Search

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.

It is well-known that when an astronomical image is collected by a telescope, the measured intensities at pixels near the edge of the image may depend on the intensity of the object outside of the field of view (FOV) of the instrument. This makes the deconvolution of astronomical images troublesome. Standard approaches for solving this problem artificially extend the object outside the FOV via the imposition of boundary conditions (BCs). Unfortunately, in many instances the artificially extended object has little in common with the object itself outside of the FOV. This is most pronounced in the case of objects close to the boundary of the image and/or extended objects not completely contained in the image domain. In such cases, an inaccurate extension of the image outside of the FOV can introduce non-physical edge effects near the boundary that can degrade the quality of the reconstruction. For example, if the BCs used result in an extended image that is discontinuous at the boundary, these edge effects take the form of ripples (Gibbs oscillations). In this paper, we extend to least-squares (LS) algorithms a method recently proposed by Bertero & Boccacci (2005, A&A, 437, 369) in the context of the Richardson-Lucy (RL) algorithm for the restoration of images contaminated by Poissonian noise. The most important characteristic of the proposed approach is that it does not impose any kind of artificial BCs and is therefore free from edge effects. For this reason it can be considered the natural method for the restoration of images via LS algorithms.

It has been shown that the restoration of a set of images of a fixed object, blurred by different space-invariant point spread functions (PFS) and contaminated by additive Gaussian noise, can be reformulated as a standard single-image least-squares (LS) deblurring problem with remarkable advantages that concern both the computational burden as well as the storage memory. The only difficulty is represented by the fact that the resulting single-image can have negative values. In a recent paper by Anconelli et al. (2005, A&A, 430, 731) this approach has been coupled with the standard Richardson-Lucy (RL) algorithm. However, their way of dealing with negative values of the single-image is not the most appropriate one. In this note we propose a different method which provides better reconstructions and convergence rates.

It is well-known that the noise associated with the collection of an astronomical image by a CCD camera is, in large part, Poissonian. One would expect, therefore, that computational approaches that incorporate this a priori information will be more effective than those that do not. The Richardson-Lucy (RL) algorithm, for example, can be viewed as a maximum-likelihood (ML) method for image deblurring when the data noise is assumed to be Poissonian. Least-squares (LS) approaches, on the other hand, arises from the assumption that the noise is Gaussian with fixed variance across pixels, which is rarely accurate. Given this, it is surprising that in many cases results obtained using LS techniques are relatively insensitive to whether the noise is Poissonian or Gaussian. Furthermore, in the presence of Poisson noise, results obtained using LS techniques are often comparable with those obtained by the RL algorithm. We seek an explanation of these phenomena via an examination of the regularization properties of particular LS algorithms. In addition, a careful analysis of the RL algorithm yields an explanation as to why it is more effective than LS approaches for star-like objects, and why it provides similar reconstructions for extended objects. We finish with a convergence analysis of the RL algorithm. Numerical results are presented throughout the paper. It is important to stress that the subject treated in this paper is not academic. In fact, in comparison with many ML algorithms, the LS algorithms are much easier to use and to implement, often provide faster convergence rates, and are much more flexible regarding the incorporation of constraints on the solution. Consequently, if little to no improvement is gained in the use of an ML approach over an LS algorithm, the latter will often be the preferred approach., High resolution images are available upon request. submitted to A&A

We consider the estimation of the regularization parameter for the simultaneous deblurring of multiple noisy images via Tikhonov regularization. We approach the problem in three ways. We first reduce the problem to a single-image deblurring for which the regularization parameter can be estimated through a classic generalized cross-validation (GCV) method. A modification of this function is used for correcting the undersmoothing typical of the original technique. With a second method, we minimize an average least-squares fit to the images and define a new GCV function. In the last approach, we use the classical $GCV$ on a single higher-dimensional image obtained by concatanating all the images into a single vector. With a reliable estimator of the regularization parameter, one can fully exploit the excellent computational characteristics typical of direct deblurring methods, which, especially for large images, makes them competitive with the more flexible but much slower iterative algorithms. The performance of the techniques is analyzed through numerical experiments. We find that under the independent homoscedastic and Gaussian assumptions made on the noise, the three approaches provide almost identical results with the first single image providing the practical advantage that no new software is required and the same image can be used with other deblurring algorithms., Comment: To appear in Astronomy & Astrophysics

Point-source contamination in high-precision Cosmic Microwave Background (CMB) maps severely affects the precision of cosmological parameter estimates. Among the methods that have been proposed for source detection, wavelet techniques based on ``optimal'' filters have been proposed.In this paper we show that these filters are in fact only restrictive cases of a more general class of matched filters that optimize signal-to-noise ratio and that have, in general, better source detection capabilities, especially for lower amplitude sources. These conclusions are confirmed by some numerical experiments. \keywords{Methods: data analysis -- Methods: statistical, Comment: 6 pages, 3 figures

The colliding-wind binary system WR140 (HD193793, WC7pd+O4-5, P=7.94 yr) was monitored in the ultraviolet by IUE from 1979 to 1994 in 35 short-wavelength high-resolution spectra. An absorption-line radial-velocity solution is obtained from the photospheric lines of the O component, by comparison with a single O star. The resulting orbital parameters, e=0.87 +/- 0.05, w=31 degrees +/- 9 degrees and Ko star=25 +/- 15 km s(-1), confirm the large eccentricity of the orbit, within the uncertainties of previous optical studies. This brings the weighted mean UV-optical eccentricity to e=0.85 +/- 0.04. Occultation of the O-star light by the WC wind and the WC+O colliding-wind region results into orbital modulation of the P-Cygni profiles of the C II, CIV and Si IV resonance lines. Near periastron passage, the absorption troughs of those resonance-line profiles increase abruptly in strength and width, followed by a gradual decrease. In particular, near periastron the blue black-edges of the P-Cygni absorption troughs shift to larger out ow velocities. We discuss that the apparently larger wind velocity and velocity dispersion observed at periastron could be explained by four phenomena: (i) geometrical resonance-line eclipse effects being the main cause of the observed UV spectral variability, enhanced by sightline crossing of the turbulent wind-wind collision zone; (ii) the possibility of an orbital-plane enhanced WC7 stellar wind; (iii) possible common-envelope acceleration by the combined WC and O stellar radiation fields; and (iv) possible enhanced radiatively driven mass loss due to tidal stresses, focused along the orbiting line of centers.

This paper deals with the performance of the cross-correlation function (CCF) for the case of time series which contain only a limited number of data. Often, in this case the data span a time interval shorter than the characteristic timescale of the underlying signal. Although various papers recently have been dedicated to this subject, most authors limit their approach to numerical simulations only, resulting in a lack of generality and no explanation of the difficulties associated with the use of the CCF in many practical situations. We show here, on the basis of theoretical considerations, that the limits of the CCF can be understood from the fact that in the construction of this function the low-frequency components of the signals contribute more than the high-frequency components. This result explains also the robustness of the CCF to the broadband noise.

The reporting period has shown that Space has become a firmly established domain in observational Astrophysics, also in the low energy astrophysics area. The launching of new spacecraft is always an important addition to the capabilities of the Astronomers, but the availability of space observatories is strongly affected by the fact that they disappear as their subsystems become damaged or, for other reasons, become inoperable. The relatively short life of astronomical space facilities has generated new dynamic in the life cycle of observational tools for the astronomer, rather different from that for ground facilities. Launch failures or the final in-orbit functionality verification can also very strongly affect the availability of observational capabilities in space astrophysics. The only spacecraft designed without this built-in life time restriction, is the Hubble Space Telescope, which can be serviced by the Space Shuttle.

We consider the question of numerical treatment of irregularly sampled time series. This problem is quite common in astronomy because of factors such as the day-night alternation, weather conditions, nonobservability of the objects under study, etc. For this reason an extensive literature is available on this subject. Most of the proposed techniques, however, are based on heuristic arguments, and their usefulness is essentially in the estimation of power spectra and/or autocovariance functions. Here we propose an approach, based on the reasonable assumption that many signals of astronomical interest are the realization of band-limited processes, which can be used to fill gaps in experimental time series. By using this approach we propose several reconstruction algorithms that, because of their regularization properties, yield reliable signal reconstructions even in case of noisy data and large gaps. A detailed description of these algorithms is provided, their theoretical implications are considered, and their practical performances are tested via numerical experiments. MATLAB software implementing the methods described in this work is obtainable by request from the authors.

We present here the analysis of ultraviolet spectra from IUE and an X-ray spectrum from ROSAT PSPC observations of the X-ray weak, far-infrared loud AGN, PG 1126-041 (Mrk 1298). The first UV spectra taken in June 1992, simultaneously with ROSAT, show strong absorption lines of NV, CIV and SiIV, extending over a velocity range from -1000 to -5000 km/s with respect to the corresponding line centre. Our analysis shows that the Broad Emission Line Region (BELR) is, at least partially, covered by the material causing these absorption lines. In the IUE spectrum taken in Jan. 1995, the continuum was a factor of two brighter and the UV absorption lines are found to be considerably weaker than in 1992, but only little variation in the emission line fluxes is found. With UV spectral indices of A_{uv} \simeq 1.82 and 1.46 for the 1992 and 1995 data, the far UV spectrum is steep. Based on the emission line ratios and the broad band spectral energy distribution, we argue that the steepness of the UV spectrum is unlikely to be due to reddening. The soft X-ray emission in the ROSAT band is weak. A simple power-law model yields a very poor fit with a UV-to-X-ray spectral index A_{uvx}=2.32. Highly ionized (warm) absorption is suggested by the ROSAT data. After correcting for a warm absorber, the optical to X-ray spectral slope is close to the average of A{uvx}\simeq 1.67 for radio quiet quasars., Comment: 8 pages, 9 postscript figures. Mon. Not. Roy. Astr. Soc., accepted

We present an analysis of the ultraviolet and X-Ray variability of the Broad- Line-Radio Galaxy 3C390.3 over 15 years. The UV continuum showed large variations with amplitudes of up to a factor of 10. We find: (1) The variations of CIV and Ly_alpha are highly correlated with the UV continuum, and are delayed with respect to the continuum variations by 50-110 days with the red wing of both CIV and Ly_alpha , leading the blue wing; (2) The CIV/Ly_alpha ratio is positively correlated with both the continuum flux and UV line strength, a behavior different from other AGNs studied so far; (3) The blue sides of the Ly_alpha and CIV profiles are similar to the blue side of the Balmer lines, while the red sides are different, suggesting a different origin for the red peak in the Balmer lines. Our results suggest: (1) The broad CIV and Ly_alpha emitting gas is infalling towards the central object; (2) The overall behaviour of the CIV/Ly_alpha ratio and the absence of a big blue bump, strongly indicate the coexistence of optically thick as well as optically thin BLR clouds; (3) Assuming circular symmetry and predominantly circular motion, the BLR gas is situated at 83$\pm$25 lightdays from the central source; (4) Under these assumptions and with the derived circular velocity of $v_{rot} \simeq$ 2850 km s$^{-1}$, the central mass inside this radius is confined to $1.3~10^8 M\odot < M_{CM}< 4.0~10^8 M\odot$; (6) Comparing our results with those obtained from VLBI and observations of the Fe $K\alpha$ line, suggests the association of the BLR with a disk, inclined at 98$\pm$12 degrees with respect to the direction of superluminal motion of the radio blobs.

The large amplitude of the variations of the Seyfert I Galaxy Fairall-9 between 1978 and 1991 make this Active Galaxy especially suitable for a combined study in terms of reverberation analysis and photoioniza- tion modeling over the velocity eld of the broad lines of its ultraviolet spectrum. We have combined our ultravio- let data with those available at other wavelengths to de- rive the intrinsic ionizing continuum and to compare the predictions of the photoionization models with the obser- vations. The UV continuum varies with a factor of 33 4 on a characteristic time scale of 182 days. The intrinsic spectral index UV-optical is = 0:07 0:02 and the optical variations do not lag behind the UV variations at the mean sampling interval of 96 days. In the near IR, the J band flux presents a direct extension of the UV-optical continuum (J UV = 0:07 0:05). Only at low flux levels is the 2 10 keV flux proportional to the UV contin- uum, at higher UV flux levels proportionality between the X-rays and the UV brightness breaks down. The con- tinuum spectral energy distribution (SED) of the nu- cleus supports the previously reported FIR-NIR excess associated with 0.02 M dust at a distance of some 400 100 light-days, as well as a soft X-ray excess, possi- bly associated with the reprocessing on an accretion disk of the hard X-rays emitted from a region above the disk. The presence of strong Fe Kline in the GINGA spec- tra of this galaxy does lend support to this model. Line prole variability has been used to isolate four gaussian line components, which are sucient to describe all lines at all levels of brightness in a consistent way: one nar- row (i.e. unresolved at the IUE resolution), and three broad components: a central (velocity same as the nar

A detailed emission-line decomposition has been made from 15 years of observations with the IUE satellite of the highly variable Seyfert 1 galaxy Fairall 9, allowing us to study the line variability as a function of velocity and continuum brightness. The variability over the different velocity domains of the broad lines has been related to the continuum variability over a large wavelength domain from the X-rays to the infrared. Clear delays were established between the redshifted and blueshifted parts of the lines in Lyα and C IV, with the red sides of the lines responding faster with no delay and the blue sides responding with a delay of some 230 days. The observed spectral variability behavior of the continuum has been used as input for photoionization model calculations and the combined constraints from the models and differences for gas at different velocities define the structure and motions in the BLR.

We summarize the nature of modern astronomical archives with special reference to spectroscopic data archives and illustrate in which ways archives can play a role in the accelerated development of Basic Space Sciences in the developing countries. Some of the conflicting issues in the current planning of archives are addressed. Astronomical spectroscopic archives constitute a tool to progress towards an intellectual environment which is required to stimulate the sociological evolution which can support the peaceful and harmonious development of states. This is especially true under the conditions generated by the rapid evolution of technology in the industrialized countries.

We present the first results of the IUE monitoring campaign of the WC7+O4-5 binary system WR140. Thirty-four high-resolution short-wavelength spectra were obtained in 1979—93, i.e., over more than one orbital period of 7.9 yr. The spectra show variations in the strong resonance lines of CIV and SiIV: large variations occur at the blue edges of the absorption parts of their P-Cygni profiles just after periastron passage. The observed profile changes are discussed in terms of a velocity variation at periastron passage and/or turbulence in the sightline to the O4—5 star at this time.

We have analysed optical spectra of the high-redshift QSO HS l700+6416 (z = 2.72) discovered during the Hamburg survey. These spectra are of moderately high resolution (0.47 A) in the Lya forest and of low resolution (10 A) longward of the Ly α emission line. In the velocity range between Ly β and Ly α-3000 km s −1 (to avoid the'proximity effect'), we detect 3 8 Ly α absorption lines at the 4 σ level. Following previous authors, we fit the rest equivalent width probability distribution of absorbers with a functional form N(W)∞exp(−W/W * ) and the H I column density probability distribution of absorbers with a functional form N(N H1 )∞N H1 −β

Unrealistic weight-loss goals may impede the success of weight-loss attempts. The aim of this study was to examine the frequency of unrealistic goals and their association with other patient characteristics at the start of a weight-loss program. For patients with a body mass index (calculated as kg/m 2 ) of 30 to 35, 35 to 40, or 40 to 50, medically advised weight-loss goals were set at 10%, 15%, and 20% of current weight, respectively. Personal weight-loss goals exceeding the medically advised goal by >50% were considered unrealistic. Obesity-related beliefs were measured by the "Obesity Cognition Questionnaire" and the eating-behavior self-efficacy scale of the "Obesity Psychosocial State Questionnaire." From September 2003 until March 2006, 90 patients were enrolled in the study, 26 men and 64 women, with a mean age of 43 years (range=18 to 68 years) and body mass indexes ranging from 30 to 50. Unrealistic goals were observed in 49% of the patients and were more frequent in younger patients ( P =0.03), in patients attributing their obesity to physical causes ( r =0.35, P =0.001), and in patients not attributing their obesity to behavioral causes ( r =−0.28, P =0.008). This study confirms that discrepancies in weight-loss goals between obese patients and professionals occur frequently. Because unrealistic goals can hamper long-term outcomes of weight-loss programs, better outcomes could possibly be achieved by addressing unrealistic weight-loss goals before treatment.

The overall development of ESA’s Space Transportation Programme can be perceived in two major phases. The first phase finished with the transfer of the ARIANE 1-4 launch systems to Arianespace for utilisation and commercialization. The second phase was started after the success of the ARIANE launcher programme had created a sound basis for Europe’s space industry in the evolving commercial space transportation market. This has lead to the definition of a second phase of the launcher development program which is expected to fulfil the needs for transport into space for many years to come. The wide objectives of the program makes it not only suitable for commercial applications but can also be expected to cover the launching needs for future Space Astrophysics missions.Market studies of the future commercial space transportation needs show growing satellite masses and an increased worldwide competition. Europe therefore needs a powerful launcher with improved cost-effectiveness and improved reliability for geostationary missions. On the other hand the discussion about the optimum launcher, spacecraft size and orbits for Astronomy missions, as well as for Space Science missions in general, is still a matter under debate, as explained by Dyson elsewhere in these Proceedings. The experience obtained with IUE and EXOSAT-Observatory satellites which, due to their general user nature, do not have a rigidly preplanned observing program - seem to suggest that, at least for operational motives, high orbits appear preferable for such satellites. This is especially true as compared to the operational and planning difficulties foreseen with the recently launched Hubble Space Telescope, which is in low earth orbit (LEO). Of course, for firmly pre-scheduled observatories with a predetermined Science program, such as COBE and HIPPARCOS, this choice may not be obvious.

The World Space Observatory project model was first introduced in the 5th UN/ESA workshop. Over time, the original concept has been further developed to evaluate how such project could become a reality. An assessment study has been made of the WSO-Ultraviolet (WSO/UV) as this was considered the best implementation model since the world-wide need for such project in the astrophysics community clearly exists. Also in the developing world considerable expertise exists through the wide distribution of the ultraviolet spectroscopic archive INES from ESA. Therefore WSO/UV presents the best chance of success for the next stage in the accelerated BSS evolution needed for sustainable development in the pre-industrial countries. The WSO/UV Implementation Committee (WIC), composed of scientists from some 14 countries, is the leading organization in this project. We will here describe the implementation model for WSO/UV and highlight the scientific importance as well as the plans for the future.

The origin and evolution of the UN/ESA Workshops on Basic Space Science (BSS) is discussed. We highlight here the motivation and results in global terms. The various new insights in the role of BSS in a sustainable development are indicated.

Contains fulltext : 56140.pdf (Publisher’s version ) (Closed access) The objective of this study was to examine whether beliefs about the cause, consequences, time line, and control of obesity are predictors of the amount of weight loss after an 8-week, low-calorie diet consisting of meal replacements. Forty-eight women and 18 men, mean age=45.9 (range=23 to 73 years) years and body mass index between 30 and 50 participated in a weight-loss program. Beliefs were measured at baseline by the Obesity Cognition Questionnaire and by an eating behavior self-efficacy scale. Correlational and regression analyses were performed to examine whether beliefs predicted weight change. Changes in body mass index, waist circumference, and blood pressure were significant (P

The World Space Observatory (WSO/UV) is a space project for an ultraviolet telescope which has to fulfill the needs and scientific requirements of a worldwide community. For this very reason, the project development is distributed among many countries, scientific institutes and companies. The technical requirements relevant for the AVO efficient performance have to be included and improved for the WSO/UV project. These requirements are briefly outlined in this contribution.

In this paper we consider the problem of the limits concerning the physical information that can be extracted from the analysis of one or more time series (light curves) typical of astrophysical objects. On the basis of theoretical considerations and numerical simulations, we show that with no a priori physical model there are not so many possibilities to obtain interpretable results. For this reason, the practice to develop more and more sophisticated statistical methods of time series analysis is not very productive. Only techniques of data analysis developed in a specific physical context can be expected to provide useful results. The field of {\it stochastic dynamics} appears to be an useful framework for such an approach. In particular, it is shown that modelling the experimental time series by means of the stochastic differential equations (SDE) represents a valuable tool of analysis. For example, the use of SDE permits to make the analysis of a continuous signal independent from the frequency sampling with which the experimental time series have been obtained. In this respect, an efficient approach based on the extended Kalman-filter technique is presented. Freely downloadable software is made available., 6 Figures. submitted to A&A

Digital deblurring of images is an important problem that arises in multifrequency observations of the Cosmic Microwave Background (CMB) where, because of the width of the point spread functions (PSF), maps at different frequencies suffer a different loss of spatial resolution. Deblurring is useful for various reasons: first, it helps to restore high frequency components lost through the smoothing effect of the instrument's PSF; second, emissions at various frequencies observed with different resolutions can be better studied on a comparable resolution; third, some map-based component separation algorithms require maps with similar level of degradation. Because of computational efficiency, deblurring is usually done in the frequency domain. But this approach has some limitations as it requires spatial invariance of the PSF, stationarity of the noise, and is not flexible in the selection of more appropriate boundary conditions. Deblurring in real space is more flexible but usually not used because of its high computational cost. In this paper (the first in a series on the subject) we present new algorithms that allow the use of real space deblurring techniques even for very large images. In particular, we consider the use of Tikhonov deblurring of noisy maps with applications to {\it PLANCK}. We provide details for efficient implementations of the algorithms. Their performance is tested on Gaussian and non-Gaussian simulated CMB maps, and PSFs with both circular and elliptical symmetry. Matlab code is made available., 14 pages, 16, figures, A&A in press; high quality figures available upon request to the authors

We consider the simultaneous deblurring of a set of noisy images whose point spread functions are different but known and spatially invariant, and the noise is Gaussian. Currently available iterative algorithms that are typically used for this type of problem are computationally expensive, which makes their application for very large images impractical. We present a simple extension of a classical least-squares (LS) method where the multi-image deblurring is efficiently reduced to a computationally efficient single-image deblurring. In particular, we show that it is possible to remarkably improve the ill-conditioning of the LS problem by means of stable operations on the corresponding normal equations, which in turn speed up the convergence rate of the iterative algorithms. The performance and limitations of the method are analyzed through numerical simulations. Its connection with a column weighted least-squares approach is also considered in an appendix., Comment: 9 pages, 16 figures. High resolution figures available upon demand. To appear in A&A

It is the purpose of the paper to describe the virtues of time-frequency methods for signal processing applications, having astronomical time series in mind. Different methods are considered and their potential usefulness respectively drawbacks are discussed and illustrated by examples. As areas where one can hope for a successful application of joint time-frequency analysis (JTFA), we describe specifically the problem of signal denoising as well as the question of signal separation which allows to separate signals (possibly overlapping in time or frequency, but) which are living on disjoint parts of the time-frequency plane. Some recipes for practical use of the algorithms are also provided., 16 pages 19 figures. A&A in press

The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibilty, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering long-slit capability over the same band with R~1,000. In addition, a number of UV and optical imagers view adjacent fields to that sampled by the spectrometers. Their performance compares well with that of HST/ACS and the spectral capabilities of WSO rival those of HST/COS., Comment: 11 pages, including 7 figures and 5 tables To be published in Proc SPIE, vol 4854

In this paper we will consider the problem of the numerical simulation of non-Gaussian, scalar random fields with a prescribed correlation structure provided either by a theoretical model or computed on a set of observational data. Although, the numerical generation of a generic, non-Gaussian random field is a trivial operation, the task becomes tough when constraining the field with a prefixed correlation structure. At this regards, three numerical methods, useful for astronomical applications, are presented. The limits and capabilities of each method are discussed and the pseudo-codes describing the numerical implementation are provided for two of them., Comment: 37 pages, 9 figures, accepted by P.A.S.P

THE intrinsic extreme ultraviolet (EUV) spectrum of quasars, in which spectral lines of He and CNO ions should appear, is in most cases strongly absorbed by the hydrogen Lyman continuum of intergalactic matter at cosmological distances. The bright quasar HS1700 + 6416 (at redshift z = 2.72), from the Hamburg survey1, is a fortuitous exception, the line of sight towards it being relatively transparent. Here we report detailed ultraviolet spectroscopic measurements of HS1700 + 6416, obtained with the Hubble Space Telescope. We observe a rich absorption line spectrum, in which many EUV resonance lines (including He I, O II to O v, and N III and N IV) are seen. The O/C abundance ratios inferred from the line-strengths are higher than Solar System values by factors of 3 to 5. This suggests that the absorbing material is halo gas of early galaxies, from which population II stars have yet to form, oxygen being a primary nucleosynthesis product from a first generation of massive stars.

We introduce some fundamental concepts relating to the nature of “Astrobiology” to evaluate the relevance of Space Science in these activities. It is clear that the strength of the current space missions is predominantly in establishing possible pre-biotic conditions. The overall importance of the missions of the ESA Science Programme Horizons 2000 to the general studies globally collected in the “Search for life” are highlighted through a description of the relevance of the missions IUE, Hipparcos, HST, ISO, SOHO, Giotto, MARS EXPRESS, ROSETTA, CASSINI-HUYGENS.

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. Sin financiación 1.630 JCR (1999) Q2, 16/36 Astronomy and Astrophysics UEM

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

Since most observational material relevant for the variability of Active Galaxies is not available in regularly sampled lightcurves, such as have been collected by the AGN WATCH, using more data, to obtain reverberation results for more objects, one will have to rely on irregularly sampled lightcurves. Previous analyses of irregularly sampled observations suggest that it is possible to obtain results from such data sets. To evaluate the statistical significance of such determinations, we constructed simulated observational data of a stochastic process with random sampling, different transfer functions and noise conditions. These allow to estimate the statistical significance of cross-correlation calculations (CCF) on irregularly sampled data, as compared with the known input process. The results suggest that, in these conditions, the CCF is sufficiently robust to allow delays to be determined, but a careful error treatment is required.

Carol Lonsdale, Infrared Processing and Analysis Center, California Institute of Technology/JPL, Pasadena, CA, USA

The presence of narrow high-temperature emission lines from nitrogen-rich gas close to SN 1987A has been the principal observational constraint on the evolu- tionary status of the supernova's progenitor. A new analysis of the complete five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A (1987.2--1992.3) provide fluxes for the N V 1240, N IV] 1486, He II 1640, OIII] 1665, NIII] 1751, and CIII] 1908 lines with significantly reduced random and systematic errors and reveals significant short-term fluctuations in the light curves. The N V, N IV] and N III] lines turn on sequentially over 15 to 20 days and show a progression from high to low ionization potential, implying an ioni- zation gradient in the emitting region. The line emission turns on suddenly at 83+/-4 days after the explosion, as defined by N IV]. The N III] line reaches peak luminosity at 399+/-15 days. A ring radius of (6.24+/-0.20)E{17} cm and inclination of 41.0+/-3.9 is derived from these times, assuming a circular ring. The probable role of resonant scattering in the N V light curve introduces systematic errors that leads us to exclude this line from the timing analysis. A new nebular analysis yields improved CNO abundance ratios N/C=6.1+/-1.1 and N/O=1.7+/-0.5, confirming the nitrogen enrichment found in our previous paper. From the late-time behavior of the light curves we find that the emission origi- nates from progressively lower density gas. We estimate the emitting mass near maximum (roughly 400 days) to be roughly 4.7E{-2} solar masses, assuming a filling factor of unity and an electron density of 2.6E4 cm^{-3}. These results are discussed in the context of current models for the emission and hydrodynamics of the ring., 38 pages, AASTeX v.4.0, 13 Postscript figures; ApJ, in press

We present the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short time-scale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the {\it International Ultraviolet Explorer} (IUE) for 9.3 days, yielding a pair of LWP and SWP spectra every $\sim$70 minutes, and during four-hour periods for 4 days prior to and 5 days after the continuous monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 \AA\ to 2688 \AA\ went through four significant and well-defined ``events'' of duration 2 -- 3 days during the continuous monitoring period. We find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller time scales (i.e., a few days). The continuum variations in all of the UV bands are {\it simultaneous} to within an accuracy of about 0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip), and do not correlate well with continuum light curves over the (short) duration of the campaign, because the time scale for continuum variations is apparently smaller than the response times of the emission lines., Comment: 39 pages, LaTeX, including 7 PostScript figures; To appear in the ApJ (October 20, 1996) Vol. 470

In the 1970s the US National Aeronautics and Space Administration (NASA), the UK Science and Engineering Research Council (SERC) and the European Space Agency (ESA) joint together to build, launch and operate the International Ultraviolet Explorer (IUE) satellite. This satellite was designed to enable scientists around the globe to study ultraviolet (UV) radiation.

We present the first results of the IUE monitoring campaign of the WC7+O4-5 binary system WR140. Thirty-four high-resolution short-wavelength spectra were obtained in 1979–93, i.e., over more than one orbital period of 7.9 yr. The spectra show variations in the strong resonance lines of CIV and SiIV: large variations occur at the blue edges of the absorption parts of their P-Cygni profiles just after periastron passage. The observed profile changes are discussed in terms of a velocity variation at periastron passage and/or turbulence in the sightline to the 04–5 star at this time.

Ultraviolet high-resolution SWP images of the binary system WR140 (HD 193793, WC7+O4-5) were taken with IUE over the period 1979 – 1993. This poster presents a radial-velocity study of the absorption lines, attributed to the O-type component, applying the infrared period of P = 2900 days.

The end product of the IUE mission will be a Final Archive containing all scientific and calibration data acquired with the satellite, uniformly processed with enhanced techniques and calibrations. This product is unique in that the development of the specifications for the IUE Final Archive has been guided to a large degree by input from the astronomical community. IUE is a collaborative project between NASA, ESA, and SERC. All three agencies have made important contributions to the development and implementation of the IUE Final Archive processing system. These new image processing techniques exploit the two-dimensional fixed pattern inherent in raw IUE data as a registration fiducial for photometric correction, utilize a single, flux-conserving resampling algorithm and a signal-weighted extraction method for the spectral data. The absolute flux calibration has also been redefined, with the relative fluxes based on models of white dwarf stars. These improvements result in increased signal-to-noise ratio and spectral resolution for many IUE images and render the dataset fully intercomparable. To maximize further the utility of the Final Archive, all fundamental observational and processing information about each image acquired with IUE has been verified and transcribed into the processed output files. Spectral data processed for the IUE Final Archive will begin to be available during 1993.

Editorial. Part 1: I. Achievements of the Present Generation of Space Observatories. II. Achievements of the Present Generation of Ground--Based Telescopes. III. Stars. IV. Interstellar Medium and Galaxies. V. Cosmology. VI. Observations at Many Wavelengths: Panel Discussion on Coordination of Observations at Many Wavelengths. VII. The New Generation of Large Ground--Based Telescopes. VIII. The New Generation Space Telescopes. IX. New Technologies for Astronomy. X. Summary, Priorities and Objectives for the 21st Century. Part 2: XI. Stars. XII. Interstellar Medium and Galaxies. XIII. New Technologies for Astronomy. Index.