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In this paper we document the results of the study which led to the ripple correction and absolute calibration algorithms applied to the high resolution spectra processed with the  software for the Final Archive of the  Project. In this analysis, based on a very large number of spectra, we find that both the Kand αparameters (not only the former as previously believed) vary with order number. This fact, together with the finding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in . The internal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute calibration algorithms here described apply also to  data processed and distributed with the  system.

This paper discusses the overall quality of  high resolution data processed with the software in terms of flux and wavelength accuracy. It also describes the processing of  high resolution spectra within the framework of the ESA “IUE Newly Extracted Spectra” () System. This system provides the  high resolution data in two formats: the high resolution “concatenated” spectra, in which the spectral orders are connected, eliminating the overlap regions through a procedure designed to optimize the signal-to-noise ratio at the edges of the orders, and the “rebinned” spectra, i.e. the high resolution concatenated spectra resampled into the low resolution wavelength domain. Our study reveals the existence of a significant discrepancy in the wavelength scales of short and long wavelength  high resolution spectra. The  processing applies a correction of +17.7 km s-1to the wavelength scale of the high resolution SWP spectra in order to provide an internally consistent velocity scale. Similarly, suitable corrections have been applied to long wavelength small aperture spectra. The new wavelength scale is, within the errors, in good agreement with the optical velocity scale.

We present the extraction and processing of the  Low Dispersion spectra within the framework of the ESA "IUE Newly Extracted Spectra” () System. Weak points of , the optimal extraction implementation to produce the  output products (extracted spectra) are discussed, and the procedures implemented in  to solve these problems are outlined. The more relevant modifications are: 1) the use of a new noise model, 2) a more accurate representation of the spatial profile of the spectrum and 3) a more reliable determination of the background. The  extraction also includes a correction for the contamination by solar light in long wavelength spectra. Examples showing the improvements obtained in with respect to are described. Finally, the linearity and repeatability characteristics of  data are evaluated and the validity of the errors provided in the extraction is discussed.

We present a wide multi-wavelength database of most observations of the quasar 3C 273 obtained during the last 30 years. This database is the most complete set of observations available for an active galactic nucleus (AGN). It contains nearly 20 000 observations grouped together into 70 light curves covering 16 orders of magnitude in frequency from the radio to the γ-ray domain. The database is constituted of many previously unpublished observations and of most publicly available data gathered in the literature and on the World Wide Web (WWW). It is complete to the best of our knowledge, except in the optical (UBV) domain where we chose not to add all observations from the literature. In addition to the photometric data, we present the spectra of 3C 273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the X-ray domain, we used the spectral fit parameters from the literature to construct the light curves. Apart from describing the data, we show the most representative light curves and the average spectrum of 3C 273. The database is available on the WWW in a homogeneous and clear form and we wish to update it regularly by adding new observations.

This paper discusses the overall quality of IUE high resolution data processed with the NEWSIPSsoftware in terms of flux and wavelength accuracy. It also describes the processing of NEWSIPS high resolution spectra within the framework of the ESA ``IUE Newly Extracted Spectra'' (INES) System. This system provides the IUE high resolution data in two formats: the high resolution ``concatenated'' spectra, in which the spectral orders are connected, eliminating the overlap regions through a procedure designed to optimize the signal-to-noise ratio at the edges of the orders, and the ``rebinned'' spectra, i.e. the high resolution concatenated spectra resampled into the low resolution wavelength domain. Our study reveals the existence of a significant discrepancy in the wavelength scales of short and long wavelength NEWSIPS high resolution spectra. The INES processing applies a correction of +17.7 km s$^{-1}$ to the wavelength scale of the high resolution SWP spectra in order to provide an internally consistent velocity scale. Similarly, suitable corrections have been applied to long wavelength small aperture spectra. The new wavelength scale is, within the errors, in good agreement with the optical velocity scale.

In this paper we document the results of the study which led to the ripple correction and absolute calibration algorithms applied to the high resolution spectra processed with the NEWSIPS software for the Final Archive of the IUE Project. In this analysis, based on a very large number of spectra, we find that both the $K$ and $\alpha$ parameters (not only the former as previously believed) vary with order number. This fact, together with the finding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in IUESIPS. The internal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute calibration algorithms here described apply also to IUE data processed and distributed with the INES system.