Developing Basic Space Science World Wide: Progress Report

The UN/ESA Workshops on Basic Space Science is a long-term effort for the development of astronomy and regional and international co-operation in this field on a world wide basis, particularly in developing nations. The first four workshops in this series (India 1991, Costa Rica and Colombia 1992, Nigeria 1993, and Egypt 1994) addressed the status of astronomy in Asia and the Pacific, Latin America and the Caribbean, Africa, and Western Asia, respectively. One major recommendation that emanated from the first four workshops was that small astronomical facilities should be established in developing nations for research and education programmes at the university level and that such facilities should be networked. Subsequently, material for teaching and observing programmes for small optical telescopes were developed or recommended and astronomical telescope facilities have been inaugurated at UN/ESA Workshops on Basic Space Science in Sri Lanka (1995), Honduras (1997), and Jordan (1999). UN/ESA Workshops on Basic Space Science in Germany (1996), France (2000), Mauritius (2001), Argentina (2002), and P.R. China (2004) emphasised the particular importance of astrophysical data systems and the virtual observatory concept for the development of astronomy on a world wide basis. Since 1996, the workshops are contributing to the development of the World Space Observatory concept. Achievements of the series of workshops are briefly summarised in this report.Comment: 3 page

World Space Observatory/Ultraviolet (WSO/UV): Progress Report

The World Space Observatory/Ultraviolet (WSO/UV) represents a new mission implementation model for large space missions for astrophysics. The process has been brought up to enable, fully scientific needs driven, a logic to be applied to the demands for large collection powers required to undertake space missions which are complementary to the continuously increasing sensitivity of ground-based telescopes. One of the assumptions associated with the idea of a WSO is to avoid the excessive complexity required for multipurpose missions. Although there may exist purely technological or programmatic policy issues, which would suggest such more complex missions to be more attractive, many other aspects, which do not need to be explored in this report, may argue against such a mission model. Following this precept and other reasons, the first implementation model for a WSO has been done for the ultraviolet domain WSO/UV. WSO/UV is a follow-up project of the UN/ESA Workshops on Basic Space Science, organised annually since 1991.Comment: 4 page

The Nature of the Broad--Line--Region in the Radio--Loud AGN 3C390.3

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.Comment: MNRAS in pres

Numerical Simulation of Non-Gaussian Random Fields with Prescribed Marginal Distributions and Cross-Correlation Structure II: Multivariate Random Fields

We provide theoretical procedures and practical recipes to simulate non-Gaussian correlated, homogeneous random fields with prescribed marginal distributions and cross-correlation structure, either in a N-dimensional Cartesian space or on the celestial sphere. We illustrate our methods using far-infrared maps obtained with the Infrared Space Observatory. However, the methodology presented here can be used in other astrophysical applications that require modeling correlated features in sky maps, for example, the simulation of multifrequency sky maps where backgrounds, sources and noise are correlated and can be modeled by random fields.Comment: 24 pages, 4 figures. To appear in PAS

Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in May 1994. II. The IUE Campaign

PKS 2155-304, the brightest BL Lac object in the ultraviolet sky, was monitored with the IUE satellite at ~1 hour time-resolution for ten nearly uninterrupted days in May 1994. The campaign, which was coordinated with EUVE, ROSAT, and ASCA monitoring, along with optical and radio observations from the ground, yielded the largest set of spectra and the richest short time scale variability information ever gathered for a blazar at UV wavelengths. The source flared dramatically during the first day, with an increase by a factor ~2.2 in an hour and a half. In subsequent days, the flux maintained a nearly constant level for ~5 days, then flared with ~35% amplitude for two days. The same variability was seen in both short- and long-wavelength IUE light curves, with zero formal lag (~<2 hr), except during the rapid initial flare, when the variations were not resolved. Spectral index variations were small and not clearly correlated with flux. The flux variability observed in the present monitoring is so rapid that for the first time, based on the UV emission alone, the traditional Delta L/Delta t limit indicating relativistic beaming is exceeded. The most rapid variations, under the likely assumption of synchrotron radiation, lead to a lower limit of 1 G on the magnetic field strength in the UV emitting region. These results are compared with earlier intensive monitoring of PKS 2155-304 with IUE in November 1991, when the UV flux variations had completely different characteristics.Comment: 45 pages, Latex, 11 PostScript figures, to appear in The Astrophysical Journa

The evolution of ultraviolet emission lines from the circumstellar material surrounding SN 1987A

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.Comment: 38 pages, AASTeX v.4.0, 13 Postscript figures; ApJ, in pres