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This paper deals with the definition of the input fluxes used for the calibration of the IUE Final Archive. The method adopted consists on the determination of the shape of the detector's sensitivity curves using IUE low resolution observations with model fluxes of the DA white dwarf G191-B2B. A scale factor was then determined so that the IUE observations of some bright OAO-2 standards match the original measurements from Meade (1978) in the spectral region 2100-2300 A. The ultraviolet fluxes of six standard stars used as input for the Final Archive photometric calibration together with the model fluxes of G191-B2B normalized to the OAO-2 scale are given. A comparison with the independent FOS calibration shows that the IUE flux scale for the Ultraviolet is 7.2% lower. We consider this mainly to be caused by the different normalization procedures. It is shown that the present flux calibration applies to spectra processed with the INES low resolution extraction software., 17 pages, 8 figures. To appear in Astronomy and Astrophysics

Pursuant to recommendations of the United Nations Conference on the Exploration and Peaceful Uses of Outer Space (UNISPACE III) and deliberations of the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS), annual UN/European Space Agency workshops on basic space science have been held around the world since 1991. These workshops contributed to the development of astrophysics and space science, particularly in developing nations. Following a process of prioritization, the workshops identified the following elements as particularly important for international cooperation in the field: (i) operation of astronomical telescope facilities implementing TRIPOD, (ii) virtual observatories, (iii) astrophysical data systems, (iv) concurrent design capabilities for the development of international space missions, and (v) theoretical astrophysics such as applications of nonextensive statistical mechanics. Beginning in 2005, the workshops focus on preparations for the International Heliophysical Year 2007 (IHY2007). The workshops continue to facilitate the establishment of astronomical telescope facilities as pursued by Japan and the development of low-cost, ground-based, world-wide instrument arrays as lead by the IHY secretariat., Comment: PDF, 9 pages

We present the intrinsic spectral energy distribution (SED) of the NLS1 Arakelian 564, constructed with contemporaneous data obtained during a multi-wavelength, multi-satellite observing campaign in 2000 and 2001. We compare it with that of the NLS1 Ton S180 and with those obtained for BLS1s to infer how the relative accretion rates vary among the Sy1 population. Although the peak of the SED is not well constrained, most of the energy is emitted in the 10-100 eV regime, constituting roughly half of the emitted energy in the optical/X-ray ranges. This is consistent with a primary spectral component peaking in the extreme UV/soft X-ray band, and disk-corona models, hence high accretion rates. Indeed, we estimate that \dot{m}~1. We examine the emission lines in its spectrum, and we constrain the physical properties of the line-emitting gas through photoionization modeling. The line-emitting gas is characterized by log n~11 and log U~0, and is stratified around log U~0. Our estimate of the radius of the H\beta-emitting region ~10 \pm 2 lt-days is consistent with the radius-luminosity relationships found for Sy1 galaxies. We also find evidence for super-solar metallicity in this NLS1. We show that the emission lines are not good diagnostics for the underlying SEDs and that the absorption line studies offer a far more powerful tool to determine the ionizing continuum of AGNs, especially if comparing the lower- and higher-ionization lines., Comment: 15 pages, 10 figures; accepted for publication in The Astrophysical Journal, LaTeX emulateapj.sty

We summarize the capabilities of the World Space Observatory (UV) Project (WSO/UV). An example of the importance of this project (with a planned launch date of 2007/8) for the study of Classical Novae is given., Comment: 4 pages, To appear in the proceeedings of the "Classical Nova Explosions" conference, eds. M. Hernanz and J. Jose, AIP

We present the extraction and processing of the IUE Low Dispersion spectra within the framework of the ESA ``IUE Newly Extracted Spectra'' (INES) System. Weak points of SWET, the optimal extraction implementation to produce the NEWSIPS output products (extracted spectra) are discussed, and the procedures implemented in INES 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 INES extraction also includes a correction for the contamination by solar light in long wavelength spectra. Examples showing the improvements obtained in INES with respect to SWET are described. Finally, the linearity and repeatability characteristics of INES data are evaluated and the validity of the errors provided in the extraction is discussed., 15 pages, 18 figures, accepted for A&ASS

We report on observations of redshifted HeII 304 A absorption in the QSO HE 2347-4342 (z=2.885, V=16.1) with the GHRS on board HST (FWHM=0.7 A). At the expected position of HeII 304 A absorption, HE 2347-4342 is the most UV-bright high redshift QSO discovered so far. We show that the HeII opacity as a function of redshift is patchy showing spectral regions with low HeII opacity (voids) and regions with high HeII opacity (troughs) and no detectable flux. Combination with high-resolution optical spectra of the Ly_alpha forest using CASPEC at the ESO 3.6m telescope shows that the voids can be explained either exclusively by Ly_alpha forest cloud absorption with a moderate N(HeII)/N(HI) ratio of 100 and turbulent line broadening or by a combination of Ly_alpha forest with N(HeII)/N(HI)=45 and thermal broadening plus a diffuse medium with tau_GP_HeII=0.3. Thus a strict upper limit to a diffuse medium is Omega_diff 2.8 is required. In case of photoionization, the troughs would require a diffuse component with a density close to Omega = 0.059 h_50^(-1.5), i.e. all baryons in the universe, which is inconsistent with the observed absence of such a component in the voids. A tentative interpretation is that we observe the epoch of partial HeII reionization of the universe with patches not yet reionized. In that case a diffuse component with Omega_diff >= 1.3 10^(-4) h_50^(-1) would be sufficient to explain the ``trough'' opacity., 12 pages, 6 figures, uses A&A l-aa.sty. To appear in A&A

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 K and the 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., Comment: 11 pages, 16 figures, accepted for publication in A&A Supplement Series