Aperture (LSA). The Milky Way interstellar lines of Mn II, Fe II, Mg II and Mg I are clearly identified.

Fig. 5 shows the restored spectrum of 3C286 (Cohen et al. 1993). The object was observed with the low resolution grating G160L of the FOS and with the large 4 3 aperture. The Pixon based restoration has eliminated most of the spurious features will it has restored quite well the real lines. The two most prominent lines at the left of the damped Lyman at are the Lyman and Lyman lines at the same z.